Category Archives: TILs

How far can a CAR get you?

July 18, 2015CAR T, CAR T cells, Chimeric Antigen Receptor, TCR therapy, TILs, tumor microenvironmentPaul Rennert

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The publication of a paper from scientists at Cellectis (NASDAQ: CLLS) got me thinking. Here is a company with a very interesting idea – to engineer “universal” off-the-shelf CAR T cells by using gene-editing techniques to knock out the elements of an allogeneic T cell that would render it visible to the host immune system. The result – an immunologically “quiet” CAR T cell that you could give to any patient needing the treatment. Sounds good I think. Two things though:

FIRST, some definitions.

A CAR T cell is typically a cancer patient-derived T lymphocyte that is genetically engineered to express a hybrid molecule on its cell surface that can both recognize and then signal the destruction of a cancer cell. The T lymphocyte is most often a cytotoxic T cell (Greek: ‘cyto’ is cell; ‘toxic’ is poison) so this equals a T cell that kills other cells that it sees as foreign to the body with poisons. Cytotoxic T cells express CD8 and can be recognized due to this expression (more on this later).

Gene editing is the use of various technologies to edit (remove in this case) specific genetic elements within a cell (or an organism, a topic for another day). Techniques of interest include those using elements of TALEN, CRISPR or ZFN gene-editing systems.

Allogeneic (Greek: ‘allo’ is other, ‘geneic’ is race) literally means a foreigner, of another race, and biologically means: “denoting, relating to, or involving tissues or cells that are genetically dissimilar and hence immunologically incompatible, although from individuals of the same species”.

So now we understand that what Cellectis is proposing is to genetically alter allogeneic CAR T cells so that, although they are foreign to the patient, they will not be recognized and eliminated. So, “off-the-shelf”, universal, CAR T cells, ready to use. But…

SECOND, to quote a friend of mine: What Problem Are We Solving? In other words, while all of these layers of technology that Cellectus is implementing sound very impressive and appealing, of what utility will they be? Do they address a fundamental and intractable issue in the CAR T field? Should we be excited? Perhaps.

We can step back and ask of the CAR T field: what problems does it have? There are several and they are well known.

1) CAR T cells must be highly selective for the target cancer to avoid unwanted killing of other cells, tissues, organs

2) CAR T cells must proliferate and persist once injected into the patient (i.e. in vivo)

3) Since most CAR T technologies are based on a personalized medicine approach – your cancer attacked by your engineered T cells – there is a fair amount of cell culture to do between harvesting your T cells, altering them (via retroviral or other cell transduction technique), expanding those altered T cells so there are enough to “take” upon injection back into the patient. All of this is expensive, with a typical guess at the price tag of 500K USD

4) CAR T therapy is dangerous (although a bit like Formula One racing – very dangerous and just barely controlled). The danger comes from the potential for off-tumor cell killing but also from tumor lysis syndrome, which happens when large numbers of tumor cells are suddenly killed – all sorts of cellular signals get released and this causes an intense and systemic physiological breakdown – very dangerous, but controllable in an appropriate intensive care unit (so recovery care is also very expensive)

5) CAR T therapy to date has had limited success outside of refractory acute lymphocytic leukemia (ALL). Now, while refractory ALL is a poster child of an indication – intensely difficult to treat, with many pediatric patients – there are about 4000 such patients in the US each year. Commercially, this is limiting.

6) Cancer-specific targets suitable for CAR T technology are very rare.

OK, back to Cellectis, whose lead product targets … refractory ALL. So, what problem are they solving? According to company messaging – control over costs by eliminating the personalzed aspects of the therapy. But we’ve already noted that, right now, that is only one of the critical issues facing CAR T cell technology. That may be enough to grab a piece of the refractory ALL market (and some other indications), and drive valuation for a few years, but a sustainable business, hmmm. And that we see here is true of all of the CAR T cells targeting the refractory ALL antigen, CD19. Refractory ALL is not a big enough pie for everyone, nor are the niche indications lumped under the non-Hodgkin Lymphoma label, like Diffuse Large B cell lymphoma and Follicular Lymphoma. CAR T companies will get a portion of these patients, but that will not sustain an industry with a dozen big players. So Cellectis will need more. Of course Cellectis knows this and is looking well past this near term application.

What else happened last week? On the heals of it’s billion dollar 10 year deal with Celgene, JUNO announced the initiation of a CAR T clinical trial employing the impressive sounding “Armoured CAR”. While the term plays nicely to our adolescent/aggressive-minded car culture, what does it actually mean, and, again, what problem are they solving? The armoured CAR T cell is not so much armoured as it is accessorized, carrying a pro-inflammatory cytokine called IL-12 that it expresses as it circulates around the patient looking for tumor cells to kill. Once it finds the tumor, or tumor metastases, the CAR T cell does its usual work, secreting poisons (perforin, granzymes, cytokines, etc) but now, in addition, secreting IL-12, which can amplify the immune response to the tumor via its effects on nearby T and natural killer (NK) cells, including induction of IFN-gamma, enhancement of cell-mediated cytotoxicity and cell proliferation. This approach may work to unlock one of the biggest issues confronting CAR T cell companies – getting solid tumors (as opposed to the “liquid” leukemias and lymphomas) to respond to CAR T therapy at all. So far the results have been disappointing, possibly because the solid tumor microenvironment is so darn immunosuppressive. The JUNO trial is targeting the ovarian cancer antigen MUC16 and will be run at partner hospital, MSKCC. While MUC16 is strongly expressed in ovarian carcinoma (and also pancreatic cancer) the literature indicates normal expression on diverse epithelial cells, including in the lung, the lining of eye and elsewhere. For this reason, as well as the threat of tumor lysis syndrome, JUNO’s armoured CAR also has a off switch that can be activated in case of toxicity. So we are rolling the dice here. Why? Ovarian carcinoma is a large indication with enormous unmet medical need, and pancreatic equally so. Improving patient outcomes in these large and difficult indications would be very notable, and of course, very good business.

Lets look at some data on CAR antigens:

LIST OF SOME ANTIGENS FOR HEMATOLOGIC CANCERS

THIS SHORT LIST IS REFLECTED IN ONGOING COMPANY-SPONSORED CLINICAL TRIALS

ACADEMIC CENTERS ARE AHEAD OF THE CURVE, AS IS ALWAYS TRUE IN THIS FIELD

BUT EVEN HERE, LEUKEMIA AND LYMPHOMA TARGETS DOMINATE (CD19, CD20, CD30, KAPPA Ig, BCMA, ETC)

AS OF 2014, CD19 TRIALS DOMINATED CLINICAL WORK IN HEMATOLOGIC MALIGNANCIES

THE SOLID TUMOR ANTIGEN FIELD IS SIMILARLY CONSTRAINED

AND ANOTHER PAGE BELOW

ALTHOUGH THE DISTRIBUTION OF TRIALS/ANTIGEN IS MORE EVEN, THE NUMBER OF PROTOCOLS IS SMALL (AS OF DATE OF THE REFERENCED PUBLICATION)

So my hope is that we can engineer CAR T cells with sufficient machinery to “rescue” CAR T technology from the reality of an antigen-poor landscape. The technology is stunning, but I wonder if in the face of such challenges one ought not to look around, and perhaps take another approach. As it turns out, nearly all cellular therapy companies that have taken on the CAR T field have begun to diversify – we’ve been asking what problems we are solving with these clever twists on the basic technology – and this is well worth pursuing. However in the face of a limited pool of targets, lets perhaps consider a technology with a much much larger target list: tumor neoantigens as recognized by T Cell Receptors (TCR). TCR and TIL technologies offer some interesting solutions, and their own unique challenges…

stay tuned.

