Modulation of Microenvironment Acidity Reverses Anergy in Human and Murine Tumor-Infiltrating T Lymphocytes

Abstract

Stimulating the effector functions of tumor-infiltrating T lymphocytes (TIL) in primary and metastatic tumors could improve active and adoptive T-cell therapies for cancer. Abnormal glycolysis, high lactic acid production, proton accumulation, and a reversed intra-extracellular pH gradient are thought to help render tumor microenvironments hostile to roving immune cells. However, there is little knowledge about how acidic microenvironments affect T-cell immunity. Here, we report that lowering the environmental pH to values that characterize tumor masses (pH 6-6.5) was sufficient to establish an anergic state in human and mouse tumorspecific CD8 þ T lymphocytes. This state was characterized by impairment of cytolytic activity and cytokine secretion, reduced expression of IL-2Ra (CD25) and T-cell receptors (TCR), and diminished activation of STAT5 and extracellular signal-regulated kinase (ERK) after TCR activation. In contrast, buffering pH at physiologic values completely restored all these metrics of T-cell function. Systemic treatment of B16-OVA-bearing mice with proton pump inhibitors (PPI) significantly increased the therapeutic efficacy of both active and adoptive immunotherapy. Our findings show that acidification of the tumor microenvironment acts as mechanism of immune escape. Furthermore, they illustrate the potential of PPIs to safely correct T-cell dysfunction and improve the efficacy of T-cell-based cancer treatments. Cancer Res; 72(11); 2746-56. Ó2012 AACR.

The acidic microenvironment as a possible niche of dormant tumor cells

“…Several studies have shown that acidic pH e inhibits T-cell proliferation [84], dendritic cell maturation [85], cytotoxic T lymphocyte activity (CTLs) [86], lymphokine-activated killer cells [87], and natural killer (NK) activity and viability [88]. Furthermore, lowering pH e to 6.5 has been reported to lead to a loss of function of human and murine tumor-infiltrating T lymphocytes consisting in a significant impairment of cytolytic activity, cytokine secretion, and reduction of T-cell receptor and interleukin-2 α-chain receptor expression [89]. T-cell function was found to be completely restored buffering pH to a physiological value; however when exposure to an acidic microenvironment was sufficiently prolonged, such as a chronic exposure, T cells were deeply damaged and underwent apoptosis [89].…”

“…Furthermore, lowering pH e to 6.5 has been reported to lead to a loss of function of human and murine tumor-infiltrating T lymphocytes consisting in a significant impairment of cytolytic activity, cytokine secretion, and reduction of T-cell receptor and interleukin-2 α-chain receptor expression [89]. T-cell function was found to be completely restored buffering pH to a physiological value; however when exposure to an acidic microenvironment was sufficiently prolonged, such as a chronic exposure, T cells were deeply damaged and underwent apoptosis [89]. Extracellular lactic acid generated by glycolytic cancer metabolism and accumulated in tumor microenvironment supports the suppressive effect on T-cell function exerted by low pH [83].…”

“…Recent studies indicate that buffering low pH at the tumor site by in vivo administration of esomeprazole, a PPI, improves tumor-infiltrating lymphocyte effector functions in melanoma lesions and delays cancer progression in tumor-bearing mice [89,93]. Inhibition of proton pumps on tumor cells with pantoprazole, another PPI, hampers tumor-induced suppression of macrophages both in vitro and in vivo [94,95].…”

Emerging functional roles of nuclear receptors in breast cancer

“…Glycolysis results in more rapid production of ATP, fatty acids and nucleotides that are needed by proliferating tumor cells that need to double their biomass to divide. Furthermore, the generation of lactic acid promotes a tumor microenvironment that is protective against immune attack (Calcinotto et al 2012). It has also been suggested through glucose flux modeling that accumulation of glucose actually promotes aerobic glycosis in preference to oxidative phosphorylation (Vazquez et al 2010); hence, glucose flux can potentially act as a trigger for the Warburg effect.…”

Ganglioside Inhibition of CD8+ T Cell Cytotoxicity: Interference with Lytic Granule Trafficking and Exocytosis

“…Only a few known soluble inhibitory factors have been suggested to inhibit cytotoxic effector function itself in CD8 + T cells. These include lactic acid/acidosis (38), extracellular adenosine (39), reactive oxygen species (3), TGF-b (40), and semaphorin-3A (41). Because the underlying intracellular mechanisms by which these factors inhibit CD8 + CTL effector function are largely undefined, elucidation of ganglioside-induced cytotoxic dysfunction may contribute to an increased understanding of this problem.…”