Silencing Mutated Cxcr4 in Mouse Hematopoietic Stem Cells as a Genetic Cure Strategy Obviating Bone Marrow Conditioning in WHIM Syndrome

Abstract

Abstract Genetic cure of diseases caused by autosomal dominant (AD) gain-of-function (GoF) mutations could require full correction of the disease allele; however, selective inactivation of the disease allele might suffice or even be superior. To test the relative efficacy of these two strategies in WHIM syndrome, a rare combined primary immunodeficiency disease caused by AD GoF mutations in chemokine receptor CXCR4 leading to impaired release of mature leukocytes from bone marrow, we have performed competitive bone marrow transplantation experiments with Cxcr4+/+, Cxcr4+/o and Cxcr4+/S338X (WHIM model) mice. Here we show a whole bone marrow donor genotype rank order of Cxcr4+/o >Cxcr4+/+> Cxcr4+/S338X for repopulating the blood of lethally irradiated recipient mice. Importantly, the strong competitive advantage of transplanted Cxcr4 haploinsufficient bone marrow cells is durable, intrinsic to hematopoietic stem cells (HSCs) and evident in the blood at the level of cell frequency and total cell numbers in both the myeloid and lymphoid lineages in both irradiated and unconditioned congenic recipients. Mechanisms included enhanced engraftment of hyperproliferative Cxcr4+/o HSCs in irradiated recipients and enhanced release of mature Cxcr4+/o leukocytes to the blood in unconditioned recipients. These results provide proof of principle that inactivation of the CXCR4 disease allele in HSCs may be a safe, effective and superior genetic cure strategy able to obviate toxic bone marrow conditioning in patients with WHIM syndrome.