Mapping the human T cell repertoire to recurrent driver mutations in MYD88 and EZH2 in lymphoma

Oncogenic driver mutations are theoretically attractive targets for the immunotherapy of lymphoid cancers, yet the proportion that can be recognized by T cells remains poorly defined. To address this issue without any confounding effects of the patient's immune system, we assessed T cells from 19 healthy donors for recognition of three common driver mutations in lymphoma: MYD88(L265P), EZH2(Y641F), and EZH2(Y641N). Donors collectively expressed the 10 most prevalent HLA class I alleles, including HLA-A*02:01. Peripheral blood T cells were primed with peptide-loaded dendritic cells (DC), and reactive T cells were assessed for recognition of naturally processed mutant versus wild type full-length proteins. After screening three driver mutations across 17-26 HLA class I alleles and 3 x 10(6)-3 x 10(7) T cells per donor, we identified CD4(+) T cells against EFISENCGEII from EZH2(Y641N) (presented by HLA-DRB1*13:02) and CD8(+) T cells against RPIPIKYKA from MYD88(L265P) (presented by HLA-B*07:02). We failed to detect RPIPIKYKA-specific T cells in seven other HLA-B*07:02-positive donors, including two lymphoma patients. Thus, healthy donors harbor T cells specific for common driver mutations in lymphoma. However, such responses appear to be rare due to the combined limitations of antigen processing, HLA restriction, and T cell repertoire size, highlighting the need for highly individualized approaches for selecting targets.