Immunoisolation of hybrid liver support systems by semipermeable membranes

Immunoisolation of hybrid liver support systems (LSS) utilizing suitable semipermeable membranes as an immune barrier enables neither immunocompetent cytotoxic factors to cause damage to the hepatocytes in the bioreactor nor xenogenic hepatocyte products to cause immunological side effects in patients. To determine the capability of membranes as an immune barrier, 6 flat membranes were investigated: Cuprophan (C-100), cut-off MW 1000, Cuprophan (C-240), cut-off MW 10,000, Polypropylen hydrophilic and hydrophobic (PPhi, PPho), cut-off MW 500,000-1,000,000, Polysulfon (PS), cut-off MW 1,000,000, Polyamid (PA), cut-off beyond MW 1,000,000. The permeability of the membranes to plasma factors and liver protein fractions (LP) was studied by routine biochemical methods and gel electrophoresis. In a second study, pigs (n=7) were immunised by LP after membrane passage. The results showed PA, PS, and PPhi to be completely permeable for plasma factors and LP C-100 and C-240 for urophanic substances, and C-240 again for LP under MW 14.000. All 7 pig sera studied by Western blot discovered pre-formed xenoreactive natural IgG-antibodies (NAB) against human liver antigen (AG) with MW 26.000. AB de-novo-synthesis was demonstrated for AG with MW 45.000. No AB-synthesis was induced for epitopes under MW 26,000. These results suggest that limiting the cut-off of bioreactor outflow membranes to MW < 26,000 could avoid immunological side effects to patients.