Hoxa-9^-/- marrow cells have impaired recovery following hematopoietic stress. (A) Peripheral-blood counts in recipient animals following transplantation of either 200 000 Hoxa-9^-/- or 200 000 wild-type unfractionated nucleated bone marrow cells. Recipient mice were pretreated with 800 cGy x-ray irradiation prior to transplantation, and then monitored with serial peripheral-blood counts beginning 4 weeks after transplantation and then every 2 to 6 weeks for up to 41 weeks. Graphs represent composite data from 2 separate experiments, involving a total of 4 Hoxa-9^-/- and 3 wild-type donors, and 10 recipients each of Hoxa-9^-/- and wild-type marrow cells. ^*P < .05 for Hoxa-9^-/- versus wild-type value. (B) Blood counts in primary animals following sublethal irradiation. Groups of Hoxa-9^-/- and wild-type mice were exposed to 500 cGy x-ray irradiation, and peripheral-blood counts were monitored every 2 to 4 weeks, starting 9 weeks after irradiation and continuing to 19 weeks. Graphs represent a composite of 3 separate experiments involving 13 Hoxa-9^-/- animals and 7 wild-type animals. ^*P < .05 for Hoxa-9^-/- versus wild-type value.