American Association for Cancer Research
10780432ccr202293-sup-245236_3_supp_6729907_qjy9mc.pptx (666.64 kB)

Supplementary fig 4 from High-dose per Fraction Radiotherapy Induces Both Antitumor Immunity and Immunosuppressive Responses in Prostate Tumors

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posted on 2023-03-31, 22:33 authored by Lin Lin, Nathanael Kane, Naoko Kobayashi, Evelyn A. Kono, Joyce M. Yamashiro, Nicholas G. Nickols, Robert E. Reiter

Supplemental 4. anti-Gr-1 eradiated MDSC in spleen, blood and tumor.


Prostate Cancer Foundation



The use of high-dose per fraction radiotherapy delivered as stereotactic body radiotherapy is a standard of care for prostate cancer. It is hypothesized that high-dose radiotherapy may enhance or suppress tumor-reactive immunity. The objective of this study was to assess both antitumor and immunosuppressive effects induced by high-dose radiotherapy in prostate cancer coclinical models, and ultimately, to test whether a combination of radiotherapy with targeted immunotherapy can enhance antitumor immunity. We studied the effects of high-dose per fraction radiotherapy with and without anti-Gr-1 using syngeneic murine allograft prostate cancer models. The dynamic change of immune populations, including tumor-infiltrating lymphocytes (TIL), T regulatory cells (Treg), and myeloid-derived suppressive cells (MDSC), was evaluated using flow cytometry and IHC. Coclinical prostate cancer models demonstrated that high-dose per fraction radiotherapy induced a rapid increase of tumor-infiltrating MDSCs and a subsequent rise of CD8 TILs and circulating CD8 T effector memory cells. These radiation-induced CD8 TILs were more functionally potent than those from nonirradiated controls. While systemic depletion of MDSCs by anti-Gr-1 effectively prevented MDSC tumor infiltration, it did not enhance radiotherapy-induced antitumor immunity due to a compensatory expansion of Treg-mediated immune suppression. In allograft prostate cancer models, high-dose radiotherapy induced an early rise of MDSCs, followed by a transient increase of functionally active CD8 TILs. However, systemic depletion of MDSC did not augment the antitumor efficacy of high-dose radiotherapy due to a compensatory Treg response, indicating blocking both MDSCs and Tregs might be necessary to enhance radiotherapy-induced antitumor immunity.

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