Human embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) can only be used effectively in recipients with the same (or nearly the same) histocompatibility type, to avoid rejection or toxic immunosuppression. To overcome this, various strategies have been proposed to derive patient-specific stem cells. These often involve controversial procedures such as therapeutic cloning, and they require a major investment in time and money for every patient that is impractical for routine clinical use. The goal of this proposal is to solve this problem and create a panel of pluripotent stem cells that is histocompatible with a significant percentage of the U.S. population. This panel will consist of cells that are homozygous at the HLA locus, so only one set of major histocompatibility antigens is expressed. By choosing the most common haplotypes, 5-10 HLA-homozygous lines should match over 20-25% of Americans at HLA-A, B and DR loci, and 50 lines should match over 70% of the population. To accomplish this, we will derive a set of iPSCs with common HLA haplotypes from different types of non-embryonic cells. Integrating vectors will be used to deliver reprogramming transgenes, then they will be removed from the cells to create transgene-free iPSCs. Adeno-associated virus (AAV) gene targeting vectors will be used to insert a plus/minus selectable marker next to the HLA locus on human chromosome 6, then mitotic recombinants will be isolated that lost the marker gene and converted the short arm of chromosome 6 to homozygosity, including the entire HLA locus (an approach that has already succeeded in our pilot experiments). The parental iPSCs and their HLA-homozygous derivatives will be characterized extensively by SNP-chip analysis, karyotyping, and differentiation potential. This project will establish a bank of """"""""patient-specific"""""""" HLA/MHC-homozygous stem cells that can be used for all types of regenerative medicine, avoiding the problems of graft rejection and immunosuppression, with significant potential for improving the health of Americans.
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