Genetic editing of HLA expression in hematopoietic stem cells to broaden their human application

Abstract

Mismatch of human leukocyte antigens (HLA) adversely impacts the outcome of patients after allogeneic hematopoietic stem-cell transplantation (alloHSCT). This translates into the clinical requirement to timely identify suitable HLA-matched donors which in turn curtails the chances of recipients, especially those from a racial minority, to successfully undergo alloHSCT. We thus sought to broaden the existing pool of registered unrelated donors based on analysis that eliminating the expression of the HLA-A increases the chance for finding a donor matched at HLA-B, -C, and -DRB1 regardless of a patient’s race. Elimination of HLA-A expression in HSC was achieved using artificial zinc finger nucleases designed to target HLA-A alleles. Significantly, these engineered HSCs maintain their ability to engraft and reconstitute hematopoiesis in immunocompromised mice. This introduced loss of HLA-A expression decreases the need to recruit large number of donors to match with potential recipients and has particular importance for patients whose HLA repertoire is under-represented in the current donor pool. Furthermore, the genetic engineering of stem cells provides a translational approach to HLA-match a limited number of third-party donors with a wide number of recipients.

The Nexus of Stem Cell-Derived Beta-Cells and Genome Engineering

“…By eliminating expression of HLA-A complex, they demonstrated that these cells maintained the ability to engraft in immunocompromised mice. Furthermore, there was an increased chance of finding HLA-matched donors by deleting these regions [59]. These results highlight the possibility for generating applications which avoid immune recognition by nature killer cells.…”

Islet Encapsulation: Physiological Possibilities and Limitations

“…The huge variation in human HLA is illustrated by the 25-50% failure rate in identifying an HLA-identical unrelated donor for allogeneic hematopoietic stem cell transplantation among the 25 million HLA-typed healthy volunteers listed in databases worldwide (52). Modern genetic techniques provide an elegant, and thus far almost unexplored, way of circumventing the HLA barrier and allowing transplantation without the need for systemic immunosuppression (53,54). A stem cell line, human embryonic stem cells or induced pluripotent stem cells, could be genetically modified by removal of all HLA alleles except one, e.g., HLA A2.…”

Strategies for Genetically Engineering Hypoimmunogenic Universal Pluripotent Stem Cells

“…Furthermore, inhibitory receptors such as the Killer Cell Immunoglobulin-like receptors (KIRs) and the NKG2A receptor are responsible for sensing the ''missing self,'' which identifies cells with lower HLA-I expression. Given many NK cell subsets exhibit heterogeneous receptor expression and different specificity toward HLA-A, HLA-B, HLA-C, and HLA-E (Ichise et al, 2017), complete elimination of HLA Class I in donor cells will activate host NK cells to attack the HLA Class I-deficient cells (Gornalusse et al, 2017;Torikai et al, 2016;Xu et al, 2019). Thus, researchers now seek to develop comprehensive strategies to cope with NK cell attack resulting from B2M knockout as described in the following paragraph.…”