Long-Term IgG Response to Porcine Neu5Gc Antigens without Transmission of PERV in Burn Patients Treated with Porcine Skin Xenografts

Abstract

Acellular materials of xenogenic origin are used worldwide as xenografts and Phase I trials of viable pig pancreatic islets are currently being performed. However, limited information is available on transmission of porcine endogenous retrovirus (PERV) after xenotransplantation and on the long-term immune response of recipients to xenoantigens. We analyzed the blood of burn patients who had received living pig skin dressings for up to 8 weeks for the presence of PERV as well as for the level and nature of their long term (maximum 34 years) immune response against pig antigens. Whilst no evidence of PERV genomic material or anti PERV antibody response was found, we observed a moderate increase in anti αGal antibodies and a high and sustained anti non-αGal IgG response in those patients. Antibodies against the non-human sialic acid Neu5Gc constituted the anti non-αGal response with the recognition pattern on a sialogly can array differing from that of burn patients treated without pig skin. These data suggest that anti-Neu5Gc antibodies may represent a barrier for long-term acceptance of porcine xenografts. As anti-Neu5Gc antibodies can promote chronic inflammation, the long-term safety of living and acellular pig tissue implants in recipients warrants further evaluation.

Rabbit antithymocyte globulin–induced serum sickness disease and human kidney graft survival

“…Furthermore, our sera were diluted to 1:100 (instead of 1:2), diluting other potential antibodies, and with final anti-Neu5Gc concentration close to that of the unaffected individual's sera. As mentioned previously, anti-Neu5Gc epitope recognition by serum IgG drastically differs between primed and unprimed individuals (26). Therefore, different patterns of Neu5Gc epitopes recognized by elicited anti-Neu5Gc antibodies in primed individuals, as in our study, in addition to exposure to increased levels of anti-Neu5Gc, may be important in understanding a potential role of such antibodies in this unique situation of a "physiological" immune complex condition.…”

“…However, anti-Gal antibody levels were not increased, arguing against this interpretation. In addition, as elicited anti-Neu5Gc antibodies recognize different patterns of Neu5Gc epitopes than "natural" ones (26) and their presence results in increased long-term exposure of Neu5Gc-positive ECs to these antibodies, they may trigger a chronic inflammation of graft vascular walls, as further discussed below. Indeed, in Cmah KO mice, an animal model unable to biosynthesize Neu5Gc, similarly to humans, it has been demonstrated that anti-Neu5Gc antibodies can stimulate chronic inflammation in dietary Neu5Gc-charged tissues (36).…”

“…Anti-Neu5Gc antibodies were quantified using a modified ELISA originally described by V. Padler-Karavani et al (26,48). This assay uses mouse serum proteins as coating antigens in the ELISA plate, offering an exhaustive display of the major epitopes containing Neu5Gc (48).…”

“…After washing and blocking, pretreated human sera were added to the plates for 2 hours at room temperature. IgGs were detected as described previously (26). Again, serial dilutions of IVIg at concentrations starting from 200 ng/ml served as standards.…”

Role of DNA Methylation in Expression and Transmission of Porcine Endogenous Retroviruses

“…Although PERVs were shown to be able to infect human cells in vitro (8), to date there is no evidence of transmission to recipients of xenografts (63)(64)(65)(66)(67)(68), apparently due to an efficient protective mechanism of the recipient. Epigenetic silencing is a common mechanism of host protection against retroviral infection; however, here we show that human cells are very inefficient in PERV silencing by DNA methylation.…”