Cytotoxicity of Tumor Antigen Specific Human T Cells Is Unimpaired by Arginine Depletion

Abstract

Tumor-growth is often associated with the expansion of myeloid derived suppressor cells that lead to local or systemic arginine depletion via the enzyme arginase. It is generally assumed that this arginine deficiency induces a global shut-down of T cell activation with ensuing tumor immune escape. While the impact of arginine depletion on polyclonal T cell proliferation and cytokine secretion is well documented, its influence on chemotaxis, cytotoxicity and antigen specific activation of human T cells has not been demonstrated so far. We show here that chemotaxis and early calcium signaling of human T cells are unimpaired in the absence of arginine. We then analyzed CD8+ T cell activation in a tumor peptide as well as a viral peptide antigen specific system: (i) CD8+ T cells with specificity against the MART-1aa26–35*A27L tumor antigen expanded with in vitro generated dendritic cells, and (ii) clonal CMV pp65aa495–503 specific T cells and T cells retrovirally transduced with a CMV pp65aa495–503 specific T cell receptor were analyzed. Our data demonstrate that human CD8+ T cell antigen specific cytotoxicity and perforin secretion are completely preserved in the absence of arginine, while antigen specific proliferation as well as IFN-γ and granzyme B secretion are severely compromised. These novel results highlight the complexity of antigen specific T cell activation and demonstrate that human T cells can preserve important activation-induced effector functions in the context of arginine deficiency.

T‐cell metabolism governing activation, proliferation and differentiation; a modular view

“…Myeloid cells, including polymorphonuclear leucocytes, macrophages and myeloid‐derived suppressor cells, as well as epithelial cells, all express arginase and can release this enzyme into the extracellular environment – leading to decreased local and systemic arginine levels . Co‐culture and in vivo experiments indicate that these cells thereby impair T‐cell proliferation and cytokine production in an arginase‐dependent manner, through a mechanism involving down‐regulation of the CD3 ζ chain . This phenomenon is implicated in pathophysiological suppression of T‐cell responses in chronic infection and cancer, and additionally in immune regulation at immune privileged sites such as the cornea, or during pregnancy …”

Granulocyte functions are independent of arginine availability

“…PMNs also interact with other cells of the innate and adaptive immune system [3,33], and they can, e.g., inhibit the proliferation and activation of T cells by arginine depletion via PMN arginase I [12,34,35] or H 2 O 2 secretion [36,37]. Whereas our data show clear differences in arginine dependence of PMN versus T cells [12] or NK cells [21], there are also common themes: cellular viability, cytokine and chemokine mRNA induction, IL-8 protein synthesis, as well as cytotoxicity and chemotaxis are unimpaired in the absence of arginine in T cells [14,38] and in PMN (this manuscript). Finally, our results are relevant for the therapeutic use of novel, arginine-depleting, metabolic anti-tumor strategies [16].…”

Mouse versus Human Neutrophils in Cancer: A Major Knowledge Gap

“…It is generally assumed that granulocyte-induced arginine deficiency in the tumor microenvironment induces suppression of T cell responses and represents one of the mechanisms of tumor-mediated immune escape [26,37]. However, a recent study convincingly demonstrated that human CD8 + –T cell antigen-specific cytotoxicity and perforin secretion are completely preserved in the absence of arginine, while antigen-specific proliferation as well as IFN-γ and granzyme B secretion are severely compromised [38]. Importantly, the production of the immunosuppressive cytokine IL-10 is also suppressed in an arginine-poor environment [39].…”