Abstract 6290: Microenvironment begets phenotype: Tumor specific CD8+ T cells derived from bone marrow and other lymphoid sites exhibit differential exhaustion profiles
Authors: Zawidzka Elizabeth Maria , Biavati Luca , Thomas Amy , Heimann Megan , Griffin Ervin , Borrello Ivan 
Published: June 2022

Abstract
Current immunotherapy approaches aim to mitigate or reverse CD8+ T cell exhaustion to generate meaningful anti-tumor immune responses. However, the multi-step process of exhaustion fixes epigenetic programs that permanently scar T cells, limiting immunotherapeutic efficacy. Rather than reversing T cell exhaustion, we hypothesize that exploiting tumor-specific T cells from protected niches could yield therapies with improved anti-tumor benefit. A subset of TCF1-expressing precursor exhausted CD8+ T cells (TPEX) drives the anti-tumor immune response. The tumor draining lymph nodes (dLN) maintain a reservoir of TPEX cells which replenishes intra-tumoral effector T cells. Similarly, the bone marrow (BM) houses long-lived memory T cells with specificity against a broad spectrum of antigens, including tumor-associated antigens. Unlike T cells from the dLN or tumor infiltrating lymphocytes (TILs), BM T cells can be easily acquired from all patients at any disease stage. We used the B16.OVA-OT-I model to delineate how exhaustion affects tumor-specific T cells within the BM, dLN, spleen (SP), and tumor (TUM) during tumor progression. This model uses adoptively transferred transgenic, OVA-specific OT-I cells as a source of tumor-specific CD8+ T cells. High-dimensional immune profiling using spectral flow cytometry enabled us to characterize in vitro and in vivo anti-tumor functionality and the phenotype of OT-I cells derived from different compartments. Interestingly, upon adoptive transfer, OT-I cells resident in the TUM, dLN, BM, and SP or found in circulation were heterogenous in terms of function, persistence, and stemness. These findings suggest that discrete tissues impart location-specific T cell adaptations, and that tissue microenvironment markedly influences the exhaustion profile of tumor-specific T cells. OT-I cells derived from distinct lymphoid organs exhibited differential capacity for cytokine production and response to cognate antigen, especially compared to their TIL counterparts. Importantly, we identified BM- and dLN-derived CD8+ T cells as less exhausted and more functional than TILs. Moreover, BM resident T cells appear phenotypically more stem-like and similar to TPEX. Further studies to characterize this population are ongoing. This work implies that, in the context of localized disease, the kinetics of T cell exhaustion differ in lymphoid organs as compared to TILs. Leveraging a less-exhausted pool of tumor-specific cells may lead to greater anti-tumor benefit with new approaches to adoptive cell therapy. As the BM is accessible in all patients, understanding where tumor-specific BM T cells fall on the spectrum of exhaustion and memory could justify their use for such applications. Ongoing work aims to transcriptionally characterize tumor specific BM CD8+ T cells and evaluate their role in anti-tumor immunity.
Citation Format: Elizabeth Maria Zawidzka, Luca Biavati, Amy Thomas, Megan Heimann, Ervin Griffin, Ivan Borrello. Microenvironment begets phenotype: Tumor specific CD8+ T cells derived from bone marrow and other lymphoid sites exhibit differential exhaustion profiles [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6290.