Gene Correction of Wiskott–Aldrich syndrome iPS Cells Rescues Proplatelet Defects and Improves Platelet Size

Wiskott-Aldrich syndrome (WAS) is a severe X-linked disorder caused by loss-of-function mutations in the <i>WAS</i> gene, responsible for encoding WAS protein (WASP), a key regulator of the actin cytoskeleton in all hematopoietic cells, except red blood cells. The mechanism underlying microthrombocytopenia, a distinctive feature of WAS and a major contributor to mortality, remains not fully elucidated. In this study, using different gene-editing strategies, we corrected mutations in patient-derived WAS-induced pluripotent stem cell (iPSC) lines, generating isogeneic WAS-iPSC lines. These included lines with direct mutation-specific correction and lines incorporating a <i>WASP</i> transgene cassette regulated by the MND or WAS1.6 kb promoter integrated at the safe harbor AAV1 site. Our results demonstrated that direct mutation correction successfully restored WASP levels to the equivalent of the wild-type in iPSC-derived megakaryocytes (MKs). In contrast, the AAV1-targeted strategy using the MND and WAS1.6 promoters yielded a lower level of WASP. Notably, only the mutation-specific correction lines exhibited improvements in proplatelet structures and generated larger-sized platelets. Our findings underscore the crucial roles of WASP during human thrombopoiesis and suggest that therapeutic approaches, such as direct gene correction, which can achieve physiologic levels of WASP in MKs, hold promise for ameliorating platelet defects in individuals with WAS.