Background: Type 1 Diabetes affects over 2.1 million patients in the United States and cost the healthcare system $14.4B in 2016. The current clinical standard for Type 1 Diabetes is daily glucose monitoring and exogenous insulin administration, which is medically and financially intensive. Islet cell transplantation could provide a curative solution but requires intense immunosuppression to avoid graft rejection. Rapamycin, one part of this immunosuppressive protocol, delivered directly to antigen-presenting cells (APCs) maintains them in an immature state that leads to “co-stimulation blockade”, leading to anergy of T-cells. Polyethylene glycol- b-polypropylene sulfide polymers self-assemble into nanovesicles (PS) that can be loaded with hydrophobic drugs such as rapamycin (rPS). When injected subcutaneously, rPS is preferentially uptaken by macrophages, leading to targeted costimulation blockade4. Burke et al. (2022) demonstrate that rPS induces extended survival of MHC- mismatched islet allografts and normoglycemia in a drug-induced diabetic mouse model4. We seek to validate these results in a non-obese diabetic (NOD) mouse model that replicates the inflammatory and autoimmune environment of Type 1 Diabetes pathology. Studies (Table 1) show that certain gut microbiome bacteria have increased populations in the states of immune tolerance.

Methods: NOD mice (age = 12 weeks) were injected with varying concentrations of rPS (0 mg/kg PBS, 0.5 mg/kg, 1 mg/kg, 2 mg/kg, n =5 for each group) every 3 days for 18 days (total 6 doses). After the final dosing, mice were euthanized and their brachial/pancreatic lymph nodes, spleen, and cecal content were harvested. Cecal content was sent to Zymo Research for microbiological sequencing while lymph node and spleen samples were processed for flow cytometry.

Results: rPS exhibits a significant and positive dose dependent effect on the prevalence of the Blautia genus associated with induction of regulatory T cells and allograft survival. In the Lactobacillus genus, a statistically non-significant increase in prevalence is seen in the rPS 2 mg/kg group. Genus Alistipes was significantly decreased in prevalence in the 0.5 mg/kg rPS group. Many rejection associated bacteria were not prevalent at all in the microbiota of both the controls and treatments.

Conclusions: The significant and dose associated effect of rPS on the Blautia genus shows that one mechanism of rPS’s tolerogenic effects may be through change of the gut microbiome. These results agree with previous pharmacologic characterization of rPS in significantly changing the immune population of CD80/86+ APCs and regulatory T cells. The mechanism by which rPS affects the gut microbiome still needs to be elucidated. It is unclear whether rPS modulates the microbiome directly or if rPS’s previously established effects on the immune system allow for bacterial species associated with tolerance to flourish. In addition, each experimental group was not adequately powered to find significant associations in species outside of the Blautia genus. A larger study is required to confirm these results and establish the mechanism of causality.