Three-year randomized study of high-purity or intermediate purity factor VIII concentrates in symptom-free HIV-seropositive hemophiliacs: effect on immune status - Seremitis, S; Aledort, L M; Bergman, G; Bona, R; Bray, G; Brettler, D B; Eyster, M E; Kessler, C; Lan, T S; Lusher, J M; Rickerts, F (Lancet, 1993)