Abstract
There is clinical interest in the modulation of regulatory T cells for cancer therapy. The safety of these therapies in combination with conventional anti-cancer therapies, including radiation therapy, can be studied in animal models. The effects of partial depletion of regulatory T (Treg) cells with an anti-CD25 antibody in conjunction with ionizing radiation on inflammation and tissue injury were analyzed in C57BL/6 mice. An anti-CD25 antibody (PC61) was administered 3 days prior to 13 Gy lower-half hemi-body irradiation (HBI). The blood, spleen, mesenteric lymph nodes (mLNs) and inguinal lymph nodes (iLNs) were harvested at various times thereafter. Alterations in the proportion of leukocyte subsets including CD4+ T cells, CD8+ T cells, Treg cells, B cells, NK cells, NK1.1+ T cells, macrophages and granulocytes were analyzed by FACS. The lungs, liver, pancreas, stomach, jejunum, duodenum, ileum, colon and kidney were harvested and studied by H&E staining. Expression of inflammatory mediators in plasma and tissue were investigated by ELISA. HBI significantly decreased the leukocyte pool though the various leukocyte subsets had different sensitivities to HBI. The administration of PC61 significantly decreased the proportion of Treg cells in spleen, iLN, mLN and blood (reduction of approximately 60%). Irradiation significantly increased the proportion of Treg cells in the spleen, iLN and mLN. HBI induced a systemic inflammatory reaction as demonstrated by increased plasma levels of IL-6, KC/CXCL1 and circulating granulocytes in the blood. Neutrophils also infiltrated the small bowel. The same general patterns were observed whether or not Treg cells were partially depleted with PC61 prior to HBI. These data demonstrate that partial depletion of Treg cells in these mice does not influence HBI-induced inflammatory response and tissue injury, and that combining anti-CD25 therapy with radiation may be safe and well tolerated in a clinical setting.
Highlights
Radiation therapy (RT) is a first-line treatment option for patients with many different types of solid tumors
To determine the effects of radiation with and without the depletion of Treg cells on systemic leukocyte counts, alterations in the total number of cells in the spleen, inguinal lymph nodes (iLNs) and mesenteric lymph nodes (mLNs), as well as alterations in the proportions of various leukocyte subsets were determined at 4 hrs and 1, 3, 7 and 14 days following irradiation
Radiation significantly decreased the number of total spleen, iLN and mLN cells in the mice treated with both hemi-body irradiation (HBI) and rat IgG and HBI+PC61
Summary
Radiation therapy (RT) is a first-line treatment option for patients with many different types of solid tumors. RT is often very effective at controlling tumors, it can injure normal tissues. This collateral damage is a critical consideration whenever radiation is combined with other cytotoxic or biological therapies such as chemotherapy and immunotherapy [1]. There is increasing evidence that local tumor irradiation can enhance host anti-tumor immunity [2]. Irradiation of tumors can enhance the ability of dendritic cells injected intratumorally to capture tumor antigens, migrate to the draining lymph node, and present processed antigens to tumorspecific T cells [5,6]. Often viewed as an immunosuppressive treatment modality, by promoting antigen presentation in an inflammatory setting radiation can synergize with antigen-presenting cells to stimulate anti-tumor immunity
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