Abstract IA007: B cell immunity generation in tertiary lymphoid structures, a major determinant of sarcoma immune response to immunotherapy

Abstract

Abstract The presence of tertiary lymphoid structures (TLSs) and a high intratumoral density of B lymphocytes have been associated with improved survival in several tumor types. We investigated the impact of TLS on responses to immunotherapy and, analyzing a large-scale retrospective analysis of three independent cohorts of patients with cancer, including sarcomas, who were treated with anti-PD-1 or anti-PD-L1 antibodies, we showed that the presence of mature TLSs was associated with improved objective response rates, progression-free survival and overall survival, independent of PD-L1 expression status and CD8+T cell density. To decipher the role of B cells in such responses, we performed spatial transcriptomics and examined the nature of B cell responses within TLS structure. B cells were enriched in TLS, and therein we could identify all B cell maturation stages toward plasma cell (PC) formation. B cell repertoire analysis revealed clonal diversification, selection, expansion in TLS and the presence of full mature clonotypes at distance. In TLS+ tumors, IgG producing PCs disseminated into the tumor beds along fibroblastic tracks. TLS+ tumors exhibited high frequencies of IgG-producing PCs and IgG-stained and apoptic malignant cells, suggestive of anti-tumor effector activity. We validated these findings in a prospective trial in metastatic Soft Tissue Sarcoma (STS) bearing patients. PEMBROSARC is a multi-cohort phase II study of pembrolizumab combined with low-dose cyclophosphamide in patients with advanced STS. The 6-months non-progressive rate (NPR) and the objective response rates previously reported in cohorts including all comers were 4.9% and 2.4%, respectively. In the cohort enrolling patients selected based on the presence of TLS, the 6-month NPR was 40% and the objective response rate was 30%. Exploratory analyses reveled that infiltration by IgG antibody-producing plasma cells was associated with improved clinical outcome as well as the presence of IgG antibodies on tumor cells. Altogether, these results establish that maturation, selection and amplification of B cells in intratumoral TLSs results in Plasma Cells generation which may produce anti-tumor antibodies. The latter may amplify in situ antitumor immune responses leading to better therapeutic responses to immunotherapy. Citation Format: Wolf H. Fridman. B cell immunity generation in tertiary lymphoid structures, a major determinant of sarcoma immune response to immunotherapy [abstract]. In: Proceedings of the AACR Special Conference: Sarcomas; 2022 May 9-12; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2022;28(18_Suppl):Abstract nr IA007.