Phase I/IIb trial: In-situ vaccine for metastatic colorectal cancer.

Abstract

TPS871 Background: Except for MSI-H tumors, CRC does not respond to immunotherapy. CRC does respond to the graft vs. tumor (GVT) immune effect that occurs after allogeneic stem cell transplantation. GVT is associated with GVHD toxicity which limits the clinical application. A bioengineered allograft (BAG) has been developed which can elicit host-mediated GVT-like effects without GVHD toxicity, chemotherapy conditioning or a HLA-matched donor. BAG are Th1 memory cells derived from blood of healthy donors with CD3/CD28 microbeads attached. These cells have immunomodulatory properties which enable modulation of Th1/Th2 balance and dysregulation of immunosuppressive circuits. We are evaluating the safety and efficacy of BAG in third-line mCRC. Methods: The study uses a standard 3+3 design followed by an expansion phase with the optimal dosing pattern. The protocol has four components: (A) priming; (B) in-situ vaccination; (C) extravasation and trafficking; and (D) counter immune suppression/avoidance. Priming involves intradermal injections of BAG cells which activates NK cells and develops allo-specific Th1/Tc1 immunity. In-Situ vaccination involves tumor cryoablation to release endogenous HSP which chaperone tumor neoantigens, followed immediately by the intralesional injection of BAG cells as adjuvant. Released HSP are engulfed and processed by immature dendritic cells (DC) attracted to the tissue damage. The inflammatory microenvironment created by the BAG and the subsequent allo-rejection response amplified by the priming induces DC maturation. These DC display processed tumor antigens on upregulated MHCI/II and express co-stimulatory CD80/86 enabling priming of a tumor-specific Th1/Tc1 response. CD40L and interferon-gamma expressed by BAG activates allo-specific and tumor-specific memory cells upon intravenous infusion, permitting trafficking to tumor. The host rejection of BAG releases endogenous danger signals creating a sustained systemic inflammatory cytokine release which serves to counter-regulate immunosuppressive mechanisms. Longitudinal CT scans biopsies, PBMC and serum samples are collected for analysis to verify immune events within each phase of the protocol. Clinical trial information: NCT02380443.