The twisted tale of neoantigens and anti-tumor immune responses

March 13, 2015Astra Zenenca, Bristol Myers Squibb, CTLA4, Genentech, immunotherapy, ipilimumab, Merck, nivolumab, PD-1, PD-L1, pembrolizumab, Roche, T regulatory cells, TCR therapy, TILsPaul Rennert

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Two papers out this week add to a pile of data addressing the role of neoantigens in tumor therapy. While these papers address tumor neoantigen “load” in the context of immune checkpoint therapy the results have implications for TIL therapeutics, TCR therapeutics and onco-vaccine development.

A really dramatic paper from diverse groups at the University of Pennsylvania and their collaborators, just published in Nature (link-1), explores the complex interplay of radiation therapy and anti-CTLA4 antibody therapy (ipilimumab, from BMS) in patients with stage IV metastatic melanoma (relapsed or previously untreated). In this Phase 1/2 clinical trial (NCT01497808) patients with multiple melanoma metastases received various doses of radiation therapy delivered to a single metastasis, termed the “index lesion”. They then received 4 doses of ipilimumab (3 mg/kg, i.v., once every 3 weeks) and non-irradiated lesions were evaluated within 2 months of the last dose.

Although the sample size reported is small (n=22) some interesting lessons emerged from the study. The response rate was low, and the progression free survival (PFS: 3.8 months) and overall survival (OS: 10.7 months) data bear this out. It appears that just shy of 40% of patients were still alive at ~30 months (see Figure 1c in the paper). It is too early to tell if there will be a “long-tail” effect going forward. In the original ipilimumab study a very small percentage of patients lived for a very long time, “pulling” the PFS and OS curves to the right. Regardless, most patients in this study did not respond and the questions posed in this paper are directed to the mechanisms of resistance.

The mouse B16-F10 melanoma model was used to model resistance. Mice with tumors were locally irradiated then treated with an anti-mouse-CTLA4 antibody, to mimic the clinical trial. Only 17% of the treated mice responded. Two predictors of response/non-response were elucidated: 1) the ratio of effector T cells (Teff) to regulatory T cells (Treg) and 2) a gene signature in the tumor cells that is dominated by the expression of PD-L1 and IFNgamma regulated genes. In short, if the melanoma cells are expressing PD-L1 and the tumor infiltrating lymphocyte (TIL) population is dominated by Tregs (which are PD-1+), then the radiation + anti-CTLA4 therapy failed.

To further subset TIL into active Teff versus non-responsive “exhausted” Teff, the authors used an expression profile of PD-1+/Eomes+ to identify exhausted Teff and PD-1+/Eomes+/Ki67+/GzmB+ for active Teff. Importantly, exhausted Teff could be reanimated upon treatment with PD-1 pathway antagonists: anti-PD-1 antibody or anti-PD-L1 antibody. This reanimation led to an improved CD8+ Teff/Treg ratio and led to tumor control in the majority of the mice (up to 80%) when the treatment consisted of irradiation plus anti-CTLA4 plus anti-PD-L1. Of note, radiation plus anti-PD-L1 did not achieve this effect; the triple therapy was required (see Figure 2d).

The striking conclusion is that upregulation of PD-L1 on tumor cells can subvert the effect of anti-CTLA4 antibody therapy, and this therefore qualifies as a mechanism of resistance.

What about the role of irradiation? In both the patients and the mouse model irradiation was local, not systemic. Further, this local irradiation was required to achieve complete responses in the mouse model. What is going on here? Irradiation was linked to a modest increase in TIL infiltration of melanoma tumors in the mouse model, but sequencing of the T cell receptors (TCR) revealed that there was an increase in the diversity of TCRs, meaning that more antigens were being recognized and responded to by TIL after irradiation. In this context then, anti-CTLA4 reduced the Treg population, anti-PD-L1 allowed CD8+ TIL expansion, and irradiation set the antigenic landscape for response.

Returning to the patients armed with this information from the mouse study, the authors find that low PD-L1 expression on the melanoma cells correlates with productive response to irradiation plus ipilimumab therapy, while PD-L1 high expressing tumors were associated with persistent T cell exhaustion. In addition, monitoring the state of the CD8+ T cell population (PD-1+/Eomes+ versus PD-1+/Eomes+/Ki67+/GzmB+) suggested that these phenotypes might be useful as peripheral blood biomarkers. The patient numbers are very small for this analysis however, which awaits further validation.

The conclusion: irradiation combined with ipilimumab plus anti-PD-L1 antibody therapy should be a productive therapeutic combination in PD-L1+ stage IV melanoma. Similar strategies may be beneficial in other solid tumor types. This is interesting news for companies developing anti-PD-L1 antibodies, including BMS-936559 (also from BMS), MPDL3280A (Roche/Genentech), MEDI4736 (AZN) and MSB0010718C (Merck Serono).

A second paper (link) bring our focus back to PD-1, in the context of non-small cell lung cancer (NSCLC). Using the anti-PD-1 antibody pembrolizumab (from Merck) a group from the Memorial Sloan-Kettering Cancer Center sought to determine correlates of response of NSCLC patients to anti-PD-1 therapy. Their findings again hone in on neoantigen load, as the best predictors of response were the non-synonymous mutational burden of tumors, including neoantigen burden and mutations in DNA repair pathways. What all this means is that mutations that change the amino acid sequence (thus, are non-synonymous) can produce neoantigens that can be recognized by CD8+ T cells; mutations in the DNA repair pathways increase the rate that such mutations go uncorrected by a cell.

The authors sequenced the exomes (expressed exons – these encode proteins) from tumors versus normal tissue, as a measure of non-synonymous mutational burden that could produce neoantigens. Patients were subsetted based on response: those with durable clinical benefit (DCB) and those with no durable benefit (NDB). High mutational burden was correlated with clinical efficacy: DCB patients averaged 302 such mutations, while NDB patients averaged 148; ORR, PFS and OS also tracked with mutational burden. In a validation cohorts the number of non-synonymous mutations was 244 (DCB) versus 125 (NDB).

Examination of the pattern of exome mutations across both cohorts was studied in an attempt to discern a pattern of response to pembrolizumab treatment. The mutational landscape was first refined using an algorithm that predicts neoepitopes that can be expressed in the context of each patients specific class I HLA repertoire – these are the molecules that bring antigens to cell surfaces and present them to T cells for recognition (I’m simplifying this process but that is the gist of it). The algorithm identified more potential neoepitopes in the DCB patient tumors than in the NDB cohort, more impressively, a dominant T cell epitope was identified in an individual patient using a high-throughput HLA multimer screen. At the start of therapy this T cell clone represented 0.005% of peripheral blood T cells, after therapy the population had risen 8-fold, to 0.04% of peripheral blood T cells. Note that most of this clone of T cell would be found in the tumor, not in circulation, so that 8-fold increase is impressive. The T cells were defined as activated CD8+ Teff cells by expression markers: CD45RA-/CCR7-/LAG3-. As in the first paper we discussed, it is useful that these markers of systemic response to immunotherapy treatment are being developed.

