Introduction: Type 1 diabetes (T1D) is an autoimmune condition characterized by the immune system attacking insulin-producing beta cells in the pancreas. Insulin remains the primary treatment for T1D patients with diminished beta cell function. Islet cell transplantation has shown promise in achieving insulin independence following multiple infusions. However, this approach faces challenges including limited supply of suitable donors and risk of acute rejection. Despite advancements in clinical immunosuppressants, incidence of acute rejection leading to graft failure remains significant. Rejections typically manifest days to months after transplantation, primarily driven by innate immune cells targeting grafted islets. Previous large cohort studies conducted by our group identified 14key modulators associated with acute rejection, with Caspase-1 emerging as a pivotal driver gene instigating inflammation and initiating the innate immune response. Building upon this, our objective is to replicate the study using a diabetic mouse model harbouring enzymatically inactive Caspase-1. Our study aims to provide deeper insights into the mechanistic pathways underlying acute rejection.
Methods: Ten-week-old Caspase-1 C284A/ C284A mice on C57BL/6(H-2b) background and C57BL/6 wild type mice were induced with streptozotocin at doses of 200mg/kg and 190mg/kg, respectively, to induce diabetes (blood sugar level >15mmol/l). Age-matched BALB/C(H-2d) mice served as donors for allogeneic MHC mismatch. Upto 200 islets from the donor mice were transplanted under the kidney capsule of recipient mice, with the endpoint defined as a significant increase in blood sugar levels. Gene expression, flow cytometry, and insulin staining, were conducted, followed by appropriate statistical analyses.
Results: Although both caspase-1 C284A/ C284A and wildtype mice had successful transplants, both groups had an end-point at 15 days post-transplant. Overall blood sugar was found to be lower in caspase-1 mice. As expected, caspase-1 mice exhibited significantly lower gene expression of pro-inflammatory cytokines including IL18, IL-1α and IFNγ. Using flow cytometric analyses, caspase1 mice had a significantly lower population of Ly6G positive neutrophils compared to wildtype at end-point which is in keeping with reduced pro-inflammatory cytokine gene expression. 
Conclusion: In our study, we found that the enzymatically inactive caspase-1 C284A/C284A decreases Ly6G neutrophils, potentially enhancing graft protection and function, as indicated by lower mean blood sugar levels post-transplantation. Neutrophils exhibit heterogeneity, and further investigation is needed to identify specific subpopulations responsible for graft protection. Our findings serve as an initial step toward considering an alternative approach to mitigate the risk of acute rejection. Previous research has shown that minocycline, a caspase-1 inhibitor, can mitigate allograft rejection in heart transplantation, suggesting that caspase-1 could be a potential target for preventing acute rejection