Abstract 3449: Radiation therapy for bridging and improving CAR-T cells therapy
Authors: Kostopoulos Nektarios , Koumeins Costanitnos , Plastaras John P. , Schuster Stephen J. , Facciabene Andrea 
Published: June 2022

Abstract
CD19-targeted chimeric antigen receptor (CAR) T cells have transformed the treatment of patients with relapsed or refractory CD19-positive hematologic malignancies. However, a significant subset of these patients either fails to respond or eventually relapses. Moreover, patients who are candidates for CART-19 therapy often have symptomatic disease that requires some form of treatment to support them during the manufacture period. An ideal bridging therapy would simultaneously both (1) sensitize the tumor to CART-19 attack to increase antitumor control and (2) debulk the disease during manufacture. Radiotherapy (RT) is an established curative and palliative cancer treatment regimen, with approximately half of cancer patients with solid tumors receiving RT some time during their disease. Several reports have underscored the existence of threshold doses (and regimens) that are able to switch on different damage programs that profoundly affect responses to therapy by eliciting potent immune modulatory effects, prompting immunologically mediated tumor cell death. These effects have been attributed to multiple pathways, including the activation of the cGMP-cAMP Synthetase (cGAS), Stimulator of Interferon Genes (STING) pathway with Type I Interferons expression, and tumor associated antigen (TAA) cross priming with anti-tumor CD8+ T cell elicitation, ultimately inducing “abscopal” effects. By virtue of the immunomodulatory effects of RT, we hypothesize that RT could serve as a successful bridging strategy for CAR T-cell therapy. To investigate this hypothesis we established the A20 Lymphoma CART-19 therapy mouse model in our lab and use it to perform preliminaries experiments. A20 cells were implanted into both flanks of the animals. Mimicking human immune adjuvant dose used in our institute for RT bridging, 20 days after the A20 challenge we RT treated one of the two tumors using a dose of 8Gy divided in two fractions of 4Gy each. Twenty-four hours later 1x10ep6 CART-19 cells were infused intravenously. While the effects of RT in combination with CART-19 have similar impact on the tumor growth of the irradiated mass a significant increase of the antitumor effects of the single therapy was observed on the non-irradiated tumor. FACS studies demonstrated heavy leukocytes infiltration with increased presence of infused CART-19 as well indigenous T cells. To investigate possible molecular mechanisms involved in the increased effects on the non-irradiated tumor, we perform a qPCR array and observed increased expression of genes linked to cross priming, including IFN type I and Batf3. A20 cells express the ectopic retroviral antigen gp70 with well characterized AH1 immune-dominant epitope. AH1 tetramer staining on infiltrating T cells demonstrated increase staining in tumor from mice treated with the combination. Overall these results suggest RT may serve as optimal debulking and adjuvant bridging therapy for CAR-T cells therapy.
Citation Format: Nektarios Kostopoulos, Costanitnos Koumeins, John P. Plastaras, Stephen J. Schuster, Andrea Facciabene. Radiation therapy for bridging and improving CAR-T cells therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3449.