Therapeutic Transplant Efficacy of Endothelial Progenitor Cells is Impaired by NK Cells

Abstract

Adult stem cells, including endothelial progenitor cells (EPCs), have long been proposed as a source of cells for therapeutic transplantation in cardiovascular (CV) disease. Studies investigating the therapeutic potential of EPCs have shown mixed results, likely due to the negative impact of chronic disease and aging on EPC function in the high CV risk patients enrolled in such studies. Using genetically controlled rats, we have established a model of EPC dysfunction in the setting of hypertension. In the SS/MCWi rat, a genetic model of salt‐sensitive hypertension, EPC function is compromised. Introgression of the 13th chromosome of the Brown Norway rat onto the SS background results in the SS‐13BN/MCWi (BN13) rat, which is protected from both hypertension and EPC dysfunction. Previously, we found increased expression of the natural killer cell receptor/ligand 2B4 (CD244) on the cell membrane of EPCs isolated from SS rats. This increase in CD244 expression was correlated with increased destruction by NK cells from both SS and BN13 rats. Here, we hypothesize that increased membrane expression of CD244 by SS EPCs leads to destruction by NK cells in vivo, which compromises their therapeutic efficacy. We first found that siRNA mediated CD244 knockdown rescued EPCs from NK cell mediated killing in vitro using an LDH release assay. We next used an NK cell depleting antibody to assess whether NK cells were responsible for EPC dysfunction in animals receiving EPCs as therapy. Finally, we transplanted EPCs treated with CD244 siRNA into naïve recipient animals to confirm that CD244 impacts EPC function in vivo. Our results suggest that increased CD244 on the SS EPC membrane leads to increased NK cell mediated killing of SS EPCs in vivo, contributing to the impaired therapeutic efficacy in our model.Support or Funding InformationNational Institutes of Health grant HL082798 awarded to A.S. Greene, PhD; T32 HL007852 PI: H.V. Forster