Category Archives: pembrolizumab

Enumeral update – guest post by Cokey Nguyen, VP, R&D

Paul’s introduction:  Enumeral has been sending ’round some interesting updates to several of their programs and I asked for some more detail. Below is a quick primer sent along by Cokey Nguyen. More detail is available in Enumeral’s recent 8K filings, including one that dropped this morning. Also the company will present this and other work at the AACR Tumor Microenvironment Meeting in January (http://www.aacr.org/Meetings/Pages/MeetingDetail.aspx?EventItemID=73#.VlyGS7_QO2k - see below).

New data from Enumeral, by Cokey Nguyen

PD-1 biology in human lung cancer is an active area of research, as these cancers have shown PD-1 blockade responsiveness in clinical trials.  Enumeral has a drug discovery effort aimed at generating novel anti-PD-1 antibodies to develop into potential therapeutic candidates.  Using a proprietary antibody discovery platform, two classes of PD-1 antagonist antibodies were discovered:  the canonical anti-PD-1 antibody which blocks PD-L1/PD-1 interactions and a second class of antibody which is non-competitive with PD-L1 binding to PD-1.  These antibodies were validated first in a pre-clinical model of NSCLC using NSG mice with a humanized immune system and a patient derived NSCLC xenograft (huNSG/PDX) (Figure 1).  Here either class of antibody demonstrated activity on par with pembrolizumab, confirming that PD-1 blockade can slow tumor growth.

Figure 1

Figure 1

In order to confirm these pre-clinical findings, Enumeral began proof of concept studies with NSCLC samples.  The first question was if resident TILs, as found in tumors, could be reinvigorated (Paukken and Wherry, 2015) or if PD-1 blockade is mainly a phenomenon that affects lymph node-specific T cells that have yet to traffic to the tumor.  In these studies, Enumeral found PD-1 blockade can, in fact, increase effector T cell function, as readout by IFNg, IL-12, TNFa and IL-6.  In addition, in a NSCLC sample that showed PD-1hi/TIM-3lo expression, PD-1 blockade strongly upregulated TIM-3 expression (~5% to ~30%, see Figure 2).

Figure 2

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In these NSCLC-based studies, it was also found that an anti-PD-1 antibody (C8) which does not bind to PD-1 in the same manner as nivolumab or pembrolizumab (PD-L1 binding site) displays differentiated biology:  increased IFNg production and significantly higher levels of IL-12 in these bulk (dissociated) tumor cultures (Figure 3).  As IL-12 is thought to be a myeloid derived cytokine, this mechanism of action is not yet well understood, but has been now observed in multiple NSCLC samples as well as in MLR assays.

Figure 3

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In these NSCLC studies, while a subset of patient samples demonstrates PD-1 blockade responsiveness, the co-expression of TIM-3 on NSCLC TILs suggests this is a validated path forward to increase the response rate in lung cancer.  As with the PD-1 program, armed with a substantial portfolio of diverse anti-TIM-3 binders, Enumeral is actively testing single and dual checkpoint blockade on primary human lung cancer samples.

Look for the companies 2 posters at AACR/TME in January

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“Combination Cancer Immunotherapy and New Immunomodulatory Targets” published in Nature Reviews Drug Discovery

Part of the Article Series from Nature Reviews Drug Discovery, our paper hit the press today

Combination cancer immunotherapy and new immunomodulatory targets. Nature Reviews Drug Discovery 14, 561–584. 2015.  doi:10.1038/nrd4591

by Kathleen Mahoney, Paul Rennert, Gordon Freeman.

a prepublication version is available here: nrd4591 (1)

ICI15 presentation is now available

Over 100 slides on immune checkpoint combination therapy, novel targets and drug development in immuno-oncology, created for a 3 hour workshop at ICI15 (link).

As always we work from indications to discovery and back again, keeping one eye on the rapid evolution of clinical practice in oncology and the other on novel targets and therapeutics.

on SlideShare now:

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.

