2146 - Convergent Mechanisms of Immune Sensitization: scRNA-seq Reveals Shared TME Remodeling in Rectal Cancer Treated with Anti-PD-1 ± SCRT
Presenter(s)
Y. Liu1, R. Wu1, L. Huang1, Y. Wang1, J. Wang1, J. Wan1, L. Shen1, Y. WANG1, F. Xia1, and Z. Zhang2; 1Department of Radiation Oncology, Fudan University Shanghai Cancer Center, Shanghai, China, 2Department of Radiation Oncology, Fudan University Shanghai Cancer Center; Department of Oncology, Shanghai Medical College, Fudan University; Shanghai Clinical Research Center for Radiation Oncology; Shanghai Key Laboratory of Radiation Oncology, Shanghai, China
Purpose/Objective(s): Deficient mismatch repair (dMMR) locally advanced rectal cancers (LARC) are inherently "hot" and sensitive to PD-1 blockade, whereas proficient mismatch repair (pMMR) tumors are typically "cold" and resistant. However, short-course radiotherapy (SCRT) combined with PD-1 blockade significantly improves complete response (CR) rates in pMMR LARC. To elucidate how SCRT reprograms this resistant tumor microenvironment (TME), we integrated single-cell RNA sequencing (scRNA-seq) data from LARC patients receiving anti-PD-1 therapy±SCRT. This study investigates whether the TME remodeling induced by SCRT plus PD-1 blockade in pMMR tumors converges with the responsive mechanisms of dMMR tumors treated with anti-PD-1 therapy. Ultimately, we aim to elucidate the shared therapeutic pathways governing immune sensitization and treatment response.
Materials/Methods: scRNA-seq datasets were integrated from three independent cohorts (GSE205505, GSE236581 and our TORCH study), totaling 144 tumor samples from 77 LARC patients. Treatment arms comprised anti-PD-1 therapy (n=41) and SCRT+PD-1 blockade (n=36). Following comprehensive cell annotation, we performed comprehensive computational analyses, including cellular module identification, Gene Set Enrichment Analysis (GSEA) and survival analysis.
Results: We identified a mixed immune-stromal module (CM6, featuring eCAF_CTHRC1, Mac_SPP1, and Tip_KDR) that decreased post-treatment in responders to both anti-PD-1 (P<0.001) and SCRT+PD-1 (P=0.027). In the TCGA-COAD/READ cohorts, higher CM6 abundance was associated with worse overall survival (OS), whereas a top 30-gene shared post-treatment upregulated signature correlated with improved OS. The ratio of Tip_KDR decreased following both therapies (PD-1: P<0.001; SCRT+PD-1: P=0.016). However, Treg_FOXP3, Mac_SPP1, EC_MKI67 and Treg_TNFRSF4 exclusively decreased after receiving PD-1 blockade, whereas eCAF_CTHRC1 and Bifn_ISG15 were exclusively decreased after receiving SCRT+PD-1 blockade. Furthermore, cellular module membership (cMM) analysis identified Mac_SPP1 and eCAF_CTHRC1 as the dominant hub cells driving treatment response in the anti-PD-1 therapy and SCRT+PD-1 blockade cohorts, respectively.
Conclusion: These findings reveal a convergent mechanism of immune sensitization in LARC, where both anti-PD-1 therapy and SCRT+PD-1 blockade promote anti-tumor immunity by depleting the CM6 module. Mechanistically, treatment efficacy hinges on the attenuation of distinct Tip_KDR-mediated cellular crosstalks. While PD-1 blockade disrupts Tip_KDR-Mac_SPP1 interactions in "hot" dMMR/MSI responders, SCRT uniquely dismantles the Tip_KDR-eCAF_CTHRC1 axis to sensitize "cold" pMMR tumors. Targeting these distinct stromal-vascular networks provides a compelling mechanistic rationale for utilizing radiotherapy to overcome inherent immunotherapy resistance in rectal cancer.