Phenotypic and clonal evolution of CD4 T cells in HNSCC during immunotherapy: a case report 3277

Abstract Description Background Single cell RNA-seq combined with CITE-seq and TCR-seq has allowed for a deep characterization of anticancer immunity. Here we report on a single patient with head and neck squamous cell cancer (HNSCC) who underwent initial resection in 2020. Twenty-one months later, when the patient recurred and went on a combination immunotherapy trial, they had three serial biopsies performed. Methods Samples of blood and tumor from 2020 were sorted into 6 CD4 subsets: Blood Mem CD4, Blood Treg, PD1/ICOS(-/-) TIL, PD1/ICOS(+/+) TIL (putative tumor-specific CD4), PD1/ICOS(+/-) TIL, and TIL Treg. On progression the patient received a biologic containing >300 proteins for genes that are overexpressed by HNSCC followed by anti-PD-1 at wk 2, with biopsies taken at baseline, wk 2 and 8. Phenotypic and molecular studies were performed. Results Over 20% of the total peripheral T cell repertoire at the start of immunotherapy were CD4 clonotypes present in 2020; this shrank to less than 15% by week 8. Within the biopsy samples PD1+ TIL expanded while Treg contracted during immunotherapy. Blood Mem, Blood Treg and PD1/ICOS(-/-) TIL were all mainly found in the periphery, while PD-1 TIL were found in both blood and tumor. Interestingly, the majority of TIL Treg were later found in either the blood or tumor, not both. Conclusions These results provide insights into how Immunotherapy may change the clonal and phenotypic distribution of CD4 T cells. Ethics Approval: PSJH IRB# 2020000480 Funding Sources Support: Incyte, Murdock Charitable Trust, Providence Portland Medical Foundation, Nancy Lematta, Lynn Loacker, Cindy and Steve Harder, The Chiles Foundation, Robert W. Franz and Elsie Franz Finley Topic Categories Tumor Immunology: Cellular Responses and Tumor Microevironment (TIME)