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

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:

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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:

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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

Side Effect Profiles of Immune Checkpoint Therapeutics – Parts 2 and 3

Part 2 – The Border Wars.

One of the fascinating aspects of the toxicity of immune checkpoint therapeutics is that it is a lot of is triggered at the border between self and non-self, where non-self is everything that the immune system must encounter and sort through continuously. The sorting serves to identify pathogens and ignore non-pathogens among the myriad components of the microfauna and flora that inhabit these borders. The “sampling” of these ecosystems is continuous and highly reactive – one glass of unpurified water taken on foreign soil will teach you this lesson pretty quickly. When the immune system is unrestrained by blockade of CTLA4 and/or PD-1 it is not surprising that we see the breakdown of immune tolerance in these border zones.

There are three major surfaces where toxicity has been an issue: the skin, the gut mucosa, and the airspaces of the lung. Ipilimumab treatment can cause pretty intense inflammation of the skin, generally dismissed in the clinical trial literature as “rash”. In a pooled analysis of nearly 1500 patients enrolled in various ipilimumab clinical trials, 45% developed dermatological AEs considered drug related, and 2.6% (so 39 people) developed severe symptoms rating a grade 3-4 (where grade 5 is lethal) (see Tarhani, A. Scientifica 2013, Article ID 857519). A fair amount of the milder skin AEs can be ascribed to an anti-melan-A response, as this antigen is abundant in melanoma, the setting for the clinical development trials. In the Phase 3 registrational trials dermatologic AEs were reported in more than 40% of patients in the ipilimumab arms, and there were very severe AEs that cannot be ascribed to an anti-melan-A (i.e melanocyte) immune response. This is from Tarhani’s review of patients in the ipilimumab + gp100 (vaccine) and ipilimumab monotherapy arms having dermatological irAEs,

“of these, 2.1% and 1.5%, respectively, were grade 3 or higher … Severe, life threatening, or fatal immune-mediated dermatitis (Stevens- Johnson syndrome, toxic epidermal necrolysis, … full thickness dermal ulceration, or necrotic, bullous, or hemorrhagic manifestations; grade 3–5) occurred in 13 of 511 (2.5%) patients treated with ipilimumab. One patient (0.2%) died as a result of toxic epidermal necrolysis, and one additional patient required hospitalization for severe dermatitis… .”

That’s some rash. We note in passing that dermatologic AEs were see in a phase 2 trial of ipilimumab plus chemotherapy in non-small cell lung cancer (NSCLC) and so this is certainly not limited to the melanoma setting. PD-1 pathway antagonists also cause skin inflammation in both the melanoma and other settings, similarly suggesting that what we are seeing here are immune responses to antigenic stimulation that is normally immunologically inert. Nivolumab-induced dermatologic toxicity can be severe, but is less common than seen with ipilimumab therapy.

The issue of skin toxicity is well known clinically, and there are established treatment protocols requiring cessation of therapy and treatment with anti-inflammatories, usually steroids (i.e the REMS protocols). The gastrointestinal (GI, “gut”) AEs are also common, can arise suddenly, be resistant to therapy (corticosteroids, and rarely, anti-TNF antibody), and are of significant concern. Returning to the pooled analysis of ~1500 ipilimumab patients we see roughly half of the patients developing GI symptoms (this includes diarrhea). If we focus on grade 3/4 SAEs we have 10-12% of patients with GI disorders that include colitis, enterocolitis, intestinal perforations etc that can proceed to lethal septic complications. Of note, inflammatory infiltrates in the intestines include abundant T cells and neutrophils, showing that acute ongoing inflammation is occurring. GI toxicity is less common and less severe in nivolumab-treated patients, and this is true also of Merck’s anti-PD-1 antibody pembrolizumab and the anti-PD-L1 antibody MPDL3280A from Roche. Colitis is generally not a big issue, for example, GI SAEs are seen in less than 1% of nivolumab-treated patients. We might conclude here that other pathways are maintaining tolerance in the gut mucosa when the PD-1 pathway is blocked.

