Person:

Mei, Shaolin

ABSTRACTSynovial sarcoma is an aggressive mesenchymal neoplasm, driven by the SS18-SSX fusion, and characterized by immunogenic antigens expression and exceptionally low T cell infiltration levels. To study the cancer-immune interplay in this disease, we profiled 16,872 cells from 12 human synovial sarcoma tumors using single-cell RNA-sequencing (scRNA-Seq). Synovial sarcoma manifests antitumor immunity, high cellular plasticity and a core oncogenic program, which is predictive of low immune levels and poor clinical outcomes. Using genetic and pharmacological perturbations, we demonstrate that the program is controlled by the SS18-SSX driver and repressed by cytokines secreted by macrophages and T cells in the tumor microenvironment. Network modeling predicted that SS18-SSX promotes the program through HDAC1 and CDK6. Indeed, the combination of HDAC and CDK4/6 inhibitors represses the program, induces immunogenic cell states, and selectively targets synovial sarcoma cells. Our study demonstrates that immune evasion, cellular plasticity, and cell cycle are co-regulated and can be co-targeted in synovial sarcoma and potentially in other malignancies.

Despite initial responses, most melanoma patients develop resistance to immune checkpoint blockade (ICB). To understand the evolution of resistance, we studied 37 tumor samples over 9 years from a metastatic melanoma patient with exceptional response followed by delayed recurrence and death. Phylogenetic analysis revealed co-evolution of 7 lineages with multiple convergent, but independent resistance-associated alterations (RAAs). All recurrent tumors emerged from a lineage characterized by loss of chromosome 15q, with post-treatment clones acquiring additional genomic driver events. Deconvolution of bulk RNAseq and highly-multiplexed immunofluorescence (t-CyCIF) revealed differences in immune composition amongst different lineages. Imaging revealed a vasculogenic mimicry phenotype in NGFR-High tumor cells with high PD-L1 expression in close proximity to immune cells. Rapid autopsy demonstrated 2 distinct NGFR spatial patterns with high polarity and proximity to immune cells in subcutaneous tumors versus a diffuse spatial pattern in lung tumors, suggesting different roles of this neural crest-like program in different tumor microenvironments. Broadly, this study establishes a high-resolution map of the evolutionary dynamics of resistance to ICB, characterizes a de-differentiated, neural crest tumor population in melanoma immunotherapy resistance, and describes site specific differences in tumor-immune interactions via longitudinal analysis of a melanoma patient with an unusual clinical course.