From Research to Cure: 2019 BioLegend Symposium Proceedings Introduction To celebrate the grand opening of its new 8-acre campus, BioLegend hosted an inaugural symposium on May 8, 2019 that featured presentations from leading researchers in cancer immunotherapy, including 2018 Nobel Laureate Dr. James Allison. The speakers overviewed the state of immune checkpoint research, presented novel unpublished data, and addressed future challenges facing the field. The lectures sparked valuable discussion among symposium attendees and helped form new connections and partnerships, marking the start of a new era of legendary discovery. This article serves to present the abstracts provided by the speakers. Symposium Summary Gene Lay, BioLegend President and CEO, began the symposium with a welcome and introduction of the five world-renowned speakers: James Allison, Jeff Bluestone, Vijay Kuchroo, Robert Schreiber, and Arlene Sharpe. The speakers discussed the limitations of current checkpoint blockade strategies and their research efforts to address these challenges. There was a common emphasis on the importance of defining specific T cell populations’ roles in enhancing or restricting anti-tumor responses. To this end, they described novel approaches to investigate the function of cell subsets and characterize cellular factors that control anti-tumor immunity. Findings from these studies demonstrated the ability of cutting-edge screening and exploratory methods to identify new therapeutic targets. These innovations, along with the continual development of in vivo research tools, have allowed the speakers to make progress on improving the efficacy of immunotherapies while reducing their toxicity. Research presented at this symposium will significantly advance our understanding of the mechanisms behind successful combination therapies, and establish ideal outcomes for future treatments.

San Diego, CA 92121 1.877.246.5343 (877-BIOLEGEND) | International: 1.858.768.5800 biolegend.com Speaker Abstracts James P. Allison, PhD, MD Anderson Cancer Center, University of Texas Immune Checkpoint Therapy: Lessons Learned and Next Steps Since the finding that CTLA-4 is an immune checkpoint which inhibits T cell proliferation, the existence of multiple non-redundant pathways that limit T cell responses, including the PD-1/PD-L1 axis, has been shown. Ipilimumab, a checkpoint inhibitor antibody to CTLA-4 that blocks its interaction with B7 molecules on the surface of antigen presenting cells and prohibits T cell co-activation, provides long-term survival benefit in ~20% of late stage melanoma patients. Many patients appear cancer-free after a decade or more. PD-1/PD-L1 antagonist antibodies provide objective responses against several tumor types with response rates of about ~25%. Combination of anti-PD-1 and anti-CTLA-4 increases the response rate to ~50% in late stage melanoma and is now standard of care. The FDA has now approved 6 different checkpoint antibodies for a variety of cancers. Rational checkpoint inhibitor combination requires an understanding of how individual treatments affect the immune system and how the immune system integrates multiple signals. Analysis of T cell populations that arise in CTLA-4-/- and PD-1-/- mice suggest that the normal functions of CTLA-4 and PD-1 are to restrict the differentiation space of CD4+ and CD8+ T cells, respectively. Combined CTLA-4 and PD-1 blockade, which provides higher response rates against a wider range of cancers than either monotherapy, acts through a T cell population not enriched in either single treatment. These findings provide a blueprint in how studies into the fundamental mechanisms of immune modulatory treatments can inform rational combinations that increase the range and efficacy of current checkpoint inhibitors.