There is an interesting biology at work here. It is often noted that high mutational burden is associated with better outcome, for example to chemotherapy in ovarian cancer, and irrespective of therapy across different tumor types (link-2). This suggests that tumor neoepitopes are stimulating an ongoing immune response that is stifled by active immunosuppression, yet is still beneficial. Once unleashed by immune checkpoint blockade, the immune system can rapidly expand it’s efforts.

We recently reviewed the importance of neoantigens in anti-tumor therapy (link-3) although the focus then was on cellular therapeutics rather than on immune checkpoint modifiers such as anti-CTLA4 and anti-PD-1 or PD-L1 antibodies. We can mow add that our ability to track neoantigens and the immune response to neoantigens is opening new avenues for investigating immuno-oncology therapeutics and their efficacy.

SugarCone Biotech comments in Biocentury’s Immune Checkpoint Landscape Review

January 30, 2015immunotherapy, mutations, News, oncology, TCR therapy, TILsPaul Rennert

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Paul Rennert, Founder & Principal of SugarCone Biotech, discusses advances in tumor antigen characterization in the current issue of Biocentury Innovations, formally SciBx. The current issue covers the Immune Checkpoint scientific and competitive landscape and related subjects, see http://www.biocentury.com/scibx/currentissue.

Paul commented on several tumor antigen papers that have set the stage for a more sophisticated understanding of the meaning and potential utility of neoantigens in cancer therapeutics, including the cellular therapeutic field (TCR, TIL) and the onco-vaccine field. These papers were recently covered in our blog as well.

We’re happy to have been able to contribute to the Biocentury story, and hope you’ll enjoy their very timely current issue.

Holiday Reading

December 24, 2014CRISPR, fibrosis, immunology, inflammation, autoimmunity, fibrosis, immunotherapy, IPF, lupus, Lymphomas, Leukemias, Myelomas, MS, oncology, TALEN, TILs, tumor microenvironment, Zinc Finger NucleasePaul Rennert

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some of the stuff we’re reviewing over the holiday break. N.b. paywalls ahead! And at the very end, some current non-science favorites.

Tumor Mutational Landscape

Age related variants of variants occurred in three genes (DNMT3A, TET2, and ASXL1) are associated with hematological malignancy risk http://www.nejm.org/doi/full/10.1056/NEJMoa1408617 and http://www.nejm.org/doi/full/10.1056/NEJMoa1409405

News and Views on the NEJM papers http://www.nature.com/nrg/journal/vaop/ncurrent/full/nrg3889.html

using siRNA to identify driver genes in breast cancer http://www.nature.com/nrg/journal/v16/n1/full/nrg3875.html

Immunotherapy

a primer on the role of PD-1 pathway inhibitors in Hodgkin’s Lymphoma, from Nat Rev Clin Oncol http://www.nature.com/nrclinonc/journal/vaop/ncurrent/full/nrclinonc.2014.227.html

the role of TILs and TIL-associated TNF in the survival of CRC patients http://www.jci.org/articles/view/74894

nivolumab in metastatic RCC, published data http://jco.ascopubs.org/content/early/2014/12/22/JCO.2014.59.0703.abstract

resistance to T cells in melanoma (hint: they lose MHC expression) http://clincancerres.aacrjournals.org/content/20/24/6593.abstract

interesting look at PD-L1 expression of the response of RCC to targeted therapies http://clincancerres.aacrjournals.org/content/early/2014/12/23/1078-0432.CCR-14-1993.abstract

it’s hard to control ipilimumab-induced tox http://clincancerres.aacrjournals.org/content/early/2014/12/23/1078-0432.CCR-14 2353.abstract

IO combination review http://clincancerres.aacrjournals.org/content/20/24/6258.abstract

tumor/microenvironment cross-talk mediated by microRNAs http://clincancerres.aacrjournals.org/content/20/24/6247.abstract

functional blockade of miR-23a releases TILs in an ex vivo NSCLC assay http://www.jci.org/articles/view/69094

neutrophils, T cells and lung cancer http://www.jci.org/articles/view/77053

Given the new immunotherapy data in bladder cancer, a review of the molecular drivers of this tumor type is most welcome http://www.nature.com/nrc/journal/v15/n1/abs/nrc3817.html

MDSC requirements for survival http://www.cell.com/immunity/abstract/S1074-7613(14)00436-1

Gene Therapy and CAR T

Novel gene therapy methods puts a safety brake on a retrovirus-based vector http://www.nature.com/nrd/journal/v13/n12/full/nrd4495.html

a new review of the CRISPR, Talen, and ZFN technologies for gene editing http://www.jci.org/articles/view/72992

NY-ESO-1 CAR T P1 results in solid tumors: long term follow-up and correlates of response http://clincancerres.aacrjournals.org/content/early/2014/12/23/1078-0432.CCR-14-2708.abstract

Targeted Therapies

A very timely primer of the role of different PI3K isoforms in diverse cancers http://www.nature.com/nrc/journal/v15/n1/abs/nrc3860.html

a Notch in the cancer treatment belt? Nope, a bit of a toxic mess made with anti-DLL4 antibody Demcizumab from OncoMed http://clincancerres.aacrjournals.org/content/20/24/6295.abstract

IL-17 and colon cancer? http://www.cell.com/immunity/abstract/S1074-7613(14)00446-4

Hematological Malignancies

von Adrian and Sharpe tease apart Follicular Lymphoma http://www.jci.org/articles/view/76861

the role of one of gp130 in multiple myeloma http://www.jci.org/articles/view/69094

Fibrosis, Inflammation, Metabolism, MS

a brand new fibrosis review http://www.jci.org/articles/view/74368

the TRPV4 pathway, TGFbeta and IPF http://www.jci.org/articles/view/75331

The role of novel branched fatty acid esters of hydroxy fatty acids in Type 2 diabetes http://www.nature.com/nrd/journal/v13/n12/full/nrd4501.html

will STING finally yield a useful target in lupus? http://www.jci.org/articles/view/79100

an animal model of JCV infection and PML http://www.jci.org/articles/view/79186

Investment and Deals

Pharma funding to pull programs out of the academic space http://www.nature.com/nrd/journal/vaop/ncurrent/full/nrd3078-c2.html

some color from NRDD on the Genentech + NewLink IDO-1 inhibitor deal http://www.nature.com/nrd/journal/v13/n12/full/nrd4502.html

Also notable

300,000,000. A violent graphic lurid hypnotic novel of the dissolution of consciousness and the consequence of multiple realities converging within our unprepared empty minds and upon our decadent culture. Horrific and wonderful, but not for the squeamish.

Thug Kitchen – eat like you give a #$%@^. Fun, but you get the idea.

Death & Co: Modern Classic Cocktails. Drink like an adult.

