Primitive progenitors are targets for host resistance.

(A) Recipient B6 mice, either naive or primed to BALB.B MiHA, received 9.0 Gy TBI 1 day prior to transplantation of 2 × 10⁶BALB.B BM-TCD. Average number ± SD of CFU-HPP per 1 × 10⁵ marrow cells in duplicate culture from each recipient group is indicated. (B) Cells from HPP-CFU were collected on day 6 of culture for the isolation of RNA and analyzed for the expression of genetic markers by RT-PCR. RT-PCR of GAPDH message is shown as internal control. Primers used were described in “Adoptive transfer of allograft resistance to unprimed recipients.” RT−, no reverse transcription control. H₂O only, negative control for PCR.