HLA typing immunogenetics and transplantation

Permanent, lowered HLA class I expression using lentivirus vectors with shRNA constructs: Averting cytotoxicity by alloreactive T lymphocytes

Transplantation of many tissues requires histocompatibility matching of human leukocyte antigens (HLA) to prevent graft rejection, to reduce the level of immunosuppression needed to maintain graft survival, and to minimize the risk of graft-versus-host disease, particularly in the case of bone marrow transplantation. However, recent advances in fields of gene delivery and genetic regulation technologies have opened the possibility of engineering grafts that display reduced levels of HLA expression. Suppression of HLA expression could help to overcome the limitations imposed by extensive HLA polymorphisms that restrict the availability of suitable donors, necessitate the maintenance of large donor registries, and complicate the logistics of procuring and delivering matched tissues and organs to the recipient. Accordingly, we investigated whether knockdown of HLA by RNA interference (RNAi), a ubiquitous regulatory system that can efficiently and selectively inhibit the expression of specific gene products, would enable allogeneic cells to evade immune recognition. For efficient and stable delivery of short hairpin-type RNAi constructs (shRNA), we employed lentivirus-based gene transfer vectors, which provide a delivery system that can achieve integration into genomic DNA, thereby permanently modifying transduced graft cells. Our results show that lentivirus-mediated delivery of shRNA targeting pan-Class I and allele-specific HLA can achieve efficient and dose-dependent reduction in surface expression of HLA in human cells, associated with enhanced resistance to alloreactive T lymphocyte-mediated cytotoxicity, while avoiding MHC-non-restricted killing. We hypothesize that RNAi-induced silencing of HLA expression has the potential to create histocompatibility-enhanced, and, eventually, perhaps "universally" compatible cellular grafts.

Significant HLA matching effect in a large urban transplant center composed primarily of minorities

In more than 1300 deceased donor transplants, including 75% Hispanics, African-Americans, and Asians, a significant effect of mismatching (MM) was observed for zero to three MM compared to more than three MM (P < .02). There was a significantly better patient survival (P < .002), shorter hospital stay (P < .001), and a trend toward lowered immunosuppression. Zero to three MM were present in 48% of the recipient population in part due to the pre-UNOS algorithm that assigns points for zero MM and other MM grades. However, recently only zero MM receive points, therefore fewer zero to three MM recipients would be expected. The largest minority population is Hispanic. We postulated that at least part of the effect was associated with socioeconomic status and English as a second language parameters of our Hispanic population. Zero to three MM was found to decrease risk and should be used prospectively in minority donor/recipient combinations.