Requirement of CD4⁺ and CD8⁺ T cells for prolonged survival induced by combined therapy. Survival was analyzed by the Kaplan-Meier method; comparison between groups was analyzed by log-rank tests. Survival curves of (A) APL mice treated with ATRA + PML-RARαFrC DNA (ATRA + DNA; ●, isotype control undepleted, n = 12; and ○, CD4-depleted, n = 12; P < .001) and APL mice treated with ATRA alone (◇, isotype control undepleted, n = 8; and ♦, CD4-depleted, n = 12). (B) APL mice treated with ATRA + DNA (●, isotype control undepleted, n = 12; and ○, CD8-depleted, n = 12; P < .001) and APL mice treated with ATRA alone (◇, isotype control undepleted, n = 8; and ♦, CD8-depleted, n = 12). APL mice were depleted of either CD4⁺ (A) or CD8⁺ (B) T cells by repeated (5-day interval) intraperitoneal injections of 0.2 mg of subset-specific monoclonal antibodies starting from day 10 after leukemia engraftment (1 day after the DNA vaccination). Isotype control group mice received 0.2 mg of rat IgG per injection. The efficiency of depletion was monitored by flow cytometry (representative dot plots of PB gated on CD3⁺ populations). These early depletions were conducted at least twice. (C) LTSs from ATRA + DNA–treated groups were CD4- or CD8-depleted as described. The injection of subset-specific (CD4 [■]; and CD8 [□]; depletion, respectively) or rat IgG (isotype control, ▨) started on day 120 after engraftment of leukemic cells. Days of death after the beginning of depletion are indicated. The efficiency of depletion was monitored by flow cytometry (representative dot plots of PB gated on CD3⁺ populations). ATRA (5 mg) was administered by subcutaneous implantation of 21-day release pellets.