Category Archives: TIGIT

Fidgeting about TIGIT

Part 1 of 2

Pathways and targets covered: TGF-beta, PD-L1, PD-1, TIGIT

Companies mentioned: Merck KgaA, GSK, Roche, Merck, Mereo, iTeos, BMS, Arcus/Gilead, Compugen, Seagen, Beigene, Innovent, Agenus

Last week we had the bad news that Merck KGaA and GSK had thrown in the towel on bintrafusp alfa therapy for first-line advanced NSCLC.  Bintrafusp alfa is an anti-PD-L1/TGFbR2 TRAP therapeutic designed to selectively antagonize TGF-beta isoforms 1 and 3 while also blocking PD-L1, thereby delivering two-for-one anti-immunosuppression.  Bintrafusp alfa was being tested in a head-to-head trial vs. pembrolizumab and showed no added benefit in a patient population selected for PD-L1-high tumor expression (50%+ of cells in the tumor biopsy sample positive for expression).

This stirred up a fair amount of discussion, as TGF-beta blocking therapies are in vogue for immuno-oncology (IO), with small molecules, biologics, RNA-antagonists and genetic knockouts (in CAR T cells) all in the pipeline. I have high hopes for this space, despite the news out of Darmstadt. And to be fair, the press release stressed the ongoing bintrafusp alfa trials in bladder cancer, cervical cancer, and NSCLC using various drug combinations, and noted new trials in urothelial cancer and TNBC (https://www.emdgroup.com/en/news/bintrafusp-alfa-037-update-20-01-2021.html).  Still, the failure stung, due mainly to the promise of the early (open label) Phase 1 expansion cohort data that had suggested significant benefit from the therapy.

This got me thinking about TIGIT, another hot IO target.  The last time I wrote about TIGIT I ended with this question: “How to select patients who should respond to anti-TIGIT co-therapy (or anti-TIM-3 or anti-LAG-3)…?” (http://www.sugarconebiotech.com/?p=841). This is a question we should ask about any pathway – including TGF-beta of course – particularly as we are now in the post-immune-checkpoint era, that is, in a setting where many patients in the most IO-responsive indications like melanoma and NSCLC will have already been treated with an anti-PD-1 or anti-PD-L1.  So, is there anything known about TIGIT expression that can guide us in patient (or indication) selection?

Roche leads the field with tiragolumab an anti-TIGIT Fc-competent IgG1 that has shown activity in combination with the anti-PD-L1 antibody atezolizumab in first-line NSCLC, and only in patients with PD-L1- expressing tumors (> 1% of cells in the tumor biopsy sample positive for expression).  We can pause here to recall that this is about where we started the discussion above regarding the TGF-beta TRAP/anti-PD-L1 asset from Merck KGaA, being trialed in the PD-L1-high (>50%) setting in NSCLC.

In front-line NSCLC (EGFR and ALK wildtype), Roche reported responses higher than with atezolizumab alone. Data were shown at AACR and then updated at ASCO.  Here are some of the ASCO data:

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The response rate with dual therapy looks rather better than atezo alone, especially in the PD-L1 high cohort (middle panel).  Atezo alone appears to have underperformed, with an ORR = 21% (left panel, all patient data (ITT)).  In the comparable phase 3 trial of atezo vs chemotherapy in front-line NSCLC (also EGFR and ALK wildtype) the ORR = 38.3% in the atezo arm (n=285) and 28.6% in the chemotherapy arm (n=287), see nejm.org/doi/full/10.1056/NEJMoa1917346. Regardless the 66% response rate in the PD-L1-high cohort (middle panel) attracted attention.

The PFS data were also striking when compared to the prior trial.  This is tiragolumab plus atezolizumab / PD-L1 high cohort:

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We can go back and compare this to the atezo alone Phase 3 interim data shown at ESMO in 2019 (I was stuck in the overflow “room” which was a curtained space on the floor of the Barcelona convention center).  This is the PD-L1-high cohort:

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Here the median PFS is 8 months, certainly shorter than what is shown for tiragolumab plus atezolizumab, but again, note the disparity with the atezo alone arm of the study (medPFS for = 4 months).

Just to be clear, here are the PD-L1-high patient data compared:

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We’re left with the always troubling question of variability between trials and the possibility that the tiragolumab plus atezolizumab results are a fluke.  Unfortunately, we will have to wait and see.

