PD-1 identifies the patient-specific CD8+ tumor-reactive repertoire infiltrating human tumors

TLDR

Tumor‑infiltrating lymphocytes can regress metastatic melanoma, but their heterogeneity and lack of specific biomarkers hinder the identification of tumor‑reactive CD8⁺ cells and limit therapeutic advancement. The study aimed to identify patient‑specific repertoires of tumor‑reactive CD8⁺ lymphocytes in melanoma. The authors evaluated phenotypic traits of CD8⁺ TILs and TCRβ clonotypic frequency in melanoma tumors to achieve this goal. In six melanoma tumors, PD‑1, LAG‑3, and TIM‑3 expression on CD8⁺ TILs pinpointed the tumor‑reactive repertoire—including neoantigen‑specific cells—while deep TCRβ sequencing revealed oligoclonal expansion of these PD‑1⁺ cells, demonstrating that PD‑1 marks clonally expanded tumor‑reactive lymphocytes and has dual regulatory and identification roles.

Abstract

Adoptive transfer of tumor-infiltrating lymphocytes (TILs) can mediate regression of metastatic melanoma; however, TILs are a heterogeneous population, and there are no effective markers to specifically identify and select the repertoire of tumor-reactive and mutation-specific CD8+ lymphocytes. The lack of biomarkers limits the ability to study these cells and develop strategies to enhance clinical efficacy and extend this therapy to other malignancies. Here, we evaluated unique phenotypic traits of CD8+ TILs and TCR β chain (TCRβ) clonotypic frequency in melanoma tumors to identify patient-specific repertoires of tumor-reactive CD8+ lymphocytes. In all 6 tumors studied, expression of the inhibitory receptors programmed cell death 1 (PD-1; also known as CD279), lymphocyte-activation gene 3 (LAG-3; also known as CD223), and T cell immunoglobulin and mucin domain 3 (TIM-3) on CD8+ TILs identified the autologous tumor-reactive repertoire, including mutated neoantigen-specific CD8+ lymphocytes, whereas only a fraction of the tumor-reactive population expressed the costimulatory receptor 4-1BB (also known as CD137). TCRβ deep sequencing revealed oligoclonal expansion of specific TCRβ clonotypes in CD8+PD-1+ compared with CD8+PD-1– TIL populations. Furthermore, the most highly expanded TCRβ clonotypes in the CD8+ and the CD8+PD-1+ populations recognized the autologous tumor and included clonotypes targeting mutated antigens. Thus, in addition to the well-documented negative regulatory role of PD-1 in T cells, our findings demonstrate that PD-1 expression on CD8+ TILs also accurately identifies the repertoire of clonally expanded tumor-reactive cells and reveal a dual importance of PD-1 expression in the tumor microenvironment.