[Pancreatic islet transplantation: isolation techniques and in vitro immunomodulation]

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.

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).

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.

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.