Caloric Restriction Impairs Regulatory T cells Within the Tumor Microenvironment After Radiation and Primes Effector T cells

Int J Radiat Oncol Biol Phys. 2021 Aug 1;110(5):1341-1349. doi: 10.1016/j.ijrobp.2021.02.029. Epub 2021 Feb 26.

Abstract

Outcomes for triple negative breast cancer (TNBC) are poor and may be improved by increasing CD8+ tumor infiltrating lymphocytes (TIL) to augment antitumor immunity. Radiation (RT) can promote immunogenic cell death with increased antitumor T cell activity but also stimulates suppressive regulatory T cells (Tregs). Because metabolic alterations affect immune homeostasis and prior studies show caloric restriction (CR) combined with RT improves preclinical TNBC outcomes, we hypothesized that CR augments RT, in part, by altering intratumoral immunity. Using an in vivo model of TNBC, we treated mice with ad libitum (AL) diet, radiation, a CR diet, or CR + RT, and demonstrated an immune suppressive environment with a significant increase in CD4+ CD25+Foxp3+ Tregs after RT but not in CR-fed mice. CD8:Treg ratio in CR + RT TIL increased 4-fold compared with AL + RT mice. In vivo CD8 depletion was performed to assess the role of effector T cells in mitigating the effects of CR, and it was found that in mice undergoing CR, depletion of CD8 T cells resulted in increased tumor progression and decreased median survival compared with isotype control-treated mice. In addition, PD-1 expression on CD3+CD8+ T cells within the tumor microenvironment was significantly increased in CR + RT versus AL + RT treated mice as per immunofluorescence. Serum from breast cancer patients undergoing RT alone or CR and RT was collected pre- and postintervention, and a cytokine array demonstrated that patients treated with CR + RT had notable decreases in immunosuppressive cytokines such as IL-2Rγ, IL-10Rβ, and TGF-β2 and 3 compared with patients receiving RT alone. In conclusion, combining CR with RT decreases intratumoral Tregs, increases CD8:Treg, and increases PD-1 expression via a process dependent on CD8 T cells in a TNBC model. Breast cancer patients undergoing CR concurrently with RT also had significant reduction in immunosuppressive cytokine levels compared with those receiving RT alone.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Animals
  • CD4-Positive T-Lymphocytes / chemistry
  • CD4-Positive T-Lymphocytes / cytology
  • CD4-Positive T-Lymphocytes / immunology
  • CD4-Positive T-Lymphocytes / radiation effects
  • CD8-Positive T-Lymphocytes / chemistry
  • CD8-Positive T-Lymphocytes / metabolism
  • CD8-Positive T-Lymphocytes / radiation effects
  • Caloric Restriction*
  • Combined Modality Therapy / methods
  • Disease Progression
  • Female
  • Flow Cytometry
  • Forkhead Transcription Factors
  • Humans
  • Interleukin Receptor Common gamma Subunit / blood
  • Interleukin-10 Receptor beta Subunit / blood
  • Interleukin-2 Receptor alpha Subunit
  • Lymphocyte Depletion / methods
  • Lymphocytes, Tumor-Infiltrating / cytology
  • Lymphocytes, Tumor-Infiltrating / immunology
  • Lymphocytes, Tumor-Infiltrating / radiation effects*
  • Mice
  • Mice, Inbred BALB C
  • Middle Aged
  • Programmed Cell Death 1 Receptor / metabolism
  • Random Allocation
  • T-Lymphocytes, Regulatory / cytology
  • T-Lymphocytes, Regulatory / immunology
  • T-Lymphocytes, Regulatory / radiation effects*
  • Transforming Growth Factor beta2 / blood
  • Transforming Growth Factor beta3 / blood
  • Triple Negative Breast Neoplasms / blood
  • Triple Negative Breast Neoplasms / immunology
  • Triple Negative Breast Neoplasms / mortality
  • Triple Negative Breast Neoplasms / radiotherapy*
  • Tumor Microenvironment / immunology
  • Tumor Microenvironment / radiation effects*

Substances

  • FOXP3 protein, human
  • Forkhead Transcription Factors
  • IL2RA protein, human
  • IL2RG protein, human
  • Interleukin Receptor Common gamma Subunit
  • Interleukin-10 Receptor beta Subunit
  • Interleukin-2 Receptor alpha Subunit
  • Pdcd1 protein, mouse
  • Programmed Cell Death 1 Receptor
  • Transforming Growth Factor beta2
  • Transforming Growth Factor beta3