There are two features here worth noting.  One is that TIGIT, the target, is expressed on T cells, along with PD-1.  So far this makes sense – they might very well synergize, particularly given the function of DNAM-1 in the context of T cell signaling (see part 2).  But the anti-TIGIT antibody is an IgG1 isotype, thought to trigger ADCC and CDC-mediated target cell (ie. the T cell) death.  But we want the T cells, that’s the whole point of blocking PD-L1 with atezo.  So what the heck is going on here?

Merck seems to have an answer, but first, some more data.  Merck’s anti-TIGIT antibody, vibostolimab, like Roche’s tiragolumab, is a wildtype IgG1.  Early data on the combination of vibostolimab and pembrolizumab (anti-PD-1), presented at ESMO2020, looked promising in immune checkpoint naïve patients (75% had prior chemotherapy, the rest were treatment naïve):

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We can benchmark these results to monotherapy, just as we did with the Roche data, focusing on the PD-L1-positive subset (here we can see data using a cutoff of >1% or >50% of cells positive in the tumor biopsy):

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The results compare favorably with pembro-alone using the >1% PD-L1 cutoff and are similar to pembro-alone using the >50% PD-L1 cutoff.  As usual it is difficult to compare between trials, but the signal is encouraging.

Preclinically, Merck has addressed the MOA, stressing the requirement for the intact Fc functionality imparted by the IgG1 antibody isotype.  As mentioned earlier, the mechanistic puzzle is that canonical IgG1 activity includes the triggering of target cell killing via ADCC and CDC mediated cytotoxicity.  Of course, TIGIT is expressed on the very T cells we want to preserve and activate, not kill.  Given this reality we need alternate hypotheses for the action of the IgG1 antibodies.  The predominant hypothesis is that anti-TIGIT antibodies are selectively depleting T-regulatory cells that are TIGIT-bright and immunosuppressive.  This is reminiscent of the now-T-regulatory cells that are TIGIT-bright and immunosuppressive.  It’s an easy hypothesis to advance, similar to the now-debunked arguments made on behalf of anti-CTLA4 and anti-GITR antibodies, and very likely incorrect.

Merck has demonstrated in preclinical models that antagonistic anti-TIGIT antibodies having a  FcgR-engaging isotype induce strong anti-tumor efficacy whereas anti-tumor activity is drastically reduced when using the same anti-TIGIT antibodies that are null for FcgR-engagement (doi: 10.3389/fimmu.2020.573405). These results are consistent with data presented by multiple groups, eg. Mereo and iTeos.  The Merck team further showed shown that FcgR engagement persistently activated myeloid lineage antigen-representing cells APCs, including the induction of proinflammatory cytokines and chemokines while TIGIT blockade simultaneously enhanced T cell activation including elevated secretion of granzyme B and perforin, which synergizes with anti-PD-1 antagonism.  I favor this hypothesis.  Nb. This suggests we’ve a lot to learn still about the best way to engage Fcg receptors, a theme I introduced in the last post (link).

Where does this hypothesis leave everyone else in the TIGIT space?  Let’s line them up:

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A few quick notes: EMD Serono/Merck KGaA and Innovent have anti-TIGIT programs without disclosed isotype information; Arcus has disclosed a second, Fc-competent, anti-TIGIT program (AB308); Agenus is developing both IgG1 and IgG4 anti-TIGIT antibodies.

A question: is Seagen’s hyper-killing IgG1 a step too far?

In summary, we have preliminary data in NSCLC that suggest that anti-TIGIT may synergize with anti-PD-1 or anti-PD-L1 therapies, consistent with the expression of TIGIT on PD-1 positive (ie. activated) T cells.  We have several hypotheses addressing the Fc-end of the therapeutics, and some information on why blocking TIGIT may enhance T cell responses.

Other than selecting patients with PD-L1-positive tumors, can we gate on TIGIT expression?  Apparently not, at least not in NSCLC, as just reported at the World Conference on Lung Cancer (abstract P77.02 – Efficacy of Tiragolumab + Atezolizumab in PD-L1 IHC and TIGIT Subgroups in the Phase II CITYSCAPE Study in First-Line NSCLC).

