Blocking CTL-Based Cytotoxic Pathways Reduces Apoptosis of Transplanted Hepatocytes

Abstract

Background. A major obstacle in allogenic hepatocyte transplantation is increased apoptosis of grafted cells due to CTL-based cytotoxicity. However, whether blockade of Fas- and granzyme-mediated pathways of CTL-based cytotoxicity may provide immune protection to transplanted hepatocytes is poorly defined. Our study aimed to reduce apoptosis of allogenic transplanted hepatocytes by inhibiting granzyme B (GraB) activity and blocking Fas-FasL interaction.Materials and methods. Hepatocyte transplantation was performed by inoculating isolated liver cells from ACI rats (allogenic) or Lewis rats (syngenic) into the spleens of Lewis rats. Recipients were treated with FLIM58, an inhibitory anti-FasL mAb, and GraB inhibitor I alone or a combination of the two drugs for 5 days after transplantation, and were sacrificed at Day 7. Apoptosis of transplanted hepatocytes was detected in situ by TUNEL assay and M30 immunostaining. Glutamate dehydrogenase (GLDH) activity in recipient spleens was examined to evaluate survival of transplanted cells. Recipient spleens were assayed for FasL level with Western blotting and for GraB activity by hydrolysis of GraB substrate.Results. FLIM58 or GraB inhibitor I significantly reduced the percentage of TUNEL-positive and M30-positive hepatocytes and markedly increased GLDH levels in allogenic, but not syngenic, recipient spleens. These effects were more pronounced when the two drugs were used in combination (P < 0.05). Additionally, elevation of FasL and GraB levels in allogenic recipient spleens can be significantly reduced by FLIM58 and GraB inhibitor I, respectively.Conclusions. Inhibition of GraB activity and blockade of Fas-FasL interaction reduce the apoptosis of allogenic transplanted hepatocytes, and thus improve their survival.