Examining the Biosynthesis and Xenoantigenicity of Class II Swine Leukocyte Antigen Proteins

Abstract

Genetically engineered pig organs could provide transplants to all patients with end-stage organ failure, but Ab-mediated rejection remains an issue. This study examines the class II swine leukocyte Ag (SLA) as a target of epitope-restricted Ab binding. Transfection of individual α- and β-chains into human embryonic kidney cells resulted in both traditional and hybrid class II SLA molecules. Sera from individuals on the solid organ transplant waiting list were tested for Ab binding and cytotoxicity to this panel of class II SLA single-Ag cells. A series of elution studies from an SLA-DQ cell line were performed. Our results indicate that human sera contain Abs specific for and cytotoxic against class II SLA. Our elution studies revealed that sera bind the SLA-DQ molecule in an epitope-restricted pattern. Site-specific mutation of one of these epitopes resulted in statistically decreased Ab binding. Humans possess preformed, specific, and cytotoxic Abs to class II SLA that bind in an epitope-restricted fashion. Site-specific epitope mutagenesis may decrease the Ab binding of highly sensitized individuals to pig cells.

The desirable donor pig to eliminate all xenoreactive antigens

“…Individuals sensitized to SLA will likely require complete removal of the SLA protein, a possibility for class I but not likely for class II. An alternative approach is mutation of the offending epitope—a strategy that significantly reduced xenoantibody binding . This method of epitope mutation would likely leave intact the pig’s ability to process, present, and respond to viral antigens and produce viable genetically engineered pigs that provide a favourable crossmatch for future xenotransplant recipients.…”

Role of human and porcine MHC DRB1 alleles in determining the intensity of individual human anti‐pig T‐cell responses

“…Thus, in addition to the selection of recipients with low antibody titers, site-specific epitope mutagenesis of porcine SLA can be applied to further decrease the deleterious effects of antibodies on a xenograft. 50 Based on the data from our pig-to-rat model ( Figure 5B), it is very likely that the intensity of antibody responses to a xenograft depends on the MHC configuration of the recipient. Concerning clinical xenotransplantation, it would be of interest to identify HLA class-II allelic configurations associated with strong or weak antibody responses to porcine xenoantigen.…”

“…Studies on the specificity of cross‐reactive anti‐HLA antibodies revealed that they bind porcine SLA molecules in an epitope‐restricted pattern. Thus, in addition to the selection of recipients with low antibody titers, site‐specific epitope mutagenesis of porcine SLA can be applied to further decrease the deleterious effects of antibodies on a xenograft . Based on the data from our pig‐to‐rat model (Figure B), it is very likely that the intensity of antibody responses to a xenograft depends on the MHC configuration of the recipient.…”

Genome Engineering for Xenotransplantation

“…However, unlike the glycan epitopes described above, the SLA have a critical role in antigen presentation as part of the immune response, and thus the deletion of SLA could create risks of immune deficiencies that outweigh their risks as xenoantigens. Instead, alternate approaches seek to create engineered SLA proteins lacking the epitopes responsible for the immunogenicity while maintaining their antigen presentation functions [43].…”