CFU-GM from HLA-A2.1 negative targets are not inhibited by PR1-pulsed CTL2. Day 20 PR1-pulsed CTL2 did not inhibit CFU-GM from the HLA-A2.1 negative patient P5 (CML-CP), nor D5, the HLA identical normal marrow donor to patient P5. Effectors were incubated with target cells at E:T ratio of 5:1 for 4 hours at 37°C before plating in methylcellulose, and colonies were counted on day 14 of culture. Three replicate wells were used to determine CFU-GM and data are displayed as mean colony counts ± standard deviation.