CD8+ T tumour-infiltrating lymphocytes lacking CD5 cell surface expression exhibited increased levels of activation and exhaustion

Abstract

Background: CD5, a member of the scavenger receptor cysteine-rich superfamily, is a marker for T cells and subset of B cells (B1a). CD5 associates with T-cell and B-cell receptors and increased CD5 is an indication of B cell activation. An inverse correlation between CD5 expression and anti-tumour immunity in CD8+ T cells has been reported in several human studies. Tumour-infiltrating lymphocytes (TILs) isolated from lung cancer patients have been reported to exhibit different anti-tumour activity based on CD5 expression: CD5 levels were negatively correlated with anti-tumour activity. Increased tumour-mediated activation-induced death, which increases as T cells are activated, has been reported in T cells with undetectable CD5 levels compared to CD5high T cells, suggesting that CD5 could impair activation of anti-tumour T cells. Herein, CD5 levels in T cell subsets was determined in different organs in mice bearing syngeneic breast tumour homografts, and the relationship between CD5 and T cell activation and exhaustion was assessed.