The immune microenvironment of sarcomas : a comprehensive evaluation of infiltrating immune cells and checkpoint biomarkers in musculoskeletal tumors

Sarcomas are aggressive cancers of the connective tissues, such as bone, muscle, cartilage, and fat. Despite their diverse origins, sarcomas are predominantly treated by surgery and radiation, as conventional chemotherapy has limited benefit for most subtypes. When sarcomas recur or metastasize, there are few options for systemic therapy, and prognosis is very poor. Despite advancements in our understanding of the molecular drivers of sarcomas, almost no new treatments have proven benefit for metastatic sarcomas. Immunotherapy has shown value for other cancers, such as melanoma and lung cancer; however, sarcomas lag behind the common cancers in our understanding of their immune microenvironment and potential for treatment with immunotherapeutics. Early trials using single-agent immune checkpoint inhibitors in sarcomas delivered mixed results, but these studies somewhat indiscriminately lumped together different sarcoma subtypes that might have critical immunological differences. My study employs tissue microarrays incorporating 1360 sarcoma specimens (spanning 23 subtypes) to characterize immune infiltrates and expression of targetable immune biomarkers, using immunohistochemistry. Genomically-complex sarcoma types – driven by mutations and/or copy-number alterations – are found to have much higher levels of lymphocytic and phagocytic immune infiltrates than translocation-associated sarcomas. Across nearly all subtypes, tumor-associated macrophages outnumber tumor-infiltrating lymphocytes, predominately M2 (anti-inflammatory) macrophages. Expression of the target of first-generation immune checkpoint PD-(L)1 is uniformly low, but expression of LAG-3 and TIM-3 – emerging immune checkpoints – is significantly more common. Expression of anti-phagocytic immune checkpoint CD47 is yet more predominant, displaying all-or-nothing expression with 100% positivity seen in over half of positive cases. To further characterize the lymphocytic response, T-cell receptor (TCR) sequencing was performed on specimens from 25 sarcoma patients on a clinical trial of tremelimumab (anti-CTLA-4) with durvalumab (anti-PD-L1). We found that the TCR repertoire is richer and more diverse among the genomically-complex sarcomas relative to the translocation-associated sarcomas, and following immune checkpoint blockade, we observed an overall increase in the clonality of the peripheral TCR repertoire. My study demonstrates a tangible positive relationship between genomic complexity and immunogenicity, and highlights novel immune checkpoints of relevance to sarcomas. As such, this work provides the essential translational background to direct the use of immunotherapy in sarcoma management.Medicine, Faculty ofPathology and Laboratory Medicine, Department ofGraduat

Emerging targets in cancer immunotherapy

The first generation of immune checkpoint inhibitors (anti-CTLA-4 and anti-PD-1/PD-L1) targeted natural immune homeostasis pathways, co-opted by cancers, to drive anti-tumor immune responses. These agents led to unprecedented results in patients with previously incurable metastatic disease and may become first-line therapies for some advanced cancers. However, these agents are efficacious in only a minority of patients. Newer strategies are becoming available that target additional immunomodulatory mechanisms to activate patients’ own anti tumor immune responses. Herein, we present a succinct summary of emerging immune targets with reported pre-clinical efficacy that have progressed to active investigation in clinical trials. These emerging targets include co-inhibitory and co-stimulatory markers of the innate and adaptive immune system. In this review, we discuss: 1) T lymphocyte markers: Lymphocyte Activation Gene 3 [LAG-3], T-cell Immunoglobulinand Mucin-domain-containing molecule 3 [TIM-3], V-domain containing Ig Suppressor of T cell Activation [VISTA], T cell ImmunoGlobulin and ITIM domain [TIGIT], B7-H3, Inducible T-cell Co-stimulator [ICOS/ICOSL], CD27/CD70, and Glucocorticoid-Induced TNF Receptor [GITR]; 2) macrophage markers: CD47/Signal-Regulatory Protein alpha [SIRPα] and Indoleamine-2,3-Dioxygenase [IDO]; and 3) natural killer cell markers: CD94/NKG2A and the Killer Immunoglobulin-like receptor [KIR] family. Finally, we briefly highlight combination strategies and potential biomarkers of response and resistance to these cancer immunotherapies.Medicine, Faculty ofPathology and Laboratory Medicine, Department ofReviewedFacultyGraduat

Indoleamine Dioxygenase Inhibitors : Clinical Rationale & Current Development

Purpose of review: This review focuses on the recent clinical development of indolamine-2,3- dioxygenase-1 (IDO-1) inhibitors. Recent findings: IDO-1 alters tryptophan metabolism in a manner enhancing T-regulatory cell activity, but pre-clinical data show that its role in tumorigenesis is context-dependent on host and tumor interaction, highlighting some challenges in understanding the molecular oncology of this enzymatic drug target. Because results from phase I/II trials of IDO-1 inhibitor monotherapy have been disappointing, current clinical trials employ IDO-1 inhibitors in combination strategies with other immunotherapy agents or with chemotherapy +/- radiation. Combinations with anti PD-1/PD-L1 antibodies are already showing promise, and related strategies are under active evaluation. Summary: While further research is needed to elucidate the precise role of IDO-1 in tumor development, its mechanisms of action appear sufficiently distinct from other immunotherapy targets to warrant inclusion in combination immunotherapy regimens, an approach where multiple clinical trials are currently underway.Medicine, Faculty ofPathology and Laboratory Medicine, Department ofReviewedFacultyGraduat

The SS18-SSX Oncoprotein Hijacks KDM2B-PRC1.1 to Drive Synovial Sarcoma

Summary Synovial sarcoma is an aggressive cancer invariably associated with a chromosomal translocation involving genes encoding the SWI-SNF complex component SS18 and an SSX (SSX1 or SSX2) transcriptional repressor. Using functional genomics, we identify KDM2B, a histone demethylase and component of a non-canonical polycomb repressive complex 1 (PRC1.1), as selectively required for sustaining synovial sarcoma cell transformation. SS18-SSX1 physically interacts with PRC1.1 and co-associates with SWI/SNF and KDM2B complexes on unmethylated CpG islands. Via KDM2B, SS18-SSX1 binds and aberrantly activates expression of developmentally regulated genes otherwise targets of polycomb-mediated repression, which is restored upon KDM2B depletion, leading to irreversible mesenchymal differentiation. Thus, SS18-SSX1 deregulates developmental programs to drive transformation by hijacking a transcriptional repressive complex to aberrantly activate gene expression