c-kit expression in CD19⁻ progenitors is inversely related to lymphoid clonogenic potential in short-term culture. Affinity-column–enriched CD34⁺ cells were stained with c-kit PE and CD19 FITC. The cloning efficiency and proportion of total CFU-TdT within each sorted population, calculated as for Table 1, is indicated at right. The difference in colonies and % total colonies between each of three populations was significant (P < .05 by paired t-test); errors are ± SE as an estimate of variation of means of three replicate wells in seven separate experiments on different marrow specimens.