Here’s their text:

“Among the 135 enrolled patients with PD-L1-positive NSCLC (intent-to-treat [ITT] population), 113 had results from the SP263 assay and 105 had results from the TIGIT assay. The biomarker-evaluable populations (BEP) for both of these assays were similar to the ITT population. Comparable PFS improvement with tira + atezo relative to atezo monotherapy was seen in PD-L1–high (≥50% TC) subgroups defined by SP263 (PFS HR 0.23, 95% CI: 0.10–0.53) when compared with PD-L1-high subgroups defined by 22C3. However, for patients whose tumors were defined as TIGIT-high (≥5% IC), no strong association with PFS improvement was observed.

Biomarker subgroup Subgroup, n (BEP, N) PFS HR (CI) relative to atezo monotherapy arm
ITT (PD-L1 IHC 22C3 >1% TPS) 135 (135) 0.58 (0.39–0.88)
PD-L1 IHC 22C3 (≥50% TPS) 58 (135) 0.30* (0.15–0.61)
PD-L1 IHC SP263 (≥50% TC) 45 (113) 0.23* (0.10–0.53)
TIGIT IHC (≥5% IC) 49 (105) 0.62* (0.30–1.32)
*Unstratified HR

Prevalence of PD-L1 subgroups in the BEP was comparable with previous reports for both IHC assays. The PFS benefit observed with tira + atezo in patients with tumors defined as PD-L1-high by 22C3 was also observed using the SP263 IHC assay, but not in tumors classified as TIGIT-high using an exploratory TIGIT IHC assay. Our results suggest that PD-L1 expression, assessed by 22C3 or SP263, may be a biomarker for tira + atezo combination therapy in metastatic PD-L1-positive untreated NSCLC.”

So that the answer to the question we started with, can we pick patients, is ‘no’ for TIGIT expression, at least in this indication.

Regardless, to actually understand what blocking TIGIT does, we need to better understand the pathway.

That will be discussed in Part 2, coming soon.

Stay tuned.

“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 widget TIGIT

Genentech continues to work on TIGIT, so what the heck is this target? Lets have a look, but first, some context.

T cell constraint is a fundamental attribute of tumor-induced immunosuppression. CTLA4 and PD-1 are central regulators of this process, and antibody blockade of these pathways can restore anti-tumor responses. The state of T cell constraint (non-responsiveness) has been termed anergy in reference to CD4+ T cells and exhaustion in reference to CD8+ T cells. Exhausted CD8+ T cells have a recognizable T cell phenotype characterized by the expression of diverse inhibitory pathways and proteins, including PD-1, TIM-3, LAG-3 and TIGIT. Whether such a phenotype is absolutely selective for exhausted CD8s is a matter of debate, but is a good starting point for a discussion of the need for so many regulatory pathways.

Dual gene-deficient (knock-out) mice and the administration of blocking antibody combinations have shown that the inhibitory receptors can function synergistically to reject tumors in mouse models. The hypothesis that individual co-inhibitory receptors contribute distinct functions to collectively limit T cell responses has recently been tested in human cancer clinical trials, yielding the impressive result that co-blockade of CTLA4 and PD-1 has synergistic and beneficial anti-tumor activity. Such benefit comes with a toxicity cost, as pathological autoimmunity is revealed when the “brakes” come off the immune system.

Why does the T cell arm of immune system require so many different control pathways? This is a reasonable question, which can be answered somewhat glibly with the observation that uncontrolled immunity leads to autoimmune disease and/or chronic inflammation. Still, though, why are multiple breaks required? The working hypothesis is that one pathway (CTLA4) regulates T cell activation by CD28 that normally occurs in the spleen, lymph nodes, Peyer’s patches and other “secondary lymphoid organs” (the thymus, bone marrow and fetal liver are the major primary lymphoid organs). A second pathway (PD-1) is generally thought to regulate “peripheral” T cell activation at the sites of pathogen encounter – in this sense “peripheral” means outside of the lymphoid organs themselves, that is, in the tissues and circulation, or, in the case of cancer immunology, within the tumor. So, simplistically, there is one control pathway (CTLA4) in the house and another (PD-1) in the yard. The recent paper (link 1) describing the release of T cell recognition of tumor antigens upon CTLA4 blockade in melanoma suggests either cross-talk between the compartment (i.e. tumor beds have lymphatic or circulatory drainage to secondary lymphoid organs) or that the role of CTLA4 is more complex than we think.

