Progenitor cell numbers in bone marrow (BM) and spleen (SP) from mice transplanted with MPZenTPO virus-infected bone marrow cells. Values plotted are the percentage of BFU-E (○), CFU-E (•), GM-CFC (□), or MK-CFC (▪) from MPZenTPO recipients compared with matched MPZenNeo recipients. Identical values are superimposed. Curve fittings (power type) and symbols correspond to different types of progenitor cells.