Tumor Neo-Epitopes

December 16, 2014CTLA4, immunotherapy, ipilimumab, melanoma, oncology, PD-1, Roche, TILsPaul Rennert

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I’m asked a lot about the onco-vaccine field, and if immune checkpoint inhibitors will be the key to unlocking the potential of this long-suffering therapeutic class. The answer is never simple, since we are often looking at thin patient data that can contain compelling hints of efficacy – those immunized late-stage patients who not only regressed but stay in remission, month after month and year after year. The problem for companies and investors is that such observational data can be very misleading, and the vaccine candidates most often go on to fail in later and larger clinical trials, sometimes spectacularly. These big failures burden the field with a high evidentiary bar.

Data have emerged that suggest several issues with most vaccines, and these issues are both distinct and related.

At the end of November Nature published two interesting papers that asked a very simple question: what immunogenic antigens are present in common mouse tumor models. Yadav et al from Genentech and Immatics Biotechnologies (link 1) used a genome-wide exome and transcriptome sequence analyses, mass spectrometry and structural modeling to identify immunogenic neo-antigens in the widely used MC-38 and TRAMP-C1 mouse syngeneic tumor models. These models are considered poorly immunogenic in wild-type syngeneic (C57Bl6) mice. The sequencing analysis was used to identify mutated proteins that were present at >20% allelic frequency. From the MC-38 model, 1290 expressed mutations were identified of which 170 were considered to be neo-epitopes, that is, modeling suggested they would be expressed by MHCI and sufficient residues would be solvent exposed to allow immunogenicity. Only 67 expressed mutations were found in the TRAMP-C1 model, and of these 6 were considered to be potential neo-epitopes. Of this total of 170 (MC-38) and 6 (TRAMP-C1) only 6 bound MHC1 by Mass Spec, with a predicted IC50 for MHCI < 500nM. Of these, 3 were actually immunogenic in vivo (using C57Bl/6 mice) and could protect wild-type mice from tumor challenge. The neo-epitopes were found in the proteins Dpagt1, Reps1 and Adpgk. Here is a schematic of the filtering scheme:

Working the other way, the authors confirmed the immunogenicity of neo-epitope peptides by analyzing tumor-infiltrating lymphocytes (TIL) and staining with peptide–MHCI dextramers to identify bound T cells. CD8+ T cells specific for Reps1, Adpgk and Dpagt1 were enriched in the tumor. Using the Adpgk neo-epitope, the TIL were further investigated and found to express PD-1 and TIM-3, inhibitory receptors associated with anergic or “exhausted” CD8+ T cells, showing that the murine immune system had indeed recognized and responded to the neo-epitopes, a response that was then actively immunosuppressed in the tumor microenvironment. Importantly, none of the identified neo-epitopes would qualify as tumor-antigens, that is, they are not specifically overexpressed at a sufficient level to qualify. The neo-antigen-specific TIL are also pretty rare, suggesting that use of tumor lysate as an immunogen to elicit an anti-tumor response may “miss” by failing to present enough of the right antigen to the immune system.

We noted at the top that this paper came out of labs at Genentech and Immatics. An agreement between Roche/Genentech and Immatics will focus on the use of this technology. The two companies will develop new tumor-associated peptides (the neo-epitopes as cancer vaccine candidates, initially targeting gastric, prostate and non-small cell lung cancer. The most advanced candidate is IMA942, a peptide vaccine for the treatment of gastric cancer, in late preclinical development. Immatics CEO Paul Higham has publicly stated that a Phase I study of IMA942 with Roche’s PD-L1 inhibitor MPDL3280A in gastric cancer will be initiated soon. Immatics will also conduct research to identify neo-antigens for the additional indications. For those keeping score, Immatics received $17 million upfront, committed research funding, and potential milestones

The second work, led by Schreiber’s group at Wash U, used mouse models to ask a different but related question: what tumor antigens are recognized after immune checkpoint blockade with anti-PD-1 or anti-CTLA4 antibodies (link 2). The sarcoma lines d42m1-T3 and F244 were rejected in wild-type mice treated with either anti-PD-1 or anti-CTLA4 antibodies, in a CD4/CD8/IFNy/DC-dependent manner. As in the first paper, a filtering system built from diverse technologies was used to identify potential neo-epitopes. Mutations were identified by cDNA sequencing, translated to corresponding protein sequences, then tested against MHCI binding algorithms. Neo-epitopes were ranked by predicted median binding affinities and likelihood of productive immunoproteasome processing and antigen display. Using these methods, two MHCI restricted neo-epitopes were identified in Alg8 and Lama4.

As in the first paper, the authors then turned the system around, asking what neo-epitopes could be identified through analysis of TIL. Alg8 and Lama4 were found in tumor TIL and their frequency was increased by treatment with anti-PD-1 or anti-CTLA4. The neo-epitopes could successfully be used to induce anti-tumor immune responses. As in the first paper, these are not neo-epitopes that would qualify as tumor-antigens using the traditional criteria of selective and high expression.

So these are our two distinct but related issues with the current tumor vaccine landscape: those that have selected antigens have likely selected the wrong ones, while those that use lysates are likely too dilute.

Importantly, we can now compare these model systems to actual data from human patients treated with anti-CTLA4 antibody, as published recently in NEJM (link 3). The clinical group from Memorial Sloan Kettering Cancer Center obtained tumor tissue from melanoma patients treated with anti-CTLA4 antibodies (ipilimumab or tremelimumab). As in the mouse study, whole-exome sequencing was performed, somatic mutations identified and potential neo-antigens were characterized. Here is their schematic:

Baseline analyses showed that there was a significant difference in mutational load between patients with long-term clinical benefit and those with a minimal or no benefit, with higher mutational load associated with response. However the relationship was correlative, since some tumors with a high mutational burden were not responsive to anti-CLTA4 therapy. Using peptides predicted to bind to MHCI with a binding affinity ≤ 500 nM, the authors focused on mutated peptide sequences shared by multiple tumors and shared by patients having long-term clinical benefit. From this analysis a neo-epitope “signature” was derived, consisting of a distinct pattern of mutated peptide sequences. One of the peptide signatures identified matched an amino acid sequence in MART1, a known melanoma antigen. However the bulk of predicted neoantigens were tetrapeptide sequences shared across antigenic peptides, that is, they were encoded by diverse genes (you have to go into the huge supplemental data file to find this list, suffice to say it is very long). To make sense of this curious result the authors note that the some of the predicted sequences have high homology to viral and bacterial antigens, citing a CMV antigenic sequence as an example. They speculate, and here we quote from the paper: ” These data suggest that the neoepitopes in patients with strong clinical benefit from CTLA-4 blockade may resemble epitopes from pathogens that T cells are likely to recognize.”

The unstated null hypothesis is that there is no relationship between the shared tetrapeptide sequences and clinical response and that the association between the two phenomena is due to a productive immune system response to anti-CTLA4 antibody therapy which has released the anti-tumor response as well as many otherwise quiescent immune responses, such as those to pathogenic viruses and bacteria (and to self antigens, as shown by the autoimmune toxicity associated with anti-CTLA4 antibody treatment). The in vitro response assay data sheds no real light on this, since these assays cannot distinguish anti-tumor responses from other immune responses. So we are left with an intriguing correlation, and a nagging sense that only a very few of the vast number of predicted neo-epitopes will actually trigger bona-fide anti-tumor T cells responses. Indeed the weakness of the paper is the reliance on predictive rather than experimental identification of productive peptide/MHC interaction. As we say in the mouse studies the majority of predicted interactions are not confirmed experimentally.

