Abstract P1-04-04: A multiomic approach to the identification of immune signatures of anti-PD1/PDL1 therapy responders in metastatic triple negative breast cancer: new implications in the role of helper T-cell and B-cell interplay

Abstract Introduction Triple negative breast cancer (TNBC) is a heterogeneous breast cancer subtype which continues to portend a particularly poor prognosis compared to other breast cancer subtypes. Immune checkpoint inhibitor (ICI) therapies have emerged as promising options for locally advanced and metastatic TNBC. However, clinical trials have demonstrated mixed results with respect to ICI response. Given varied outcomes and the potential for immune-related adverse events associated with ICIs, there is critical need for identification of accurate biomarkers of response and improved strategies to counteract ICI resistance and/or toxicity. Methods Advanced immunoprofiling of peripheral blood mononuclear cells (PBMCs) and plasma from 7 metastatic TNBC patients with variable responses to anti-PD1 or anti-PDL1 therapy was performed. Samples were analyzed from blood draws obtained: (i) prior to first administration, (ii) while receiving ICI treatment, and (iii) at the time of conformed clinical progression or response to therapy. Response was determined by standard radiological assessment. Immunoprofiling included high parameter flow cytometry, single cell transcriptomics (10x genomics) and secretome analysis (Isoplexis). Single cell RNA profiles from 63,984 cells were analyzed. Results High parameter flow cytometry identified higher circulating levels of a subpopulation of activated CD4+ T cells with a phenotype of CXCR3low CD62Llow CD45RAhigh and CD57high expression in responders versus non-responders. Higher effector function of CD4+ T cells was corroborated by significantly elevated plasma concentrations of IL-2 (p=0.02) and IL-5 (p< 0.0001) among responders. Single cell transcriptomic analysis revealed clusters of B and T cells with distinct activation patterns that were associated with radiographic response. Strikingly, genes involved in B cell activation and T cell-B cell conjugation such as CD81 were found to be highly upregulated among CD4+ T cells from responders. Conclusions Our results are consistent with previous reports describing an association of increased B cell activity in TNBC with improved overall survival. We identified a subpopulation of CD4+ T cells with effector functions consistent with type 2 helper T cells that may not only target cancer cells by direct cytotoxic function, but also promote increased B cell anti-tumor activity. Our study provides insight into specific mechanisms of immune cell interplay that may drive response to ICI therapy. These cell populations and their associated pathways may represent potential biomarkers of response and/or targets for resistance reversal. Citation Format: Avia D. Wilkerson, Patricia A. Rayman, Paul G. Pavicic Jr, Hana Husic, Vladimir Makarov, Ivan Juric, Timothy Chan, Alberto J. Montero, Marcela Diaz-Montero. A multiomic approach to the identification of immune signatures of anti-PD1/PDL1 therapy responders in metastatic triple negative breast cancer: new implications in the role of helper T-cell and B-cell interplay [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P1-04-04.