A different picture emerges when we consider AEs in the lung. Pulmonary toxicity is rare in the context of ipilimumab monotherapy, with only scattered case reports in the literature (see Voskens et al for a review of rare ipilimumab-induced AEs: link). Anti-PD-1 pathway therapeutics, particularly nivolumab, are associated with pneumonitis, which is inflammation of the lung tissues. In the monotherapy setting, both nivolumab and pembrolizumab causes pneumonitis in 3-4% of patients – the condition is generally mild and treatable. Of note this AE rate is consistent across indications (e.g. melanoma, renal cell). The anti-PD-L1 antibodies (Roche’s MPDL3280A and Astra Zeneca’s MEDI4736) have not been associated with pneumonitis to date, perhaps reflecting a unique profile. The recent data from the anti-PD-L1 antibody MEDI4736 trial in NSCLC presented a tolerable profile. While response rate was low, significant numbers of patients remained on therapy with stable disease (ASCO 2014, Abstract #3002).

More worrisome is the pneumonitis rate and severity in combination therapy particularly in the NSCLC setting where diminished lung function is already a concern (smokers with lung cancer can’t breathe). When nivolumab was combined with platinum-based chemotherapy in NSCLC the SAE rate jumped to 45%, with notable findings of grade 3/4 pneumonitis (7%) and acute renal failure (5%) (ASCO 2014, Abstract #8113). Nivolumab plus erlotinib was not associated with pneumonitis (ASCO 2014, Abstract #8022) but response rates were low as well suggesting that these therapies were not particularly additive. The combination of nivolumab with ipilimumab was most worrisome, with grade 3/4 pneumonitis (6%) now seen along with grade 3/4 SAEs of skin (4%), GI (16%) and others (16%) (ASCO 2014, Abstract #8023). Most problematic is that 35% of patients discontinued, and between 3 to 5 patients died due to drug related SAEs including respiratory failure (caused by severe colitis), epidermal necrolysis (in a patient with multiple SAEs) and pulmonary hemorrhage (pneumonitis). As indicated above, the anti-PD-L1 antibody MEDI4736 may better suited for combination therapy. A combo trial in NSCLS with anti-CTLA4 mAb tremelimumab is enrolling, so we’ll wait and see.

It’s fair at this point to take a step back and say “so what?” These are close to terminal patients with deadly cancers usually highly refractory to treatment, and we cannot expect a free ride. The unmet need is acute and urgent, and these therapeutics offer potential cures and increase in life expectancy – as shown very clearly in last weeks early termination of the Phase 3 trial of nivolumab versus dacarbazine due to the obvious overall survival advantage offered by nivolumab (see John Carroll’s story in Fierce Biotech here: link)

The problem is that the response rates we are seeing are generally low, the discontinuation rates high, and for anti-CTLA4 and anti-PD-1 therapeutics there is no clear consensus regarding the use of biomarkers to select patients most likely to respond. Therefore the actual percent penetrance of therapy in the patient cohorts becomes quite low. For those relatively few patients who respond well the outcomes can be sustained and robust. It is critical however to get these response rates up. The blockbuster combination of nivolumab plus ipilimumab in metastatic melanoma gives us a sense of what is possible, if the drugs are tolerable. It is also critical to understand how and why immune therapy can make subsequent therapy intolerable, as we’ve seen in case reports, or conversely, how and why prior therapies can cause such problems for patients going onto an immune therapeutic (see that Voskens review mentioned above). We’ve seen some the issues that can bedevil combinations in metastatic melanoma (with vemurafenib) and in renal cell carcinoma clinical trials (pazopanib) When we look at all of the combination clinical trials underway with these agents we have to wonder what surprises lay in store.

Part 3 – The Fifth Column.

