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)
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
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.