Jeffrey Bluestone, PhD, Parker Institute for Cancer Immunotherapy, UCSF Tolerance in the Age of Cancer Immunotherapy Cancer immunotherapies have yielded unprecedented clinical success in the treatment of advanced cancers. However, there are many cancers that have yet to benefit from this new age of checkpoint inhibition. One such cancer is liver cancer, which is much less responsive to checkpoint inhibitors (CPIs). In this talk, I discussed a novel murine model to test the basis for poor responsiveness of this tumor, including a role for regulatory T cells in the suppression of a potent response to CPIs, at distal sites. Importantly, deletion of Tregs led to more aggressive anti-tumor immunity. In the second half of the talk, I discussed one of the outcomes of these more potent combination immunotherapies, namely, the significant increase in associated immunotoxicities, termed immune-related adverse events (irAEs). These irAEs have been reported in nearly every organ system, often leading to profound pathology and, in some cases, death. With a growing number of immunotherapies reaching clinical utility and increasing combination studies, understanding which therapeutic approaches provide improved tumor control with minimal side-effects is essential. I described current efforts in checkpoint inhibitor-treated patients to understand CPI-induced diabetes mellitus. Current evidence suggests that CPI-induced irAEs resemble their conventional autoimmune disease in some ways including the presence of autoantibodies in some patients, MHC susceptibility and, in a few instances, pre-existing autoimmunity. However, in sharp contrast with conventional disease, there are differences in acuity of disease onset and beta-cell autoantibody status in many patients suggesting novel targets and environmental triggers may underlie CPI-DM. I also discussed current studies based on the generation of transplantable syngeneic tumor cell lines derived from spontaneous and methylcholanthrene-induced tumors in the autoimmune-prone NOD mouse strain to aid our understanding of the influence of irAEs on the tumor microenvironment. Notably, individual immunotherapies displayed distinct autoimmune pathologies, with induction of certain treatment-associated immunotoxicities, such as type 1 diabetes (T1D), associated with improved tumor control. In addition, we investigated genetic and therapeutic strategies to abrogate the development of irAEs without inhibiting the anti-tumor immune response. Finally, in some cases, immune tolerance towards autoimmunity limited cancer immune surveillance. Together, these clinical and preclinical models provide a platform to assess safety profiles for cancer immunotherapies, identifying cellular mechanisms and therapeutic interventions that inhibit the development of autoimmunity while preserving anti-tumor immunity. Vijay K. Kuchroo, PhD, Evergrande Center for Immunologic Diseases and Ann Romney Center for Neurologic Diseases, Harvard Medical School and Brigham and Women’s Hospital Induction and Transcriptional Regulation of the “Checkpoint” Molecules in T Cells Expression of co-inhibitory receptors or “checkpoint” molecules, such as CTLA-4 and PD-1, on effector T cells is a key mechanism for ensuring immune homeostasis. Dysregulated expression of co-inhibitory receptors on CD4+ T cells promotes autoimmunity while sustained overexpression on CD8+ T cells promotes T cell dysfunction or exhaustion, leading to impaired ability to clear chronic viral infections and cancer. Although analyses of selected co-inhibitory receptors has indicated some degree of co-expression on T cells, the extent of co-expression across the full landscape of known co-inhibitory receptors has not been examined. Here, we used RNA and protein expression profiling at single-cell resolution to identify a module of co-inhibitory receptors, which includes not only several known co-inhibitory receptors (PD-1, Tim-3, Lag-3, and TIGIT), but also a number of novel surface receptors. We functionally validated a number of novel co-inhibitory receptors not previously associated with T cell dysfunction. Studies with a number of “novel” co-inhibitory molecules in regulating anti-tumor immunity and autoimmunity will be presented.

