Comparative Phenotype and Immunogenicity of Freshly Isolated and Immortalized Rat Hepatocytes

Adult human hepatocytes promote CD4(+) T-cell hyporesponsiveness via interleukin-10-producing allogeneic dendritic cells

The success of liver cell therapy remains closely dependent on how well the infused cells can be accepted after transplantation and is directly related to their degree of immunogenicity. In this study, we investigated the in vitro immunogenic properties of isolated human hepatocytes (hHeps) and adult-derived human liver progenitor cells (ADHLPCs), an alternative cell candidate for liver cell transplantation (LCT). The constitutive expression of immune markers was first analyzed on these liver-derived cells by flow cytometry. Human liver-derived cells were then cocultured with allogeneic human adult peripheral blood mononuclear cells (PBMCs), and the resulting activation and proliferation of PBMCs was evaluated, as well as the cytokine levels in the coculture supernatant. The effect of liver-derived cells on monocyte-derived dendritic cell (MoDC) properties was further analyzed in a secondary coculture with naive CD4(+) T-cells. We report that hHeps and ADHLPCs expressed human leukocyte antigen (HLA) class I and Fas but did not express HLA-DR, Fas ligand, and costimulatory molecules. hHeps and ADHLPCs did not induce T-cell activation or proliferation. Moreover, hHeps induced a cell contact-dependent production of interleukin (IL)-10 that was not observed with ADHLPCs. The IL-10 was produced by a myeloid DC subset characterized by an incomplete mature state. Furthermore, hHep-primed MoDCs induced an antigen-independent hyporesponsiveness of naive CD4(+) T lymphocytes that was partially reversed by blocking IL-10, whereas nonprimed MoDCs (i.e., those cultured alone) did not. hHeps and ADHLPCs present a low immunogenic phenotype in vitro. Allogeneic hHeps, but not ADHLPCs, promote a cell contact-dependent production of IL-10 by myeloid DCs, which induces naive CD4(+) T-cells antigen-independent hyporesponsiveness.

Prevention of hepatocyte allograft rejection in rats by transferring adenoviral early region 3 genes into donor cells

Hepatocyte transplantation is being evaluated as an alternative to liver transplantation for metabolic support during liver failure and for definitive treatment of inherited liver diseases. However, as with liver transplantation, transplantation of allogeneic hepatocytes requires prolonged immunosuppression with its associated untoward effects. Therefore, we explored strategies for the genetic modification of donor hepatocytes that could eliminate allograft rejection, obviating the need for immunosuppression. Products of early region 3 (AdE3) of the adenoviral genome are known to protect infected cells from immune recognition and destruction. In the present study we showed that immortalized rat hepatocytes that had been stably transduced with AdE3 before transplantation into fully MHC-mismatched rats are protected from allograft rejection. Quantitative real-time PCR analysis showed that a similar number of engrafted AdE3-transfected hepatocytes had survived in syngeneic and allogeneic recipients. AdE3 expression did not reduce expression of MHC class I on the surfaces of donor hepatocytes. Consistent with this, the in vivo cytotoxic cell-mediated alloresponse was attenuated but not abolished in recipients of AdE3-transfected allogeneic hepatocytes. In contrast, graft survival correlated with a marked reduction in cell-surface localization of Fas receptor in the transplanted cells and inhibition of Fas-mediated apoptosis, which are related to the antiapoptotic functions of the AdE3 proteins.

CONCLUSION

AdE3 gene products prevent hepatocyte allograft rejection mainly by protecting the cells from the effector limb of the host immune response and could be used as a tool to facilitate allogeneic hepatocyte transplantation.

IFN-gamma promotes Fas ligand- and perforin-mediated liver cell destruction by cytotoxic CD8 T cells

To study liver cell damage by CTL, CD8 T cells from P14 TCR transgenic (tg) mice specific for the gp33 epitope of lymphocytic choriomeningitis virus with either deficiency in IFN-gamma (P14.IFN-gamma(null)), functional Fas ligand (P14.gld), or perforin (P14.PKO) were transferred into H8 tg mice ubiquitously expressing gp33 Ag. Treatment of H8 recipient mice with agonistic anti-CD40 Abs induced vigorous expansion of the transferred P14 T cells and led to liver cell destruction determined by increase of glutamate dehydrogenase serum levels and induction of caspase-3 in hepatocytes. Liver injury was mediated by the Fas/Fas ligand (FasL) pathway and by perforin, because P14.gld and P14.PKO T cells failed to induce increased glutamate dehydrogenase levels despite strong in vivo proliferation. In addition, H8 tg mice lacking Fas were resistant to the pathogenic effect of P14 T cells. Besides FasL and perforin, IFN-gamma was also required for liver cell damage, because P14.IFN-gamma(null) T cells adoptively transferred into H8 mice failed to induce disease. Moreover, Fas expression on hepatocytes from H8 recipient mice was increased after transfer of wild-type compared with P14.IFN-gamma(null) T cells, and wild-type P14 T cells expressed higher levels of FasL than P14 T cells lacking IFN-gamma. Thus, our data suggest that IFN-gamma released by activated CD8 T cells upon Ag contact facilitates liver cell destruction.

Identification and simian immunodeficiency virus infection of CD1d-restricted macaque natural killer T cells

Natural killer T (NKT) cells express a highly conserved T-cell receptor (TCR) and recognize glycolipids in the context of CD1d molecules. We recently demonstrated that CD4+ NKT cells are highly susceptible to human immunodeficiency virus type 1 (HIV-1) infection and are selectively depleted in HIV-infected individuals. Here, we identified macaque NKT cells using CD1d tetramers and human Valpha24 antibodies. Similar to human NKT cells, alpha-galactosylceramide (alpha-GalCer)-pulsed dendritic cells activate and expand macaque NKT cells. Upon restimulation with alpha-GalCer-pulsed CD1d(+) cells, macaque NKT cells secreted high levels of cytokines, a characteristic of these T cells. Remarkably, the majority of resting and activated macaque NKT cells expressed CD8, and a smaller portion expressed CD4. Macaque NKT cells also expressed the HIV-1/simian immunodeficiency virus (SIV) coreceptor CCR5, and the CD4+ subset was susceptible to SIV infection. Identification of macaque NKT cells has major implications for delineating the role of these cells in nonhuman primate disease models of HIV as well as other pathological conditions, such as allograft rejection and autoimmunity.