Influence of the degree of myeloid cell engraftment on platelet count. Platelet counts before and after HCT were reported for 152 WAS-transplanted patients, who had at least 12 months of follow-up after HCT and for whom quantitative analysis of donor cell engraftment on myeloid cells was available. Pretransplantation splenectomized patients were separated from nonsplenectomized patients. (A) Patients of both groups were further divided according to the degree of donor myeloid cell engraftment (full or mixed/null). For each of them, platelet (PLT) counts at diagnosis and at last follow-up are shown, with pretransplantation values of splenectomized patients reported both at diagnosis and after splenectomy. **P < .01. ****P < .001. (B) Correlation between the platelet (PLT) count of nonsplenectomized patients and the percentage of donor myeloid cell engraftment is shown. A significant correlation between these 2 parameters was observed according to the nonparametric Spearman test (r = 0.584, P < .001).