Date of Award

9-10-2010

Document Type

Open Access Thesis

Degree Name

Medical Doctor (MD)

First Advisor

Daniel Goldstein

Second Advisor

Lloyd Cantley

Third Advisor

Joseph Craft

Abstract

Solid organ transplant has emerged over the last half century as an important treatment for solid organ failure. Management has matured dramatically over the past two decades with improvements in acute rejection, but long-term graft survival has improved very little and current treatment is limited by the side-effects and toxicities of immunosuppressive medications. Nanoparticle delivery of therapeutics, improving transport characteristics and decreasing systemic and local toxicity has emerged as a dynamic treatment modality, but little work has been done using nanoparticles in transplantation. Our research examined the use of CD4-targeted nanoparticles encapsulated with mycophenolic acid (MPA), a commonly used immunosuppressant in organ transplantation. This work is the first to examine antigen-specific targeting of nanoparticles in any transplant model. MPA-loaded particles show a slow and continuous release profile and biodistribution suggested retention in the spleen. Targeting of nanoparticles to CD4 T cells was suggested using ex vivo and in vitro flow cytometry. In the fully allogeneic MHCII mismatch BALB/C to C57BL/6 mice we found improved graft survival in the non-targeted MPA group and even greater graft survival in the CD4-targeted group. Targeted and non-targeted particle groups showed equal delay in rejection in the less immunogenic single MHC mismatch B6.H-2bm12 to C57BL/6 model that we showed to be CD4 dependent. In both models, graft survival times were increased over free drug and controls with roughly one thousand fold lower dose of drug in the nanoparticles as compared with free MPA. Consistent with these findings were decreased proliferation with targeted and non-targeted MPA-nanoparticles using in vitro and ex vivo mixed lymphocyte reactions. We postulated that the similar rejection times in targeted and non-targeted groups was due to dendritic cell (DC) involvement and we found active uptake of nanoparticles in DCs, a decrease in inflammatory cytokine production and a decrease in treated DCs ability to stimulate T cells via mixed lymphocyte reactions. Furthermore we found a possible mechanism in the DC interaction with T cells through the upregulation of the inhibiting co-stimulatory molecules B7-DC and B7-H1 on DCs treated with MPA-nanoparticles. We also found possible upregulation of CD4+CD25+ Foxp3 expressing Tregs which may serve to increase graft acceptance. These results explore the involvement of dendritic cells in the process of nanoparticle-induced graft acceptance and suggest the feasibility of using nanoparticle drug vectors in clinical transplant.

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