PROJECT SUMMARY
Dysregulation of blood glucose due to T1D leads to both short term consequences such as hypoglycemia
induced injury and death, and long-term complications including amputation, blindness, kidney failure, and
neuropathy. Islet transplantation has the potential to provide biologic glycemic regulation for all T1D patients,
effectively curing the disease. However, this promising therapy is plagued by the requirement for ineffective
immunosuppressive therapies. Currently, only 50 to 70% of grafts remain viable at 5 years post-transplantation,
largely due to the immunosuppressive therapy causing toxicity and failing to fully protect the graft. Currently, a
costly cocktail of immunosuppressive drugs is given in a rarely successful attempt to provide broad immune
coverage with side effect mitigation. Thus, a need exists for simpler, lower cost, and more effective alternatives
to these immunosuppressive regimens that can maintain islet transplant survival without off-target side-effects.
The objective of this proposal is to mechanistically understand how repurposing a single component of these
immunosuppressive cocktails, rapamycin, using engineered nanoscale drug carriers can provide sustained islet
protection. Vesicular polymeric nanocarriers (i.e. polymersomes, PS) encapsulating rapamycin (rPS) were found
to uniquely change the cellular biodistribution of rapamycin to avoid side-effects and significantly improve
efficacy. Importantly, rapamycin normally has a wide cellular biodistribution and functions by directly inhibiting
T cell proliferation, but rPS completely avoids T cells and instead switches the immunosuppressive mechanism
to a selective and potent costimulation blockade of antigen presenting cells (APCs). This novel cell-selective
nanocarrier-enhanced costimulation blockade was characterized by an upregulation of CD8+ regulatory T cells
and double positive CD4+CD8+ T cells, achieving sustained normoglycemia in a rigorous fully major
histocompatibility complex (MHC) mismatched allogenic intraportal (liver) islet transplantation mouse model.
Here, this proposal will investigate and benchmark the immunological mechanism of rPS against the clinically
relevant therapeutic belatacept, a CTLA4-IgG fusion protein that induces costimulation blockade via an
alternative method: the blocking of CD80/86 coreceptors on APCs. The following aims will be achieved:
Aim 1: Determine whether rPS induces general immunosuppression or antigen-specific tolerance. It is currently
not known whether rPS induce antigen-specific or general systemic immunosuppression. A novel ex vivo mixed
lymphocyte reaction assay and in vivo dual antigen-specific / non-specific islet transplantation will address this
question.
Aim 2: Compare the immunomodulatory mechanisms of costimulation blockade induced by rPS vs. CTLA4-IgG
for enhanced allogenic islet graft survival. High parameter flow cytometry using T-distributed Stochastic Neighbor
Embedding (tSNE) analysis and assessment of long-term graft survival following fully-MHC mismatch islet
transplantation will be performed.
