Time course of loss and recovery of CD4 cells, subdivided into the CD45RA⁺CD45RO⁻ (▪) and the CD45RA⁻CD45RO⁺ () subpopulations, during chemotherapy and 15 months of follow-up in four representative patients. CD4 levels are severely reduced during chemotherapy, increase rapidly from the chemotherapy nadir to an early peak, but subsequently decline. Most of the cells involved in both the initial rise and the late drop off are CD45RO⁺ CD4 cells. Inflection points in the curves represent the times of assays. Patient age is listed in the upper left corner, breast cancer stage at start of treatment (II to IV) is indicated in the upper right.