Abstract 4668: Evidence for antigen-driven TCRB chain convergence in the tumor infiltrating T cell repertoire of 85 research subjects with melanoma

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Abstract Introduction T cell convergence refers to the phenomenon whereby antigen-driven selection enriches for T cell receptors having a shared antigen specificity but different amino acid or nucleotide sequence. T cell recruitment and expansion within the tumor microenvironment (TME) may be directed by responses to tumor neoantigen, suggesting that elevated T cell convergence could be a general feature of the tumor infiltrating T cell repertoire. Here we evaluate evidence for T cell convergence within tumor biopsy research samples from a set of 85 subjects with melanoma. Methods Total RNA from 85 tumor biopsy research samples (non-FFPE) was extracted for use in long-amplicon TCRB chain sequencing (mean amplicon length of 330bp covering CDR1, 2 and 3) via the Ion AmpliSeq Immune Repertoire Assay Plus, TCRB. To evaluate T cell convergence within each biopsy, we searched for instances where TCRB chains were identical in amino acid space (shared variable gene identity and CDR3 amino acid sequence) but had distinct nucleotide sequences owing to N-addition and exonucleotide chewback within the V-D and D-J junctions of the CDR3. To provide context, we evaluated evidence for T cell convergence with T cell repertoires derived from healthy donor peripheral blood leukocytes (PBL). Results Sequencing of melanoma biopsies yielded an average of 6029 clones per sample. 11 of 85 samples yielded fewer than 100 clones and were eliminated from downstream analysis. Convergent T cell receptors were identified in 68/74 (92%) of tumor infiltrating T cell repertoires having greater than 100 detected clones. The frequency of convergent rearrangements was approximately 50-fold greater in the melanoma-infiltrating T cell repertoire than healthy PBL samples (p<.001). Conclusions These data suggest that T cell convergence may be a common feature of the melanoma infiltrating T cell repertoire. Convergence was more frequently observed within the TME than T cell repertoires derived from healthy PBL, consistent with elevated antigen-driven T cell selection within the TME. The extent to which convergence is a feature of the TME in other cancers is not yet known. T cell receptor convergence may be driven by T cell responses to tumor neoantigen within the TME. In such case, in silico identification of convergent T cell receptors by long-amplicon sequencing may serve as an approach for rapid identification of antigen-specific T cell receptors for future therapeutic use. For research use only. Citation Format: Timothy J. Looney, Sean Glenn, Sarabjot Pabla, Jeff Conroy, Carl Morrison, Alice Zheng, Lauren Miller, Elizabeth Linch, Denise Topacio, Geoff Lowman, Fiona Hyland, Mark Anderson. Evidence for antigen-driven TCRB chain convergence in the tumor infiltrating T cell repertoire of 85 research subjects with melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4668.