Iron Supplementation Interferes With Immune Therapy of Murine Mammary Carcinoma by Inhibiting Anti-Tumor T Cell Function

Abstract

Iron is both, an essential compound for many metabolic processes, and iron deficiency can impact on the proliferation of cells including lymphocytes but also tumor cells. On the other hand, excess iron-catalyzed radical formation can induce cellular toxicity which has been previously demonstrated for T cells in hereditary iron overload. Despite these interconnections, little is known on the effects of clinically approved intravenous iron supplements for curing cancer-related anemia, on T cell differentiation, tumor proliferation, anti-tumor T cell responses and, of clinical importance, on efficacy of cancer immunotherapies. Herein, we analyzed the effects of intravenous iron supplementation on T cell function and on the effectiveness of anti-cancer chemotherapy with IL-2/doxorubicin or immunotherapy with checkpoint-inhibitor anti-PD-L1 in C57Bl/6N female mice with implanted E0771 mammary carcinomas. We found that iron application resulted to an increased availability of iron in the tumor microenvironment and stimulation of tumor growth. In parallel, iron application inhibited the activation, expansion and survival of cytotoxic CD8+ T cells and of CD4+ T helper cells type 1 and significantly reduced the efficacy of the investigated anti-cancer treatments. Our results indicate that iron administration has a tumor growth promoting effect and impairs anti-cancer responses of tumor infiltrating T lymphocytes along with a reduced efficacy of anti-cancer therapies. Iron supplementation in cancer patients, especially in those treated with immunotherapies in a curative setting, may be thus used cautiously and prospective studies have to clarify the impact of such intervention on the outcome of patients.

The Iron Curtain: Macrophages at the Interface of Systemic and Microenvironmental Iron Metabolism and Immune Response in Cancer

“…Iron has been shown to trigger CD4+ T cell differentiation and alter CD8+ T cell expansion. Immunosuppressive effects of iron on T cells have been described in individuals with hereditary or transfusion mediated iron overload, where these patients have altered T cell numbers and function ( 118 ). In tumor infiltrating lymphocytes, iron may impair the proliferation, differentiation or maturation by generating mitochondrial ROS, resulting in cell death.…”

Regulation of Th1 T Cell Differentiation by Iron via Upregulation of T Cell Immunoglobulin and Mucin Containing Protein-3 (TIM-3)

“…First, iron supplementation of anti-CD3-primed splenocytes isolated from naive mice induced a slight decrease in the proliferation and dramatically slowed cell cycle progression of T cells as demonstrated by CFSE dilution ( Figure 1A ) and BrdU pulsing ( Figure 1B ) assays even at concentrations as low as 2.5 to 5 µM ( 39 ). Both effects were independent of the iron source (chloride, sulfate and citrate) and, hence, independent of iron source-inherent differences in solubility, dissociation properties, and cellular iron availability.…”

“…According to our in vitro data ( Figure 1 ) iron dose-dependently increased TIM-3 expression, and blocked cell cycle progression and differentiation of Th0 to Th1 cells. Hence, two non-exclusive mechanisms may be proposed: first, interference of iron with the Th1-specific transcription factor network and second, signaling induced by reactive oxygen species, as postulated in our previous report on iron and anti-tumor CD8 + T cells ( 39 ). While iron did not affect the expression of TIM-3-inducing cytokines, IL-12 and IL-27 in vivo , it still could affect signals mediated by those cytokines via the IL-12 receptor or via T-bet, the master switch transcription factor of Th1 cells.…”

“…In our model of chronic bacterial infection, the effects of iron were highly specific for Th1 cells as neither the number of Th2, nor Th17 or Treg subsets displayed differences after high iron diet. Interestingly, our previous report provided evidence that the function of the CD8 + IFNγ-producing T cell subset in murine mammary carcinoma was strongly hampered by intravenous iron supplementation ( 39 ).…”

“…Our recently published data ( 39 ) indicate that high cellular iron content in CD8 + T cells induces accumulation of reactive oxygen species (ROS) in mitochondria and that treatment with a mitochondria-specific ROS scavenger could restore T cell priming even in the high iron setting. Whether a ROS-mediated mechanism including ferroptosis ( 49 ) or mitochondrial dysfunction ( 50 ) as a consequence of iron loading underly the TIM-3 up-regulation and functional impairment of Th1 cells in high iron-fed Salmonella- infected animals remains to be investigated.…”