655 Landscape of helper and regulatory CD4+ T cells in melanoma

Background Within the tumor microenvironment, distinct CD4+ T cell subsets can play different and even opposite roles either promoting or suppressing anti-tumor responses through recognition of antigens presented by human leukocyte antigen (HLA) class II molecules. However, how cancers co-opt these processes to shape intratumoral landscape achieve immune evasion remains incompletely understood. Methods We performed single-cell characterization infiltrating lymphocytes (TILs) collected from four melanoma with low high HLA-class expression we utilized TCR reconstruction specificity screening unambiguously discover reactivity TILs. By testing TCR-transduced cells against autologous patient-derived lines presenting (APCs) loaded lysates, assessed capacity TCRs directly indirectly recognize cells. defined antigen-specificity antitumor assessing their towards personal neoantigens (NeoAg) public associated (MAAs). Finally, correlated NeoAg burden in a series 116 specimens 4 independent cohorts patients. Results Analysis data showed that cluster distribution within each clonotype family was highly homogeneous appeared follow 3 major phenotypes, corresponding non-exhausted memory cells, exhausted regulatory (T Regs ). Strikingly, clonally expanded Reg -TILs were abundant microenvironment HLA pos melanomas. found cytotoxic could be triggered not only restricted antigens, but also presentation I MAAs. -TCRs elicited via APCs. Notably, numerous tumor-reactive stimulated demonstrated for NeoAgs. In melanomas, clonal expansion NeoAg-specific -clones favored dramatically load. confirmed association elevated extremely burden. Conclusions Our elucidate point NeoAgs direct engagement immunosuppressive as novel mechanism melanoma.