Regardless, the paper is a remarkable and important step forward, and shows us (as do the mouse studies) the level of investigation required to identify neo-antigens that might expand be used to expand patient TIL populations, as we have discussed in other posts. Returning to onco-vaccines, these three papers together show us that neo-antigen anonymity, rarity and variability from patient to patient are critical issues that will need to be addressed if we are to efficiently develop this therapeutic class.

Last Week’s Immune Checkpoint Papers In Nature Are Complicated!

December 4, 2014CTLA4, immunotherapy, MPDL3280A, PD-1, PD-L1, pembrolizumab, T regulatory cells, TILs, tumor microenvironmentPaul Rennert

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Last week we were treated to a barrage of good news regarding PD-1/PD-L1 therapeutics and the ability to select responders. The centerpiece was a trio of papers in Nature.

Powles et al. presented data on the use of MPDL3280A, an anti-PD-L1 IgG1 antibody that has been engineered to lack all ADCC function (link 1). The antibody blocks the interaction of PD-L1 with PD-1 and with CD80, two receptors found primarily on lymphocytes. The paper focused on the application of ‘3280’ therapy in chemotherapy-resistant metastatic urothelial bladder cancer (UBC). Nearly all patients (93%) had failed platinum-based chemotherapy; 72% had failed 2 or more lines of prior therapy. 75% had visceral metastases, most had poor renal function and the majority (59%) had a performance score of 1 (very poor). In a word, these patients were incurable. Preliminary Phase 1 data demonstrating efficacy in UBC was presented at ASCO and led to breakthrough designation for ‘3280 for the treatment of UBC in June 2014.

The original Phase 1 trial had enrolled UBC patients whose resection or biopsy tissue demonstrated the presence of tumor-infiltrating lymphocytes (TIL) with dark staining (score 2 or 3) for PD-L1. The expansion cohort allowed for the enrollment of patients whose tissue specimens contained TIL which were PD-L1 dim (score = 1) or negative. 205 patient tissues were analyzed (see table 1 in the paper). 67 patients were enrolled and evaluable with PD-L1 staining results as follows:

A total of 17 patients responded and 16/17 responses were ongoing (i.e. durable) at the time of data cutoff. The longest duration of response was a remarkable 30 weeks in the cohort with the brightest PD-L1 TIL staining, although the range was broad (from 1 week to 30). Median duration of treatment was 9 weeks, so this is really an early snapshot. Regardless, the ability to invoke an anti-tumor response in a cohort of patients that are this ill, and deemed incurable, is remarkable.

With reference to the staining pattern of PD-L1 and the relevance of PD-L1 expression to successful response, the authors came to the following conclusions:

1) therapy triggered expansion of the circulation CD8+ T cell population, and transient elevation of IL-18 and IFNgamma was observed; these systemic changes reflect the proposed mechanism of action of ‘3280 but did not correlate with response.

2) expression of PD-L1 on TIL, but not on tumor cells, was predictive of response to therapy. On note, this was true whether the available tissue sample was new acquired or archival (up to 10 years old). This suggests that there is an ongoing and futile immune response in these PD-L1+/TIL+ tumors. The lack of association with tumor PD-L1+ status is discussed more extensively in the companion paper (see below).

3) the efficacy of PD-L1-directed therapy in UBC and also NSCLC and melanoma, all tumors with very high mutational burdens, suggests that antigen diversity or antigen “burden” may be important for successful induction of an anti-tumor immune response in ‘3280-treated patients.

The UBC cohort was part of a much larger clinical trial that included diverse solid tumors. A companion paper by Herbst et al. investigates the utility of PD-L1 TIL expression in other cohorts (link 2). The focus of this work is on the biomarker application, particularly with respect to PD-L1+ TIL staining, as defined in the prior paper. Patients (n=277) with advanced incurable cancers were enrolled in a ‘3280 dose ranging study, given drug iv every 3 weeks. Across tumor types high PD-L1 expression on TIL, but not tumor cells, was associated with response and increased PFS. Note here that the PFS gain, while encouraging, does not suggest that we will see a high percentage of truly durable (“long tail”) responses in this particular patient population, even in those patients with PD-L1 bright (score of 3) staining:

There were some interesting additional analyses. In NSCLC patients who had been smokers, 43% responded to therapy, while only 10% of non-smokers responded. Such data have been reported before, and are often taken to mean that the higher mutational burden seen in smokers with NSCLC biases their tumor toward immune recognition (this echoes the mutational diversity/mutational burden argument made in the Powles UBC paper). Sticking with NSCLC, 83% of patients with a PDL1+ TIL staining score of 3 (lots of cells and therefore dense/dark staining) responded versus 38% of patients with a PDL1+ TIL staining score of 2 (diffuse staining, fewer cells). Response was positively correlated with CTLA4+ staining on TIL, and negatively correlated with fractalkine expression. In melanoma (but not NSCLC or RCC) response was associated with elevated IFNgamma and IDO1 and CXCL9 that are induced by IFN gamma. Strikingly, positive anti-tumor responses were not associated with a measureable change in FoxP3 expression, suggesting the T regulatory T cells were not playing a role in the setting of ‘3280 therapy.

What about the non-responders, as these make up the majority of the patients across indications? Progressing tumors were characterized into three classes:

1) few or no TIL present – “immune ignorance”

2) TIL present but little or no PD-L1 expression – “non-functional immune response”

3) TIL present and PD-L1+ but located on the edge of the tumor – “excluded infiltrate”

Missing here I think is an analysis of tumors with PD-L1+ TIL with high staining scores (2 or 3) that progressed, i.e. did not respond to therapy. It seem to me unlikely that these all fell into category “3” above, so this analysis may be coming in a follow-up paper.

The authors make a very interesting point about this data, which is that they seem to refute the consensus model of “immune resistance” in which it is postulated that CD8+ T cells infiltrating tumors secrete IFNgamma and other cytokines that induce PD-L1 expression on the tumor cells themselves, and these tumor cells in turn produce factors that create an immunosuppressive environment that includes potently immunosuppressive, PD-L1 bright T regulatory cells. The “immune resistance” model further postulates that the expression of PD-L1 on tumor cells and T regulatory cells is responsible for shutting down CD8+ T cells by binding to PD-1.

There are several key messages in this paper – first, responses in these incurable patients are measureable and remarkable, if they respond (most do not). Second, CD8+/PD-L1+ TIL are highlighted as a potential prognostic indicator of the potential for response the ‘3280 therapy. Finally, it is clear that other signals will have to be disabled or enhanced in order to induce a productive and durable immune response in more patients and/or move PD-1/PD-L1-directed therapies to front line.

Now, the final paper in this triad turns things upside down. Tumeh et al. analyzed tumor tissue samples from 46 metastatic melanoma patients treated with pembrolizumab, an anti-PD-1 antibody (link 3). The analytic methods used are elegant and overlap but also extend the analyses used in the prior 2 papers: quantitative immunohistochemistry, quantitative multiplex immunofluorescence, and TCR deep sequencing (NGS).