The fifth column refers to enemies lurking within the boundaries of the state, in this case the human body. These are a mixed collection of AEs that can be difficult to understand. While we are used to see liver and kidney inflammation in the setting of cancer therapy, it remains a bit mysterious that immune checkpoint therapy can cause severe inflammatory responses in these organs, the most notable is probably the induction of hepatitis in patients treated with ipilimumab. Even weirder (for me anyway) are the endocrinopathies, headlined by pituitary inflammation, seen with both CTLA4 and PD-1 directed immunotherapies. Primary thyroid inflammation is also seen although less frequently. These are of course autoimmune targets in this setting, but the triggers are obscure, as is also almost always true in autoimmune disease. Somewhat remarkable is the emergence of a sometimes fatal but normally very rare condition known as autoimmune hypophysitis or lymphocytic hypophysitis, which is inflammation of the pituitary gland. Hypophysitis is a unique toxicity of immune checkpoint inhibitors, and has been been seen in patients treated with ipilimumab, tremelimumab, and nivolumab. Because the pituitary sits in the middle of the limbic hypothalamic-pituitary-adrenal axis effects on the thymus and adrenal gland are also noted, with adrenal insufficiency being a severe and life-threatening complication. It must be stressed that the frequency of this AE is stunningly high, reaching 17% in some trials, as the disease has been described only very rarely, with a good deal less than 1000 cases ever known prior to the introduction of immune checkpoint therapeutics.

So we won’t dwell on this, as clinicians now know what to watch for, and treatment paradigms have been developed. As mentioned earlier, treatment generally involves initiation of steroids to control to autoimmune response, and cessation of immune checkpoint therapy.

Let’s return to the consideration of combination therapy, which I think we all agree is essential if we are really to expand use of immune therapeutics in the treatment of these difficult cancers. Great hope has been placed in the combination of CTLA4 and PD-1 targeting agents with “safe” immune checkpoint modulators, notably the IDO-inhibitor from Incyte. We have very little information to date, but it is notable that the dose limiting toxicity in the first combination trial of ipilimumab and INCB024360 from Incyte (INCY) was liver damage as measured by ATL elevation. It may be that merely piling on ways of disrupting Treg activity will not help with the toxicity profile; in fact, one might make the prediction that this approach will make things worse in some settings.

We’ve remarked in passing on the apparently mild safety profile of the anti-PD-L1 inhibitors compared to the PD-1 inhibitors. This makes some sense, as the ligands are expressed by the target tumor cells, and this may be the main sink for the injected antibody, i.e. antibody may not be evenly bio-distributed but rather predominantly localized to the tumors. The concordance of anti-PD-L1 antibody activity with tumor PD-L1 expression is consistent with a direct and localized effect. The fact that there is less consistent concordance of anti-PD-1 antibody activity with PD-1 expression by tumor-infiltrating T cells suggests less specificity in the induced immune response, and this may be why we see autoimmune toxicity in the nivolumab setting. As CTLA-4 is exclusively T cell expressed, the same seems to hold true for anti-CTLA4 antibody therapy. So combining these may not be the most ideal way forward.

We will discuss alternative approaches next time, but first there is some new data on novel immune checkpoint therapies to consider. These are the TNF receptor superfamily proteins that we discussed last month (link): 4-1BB, CD27, OX40 and GITR. There is admittedly very little data to date. Pfizer’s (PFE) anti-4-1BB antibody PF-05082566 reached a safe dose in Phase 1 without undue toxicity signals (ASCO 2014, Abstract #3007). Pfizer disclosed combination trials with rituximab in Non-Hodgkin Lymphoma (NHL) and pembrolizumab (anti-PD-1). The BMY antibody urelumab was tolerated through its’ dose escalation cohorts, and ex vivo analysis showed activation of CD8+ T cells and NK cells (ASCO 2014, Abstract #3017). The Celldex anti-CD27 mAb also has demonstrated safe dose escalation, although to date without signs of clinical activity (ASCO 2014, Abstracts #3024 and #3027). Celldex (CLDX) claims planned studies in combination with nivolumab, ipilimumab, and the targeted therapeutics darafenib and trametinib.

