Frequency of injected CTL in tissues of BMT recipients. C57BL/6 mice were transplanted with 2 × 10⁷T-cell–depleted B10.A(4R) BM cells. Animals then received a single dose (1.5 × 10⁷) of mdm100-specific CTL at day 1 post-BMT (A) or 2 doses (4 × 10⁶ and 5 × 10⁶) of CTL at days 1 and 10 post-BMT (B). Mice in (B) were divided into a group that did receive 2 doses of 50,000 U IL-2 at the time of CTL injection and into a group that received CTL without IL-2. At the indicated weeks post-CTL injection, mice were killed (1 or 2 mice per time point) and single-cell suspensions were prepared from spleen (□), thymus (○), lymph nodes (◊), and BM (▵). These cell suspensions were used in LDA experiments as described in Materials and Methods to determine the frequency of mdm100-specific CTL. Each data point in (A) and (B) shows the calculated frequency of 1 LDA experiment. The solid symbols in (A) show the frequency data of (C57BL/6 × BALB/c) F1 mice transplanted with BM from littermates and injected with a dose of 1.5 × 10⁷ mdm100-specific CTL (▪, F1 mice: spleen; ⧫, F1 mice: lymph nodes). At weeks 3 and 5, the frequency was analyzed only in the spleen, and at weeks 12 and 13, the frequency was analyzed in the spleen, lymph nodes, thymus, and BM. Injected mdm100-specific CTL were undetectable in thymus and BM at weeks 12 and 13. The frequency was calculated using zero-linear regression analysis, and all data had statistically acceptable χ² less than 11 and P values greater than 0.1, except for 2 experiments (spleen at 8 weeks [A] had a χ² of 17.5, and the lymph nodes at 3 weeks+IL-2 [B] had a χ² of 22.5). No data points are shown for experiments in which the frequency was less than the detection limit of the LDA assay (eg, thymus and BM at 7 and 14 weeks in [B]).