This paper is strictly about melanoma. The ORR in this small study was 48% (22/46). The authors focused on expression of PD-L1 on tumor cells and of PD-1 on CD8+ T cells. Doing so they come to strikingly different conclusions than the papers discussed above. Responders in this study had PD-1+ CD8 T cells massed on the tumor margin, adjacent to PD-1+ tumor cells. Response was associated with infiltration of the tumor by those CD8+ T cells, which also increased in density (proliferated). Therefore the paper specifically supports the “immune resistance” model in which tumor-expressed PD-L1 suppresses PD-1+ CD8 T cells. CD8 T cell proliferation was associated with expression of granzyme B within the tumor and phosphorylated STAT1 at the tumor margin where CD8+ T cells were infiltrating (phospho-STAT1 in induced by IFNgamma receptor signaling). Finally, response was associated with T cell (TCR) clonality, i.e. the fewer tumor antigens, and thus the lower the antigen burden that is invoking a response, the better. This is a different take than we got from the prior papers.

So, perhaps melanoma is distinctly different.

Aside from that, these papers provide critical take-home messages and perhaps even more critical questions to be addressed:

1) CD8 T cells are good. That’s pretty clear, whatever they are expressing. We can argue more about their geography, but if they are not present, you will not respond.

2) IFNgamma is good. We see this especially in the melanoma setting as detailed in two of the papers.

Neither of these conclusions is novel nor surprising.

3) Biomarker development beyond CD8+ T cell staining remains complex.

4) Regardless of their biomarker status most patients still do not respond and we do not know why. As we consider combination therapy, will other markers be used to further sort patients into rational combination buckets, or will this simply too complex to be useful?

5) Finally, what about those T regulatory cells we’ve been obsessed with for the last decade? These are hardly mentioned in the context of PD-1/PD-L1 therapeutics in the three studies.

next time:

>>> back to those tumor antigens? New papers, preclinical and clinical, shed some light… and

>>> those T regulatory cells may be important in some settings, but were betting on the tumor microenvironment to yield interesting new targets for therapy

stay tuned

Why Adaptimmune’s TCR data are important (and it’s not what you’re thinking)

October 17, 2014immunotherapy, TCR therapy, TILsPaul Rennert

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People are excited this morning about preliminary results from Adaptimmune’s cell therapy trial in synovial sarcoma. The data are encouraging and thought-provoking. The results may even hold up in later clinical trials, we’ll see. Here is the FierceBiotech writeup.

The Phase 1 clinical trial is open label, enrolling patients with unresectable, metastatic or recurrent synovial sarcoma. These tumors express the tumor antigen NY-ESO-1, a target of many therapeutic approaches including vaccine therapies and CAR T cell therapeutics. The company is running a Phase 1/2 trial in ovarian cancer using the same technology.

In the AdaptImmune study, patient T cells were isolated, expanded ex vivo and genetically modified to express NY-ESO-1-specific T cell receptors (TCRs). They were then injected back into the patients following chemotherapy designed to deplete the lymphocyte compartment (and thus make “room” for the genetically engineered T cells to expand).

Here’s the skinny: among the 5 patients who reached the 60-day assessment period, 4 showed a clinical response, with one patient’s cancer completely gone at 9 months. So with an N = 5, we have an overall response rate (ORR) of 80% and a complete response rate (CR) of 25%. Small numbers but a nice result.

Why is this interesting, beyond the obvious hope for clinical application?

First, these data push back a bit on the emerging paradigm that tumor infiltrating lymphocytes (TILs) need to be engineered to recognize patient-specific (or at least tumor type-specific) neo-antigens, where neo-antigens are defined as peptides, derived from proteins mutated during the course of oncogenesis, that are immunogenic. This paradigm underlies ground-breaking work published in Science last year by Steve Rosenberg and colleagues (see this post). In that study patient-specific TILs that recognized specific tumor-specific antigens were identified and personalized TCRs were constructed. In a similar vein Robert Schreiber recently reported at the CRI Immunotherapy conference his results using exome sequencing to identify precise cancer antigens. This study used mice treated with a PD-1 checkpoint inhibitor to induce tumor regression. T cells isolated from these mice were specific for a small number of unique tumor antigens. These specific antigens potently induced an anti-tumor immune response when injected into mice as a vaccine. The vaccines prevented tumor growth and also induced elimination of established tumors. This work is in press at Nature.

In the Rosenberg, Schreiber and similar studies it is notable that the T cells isolated and analyzed do not recognize what we commonly believe are tumor antigens, that is, normal proteins that are selectively overexpressed in tumor. Instead they are mutated (and therefore “non-self“) antigens specific to that particular tumor.

Going back to the AdaptImmune results, we see something very different, that is, a productive T cell response to a known (and not a mutated “non-self”) antigen. This should give some renewed measure of hope to the traditional oncology vaccine companies, as they are nearly all chasing typical tumor antigens. On the other hand, maybe it takes a turbo-charged TCR-modified T cell to really break through and mediated a clinically relevant response.

For the immunologists we’ll note that even the turbo-charged TCR T cells remain HLA-restricted, and this becomes important. In a mouse xenograft model using an NY-ESO+ tumor (multiple myeloma), it was observed that mice treated with NY-ESO-specific CD8+ T cells (so, TCRs) were able to escape treatment by selective loss of the requisite HLA molecule from the tumor cell surface (link). So we’ll have to watch and see if human tumors respond as cleverly to these types of therapies.

stay tuned.

Lion Biotechnologies and TIL therapy for melanoma

August 28, 2014$LBIO, 4-1BB, immunotherapy, melanoma, OX40, TILsPaul Rennert

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There is so much here to raise suspicion.

Lion Biotechnologies was born ugly, from a merger with Genesis Biopharma, essentially forming a public company within the shell of what some people suspect was originally a pump and dump operation (link). This up-listing maneuver came at the cost of most of Lion’s equity, as Genesis shareholders held 83.6% of the combined company and Lion shareholders initially received 8.2%, with the promise of doubling that stake to 16.4% of the combined company based on achievement of certain milestones. The merger was completed in July of 2013 and the stock continued trading under the ticker symbol GNBP until September 2013, when Genesis announced a 1 for 100 reverse stock split that essentially took place immediately, locking shareholders in place. The merged company changed its name to Lion Biotechnologies and hatched the new listing symbol LBIO. Muddying the picture just a bit more, the company is run by Manish Singh, Ph.D., the former ImmunoCellular Therapeutics chief executive who resigned from that company in August 2012. One rumor circulating then was that he was sacked after suspicions were raised about ImmunoCellular’s Phase 1 data reporting and promotion. That company has stabilized since he departed, moving its’ oncology vaccine program into Phase 2.

LBIO has moved aggressively into the cellular immunotherapy space, licensing technology developed by Dr. Steve Rosenberg and colleagues at NCI (using the same CRADA model that Kite Pharma uses) and building collaborative relationships with MD Anderson and the Moffitt Cancer Research Institute. They pulled in an MD Anderson investigator, Laszlo Radvanyi Ph.D. as CSO and earlier this week appointed industry veteran Elma Hawkins Ph.D. as President and COO. These are likely all good moves toward establishing and building credibility, although the company remains dogged by bad PR, most recently being pulled (by subpoena) into an SEC investigation of Galena Biopharma, a seemingly unrelated company. Speculation about this “wide net” investigation by the SEC has focused on Dr. Singh and possible past involvement with an investor relations firm (link 2). This seems unlikely to have anything to do with LBIO itself.

