Abstract B058: Longitudinal single cell and TCRβ profiling of a melanoma patient during adjuvant immune checkpoint inhibitor therapy exhibits significant change in immune cell profiles

Abstract The advent of immune checkpoint inhibitors (ICIs) has revolutionized the treatment landscape for metastatic melanoma. The effectiveness of ICIs administered following curative surgical resection as adjuvant therapy has also been observed in many patients with advanced melanoma. However, the mechanisms by which adjuvant ICIs reshape immune cell populations to mediate anti-tumor responses remain unknown. In this study, we employed a multi-omics approach and examined T-cell population dynamics and T-cell receptor (TCR) clonotype evolution in a Stage IIIB melanoma patient treated with adjuvant nivolumab and achieved long-term recurrence free survival. Peripheral blood samples were collected at four timepoints (pre-treatment and after 1, 4, and 12 cycles of nivolumab). Single-cell RNA/TCR sequencing (scRNA/TCR-seq) was performed on peripheral blood mononuclear cells (PBMCs), and TCR sequencing was performed on tumor tissue with computational analysis included standard quality control, normalization, clustering, and VDJ annotation. Across the PBMC samples, eight distinct lymphocyte clusters were identified. Treatment was associated with a progressive increase in effector and central memory CD8+ T-cell populations, accompanied by changes in the expression of key effector molecules including GZMK, GZMA, CCL4, and CCL5. In addition, consistent with our prior work demonstrating successful ICI therapy induces expansion of CX3CR1+ CD8+ T cells, we observed early on-treatment differentiation and clonal expansion of this effector subset, correlating with the patient’s long-term clinical benefit. Furthermore, integration of scRNA/TCR-seq data from serial blood samples with tumor-derived TCR-seq identified multiple circulating CD8+ T-cell clones sharing CDR3α sequences with tumor-infiltrating T cells (TIL-TCRs). These TIL-associated clonotypes expanded in peripheral blood over the treatment period, with the most pronounced increase occurring early during therapy, followed by continued evolution of the immune landscape over time suggesting enhanced mobilization of tumor-reactive T cells during adjuvant ICI treatment. Together, these findings demonstrate that adjuvant nivolumab induces early and sustained remodeling of the immune compartment, characterized by increased effector CD8+ T-cell activity, upregulation of key immunomarkers, and expansion of TIL-associated TCR clonotypes. This work provides insight into the immune dynamics underlying successful adjuvant ICI therapy and supports further development of TCR-based biomarkers to predict and monitor response to immunotherapy. Citation Format: Joshua Ni, Ryutaro Kajihara, Mark Long, Angelina Lim, Gino In, Fumito Ito. Longitudinal single cell and TCRβ profiling of a melanoma patient during adjuvant immune checkpoint inhibitor therapy exhibits significant change in immune cell profiles [abstract]. In: Proceedings of the AACR Immuno-Oncology Conference (AACR IO): Discovery and Innovation in Cancer Immunology: Revolutionizing Treatment through Immunotherapy; 2026 Feb 18-21; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Immunol Res 2026;14(2 Suppl):Abstract nr B058.