Abstract 6639: Mechanisms of action of a killed, bacteria-based, multiple immune receptor agonist in development for pulsed anti-tumor immunotherapy

Abstract Activation of immune receptors, such as Toll-like (TLR), NOD-like (NLR) and Stimulator of Interferon Genes (STING) is required for efficient innate and adaptive immunity. Gram-negative bacteria (G-NB) contain multiple TLR, NOD and STING agonists. Potential utility of G-NB for cancer immunotherapy is supported by observations of tumor regression in the setting of infection and Coley’s Toxins. Coley reported that intravenous (i. v. ) administration was likely most effective but produced toxicity. The discovery of TLRs and their agonists, particularly the potent/multi-functional TLR4 agonist lipopolysaccharide (LPS) -endotoxin, comprising ~75% of the outer membrane of G-NB, suggests that it may be both a critical active ingredient and responsible for dose-limiting toxicity of i. v. G-NB. We have produced killed, intact bacteria products from non-pathogenic G-NB with ~90% reduction of LPS activity. One product, Decoy10, contained TLR2, 4, 8, 9, NOD2 and STING agonist activity and exhibited reduced i. v. toxicity in mice and rabbits relative to unprocessed cells. Decoy10 and closely related Decoy20 produced single agent activity or combination-mediated durable regressions, with immunological memory, in mice with syngeneic or human breast, colorectal, hepatocellular, pancreatic carcinomas or non-Hodgkin’s lymphoma. Regressions were observed in combination with chemotherapy, a non-steroidal anti-inflammatory drug, anti-PD-1, or rituximab, were associated with induction of 18-26 plasma cytokines/chemokines, activation of innate and adaptive immune pathways in tumors, and were dependent on NK, CD4+ and CD8+ T cells (Newman, Cancer Res 2023;83 (7 Suppl): Abstract nr 4165). These and preliminary clinical results demonstrating rapid clearance of Decoy20 with transient induction of 50 plasma cytokines/chemokines (Newman et al. , J Immunother Cancer 2023;11 (Suppl 2) 782-E: A1770) are supportive of a “pulse-prime” mechanism, whereby Decoy bacteria produce transient, but broad innate and adaptive immune activation. We have now analyzed immune activation by Decoy bacteria in vitro using human peripheral blood mononuclear cells (PBMCs). Decoy10 enhanced polarization of CD14+ monocytes to M1 macrophages and inhibited Treg polarization. Decoy10 enhanced monocyte-derived dendritic cell maturation and enhanced Th1, Th2 and Th17 CD4+ polarization, with Th1 at 10-100-fold lower Decoy10 concentrations than Th2 or Th17. Decoy10 also activated NKT and T cells, and enhanced PBMC-mediated tumor cell killing. The results demonstrate that Decoy bacteria stimulate polarization, maturation, or activation of cellular mediators of innate and adaptive anti-tumor immune responses, inhibit an immune-suppressive mechanism, and enhance immune cell killing of tumor cells. The results are consistent with and significantly extend our previously reported in vivo data. Citation Format: Michael J. Newman, Deepak Singh. Mechanisms of action of a killed, bacteria-based, multiple immune receptor agonist in development for pulsed anti-tumor immunotherapy abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 6639.