Category Archives: TCR therapy

How far can a CAR get you?

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

Slide036

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

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

Slide038

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

Slide039

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

THE SOLID TUMOR ANTIGEN FIELD IS SIMILARLY CONSTRAINED

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AND ANOTHER PAGE BELOW

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

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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

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

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.

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

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.

The future of cancer immunotherapy?

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

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 (Vervoytm, 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.