Th17-like cells and immunosuppressive macrophages infiltrate tertiary lymphoid structures with distinct maturation status in soft-tissue sarcoma

Tertiary lymphoid structures (TLSs) have been associated with favorable clinical outcome and improved responses to immune checkpoint inhibitors in soft-tissue sarcomas (STSs). However, due to their rarity and high heterogeneity, information regarding the mechanisms involved in TLS formation and contribution to antitumor immunity in STS are extremely elusive. To address this gap, we integrated immunohistochemistry and transcriptomic analyses from 31 treatment-naïve STS specimens from an independent cohort of patients with primary or locally recurrent disease. Further validation was conducted using external bulk, single-cell and spatial transcriptomics data from 5 publicly available datasets. We found TLSs to be highly heterogeneous in terms of amount, localization, maturation status and cellular composition, and corroborated previous findings showing that their presence, along with B cells in the STS microenvironment, are good indicators of favorable prognosis. Transcriptomic analysis showed that high expression of germinal center (GC) B cell-related genes was associated with TLS presence and with an upregulation of signatures specific for T helper 17 (Th17) cells in STS and other cancer types. Conversely, genes signatures discriminating for immunosuppressive M2-like macrophages were enriched in tumors with low expression of GC B cell-related genes. Immunohistochemistry showed distinct spatial patterns for Th17-like cells and M2-like macrophages within TLS areas, with IL17A+ cells predominantly localized within intratumoral mature TLSs, and CD163+ macrophages mainly observed in immature TLSs. Integrating these findings, we identified tumors with high expression of GC B cell- and Th17 cell-related signatures together with low fractions of M2-like macrophages, to have superior survival outcomes. Herein, our findings point out to two cellular players (Th17-like cells and M2-like macrophages) with potentially opposite roles in STS-associated TLS formation and maturation, thus providing the basis for future research efforts aiming at the development of therapeutic immunological interventions to enhance TLS-mediated antitumor immunity in STS. (Figure presented.)