Time course of loss and recovery of CD4 cells, subdivided into the CD45RA⁺CD45RO⁻ and the CD45RA⁻CD45RO⁺ subpopulations, during chemotherapy and 1 year of follow-up. CD45RA⁺ CD4 cells are severely depleted by FLAC chemotherapy and recover slowly during the first year postchemotherapy. CD45RO⁺ CD4 cells are not depleted as severely, recover rapidly in the first 3 months postchemotherapy, and then decline secondarily. Data are calculated as the mean ± SE of the CD4 cell numbers/μL; these data were calculated based on the WBC, the percentage of CD4 cells in the lymphocyte population (FACS acquistion gate), and the percentage of lymphocytes in the leukocyte populaton. When an individual was assayed more than once in the 3-month follow-up periods, only that assay closest to the 3-month interval was used in the calculation. All time points during chemotherapy and follow-up are significantly different from pretreatment. Comparison between time points is difficult because data from different patients were included at different time points.