Background. We have developed a novel bioartificial liver (BAL) composed of porcine hepatocyte spheroids in a reservoir design. A semipermeable membrane is used to protect the spheroids from immune-mediated damage. This study was designed to assess the influence of membrane pore size on performance of the spheroid reservoir BAL. Methods. Eight healthy dogs were studied during primary and secondary exposures to the spheroid reservoir BAL using membranes with small (10 nm) or large (200 nm) pores. BAL performance was assessed by multiple functional assays. Spheroids were examined microscopically before and after all BAL treatments. Titers of xenoreactive antibody were monitored until elective death of animals on day 42. Results. Viability and functional performance of spheroids were significantly greater after all BAL treatments that used membranes with 10-nm versus 200-nm pores. Reduced performance in the 200 nm group was associated with 7.7-fold and 78.0-fold rise in xenoreactive antibody titers after first and second treatments, respectively. Dogs in the 10 nm group remained hemodynamically stable during all BAL treatments, whereas those in the 200 nm group experienced acute hypotension (P<0.001) during second BAL exposures. Microscopic examination of spheroids after BAL treatments indicated that deposition of canine proteins, including complement, was associated with reductions in both viability and functional performance of the BAL. Conclusions. The elicited immune response of healthy dogs to a xenogeneic BAL was blocked and BAL performance significantly improved by reducing the permeability of the BAL membrane.
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