High-risk primary breast cancer patients treated with high-dose chemotherapy (HDC) and stem cell support (SCS) have shown prolonged disease-free survival (DFS) in many studies; however, only one trial has demonstrated an overall survival benefit (OS). We hypothesize that the period following myeloablative therapy is ideal for immunologic manipulation and studied the effects of two different methods of immunotherapy following HDC with SCS aimed at the window of immune reconstitution. Seventy-two women with high-risk stage II or III breast cancer were randomized following HDC to receive either interleukin 2 (IL-2) at 1 million units/m(2) SQ daily for 28 days or combined cyclosporine A (CsA) at 1.25 mg/kg intravenously daily from day 0 to +28 and interferon gamma (IFN-gamma) 0.025 mg/m(2) SQ every 2 days from day +7 to +28. At a median follow-up of 67 months, no significant difference was observed in DFS or OS between the two treatment groups. The IL-2 arm had a 59% DFS (95% CI (0.45, 0.78)) and a 72% OS (95% CI (0.58, 0.88)) at 5 years. The CsA/INF-gamma arm had a similar outcome with a 55% DFS (95% CI (0.40, 0.76)) and a 78% OS (95% CI (0.65, 0.94)) at 5 years. Treatment was well tolerated, without increased toxicity.