Objectives: To develop pancreatic islet isolation and purification techniques in order to be able to test two human pancreatic islet immunomodulation techniques on an in vitro model of allograft islet rejection.
Methods: Islet isolation was performed according to Ricordi's method, which was slightly modified during the study. Purification was performed according to the Euroficoll discontinuous gradient method on a Cobe 2991 centrifuge. The results of immunomodulation techniques (depletion of cells expressing class II HLA molecules, and immunomasking of HLA class I molecules) were assessed in vitro by mixed lymphocyte-islet cocultures (MLIC).
Results: Seventeen pancreatic islets were isolated then purified. Technical improvements increased the yield from 2,247 +/- 1,984 to 4,567 +/- 990 islet-equivalents per gram. The mean purity was 70 +/- 19% (40-90%). Immunomodulation by depletion of class II HLA molecules regularly inhibited (84%) MLIC in contrast with masking of class I antigens, which induced only a moderate (44%) and inconstant (4 experimentations out of 6) inhibition.
Conclusion: The modifications made to the islet isolation method improved its yield and now allow the possibility of clinical applications. The results of mixed lymphocyte-islet cocultures suggest that the suppression of nonendocrine cells expressing class II HLA molecules on their surface reduces the immunogenicity of pancreatic islet grafts.