Data from primary fetal recipients transplanted with 1.5 × 10⁵ CD34⁺ cells/fetus are presented. As expected, donor cell activity was also detected in bone marrow of some animals transplanted with 1 × 10⁶ primarily CD34⁺, AC133⁻ cells/fetus. Bone marrow mononuclear cells obtained 1 week after birth were cultured in multiple methylcellulose plates as previously described.40 Total colony numbers were counted on days 9 and 19 of incubation; all 3 progenitor types (CFU-Mix, CFU-GM, and BFU-E) were detected on both days. On day 19, colonies were removed from the plate and individually processed for karyotyping.40 Percent values indicate the percentage of total colonies enumerated on day 9 (denominator) of culture that were determined to be of human origin (numerator) and were calculated as % human colonies = (no. of human colonies on day 19 × 100)/total no. of colonies on day 9.

Each value represents the mean ± 1 SEM of results from 4 separate determinations at 1 week, 1 month, 2 months, and 3 months after birth. Expression of human cells was multilineage as determined by flow cytometric analysis of bone marrow with the following antibodies: CD34, 0.26%; CD4, 0.2%; CD5, 0.35%; CD13, 1.12%; CD14, 0.19%; gly A, 0.05%; CD33, 0.37%; CD7, 4.17%; CD13/CD45, 0.31%; CD5/CD10, 0.32%.