Abstract 5857: Targeting KDELR2 remodels the immune tumor microenvironment for enhanced anti-cancer response

Abstract Inflammation within the tumor microenvironment (TME) boosts anti-cancer immune responses by activating both innate and adaptive immunity. In situ inflammation enhances antigen presentation, immune cell infiltration and supports immune-cancer cycle. KDEL receptors (R1, R2 & R3) are critical for retaining KDEL proteins in the endoplasmic reticulum (ER). Their compromise can cause a concerted release of pro-immunogenic molecule, such as calreticulin. This can provoke conditions similar to immunogenic cell death (ICD) in the absence of chemotherapy. To address the role of KDEL receptors in immune-cancer interactions, we generated a mouse colon cancer model equipped with doxycycline (DOX)-induced silencing of the KDELRs. We found that in these cells KDEL-R2 isoform controls the intracellular retention of a large number of secretory proteins including calreticulin. Surprisingly, in vivo when cells with silenced KDEL-R2 were mixed with normal tumor cells in a 1:10 ratio and treated with DOX, tumors significantly regressed in mice. Analysis of the TME (via flow cytometry, IHC, and IF) revealed a massive infiltration of neutrophils and macrophages, most are polarized to M1. In vitro macrophage polarization studies confirmed that from the silencing of KDEL-R2 confers polarization. Using a novel biotin-labeled probe to detect extracellular PDIs, we confirmed the robust ICD intensity of KDEL proteins in the TME. In athymic Nu/Nu mice, KDEL-R2 silencing also induced tumor regression, underscoring the dominant role of innate immunity. Re-challenge experiments demonstrated T-cell priming and the establishment of immune memory, supported by T-cell and macrophage infiltration in the TME. Additionally, using tumor cells that present an antigenic MHC class I peptide, we demonstrate T cell priming in the absence of vaccination. This study reveals a significant advancement in cancer immunotherapy and potential for synergistic effect with other treatments such as CAR-T therapy and checkpoint inhibitors through immune memory and inflammation-driven immunity. Citation Format: Shakti Prasad Pattanayak, Boaz Tirosh. Targeting KDELR2 remodels the immune tumor microenvironment for enhanced anti-cancer response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 5857.