Characterization of tumour-infiltrating lymphocytes in a tumour rejection cynomolgus macaque model

Immunotherapy has emerged as a promising and effective treatment for cancer, yet the clinical benefit is still variable, in part due to insufficient accumulation of immune effector cells in the tumour microenvironment. Better understanding of tumour-infiltrating lymphocytes (TILs) from nonhuman primate tumours could provide insights into improving effector cell accumulation in tumour tissues during immunotherapy. Here, we characterize TILs in a cynomolgus macaque tumour model in which the tumours were infiltrated with CD4⁺ and CD8⁺ T cells and were eventually rejected. The majority of CD4⁺ and CD8⁺ TILs exhibited a CD45RA^-CCR7^- effector memory phenotype, but unlike circulating T cells, they expressed CD69, a marker for tissue-resident memory T (T_RM) cells. CD69-expressing CD8⁺ TILs expressed high levels of the cytotoxic molecule granzyme B and the co-inhibitory receptor PD-1. Consistent with the T_RM cell phenotype, CD8⁺ TILs minimally expressed CX3CR1 but expressed CXCR3 at higher levels than circulating CD8⁺ T cells. Meanwhile, CXCL9, CXCL10 and CXCL11, chemokine ligands for CXCR3, were expressed at high levels in the tumours, thus attracting CXCR3⁺CD8⁺ T cells. These results indicate that tumour-transplanted macaques can be a useful preclinical model for studying and optimizing T cell accumulation in tumours for the development of new immunotherapies.