Probing the Diversity of T Cell Dysfunction in Cancer

Abstract

T cell dysfunction in cancer comes in many forms, with two new varieties reported in this issue. Daley et al. find that T cells expressing γδ T cell receptors (TCR) promote pancreatic tumor growth by inhibiting activation of T cells with conventional TCRs. Singer et al. characterize dysfunctional tumor infiltrating lymphocytes to reveal a role for zinc homeostasis in anti-tumor immunity.

Figure 1. Releasing Brakes on Tumor T Cells

(Left and center) γδ T cells, in concert with myeloid-derived suppresor cells and tumor-associated macrophages, foster a suppressive tumor microenvironment in pancreatic cancer. γδ T cells promote tumor growth through upregulation of co-inhibitory molecules PD-L1 and Galectin-9, directly blocking αβ CD4 and CD8 T cell activation. Deletion of γδ T cells through various means (i.e., CCR2, CCR5, CCR6, and TCRδ-genetic deficiency) restores αβ T cell cytokine production, co-stimulatory molecule expression, and control of tumor growth. Therapeutic benefit of PD-L1 or Galectin-9 antibody blockade primarily hinges upon targeting γδ T cells, in turn promoting increased T cell infiltration and control of tumor growth. (Right) Metallothioneins (MTs) regulate metabolism of Zn²⁺ and other trace minerals. Intracellular accumulation of Zn²⁺ promotes T cell dysfunction in the tumor microenvironment and increases activity of zinc-finger transcription factors. Genetic deletion of Gata3 reverses metallothionein-dependent T cell loss of cytokine production, independent of the expression of classic cell surface markers of T cell dysfunction.