The final piece of the puzzle is more transparent, which is that the shell merger/reverse split reboot was financed in large part via a private placement with Roth Capital. There is nothing wrong here, except that people tracking stocks in this space tire a bit of the relentless pumping that Roth does on behalf of LBIO, although it is of course their right and possibly their obligation to do so. One puff piece stated “we see 196% upside!” – and I’d have to comment, stealing a line here from Billy Bob Thornton, “that’s a pretty specific number”. I guess we could also wonder what if anything the original shareholders of Genesis and Lion have left of their equity.

Moving on.

LBIO’s CSO, Dr. Laszlo Radvanyi, spoke a few weeks ago at the Immunomodulatory Antibodies for Cancer Conference in Boston, part of the ImVacs package. It was an impressive talk, very upbeat, and contained some data and technology that was new to me. So I took a closer look.

The basis for the technology is a riff on something we discussed earlier, as presented by the NCI’s Rosenberg at ASCO (link 3). Tumor infiltrating lymphocytes (TILs) are found in large numbers in some solid tumor types, and can be isolated when the tumor is removed. The presence of TILs is correlated with improved survival at least in some indications. It has been known for quite some time that expanded TILs can be injected back into the patient where they, sometimes, effectively attack and eradicate the tumor. The problem with the technology is that, like all personalized cellular therapies (CAR, TCR, some types of tumor vaccines), it is cumbersome to perform. When logistics are such a challenge, you really want to see robust benefit from the treatment. This is what LBIO is suggesting it can deliver. Dr. Radvanyi walked us through a brief history of TIL technology, hitting the highpoints. His statement that standard TIL therapy has shown overwhelming and superior efficacy versus competing therapeutics for in melanoma was one I had not heard before, and I reserve judgment on this – after all if it was really that good everyone would be adopting this technology, and I really don’t see that happening.

What was really interesting though was the more experimental system that he introduced, and if you look at the LBIO website you’ll see it under “next-generation TIL” (link 4). In this system tumor fragments are made from biopsy samples and cultured with IL-2. This apparently works optimally because dendritic cells and monocytes persist in the culture for a week or so. They first activate and then sort the TILs using an agonist anti-4-1BB antibody to enrich for antigen specific activated T cells. This allows you to reduce the number of cells injected (a good thing). He did show dramatic enrichment of TILs that recognized known melanoma antigens, so at the very least this model system works. I think this also suggests the importance of the 4-1BB pathway, at least in this system. Notably, anti-OX-40 antibody failed to expand antigen-specific T cells (note we are talking specifically about CD8+ T cells here, in part because that’s all you’ll have left after a few weeks culture in IL-2).

It seems a nice simple system and worth watching. There were other bells and whistles (transduction techniques) that we’ll skip for now. Other technology LBIO is funding includes the use of the anti-CTLA4 antibody ipilimumab in conjunction with TIL therapy (to turn off active immune suppression in the tumor microenvironment). That is being done at Moffitt in a Phase 1 expansion cohort. Be interesting to see what else the company has in mind.

Can LBIO – using this new TIL technology – achieve clinical and commercial success?

stay tuned…

The future of cancer immunotherapy?

May 9, 2014AACR14, immunotherapy, TCR therapy, TILsPaul Rennert

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Matthew Herper posed a provocative question the other day while discussing CAR T technology: is this how we’ll cure cancer? (link).

Lets look at another example that promises to evoke the same question. Back in April, Steve Rosenberg gave a remarkable talk on the subject of patient-specific tumor-infiltrating-lymphocytes (TILs). We covered this talk in an earlier post (link). Today Dr Rosenberg further exemplified this personalized immunotherapy approach, via a case report in Science (link).

The patient had a highly metastasized gastrointestinal epithelial cell tumor called a cholangiocarcinoma. The patient had been through multiple rounds of chemotherapy, relapsed, and was enrolled in a clinical trial (NCT01174121). Lung metastases were isolated and subjected to whole exome sequencing. At the same time, these tumor samples were processed to derive TILs. The data from the sequencing identified multiple gene (and therefore proteins) that were mutated, and and expression constructs were used to determine if any of the mutated proteins were recognized by the TILs, which would proliferate when stimulated by interaction with antigen. Remarkably, a peptide fragment of the mutated ERRB2IP protein stimulated CD4+ Th1-type T cells in a HLA-restricted manner. These T cells were then expanded ex vivo.

The patient first received an expanded, activated TIL pool containing about 30% CD4+ T cells reactive to the mutated ERRB2IP protein. 40 Billion (yes, ‘B’) T cells were administered along with IL-2, a cytokine that keeps T cells alive and proliferating upon activation. The reactive TILs persisted for many months after administration and impacted the tumor, reducing tumor volume and inducing stable disease (a defined clinical endpoint). Ex vivo stimulation of recovered TILs demonstrated strong expression of the T cell activation receptors 4-1BB and OX40, and the secretion of the cytokines IFN-gamma, TNF and IL-2. The patient maintained tumor regression for 13 months, at which point metastases were observed in the lungs. A second infusion of activated TILs was given. In this case >95% of the TILs were reactive to the mutated ERB2IP protein. 10 Billion cells were administered. The patient then experienced a tumor regression that was maintain and progressive over time, up to and including 6 months post-administration (the last timepoint provided in the report).

This is an exciting step, moving immunotherapy into a class of tumors that are stubbornly resistant to many immunotherapeutic agents. A few interesting questions arise: 1) would induction of a CD8 response have an additive impact on the tumor? 2) would use of an agonist antibody to OX40 or 4-1BB synergize with this technique? 3) What was the immunosuppressive phenotype of the tumor and metastases, and could this information be exploited in the context of immune checkpoint blockade. 4) How often will metastases reflect the mutational landscape of the parental tumor (or other metastatic clones)? 5) Can the TIL technique be wedded to CAR T technology? I suppose there are many questions and issues.

This is a great next step in the rapid evolution of oncology treatment, and I’m looking forward to seeing much more.

stay tuned.

Novel Synergies Arising in the Immunotherapy of Melanoma

April 22, 2014AACR14, immunotherapy, melanoma, mutations, oncology, TCR therapy, TILsPaul Rennert

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Steven Rosenberg gave an interesting talk at this year’s American Association for Cancer Research meeting (AACR 2014). He discussed various cell therapies that were developed at the National Cancer Institute (NCI). He began with a review of 3 trials in metastatic melanoma that used the patient’s own tumor infiltrating lymphocytes (TILs), isolated, expanded and re-injected, as the treatment. Ninety-three patients were enrolled in the trials. The partial response rate (PR) was 32% and the complete response rate (CR) was 22%. Notably, some of the CRs were durable; Dr Rosenberg went so far as to state that TIL therapy could be curative, albeit in a relatively low percentage of patients treated. In a new trial of 110 patients they are seeing similar results, including durable PRs.

