| Neonatal porcine islets NPI may potentially solve the shortage of tissues for human transplantation, however, it is critical that we must further characterize these tissues before they can be used in clinical transplantation. It is not known to what extent NPI will be susceptible to destruction by both humoral and cell-mediated mechanisms. Galalpha(1,3)Gal is the major xenoantigen responsible for hyperacute rejection of pig organs. This antigen is recognized by human xenoreactive natural antibodies and when these bind and activate complement, the transplanted organs or tissues are rapidly destroyed. It is generally believed that Galalpha(1,3)Gal is not expressed on islet endocrine cells and therefore it has been speculated that these cells would be spared from humoral-mediated destruction. However, we found that a subset of NPI consists of cells which expressed Galalpha(1,3)Gal and expression was detected on both endocrine and non-endocrine cells. Interestingly, both Gal-positive and Gal-negative cells were susceptible to humoral-mediated destruction in vitro. To further characterize the expression of this antigen on porcine islets, 9-day cultured (non-matured) NPI, NPI which have been matured by in vitro culture, or by transplantation into nude mice, and adult pig islets were immunostained with IB4 lectin and/or antibodies to insulin and cytokeratin 7. Galalpha(1,3)Gal expression on porcine islet cells is age-dependent being most abundant on non-matured beta cells. This may explain in part why other studies did not detect this antigen on endocrine cells.;One strategy to prevent destruction of islets by human immune cells is to use immunoisolation device such as microcapsules. To test the efficacy of microencapsulation in protecting NPI from the cytolytic effects of human antibody and complement we exposed microencapsulated NPI to human serum and complement. Microencapsulation protected NPI from the in vitro cytolytic effects of human antibody and complement and the microencapsulated tissues can reverse diabetes in nude mice. Finally, to examine the susceptibility of NPI to cell-mediated immune injury, the proliferative response of human peripheral blood lymphocytes, as well as the ability of natural killer (NK) and cytotoxic T lymphocytes (CTL) to lyse NPI cells were measured. NPI cells were not susceptible to injury mediated by NK cells and/or CTL in vitro.;Taken together, these studies provided important information on the nature of human immunological responses against NPI and the potential of these tissues to one day be successfully transplanted into patients with type 1 diabetes. |
