alpha-Gal epitopes on viral glycoproteins

Virus-like Particle Display of the α-Gal Carbohydrate for Vaccination against Leishmania Infection

Secreted and surface-displayed carbohydrates are essential for virulence and viability of many parasites, including for immune system evasion. We have identified the α-Gal trisaccharide epitope on the surface of the protozoan parasites Leishmania infantum and Leishmania amazonensis, the etiological agents of visceral and cutaneous leishmaniasis, respectively, with the latter bearing larger amounts of α-Gal than the former. A polyvalent α-Gal conjugate on the immunogenic Qβ virus-like particle was tested as a vaccine against Leishmania infection in a C57BL/6 α-galactosyltransferase knockout mouse model, which mimics human hosts in producing high titers of anti-α-Gal antibodies. As expected, α-Gal-T knockout mice infected with promastigotes of both Leishmania species showed significantly lower parasite load in the liver and slightly decreased levels in the spleen, compared with wild-type mice. Vaccination with Qβ-α-Gal nanoparticles protected the knockout mice against Leishmania challenge, eliminating the infection and proliferation of parasites in the liver and spleen as probed by qPCR. The α-Gal epitope may therefore be considered as a vaccine candidate to block human cutaneous and visceral leishmaniasis.

Possible role of a cell surface carbohydrate in evolution of resistance to viral infections in old world primates

Due to inactivation of the α1,3-galactosyltransferase gene (GGTA1, or the α1,3GT gene) approximately 28 million years ago, the carbohydrate αGal (Galα1,3Galβ1,4GlcNAc) is not expressed on the cells of Old World monkeys and apes (including humans) but is expressed in all other mammals. The proposed selective advantage of this mutation for these primates is the ability to produce anti-Gal antibodies, which may be an effective immune component in neutralizing αGal-expressing pathogens. However, loss of α1,3GT expression may have been advantageous by providing natural resistance against viral pathogens that exploited the α1,3GT pathway or cell surface αGal for infection. Infections of paired cell lines with differential expression of α1,3GT showed that Sindbis viruses (SINV) preferentially replicate in α1,3GT-positive cells, whereas herpes simplex viruses type 1 and type 2 (HSV-1 and HSV-2) preferentially grow in cells lacking α1,3GT. Viral growth and spread correlated with the ability of the different viruses to successfully initiate infection in the presence or absence of α1,3GT expression. GT knockout (KO) suckling mice infected with SINV strains (AR339 and S.A.AR86) experienced significant delay in onset of disease symptoms and mortality compared to wild-type (WT) B6 suckling mice. In contrast, HSV-2-infected GT KO mice had higher viral titers in spleen and liver and exhibited significantly more focal hepatic necrosis than WT B6 mice. This study demonstrates that α1,3GT activity plays a role in the course of infections for certain viruses. Furthermore, this study has implications for the evolution of resistance to viral infections in primates.

Human CD59 incorporation into porcine endogenous retrovirus particles: implications for the use of transgenic pigs for xenotransplantation

Transgenic pigs have been engineered to express human CD59 (hCD59) in order to suppress hyperacute rejection of xenotransplants in human recipients. In this study, porcine endogenous retrovirus (PERV) was produced in a porcine cell line expressing hCD59 in order to examine the effect of this complement control protein on PERV neutralization by human sera. hCD59 was found to be incorporated into PERV particles produced from engineered ST-IOWA cells. PERV incorporation of hCD59 resulted in a dramatic inhibition of complement-mediated virolysis by human serum. However, incorporation of hCD59 had no effect on neutralization of PERV by human serum, as measured in infectivity assays. Our results suggest that the use of organs from hCD59 transgenic pigs will inhibit complement-mediated virolysis, but will not compromise the protective effects of human sera on the neutralization of PERV particles.