What about the other control pathways? LAG-3 is a competitive regulator of CD4/MHCII antigen recognition activity and was shown to confer Treg function when transfected into naive CD4+ T cells. The expression of LAG-3 on CD8+ T cells (which are critical for anti-tumor activity) suggests a role in the interaction of CD4+ and CD8+ T cells. LAG-3 is also expressed on tumor cells and may mask tumors from immune recognition. LAG3/PD-1 doubly gene-deficient mice can reject poorly immunogenic tumors that wild-type mice cannot reject. However, the doubly deficient knockout mice also develop pathological and aggressive autoimmunity. These results show that these proteins have distinct roles in regulating immune responses.

TIM-3 has several immune regulatory activities, one of which is to suppress T cell recognition of phosphatidylserine, a molecule expressed on dead and dying cells but also on tumor cells. As with LAG-3 the combination of anti-PD-1 and anti-TIM-3 antibodies had enhanced anti-tumor efficacy in mouse tumor models when compared to either antibody alone.

And now we have TIGIT, an Ig superfamily protein and a member of the PVR/nectin family that includes CD226 (DNAM-1), CD96, CD112 (PVRL2), and CD155 (PVR), among others. The biology of this family of proteins is complex and a little intimidating. Genentech has been prosecuting this pathway for several years, and their new paper (link 2) has perhaps shed additional light on the biology and utility of this target.

One mechanism by which TIGIT modulated immune responses is via the interaction of TIGIT on T cells with CD155 expressed on immature or resting dendritic cells, which blocks maturation signals normally delivered by CD226, that is, TIGIT is a competitive inhibitor of the interaction of CD226 with CD155. The authors note that this system resembles the co-stimulatory/co-inhibitory receptor pair of CD28 and CTLA-4, where CTLA4 is a competitive inhibitor of the interaction of CD28 with B7-1/CD80 and B7-2/CD86. The expression pattern of the receptors is also similar: both TIGIT and CTLA-4 are induced upon cell activation, while the expression of CD226 and CD28 is constitutive.

As alluded to above, and noted explicitly by the Genentech team, the molecular and functional relationships between TIGIT and it’s various ligands/co-receptors are poorly characterized. Furthermore, TIGIT’s role in regulating CD8+ T cell responses and the mechanisms underlying such regulation are not known. Of note, antibodies to TIGIT or PD-L1 alone enhanced CD8+ T cell effector function in tumor-draining lymph nodes, but blockade of both receptors was required to allow activation of CD8+ T cells within the tumor microenvironment, as measured by IFNy production. The authors conclude that TIGIT is a critical and regulator of CD8+ T cell anti-tumor activity. The mechanism of action evoked to explain the role of TIGIT in the tumor setting was addressed using FRET and other analyses. The authors show that TIGIT interacts directly with CD226 to prevent homodimerization, a component of the interaction of CD226 with CD155.

There are a few things to consider here. The animal models were run with very high amounts of anti-TIGIT and anti-PD-L1 antibodies on board (10 mg/kg anti-PD-L1 and 25 mg/kg anti-TIGIT) given 3 times a week. That’s nearly a gram of antibody approximately every 2.5 days. While the anti-PD-L1 antibody used has a mutated Fc domain that cannot mediate direct cell killing by ADCC, the anti-TIGIT antibody used is a wild-type IgG2a isotype antibody and almost certainly mediates direct killing of TIGIT+ cells. While the in vitro FRET assays are suggestive of the proposed mechanism of action, what is actually occurring in vivo is less clear. TIGIT expression on NK cells is also worthy of further exploration.

So I have a doubt. Not that the pathway is important, but that we really have a good sense of how it functions, nor how antagonism of the pathway in patients will impact anti-tumor activity and baseline immune responses. Locally, Drs Vijay Kuchroo and Ana Anderson have done wonderful work on TIGIT biology, and no doubt one or more of the Cambridge immunotherapy companies is working on this target and exploring it’s utility in the tumor setting. Given the expression pattern of TIGIT in tumors – i.e. on PD-1+/TIM3+ “exhausted” T cells – it is certainly worth the effort to find out.

How to select patients who should respond to anti-TIGIT co-therapy (or anti-TIM-3 or anti-LAG-3) is a critical question, best left for another day.

stay tuned

AND HAPPY HOLIDAYS AND PEACE TO ALL