T-cell responses to TP53 "hotspot" mutations and unique neoantigens expressed by human ovarian cancers

Purpose: This was a study prospectively evaluating intratumoral T-cell responses to autologous somatic mutated neoepitopes expressed by human metastatic ovarian cancers.Experimental Design: Tumor infiltrating lymphocytes (TILs) were expanded from resected ovarian cancer metastases, which were analyzed by whole exome and transcriptome sequencing to identify autologous somatic mutations. All mutated neoepitopes, independent of prediction algorithms, were expressed in autologous antigen presenting cells then co-cultured with TIL fragment cultures. Secretion of interferon-gamma or up-regulation of 41BB indicated a T-cell response. Results: Seven women with metastatic ovarian cancer were evaluated and 5 patients had clear, dominant T-cell responses to mutated neoantigens, which were corroborated by comparison to the wild type sequence, identification of the minimal epitope, human leukocyte antigen (HLA) restriction element(s) and neoantigen-specific T-cell receptor(s). Mutated neoantigens were restricted by HLA-B, -C, -DP, -DQ and/or -DR alleles and appeared to principally arise from random, somatic mutations unique to each patient. We established that TP53 "hotspot" mutations (c.659A>G; p.Y220C and c.733G>A; p.G245S) expressed by two different patient's tumors were immunogenic both in the context of HLA-DRB3*02:02. Conclusions: Mutation-reactive T cells infiltrated ovarian cancer metastases at sufficient frequencies to warrant their investigation as adoptive cell therapy. Additionally, transfer of TP53 "hotspot" mutation-reactive T-cell receptors into peripheral blood T cells could be evaluated as a gene therapy for a diverse range of tumor histologies.

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