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Experimental treatments (A) and tumor size follow-up until sacrifice (B) of tumors used to prepare cell suspensions for figures 3, 5 and supplementary figure 4. (C) Shows individual tumor lesion weights used to calculate lymphocytes/gram densities.

FACS analyses on cell suspensions (n=4) derived from non-irradiated MC38-derived tumors

Myeloid cell content (density per gram) in cell suspension from non-irradiated tumors as those in figure 5. Macrophages are defined as CD45+ CD11b+ F4/80+; Dendritic cells (DC) as CD45+CD11b+CD11c+; myeloid-derived suppressor cells (MDSC) as CD45+CD11b+Ly6C+ or CD45+CD11b+Ly6G+ to estimate monocytic (M-MDSC) and granulocytic (G-MDSC) subtypes.

Radiotherapy can be synergistically combined with immunotherapy in mouse models, extending its efficacious effects outside of the irradiated field (abscopal effects). We previously reported that a regimen encompassing local radiotherapy in combination with anti-CD137 plus anti–PD-1 mAbs achieves potent abscopal effects against syngeneic transplanted murine tumors up to a certain tumor size. Knowing that TGFβ expression or activation increases in irradiated tissues, we tested whether TGFβ blockade may further enhance abscopal effects in conjunction with the anti–PD-1 plus anti-CD137 mAb combination. Indeed, TGFβ blockade with 1D11, a TGFβ-neutralizing mAb, markedly enhanced abscopal effects and overall treatment efficacy against subcutaneous tumors of either 4T1 breast cancer cells or large MC38 colorectal tumors. Increases in CD8 T cells infiltrating the nonirradiated lesion were documented upon combined treatment, which intensely expressed Granzyme-B as an indicator of cytotoxic effector capability. Interestingly, tumor tissue but not healthy tissue irradiation results in the presence of higher concentrations of TGFβ in the nonirradiated contralateral tumor that showed smad2/3 phosphorylation increases in infiltrating CD8 T cells. In conclusion, radiotherapy-induced TGFβ hampers abscopal efficacy even upon combination with a potent immunotherapy regimen. Therefore, TGFβ blockade in combination with radioimmunotherapy results in greater efficacy.

Assessment of spontaneous lung metastases of 4T1 tumors in the indicated treatment groups corresponding to mice treated as in figure 2A. Metastases were detected and quantitated -number of lesions in the surface of the lung counted upon inspection under a magnification lens (left) and by real time RT-PCR for tumor specific gp70 RNA (right)-.

single dose radiotherapy and hypofractionated doses increase the level of CD137 and PD-1 expression on the surface of tumor-infiltrating T cells.

Radiotherapy reduced the density and absolute numbers of CD4+, CD8+ and CD25+FOXP3+ T cells and Myeloid-derived suppressor cells both in the irradiated and non-irradiated lesions.

Statistical comparisons for figures 1, 2, 4 and supplementary figure 1.

4T1-derived spontaneous lung metastases

Preclinical and clinical evidence indicate that the proimmune effects of radiotherapy can be synergistically augmented with immunostimulatory mAbs to act both on irradiated tumor lesions and on distant, nonirradiated tumor sites. The combination of radiotherapy with immunostimulatory anti-PD1 and anti-CD137 mAbs was conducive to favorable effects on distant nonirradiated tumor lesions as observed in transplanted MC38 (colorectal cancer), B16OVA (melanoma), and 4T1 (breast cancer) models. The therapeutic activity was crucially performed by CD8 T cells, as found in selective depletion experiments. Moreover, the integrities of BATF-3–dependent dendritic cells specialized in crosspresentation/crosspriming of antigens to CD8+ T cells and of the type I IFN system were absolute requirements for the antitumor effects to occur. The irradiation regimen induced immune infiltrate changes in the irradiated and nonirradiated lesions featured by reductions in the total content of effector T cells, Tregs, and myeloid-derived suppressor cells, while effector T cells expressed more intracellular IFNγ in both the irradiated and contralateral tumors. Importantly, 48 hours after irradiation, CD8+ TILs showed brighter expression of CD137 and PD1, thereby displaying more target molecules for the corresponding mAbs. Likewise, PD1 and CD137 were induced on tumor-infiltrating lymphocytes from surgically excised human carcinomas that were irradiated ex vivo. These mechanisms involving crosspriming and CD8 T cells advocate clinical development of immunotherapy combinations with anti-PD1 plus anti-CD137 mAbs that can be synergistically accompanied by radiotherapy strategies, even if the disease is left outside the field of irradiation. Cancer Res; 76(20); 5994–6005. ©2016 AACR.

supplementary figure legends and supplementary material and methods section.

Mouse external beam irradiation setting and combinations of radiotherapy and anti-CD137 and/or anti-PD1 immunostimulatory monoclonal antibodies are safe and effective to treat MC38-derived bilateral tumors of which only one of the tumor sites is irradiated.

Ex-vivo irradiation of human carcinoma surgical expecimens gives rise to more intense expression of CD137 and PD-1 on infiltrating lymphocytes.

A course of radiotherapy plus immunostimulatory monoclonal antibodies anti-CD137 and anti-PD-1 mAb increases CD4 and CD8 T cells in the tumor infiltrate as well as the number of tumor antigen-specific CD8 T cells.