Robert D. Schreiber, PhD, The Bursky Center for Human Immunology and Immunotherapy Programs, Washington University School of Medicine What a Chemically Induced Mouse Tumor Taught Us About Cancer Immunoediting and Immunotherapy In 2001, we proposed the term “Cancer Immunoediting” to explain the complex interaction of the immune system with a developing tumor. We specifically chose this term to highlight the paradoxical role of immunity in protecting the host against cancer outgrowth while also shaping tumor immunogenicity. We showed that this process occurs in three phases—Elimination (where the immune system senses the presence of a developing tumor and destroys it before it becomes clinically apparent); Equilibrium (where tumor cells that might have survived are held in a state of immune-mediated dormancy); and Escape (where tumor cell variants undergo editing, are released from immune system restraint, begin to grow progressively, establish an immunosuppressive tumor microenvironment and emerge as clinically apparent cancers). We subsequently showed that certain somatic mutations in tumor cells functioned as tumor-specific neoantigens for CD8+ T cells and that these T cells either completely eliminated the developing tumor or selected for tumor cell variants that expressed reduced antigenicity. However, the latter “edited” tumor cell populations often still expressed weak tumor-specific mutant neoantigens and could be rejected following treatment of tumor bearing mice with immune checkpoint therapy (ICT). We then generated personalized synthetic long peptide (SLP) cancer vaccines based on the neoantigen targets of ICT-reactivated CD8+ T cells and showed that they were as therapeutically effective and potentially less toxic as ICT. In addition, mice bearing large bulky tumors that were insensitive to either anti-PD-1 or personalized SLP vaccine monotherapy rejected their tumors when treated with the combination of anti-PD-1 plus SLP vaccine. Using high dimensional profiling approaches [single cell RNASeq and Mass Cytometry (CyTOF)], we showed that successful cancer immunotherapy in tumor bearing mice involved massive remodeling of both the lymphoid and myeloid compartments, and that Interferon-gamma played a major role in this remodeling. Most recently, we demonstrated an obligate and critical role for CD4+ T cells in successful ICT. Using a combination of immunogenomics and novel bioinformatics approaches, we identified a major MHC class II restricted neoantigen in the T3 mouse methylcholanthrene induced sarcoma and validated that it plays an important role in promoting ICT-induced anti-tumor responses. We showed that neoantigen-specific CD4+ T cell help is required for ICT-induced, CD8+ CTL-dependent tumor rejection and that MHC class II neoantigen-specific CD4+ T cell help extends beyond initial priming of tumor specific CD8+ T cells. Strikingly, we find a requirement for co-expression of both MHC class I and MHC class II neoantigens in tumor cells that are ultimately rejected following ICT. These results show that the expression of MHC class II neoantigens in tumors is a critical determinant of responsiveness to ICT, personalized cancer vaccines, and potentially, other immunotherapies. Arlene H. Sharpe, MD, PhD, Blavatnik Institute, Harvard Medical School The Biology of PD-1 Checkpoint Blockade The PD-1 co-inhibitory pathway delivers inhibitory signals that function as a brake for immune responses. PD-1 inhibitory signals regulate the critical balance between stimulatory and inhibitory signals needed for effective immune responses to microbes and tumors, as well as self-tolerance. The PD-1 pathway limits the initiation and duration of immune responses, and protects tissues from immunopathology and autoimmune attack. In addition, the PD-1 pathway inhibits immune responses to tumors. PD-1 pathway blockade has had transformative effects in a subset of cancers, but many patients do not respond to single agent immunotherapy. Combination approaches are being actively investigated. This talk discusses the PD-1 pathway from two perspectives: understanding the biology of this pathway and how to develop combination therapies with PD-1 checkpoint blockade. First, mechanisms by which the PD-1:PD-L1 pathway regulates optimal immune homeostasis, tolerance, and tumor immunity will be discussed. Next, a CRISPR-Cas9 based platform for in vivo screening of immune genes will be discussed. This platform facilitates discovery of regulators of tumor immunity and targets for combination therapy. We will discuss the use of this platform to perform in vivo pooled genetic screens to enable rapid discovery of therapeutic targets in immune cells, and our identification of Ptpn2 as a negative regulator of exhausted CD8+ T cell responses using this genetic platform.

Conclusions The 2019 BioLegend Symposium celebrated the success and progress of cancer immunotherapy, but also emphasized the limitations of current drugs. It is clear that improving the efficacy of PD-1 and CTLA-4 blockade treatment will require us to expand our understanding of basic T cell biology. How does checkpoint inhibition differentially affect T cell subsets, and can anti-tumor functions of T cells be selectively boosted without stimulating autoimmunity? In answering these questions, scientists can begin developing combination therapies to fine-tune the effects of checkpoint blockade, and even personalize treatments to individual cancers. The speakers shared their recent discoveries of transcription factors, signaling proteins, and neoantigens found to be critical for controlling anti-tumor responses. Translating these findings into treatment options and defining the optimal therapeutic combinations will be a challenge. BioLegend is aligned with researchers in this common goal, and will always be devoted to providing scientists with the tools they need to bring their innovations from the bench to the bedside.

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