The treatment of acute and chronic liver failure is still a challenge despite modern therapeutic innovations. While liver transplantation can restore liver function and improve patient survival, donor shortages limit this treatment to a small number of patients. Cellular xenotransplantation has emerged as an alternative for treating liver failure. Xenohepatocytes could be readily available in sufficient quantities to treat patients in critical condition and thereby reduce the donor shortage. The use of isolated encapsulated or non-encapsulated cells can reduce the immunorejection response. Several studies using animal models of acute or chronic liver failure have demonstrated improved survival and recovery of liver function after xenotransplantation of adult hepatocytes. Porcine liver cells are a potential source of xenohepatocytes due to similarities with human physiology and the great number of hepatocytes that can be obtained. The recent development of less immunogenic transgenic pigs, new immunosuppressive drugs, and cellular encapsulation systems represents important advances in the field of cellular xenotransplantation. In this study, we review the work carried out in animal models that deals with the advantages and limitations of hepatocyte xenotransplantation, and we propose new studies needed in this field.

The importance of the cellular immune response against DENV has been increasingly highlighted in the past few years, in particular for vaccine development. We have previously constructed two plasmids, pE1D2, and pcTPANS1, encoding the envelope (E) ectodomain (domains I, II, and III) and the non-structural 1 (NS1) protein of dengue virus serotype 2 (DENV2), respectively. In the present work, we analyzed the induction of the cellular response in mice immunized with these DNA vaccines and identified the immunogenic peptides. Vaccinated BALB/c mice became protected against a lethal challenge of DENV2. Depletion of CD4 + cells in vaccinated animals almost completely abolished protection elicited by both vaccines. In contrast, a significant number of pE1D2- and pcTPANS1-immunized mice survived virus challenge after depletion of CD8 + cells, although some animals presented morbidity. To identify immunogenic peptides recognized by T cells, we stimulated splenocytes with overlapping peptide libraries covering the E and NS1 proteins and evaluated the production of IFN-γ by ELISPOT. We detected two and three immunodominant epitopes in the E and NS1 proteins, respectively, and four additional NS1-derived peptides after virus challenge. Characterization by intracellular cytokine staining (ICS) revealed that both CD4 + and CD8 + T cells were involved in IFN-γ and TNF-α production. The IFN-γ ICS confirmed reaction of almost all E-derived peptides before challenge and identified other epitopes after infection. All NS1-derived peptides were able to elicit IFN-γ production in CD4 + cells, while only a few peptides induced expression of this cytokine in CD8 + T lymphocytes. Interestingly, we observed an increase in the frequency of either CD4 + or CD8 + T cells producing TNF-α after immunization with the pE1D2 and challenge with DENV2, while lymphocytes from pcTPANS1-vaccinated animals maintained ordinary TNF-α production after virus infection. We also assessed the recognition of E and NS1 immunogenic peptides in C57BL/6 mice due to the difference in MHC haplotype expression. Two NS1-derived epitopes featured prominently in the IFN-γ response with cells from both animal strains. Overall, our results emphasize the importance of the T cell response involved in protection against dengue induced by E and NS1 based DNA vaccines.

Acute liver failure (ALF) has a poor prognosis and, despite intensive care support, reported average survival is only 10-40%. The most common causes responsible for ALF are viral hepatitis (mainly hepatitis A and B) and acetaminophen poisoning. Hepatic transplantation is the only appropriate treatment for patients with unlikely survival with supportive care alone. Survival rates after transplantation can be as high as 80-90% at the end of the first year. However, there is a shortage of donors and is not uncommon that no appropriate donor matches with the patient in time to avoid death. Therefore, new technologies are in constant development, including blood purification therapies as plasmapheresis, hemodiafiltration, and bioartificial liver support. However, they are still of limited efficacy or at an experimental level, and new strategies are welcome. Accordingly, cell transplantation has been developed to serve as a possible bridge to spontaneous recovery or liver transplantation. Xenotransplant of adult hepatocytes offers an interesting alternative. Moreover, the development of transgenic pigs with less immunogenic cells associated with new immunosuppressor strategies has allowed the development of this area. This article reviews some of the newly developed techniques, with focus on xenotransplant of adult hepatocytes, which might have clinical benefits as future treatment for ALF.