As we discussed in an earlier post, 4-1BB, CD27, OX40 and GITR are evolutionarily closely related receptors. Biomarker studies such as the one performed in the urelumab trial will be essential in understanding how these immune stimulatory pathways will differentiate clinically and which will be safe in combination settings. We’ve reviewed the biology of this superfamily recently (see these posts) so won’t do so again until we get some more clinical data.

Next we will introduce some novel targets in the TNF receptor superfamily, revisit some apoptotic pathway “influencers”, and will swing back around to PD-1 and PD-L1 in some other solid tumor settings (not necessarily in that order).

stay tuned.

Side Effect Profiles of Immune Checkpoint Therapeutics – 1

Part 1 – wherein we introduce the issues

I think we are underestimating the impact of immune checkpoint mediated adverse events (AEs) and are too easily calmed by the notion that severe AEs (SAEs) can be managed or will reverse when drug is withdrawn. Indeed, we are beginning to see that the toxicity profiles of the anti-CTLA4 antibody ipilimumab and the anti-PD-1 antibody nivolumab will limit their use, at least in some settings. Anyone needing proof can look at Bristol-Myers Squibb (BMY) and their recent $50MM USD engagement with CytomX, a neat little Bay Area biotech that has developed “masking” technology for antibodies, called Probodies, that creates antibodies that are inert until they reach the tumor environment. Their website at http://www.cytomx.com/probodies.php has links to their Science Translational Medicine paper and also their 2014 AACR presentation.

So for their fifty million upfront, plus R&D support, BMY gets to apply the Probody technology to ipilimumab, and three other targets. Since BMY also owns nivolumab, we might make the reasoned guess that this is a second target, although that has not been disclosed and remains unclear. Another interesting target for masking is urelumab, the agonist anti-CD137 (aka 4-1BB) antibody. And it’s clear that there are other targets for which antibodies could benefit from being masked.

Why “mask” immune checkpoint antibodies? The issue is that these antibodies can induce immune responses that are off-target, that is, not directed at the tumor. Some off-target AEs induced by different agents are similar, some are quite unique and others appear only in combination settings. Lumping these all together as “immune-related” AEs (irAE) may be convenient but teaches us nothing about the underlying mechanisms.

So lets have a look at some general mechanisms.

Recent posts have concentrated on ipilimumab and the PD-1 pathway antagonists (see here) and have detailed some of the AE issues arising. Other toxicities have been seen with the TNFR agonists, such as 4-1BB and related receptors, whose biology and use are reviewed in another recent post (link).

Breaking irAEs down by class is helpful. The irAEs are most commonly associated with barrier tissues: skin, gut mucosa, the lung airways and the eyes. Less common are irAEs triggered in the context of “sterile” inflammation, that is, inflammation directed toward tissues and organs within the body and walled off from the outside environments. This class includes the endocrinopathies and abnormalities in liver, kidney and other organs. The third class captures central nervous system (CNS) toxicities. Some irAEs can appear with monotherapy, some are worse in the context of dual immune checkpoint blockade and some are associated with immunotherapy in the context of combination therapy with other types of drugs.

The cause of irAEs is very likely to be due to the breakdown of immune tolerance to commensal flora antigens and/or to self-derived antigens. We can look at the biology of the pathways targeted by ipilimumab and the PD-1 inhibitors for some clues to how this arises. The ipilimumab target CTLA4 normally acts as a shut-off switch for primary immune responses, blocking the activity of the closely related T-cell costimulatory receptor CD28, normally triggered by the B7 proteins, B7-1 and B7-2. The nivolumab target PD-1 acts as a similar stop signal but is associated with shutting off activated T cells by binding to its’ ligands PD-L1 and PD-L2. It is worth noting that these two families of receptors and ligands are closely related – CD28, CTLA4 and PD-1 are evolutionarily related receptors and B7-1, B7-2, PD-L1 and PD-L2 are closely related ligands. One consequence of this relatedness is seen in the ability of B7-1 to bind to and activated PD-1. Of interest, the evolutionary tales suggests a primordial single pathway that has diverged and specialized to control different aspects of the adaptive immune response. This is very similar to the situation we described for the closely related TNFR family members 4-1BB, OX-40, CD27 and GITR, and their ligands 4-1BBL, OX-40L, CD70 and GITRL.