Similar attempts to use TIL therapy in other solid tumors have mainly failed. So one interesting question, posed by Dr Rosenberg, is why do melanomas readily respond immune therapies? Such therapies include not just TIL-based treatment but also to high-dose IL-2, checkpoint inhibitors: blocking CTLA4, blocking the PD-1 pathway, even agonist anti-CD40 antibody (mAb) treatment. All of these therapies will activate cytotoxic T cells and should also activate the rest of the immune system either secondarily, or in the example of agonist anti-CD40 mAb therapy, directly.

Melanomas are unusual in the abundance of TILs that are found within the tumor and the tumor microenvironment. Rosenberg floated the “mutation” hypothesis to explain why TILs are abundant in melanoma: melanoma tumors are highly mutated, with an average of 34 mutations per individual patient tumor. The mutation hypothesis posits that it is the abundance of mutations and therefore mutated proteins that drive TIL accumulation, that is, the mutations produce antigenic protein fragments that can be presented in context of MHC (MHC class I and class II are complexes found on antigen-presenting cells that activate T cells).

If this hypothesis is correct than several predictions can be made. One is that we should be able to find antigenic peptides that activate the TILs from specific patients. Another is that the TILs should be disabled by the tumor or tumor microenvironment (this is already suggested by the success of immune checkpoint inhibitors like ipilimumab and nivolumab in melanoma). Indeed, TILs isolated from patient melanomas express multiple immune control pathways, both in the immune response inhibitory pathways (PD-1, CTLA4, TIM-3) but also immune response activation pathways (4-1BB, OX-40, CD25, CD28, CD27, CD70) and others (LAG-3). So, these calls appears primed to respond, but are held in check.

Further, the TILs are primed to respond, at least in part, to tumor-derived peptides. Dr Rosenberg and colleagues sequenced the tumors from individual patients and used an algorithm to scan the data and identify immunogenic peptide fragments. They then synthesized the peptides and ask whether any of them could stimulate patient TILs. For each patient they found several immunogenic peptides. They could then isolate the T cell receptor (TCR) that mediated that recognition, and use it in an expression construct to develop mutation specific T cells. Note here that it is the TCR on the T cell that interacts with the MHC complex on antigen-presenting cells to trigger T cell activation. We have moved now from bulk TILs expanded ex vivo and re-injected to patient-specific engineered T cells specific for tumor antigens. This TCR-based cell therapy has now shown activity beyond melanoma and may be useful for other solid tumors that contain large populations of TILs. Finally, it may also be feasible to use the TIL immunogenic peptide data to craft highly tumor specific CAR constructs, i.e. by raising the CAR Vh domain (engineered as a scFV) to tumor-mutated antigens.

There remain significant unanswered questions. Other tumor types carry very high mutational burdens but do not accumulate large numbers of TILs – why not? The expression of immune control pathways on TILs derived from melanomas is complex – how best to manipulate these pathways? Also, how do TIL immune control phenotypes vary among patients? The identification of patient-specific immunogenic peptides may be useful in moving tumor vaccine therapy forward – how best to incorporate this data? Finally, a theme we always return to – how should doctors and patients use TCR-based therapeutics in the context of other available therapies.

The TIL data remind us that tumors raise an immune response to tumors, and this has implications for the re-emerging tumor vaccine field. Perhaps these mutated tumor antigens could be used in the context of tumor vaccination. There were several talks at AACR14 describing successful application of tumor vaccines in early phase clinical trials. There have been high-profile failures in this space – GSK’s phase 3 bust with their MAGE-A3 vaccine being a notable recent example. But sticking to melanoma, we see a few strong signals emerging.

Roger Perlmutter updated results from Amgen’s Phase 3 trial with T-Vec, which was initiated during his tenure (he is now at Merck). The T-Vec program was brought into Amgen with the $1 billion buyout of BioVex. T-Vec is a engineered viral vaccine that can infect and then replicate in tumor cells, pumping out the pleiotropic, immune-system priming growth factor GM-CSF along with encoded antigen. The injection is given at accessible tumor sites, e.g. in the skin, causing the melanoma to shrink. Importantly, not just the injected tumors, but tumors distant from the injection site responded, indicating that a systemic immune response had been triggered. T-Vec was compared to GM-CSF injection alone. While the overall response rate was high (about 60%) the interesting data are the comparisons of duration of response.

	time to progression or death (primary endpoint)	overall survival (OS) (a secondary endpoint)
GM-CSF	2.9 months	19 months
T-Vec	9.2 months	23.3 months

The response can be traced to cytotoxic T cells. These initially resemble patient TILs. However, after immunization these T cells have up-regulated immune response proteins (CD28, CD137, CD27, GITR) and down-regulated immune checkpoint proteins (PD-1, CTLA4, Lag3, TIM-3). So this immunization protocol is resetting the T cell phenotype, from immunosuppressed or anergic, to immune-competent and activated. This biological response is likely driven by the effect of GM-CSF on monocytes, macrophages and related cells. The mechanism of action bears further study.

We have not seen enough data yet to determine if there will be long-term responders (those that contribute to the “long tail” phenomena on OS curves) as we see in the immune checkpoint inhibitor trials. Regardless, Amgen is moving forward with clinical trials of T-Vec in combination with anti-CTLA4 mAb (Vervoy^tm, from Bristol-Myers Squibb) and with anti-PD-1 mAb MK-3475, in collaboration with Merck.

Lindy Durrant and colleagues from the University of Nottingham used a different approach to engage the immune system in the vaccine setting. They developed SCIB1, a DNA immunotherapy that encodes epitopes from gp100 and TRP-2 (melanoma antigens) into a human IgG1 antibody (honestly I need to understand better how they engineered this). The DNA vaccine is electroporated directly into muscle weekly x 3 and then at 3 months and 6 months. The transfection results in expression of the construct that is then taken up by Fc-receptor bearing cells via the CD64 Fc-receptor. CD64+ cells include monocytes, macrophages, dendritic cells and other immune cells. This Phase 1 study was designed as a 3×3 dose escalation study with an expansion cohort at the maximum tolerated dose, determined to be 4mg. Stage III and Stage IV melanoma patients were enrolled. 19/20 patients were shown to have an immune response to vaccination. There was a clear dose response. In the expansion cohort (n = 14) all patients showed an immune response despite expression of PD-L1 on tumor cells. Epitope recognition by both CD4 and CD8+ T cells was observed. Median survival of the expansion cohort is currently 15 months.

While this is a small early stage trial, such results are dramatic and highlight the concept that productively engaging the immune response requires recruitment of the patient’s antigen presenting cell populations (as noted above in the T-Vec example, this is what GM-CSF does). The tumor cell profile data hint at the potential use of PD-1 pathway blockade as a co-therapy for this DNA vaccine approach.

For smaller companies developing cancer vaccine modalities the potential to develop their technology alongside immunotherapy agents should be attractive. While PD-1 and CTLA4 targeting antibodies remain one obvious approach, data presented at AACR suggest that immune activating pathways (GITR, OX40 and others) might also be useful in the context of immune vaccine approaches. The trick will be to aim carefully.

We’ll follow up with a look at immune activation pathways.

stay tuned.