Abstract IA01: Longitudinal landscape analysis of the neoantigen-specific T-cell responses in patients with melanoma with or without response to PD1 blockade

Abstract T-cell responses induced by immune checkpoint blockade therapy target, among others, neoantigens derived from non-synonymous mutations. The large HLA allele diversity and limiting clinical samples have restricted the study of the landscape of neoantigen-targeted T-cell responses in patients over their treatment course. In this educational session, we will discuss a recently developed technology that allows the capture of low-frequency neoantigen-specific T cells and its application to characterize the neoantigen-specific T-cell responses in the blood and tumor from patients with metastatic melanoma with or without response to anti-programmed death receptor 1 (PD-1) immunotherapy. This approach uses personalized libraries of neoantigen-HLA capture reagents to single-cell isolate the T cells and clone their T-cell receptors. Our results show that multiple T cells with different TCR sequences (T-cell clonotypes) recognized a limited number of mutations in samples from seven patients with long-lasting clinical responses. These TCR clonotypes were recurrently detected over time in the blood and tumor. Samples from four patients with no response to anti-PD-1 also demonstrated neoantigen-specific T-cell responses in the blood and tumor to a restricted number of mutations with lower TCR polyclonality and were not recurrently detected in sequential samples. Reconstitution of the neoantigen-specific TCRs in donor T cells using non-viral CRISPR-Cas9 gene editing demonstrated specific recognition and cytotoxicity to patient-matched melanoma cell lines. Our results show that effective anti-PD-1 immunotherapy is associated with a polyclonal CD8+ T-cell response in the tumor and blood specific for a limited number of immunodominant mutations, which are recurrently recognized over time. Citation Format: Cristina Puig Saus. Longitudinal landscape analysis of the neoantigen-specific T-cell responses in patients with melanoma with or without response to PD1 blockade [abstract]. In: Proceedings of the AACR IO Conference: Discovery and Innovation in Cancer Immunology: Revolutionizing Treatment through Immunotherapy; 2025 Feb 23-26; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Immunol Res 2025;13(2 Suppl):Abstract nr IA01.