[1] Nuffield Dept Med, Oxford OX1 3SY, England
[2] Univ KwaZulu Natal, Doris Duke Med Res Inst, HIV Pathogenesis Programme, ZA-4013 Durban, South Africa
[3] Massachusetts Gen Hosp, Partners AIDS Res Ctr, Boston, MA 02115 USA
[4] Harvard Univ, Sch Med, Div AIDS, Boston, MA 02115 USA
[5] Howard Hughes Med Inst, Chevy Chase, MD 20185 USA