Effects of PF4 and TGFβ1 on survival of hematopoietic progenitors. (A) Effects on the number of remaining CD34⁺ cells after 12 days of incubation from an initial 5 × 10³ CD34⁺ cells. (B) Effects on the survival of CD34⁺ cells as measured by megakaryocyte colony-regenerating capacity. *P < .05 v cells without PF4 and TGFβ1 treatment.