The irAE story begins with ipilimumab, as does the immune checkpoint field. There are several mechanisms by which CTLA4 blockade might induce irAEs. The first is by lowering the threshold for activation of T cells, thereby allowing these cells to respond to antigens they would normally ignore. CTLA4 is expressed exclusively on T cells and regulates T cell activation. The second, related, mechanism is the breakdown of tolerance to antigens. On the surfaces of the organism antigens to which were have become tolerant (microorganisms, commensal flora) are routinely presented by APCs (antigen-presenting cells including dendritic cells and monocytes/macrophages) in the draining lymph nodes, Peyer’s patches, spleen and other lymphoid organs. Normally, these antigens are ignored. Furthermore, any aberrant T cells response to tolerant antigens is blocked by the action of T regulatory cells (Tregs). These Tregs “see” tolerant antigens and secrete immune suppressive factors to keep nearby T cells from becoming activated (T-effectors) and moving out into the environment to respond wherever antigen is encountered. It has been demonstrated that ipilimumab derails Treg function as well as pumping up T-effector cell function. As a consequence, in the presence of ipilimumab, T-effectors overwhelm any tolerance mechanisms and triggers immune responses to cells and tissues presenting antigens that are normally ignored. The setting for PD-1 pathway-mediated toxicity is similar although the details are a little different. PD-1 inhibition is mediated by expression of PD-L1 and PD-L2 on diverse cells types in the periphery (i.e. outside the lymphoid organs). PD1 is highly expressed on Treg cells. Peripheral tolerance is maintained by this system, and blockade of the system disrupts Treg function directly, and licenses T-effector cells for inappropriate responses to antigens normally ignored. The irAEs seen in the context of PD-1 blockade are generally considered less common than those seen in the context of CTLA4 blockade, suggesting that compensatory mechanisms of tolerance maintenance may be operative in the periphery.

Genetic deletion studies in mice can shed some light on these mechanisms. The CTLA4 gene-deficient (aka “knockout”) mouse dies within five weeks after birth from systemic autoimmunity. I’ve seen these mice several times – they have lymph nodes the size of large peas – and are half the size of wildtype littermates due to multiorgan autoimmune inflammation that is ultimately lethal. The phenotype of the PD-1 knockout mouse is less severe. These mice develop specific autoimmune diseases depending on the background strain of mouse use to derive the knockout. Autoimmune cardiomyopathy and lupus-like nephritis have been described. The PD-L1 knockout mouse has a very mild phenotype unless crossed back on strains of mice prone to autoimmunity, as was shown for lupus nephritis. The PD-L2 knockout mouse also developed renal disease although the mechanism differed from that of the PD-L1 knockout. Both manifestations required active challenge to induce disease, i.e. autoimmunity was not spontaneous.

So in this case the mouse genetic studies have previewed the human experience to the extent that CTLA4 blockade induces more toxicity than PD-1 blockade. As we’ll soon see, the combination of these immune checkpoint blockades can be more problematic that either given alone.

We’ll return with a toxicity by indication breakdown of irAEs induced by CTLA4 antagonists, PD-1 and PD-L1 antagonists and combinations of these agents with each other and other types of therapeutics. Then we’ll swing back to the TNF receptor superfamily for a look at the known and expected issues to be encountered there. We’ll finish with a few suggestions on novel ways forward – triggering T-effector immune responses to tumor without upending the systemic Treg environment. And as we do all that we’ll highlight a few key companies to watch.

stay tuned.