GSE185311
Modulation of the human pancreatic ductal adenocarcinoma immune microenvironment by stereotactic body radiotherapy
Purpose: Stereotactic body radiotherapy (SBRT) is an emerging treatment modality for pancreatic ductal adenocarcinoma (PDAC) that can effectively prime cytotoxic T cells by inducing immunogenic tumor cell death in preclinical models. SBRT effects on human PDAC have yet to be thoroughly investigated, therefore, this study aimed to characterize immunomodulation in the human PDAC tumor microenvironment following therapy. Experimental Design: Tumor samples were obtained from patients with resectable PDAC. Radiotherapy was delivered a median of seven days prior to surgical resection, and sections were analyzed by multiplex IHC (mIHC), RNA-Seq, and T cell receptor sequencing (TCR-Seq). Results: Analysis of SBRT-treated tumor tissue indicated reduced tumor cell density and increased immunogenic cell death relative to untreated controls. Radiotherapy promoted collagen deposition, however, vasculature was unaffected and spatial analyses lacked evidence of T cell sequestration. Conversely, SBRT resulted in fewer tertiary lymphoid structures and failed to lessen or reprogram abundant immune suppressor populations. Higher percentages of PD-1+ T cells were observed following SBRT, and a subset of tumors displayed more clonal T cell repertoires. Conclusions: These findings suggest that SBRT augmentation of antitumor immunogenicity may be dampened by an overabundance of refractory immunosuppressive populations, and support the continued development of SBRT/immunotherapy combination for human PDAC. Overall design: RNA-Seq performed on 13 untreated and 9 SBRT-treated (25 Gy in 5 oligofractions) PDAC resections a median of 7 days post-SBRT.