Base-edited live microbiome therapeutics with target-aid -live biotherapeutic products (LBPS) with synergistic effects of anti-PD-1 antibodies in a syngeneic model of mice.

Abstract

e15104 Background: Base editing without DNA cleaving is a technique that introduces point mutations using enzymes that induce base conversions. Generally, only the point mutation occurs, achieving a high level of precision. Base editing can easily be applied to bacteria, for which DNA cleaving is often lethal. With Bio Palette's core technology of base editing, Target-AID, we can quickly achieve the required therapeutic effects by making pinpoint modifications to bacteria. Immune checkpoint inhibitors (ICIs) targeting CTLA-4, PD-1, or PD-L1 have shown outstanding therapeutic outcomes in various cancers. However, the therapeutic efficacy of ICIs-based immunotherapy has been limited. Recent studies have revealed that the human gut microbiome controls the efficacy of ICIs. Bacterial flagellin derived from Enterococcus spp. has been suggested to enhance immune responses to cancer through activation of TLR5 signaling (1). As a regulatory mechanism of flagellin secretion in Enterococcus spp, FliD, FlgK, FlgN, or FlgM are known as negative regulators. Thus, if the flagellar expression can be enhanced by making the negative regulator functionally deficient, it can be expected to increase the efficacy and response rate of ICIs when combination with a base-edited strain. Methods: As human TLR5 luciferase reporter assay, HEK293T cells were transfected with human TLR5-expression vector. BALB/cAnN mice (6–8 weeks’ old) were injected subcutaneously with 3 x 106 cells for murine colon cancer cell line CT-26. Six days post inoculation, the mice were randomized based on tumor volume into treatment and vehicle control groups (n = 10 per each group). Anti-mouse PD-1 antibody was dosed 5 mg/kg, q3d, iv, for up to 3 weeks either alone or in combination with each of various strains (1 x 109 CFU/mouse, po). Body weight and tumor size were routinely measured until endpoint. Results: To achieve the increased extracellular secretion of Flagellin, we created fliD dysfunctional strain because deletion of the flagellar cap component FliD was expected to promote extracellular secretion of Flagellin monomers. Comparing the wild-type strains we used, E. casseliflavus activated TLR5 compared to E. gallinarum. E. casseliflavus with a stop codon introduced into the fliD gene, BP5040 strain, was found to increase TLR5 activation by approximately 4.9-fold when compared to wild type strain. In vivo experiments indicated that antitumor effect was observed with BP5040 alone. Strikingly, a remarkable antitumor effect was also demonstrated when BP5040 was combined with an anti-PD-1 antibody. Conclusions: To achieve the desired therapeutic effect, we performed base editing without inserting foreign genes. As a result, BP5040 strain is found to be a potential candidate for the treatment of immuno-oncology, which was created using our LBP platform technology.