PS03, a bifunctional RNA therapeutic to induce exhaustion in diabetogenic T cells

T cell exhaustion is an important mechanism that controls the clinical manifestation of Type 1 (T1) diabetes in mice and humans. In humans, T cell exhaustion correlates with the length of the honeymoon phase; islets persistent in patients with a long T1D history express PDL1; and autoantibodies positive, non-diabetic patients undergoing anti-cancer treatment with PD1 inhibitors develop fulminant diabetes. In preclinical settings, PDL1 is upregulated on the β cells of NOD mice that do not develop T1D, anti-PD1 treatment induces T1D in male NOD, and transgenic expression of PDL1 on β cells prevents T1D. These data suggest that modulation of PDL1 on β cells is an important yet unexplored therapeutic opportunity to prevent diabetes clinical manifestations. We propose using a new bifunctional RNA therapeutic called PS03 to modulate PDL1 specifically on β cells. PS03 comprises the β cell-specific aptamers we have recently isolated (as targeting agents) covalently linked to a small activating RNA (saRNA) to upregulate PDL1. We hypothesize that PS03 will block diabetogenic T cell function, induce their exhaustion, and halt the autoimmune attack in T1D. We also hypothesize that PS03 will leave T1D-unrelated T cells untouched while other PD1 agonists may affect them. Our preliminary data shows that PS03, given systemically to NOD mice, PS03 upregulated PDL1 in β cells without modulating this gene in α and acinar cells nor on all other tissues evaluated. A treatment course with PS03 increased the number of pancreatic CD4+ and CD8+ T cells with an exhausted phenotype in NOD mice. A short treatment course, started one week before onset with a former unoptimized PS03 formulation, prevented T1D in 40% of the mice for over a year. Building on these promising results, we propose to compare PS03 with the soluble PD1 agonist fc-PDL1 by: 1) determining the effects of PS03-mediated PDL1 upregulation and fc-PDL1 on TCR signaling of diabetogenic and islet infiltrating T cells; 2) characterizing the effect of PS03 and fc-PDL1 treatments on diabetogenic and T1D unrelated T cells, on the immunological landscape, and β cell function; and 3) determining the effect of the two drugs on T1D progression. We will use state-of-the-art techniques such as pancreatic living slices, multiplex quantitative immunofluorescence microscopy, scRNA seq, and spectral flow cytometry to unveil the effect of PS03-induced, β cell-specific PDL1 upregulation on the immune system and insulin-producing cells. PS03 exists in both mouse and human versions; it is produced at GMP grade with an oligo synthesizer without contaminations and with a fluorinated backbone that makes it RNAse resistant and invisible to the immune system. To our knowledge, this is the only non-viral reagent that can modulate PDL1 expression selectively on murine and human β cells in vivo, allowing us to understand the mechanisms that regulate T cell exhaustion in the islets and, hopefully in the future, provide new therapeutic options to patients recently diagnosed with T1D.