Tumor infiltrating and peripheral CD4ILT2 T cells are a cytotoxic subset selectively inhibited by HLA-G in clear cell renal cell carcinoma patients.

ILT2 has recently been positioned as a major immune checkpoint in urologic cancers. In clear cell renal cell carcinoma (ccRCC), tumor-infiltrating CD8 T cells expressing ILT2 are a highly cytotoxic cell population, distinct from PD1 T cells, and whose function is inhibited by HLA-G targets. Here we report that ILT2 receptor can also be expressed by CD4 T cells in urologic cancer patients. In the course of deciphering the role of these ILT2CD4 T cells, we found a statistical association between the tumor context and these T cells, and a positive correlation between the levels of peripheral and intra-tumoral CD4ILT2 T cells. Phenotypic analyses revealed that CD4ILT2 T cells express memory T cell (CD27CD28CD57) and cytotoxicity (TbetPerforinKLRG1NKp80GPR56) markers, consistent with a CD4CTL phenotype. Functional assays showed that ccRCC-infiltrating CD4ILT2 T cells indeed have high cytolytic properties and therefore function as proper CD4CTLs, but are selectively inhibited by HLA-G targets. Clinical relevance was provided by immunohistochemical analyses on ccRCC tumor lesions with HLA-G HLA class II tumor cells next to CD4 T cell infiltrates. Our findings provide evidence supporting that ILT2 T cells constitute a reservoir of intratumor cytotoxic T cells that is not targeted by the current checkpoint inhibitors, but could be by anti-HLA-G/anti-ILT2 antibodies as novel immunotherapy in HLA-G tumors.