Donor cell frequencies and survival after nonmyeloablative transplantation. (A) Eight-month-old New Zealand black × New Zealand white mice were conditioned by sublethal irradiation and administration of antithymocyte serum and antiasialo GM-1. Approximately 50% of the mice received allogeneic hematopoietic stem cell transplants. Donor-cell frequencies of the B- and T-lymphocyte and myeloid compartments in the peripheral blood at 32 weeks is shown. Circles indicate individual mice. Horizontal lines represent the mean of each group. (B) Survival of New Zealand black × New Zealand white mice after receiving a transplant or after the conditioning regimen only. Mice were treated at 227 or 255 days of age. A subset of mice was reserved as unmanipulated age-matched controls. The mice receiving conditioning only (blue) had a survival advantage over the age-matched control mice (gray) (P < .001). The mice that received allogeneic hematopoietic stem cells (red) had far better overall survival than the other 2 groups (P < .001). Survival curves illustrate the age of mice at death. Data were combined from 2 experiments.