ESTRO 2024 - Abstract Book

S5187

Radiobiology - Immuno-radiobiology

ESTRO 2024

Purpose/Objective:

Localized hypofractionated radiotherapy (hRT) can promote the cross-presentation of tumor antigens to CD8+ T cells, but distant T cell-mediated effects can usually only be observed in conjunction with immune checkpoint blockade (ICB). Moreover, in patients, the RT-induced abscopal effect is still only rarely observed and many patients experience ICB-induced adverse events. Lenalidomide (lena) is an anti-angiogenic and immunomodulatory drug used in the treatment of multiple myeloma. We here investigated whether lena can enhance the RT-induced abscopal effect in double combination with hRT.

Material/Methods:

We used abscopal tumor models with one irradiated and one non-irradiated tumor in opposite flanks. In the B16 melanoma model, hRT was delivered to the primary tumor in two fractions of 12 Gy; in the MC38 colon carcinoma model, it was delivered in three fractions of 8 Gy. Tumor growth and survival were determined (7–12 mice per group). Lena (1 mg/mouse) was injected i.p. daily for 3 weeks. Tumor-specific CD8+ T cells were measured by FACS using MHC tetramers in single-cell suspensions of tumors and lymph nodes. Dependence on CD8+ T cells was determined by antibody blockade. Cross-presentation of tumor antigen by dendritic cells (DCs) was measured using the B16-OVA model and an antibody recognizing MHC/OVA-epitope complexes ex vivo. For RNA-seq total RNA from BMDCs generated in the presence of DMSO or 10 μM lena was extracted using TRIzol™ Reagent, and libraries were prepared using the TruSeq Stranded mRNA LT Sample Prep Kit (Illumina, San Diego, CA). RNA-seq and analysis were performed by OE Biotech Co, Ltd (Shanghai, China). In both tumor models, double combination of hRT with lena induced a pronounced abscopal effect. The control of the non-irradiated tumor was much better than after monotherapy with hRT or lena monotherapies (B16 model: p < 0.005; MC38 model: p < 0.05). Survival of the mice was also significantly improved compared to single treatment with hRT (B16: p < 0.001, MC38: p < 0.05) or lena (B16: p < 0.001, MC38: p < 0.0001). The abscopal effect was strongly dependent on CD8+ T cells and correlated with an increase in tumor-specific CD8+ T cells in the non irradiated tumor and its draining lymph nodes. We observed an increase in tumor-specific T cells with a stem-like (PD1+ TCF1+ TIM3–) and a transitory exhausted phenotype (PD1+ TIM3+ CD101–). Moreover, hRT/lena combination treatment increased the number of DCs cross-presenting OVA to CD8+ T cells. RNA-seq analysis revealed that BMDCs generated in the presence of lena upregulated genes relevant for DC differentiation, type I and II IFN response genes, and genes associated with the maturation of DCs and their migration to lymph nodes. Consistent with the increased infiltration of DCs and tumor-specific CD8+ T cells, particularly the stem-like subpopulation, RT/lenalidomide treatment also resulted in an increase of MECA-79+ endothelial cells (EC), which correspond to tumor-associated high endothelial venules within the non-irradiated tumor. Results:

Conclusion:

We demonstrate that lena can augment the hRT-induced abscopal effect in mouse solid tumor models in a CD8 T cell-dependent manner, correlating with enhanced anti-tumor CD8 T cell immunity, DC cross-presentation, and MECA79+ EC numbers.

Keywords: abscopal effect, lenalidomide, dendritic cells