Lin⁻Sca-1⁺c-kit⁺cells expanded in KFM3 in serum-free medium for 10 days have enhanced ability to reconstitute lethally irradiated secondary recipients.

Primary recipients having received 500 fresh, or the expansion equivalent of 500, Ly5.1+ LSK cells cultured for 240 hours in serum-free medium in KFM (experiments 1 and 2) or KFM3 (experiments 1, 2, and 3) and 150 000 or 200 000 Ly5.2+ BM cells were sacrificed 4 months after transplantation. Lethally irradiated secondary recipients were transplanted with a half-femur equivalent from pooled primary recipients (4 recipients per group in each experiment). The mean reconstitution (of PB) in primary recipients of fresh LSK cells was 34%, 22%, and 40% in experiments 1, 2, and 3, respectively. The decrease in reconstituting activity in secondary recipients of BM from mice transplanted with fresh LSK cells (particularly in experiment 1) must be considered with the fact that only 5% of the total BM of primary recipients (half-femur equivalent) was transplanted into secondary recipients and that HSC lose reconstituting activity with serial transplantation.53 Reconstitution is shown from 3 experiments as the percentage of Ly5.1 cells in peripheral blood ± SEM.