Among persons infected by HIV-1, the rate of progression to AIDS is multifactorial being affected by host and viral factors, including the HIV-encoded negative factor (Nef). Our aim was to define whether variations in the nef gene as well as its functions may be associated with slower HIV disease course in infected children. The proviral HIV-1 nef gene was cloned, sequenced, and compared in children with contrasting disease course: 10 long-term nonprogressors (LTNP) and six rapid progressor (RP). The CD4 and MHC-I down-modulation ability of nef alleles derived from LTNP and RP children was analyzed. We observed that only one of our 10 LTNP had a protective genetic background, and out of them, 40% had defective nef genes, carrying substitutions at the (AWLEAQ(56-61)) and the (Rxx(22-24)) domains, and that those alleles were unable of down-regulate CD4 and MHC-I. The emergence or presence of Nef L58V substitution was associated with viral attenuation, indicated by a reduction in HIV viral loads, a persistent preservation of CD4(+) T cell counts, and lack of AIDS-related symptoms. Our results demonstrate that HIV-1 perinatally infected children carrying functionally defective nef HIV-1 strains have prolonged asymptomatic phases without therapy, suggesting a relevant role of CD4 and MHC-I down-modulation Nef domains on in vivo HIV-1 pathogenesis and pediatric immunodeficiency outcome.

IntroductionHIV-1-associated CD4+ T-cell depletion is a consequence of uninfected cell death. Nef is one of the viral factors that trigger apoptosis on bystander cells, though the plasma Nef levels do not correlate with Th lymphocytes counts. The aim of our study was to evaluate whether anti-Nef antibodies were involved in paediatric AIDS development and whether they can prevent the CD4+ T-cell depletion in vertically infected children.MethodsTwo hundred and seventy three HIV-1 vertically infected children seen at Garrahan Paediatric Hospital were randomly included in the study, adding 13 selected cases: seven LTNP (long-term non-progressors) and six RP (rapid progressors) children (n total=286). Specific anti-HIV-1-Nef antibodies were titrated by indirect ELISA and compared between groups. The plasma blocking effect on Nef-dependent cytotoxicity was evaluated in Jurkat cells using recombinant Nef as apoptotic stimulus and patient plasmas as blockers, measuring the apoptotic levels using Annexin-V stain and flow cytometry.ResultsOnly 63.4% of the patients had specific anti-Nef antibodies, and the levels of anti-Nef antibodies found in the selected LTNPs plasmas were always significantly higher (p=1.55×10−4) than those in RPs or general HIV-1+ paediatric populations. The LTNPs’ plasma had a strong inhibitory effect on Nef-dependent cytotoxicity even at high dilutions, while RP plasmas had little or no effect on Nef-induced apoptosis.Discussion and conclusionsHigh anti-Nef antibody levels are associated and predict slow or non-progression to AIDS in vertically HIV-1-infected children. They could be an efficient tool in preventing Nef-associated bystander effect, preserving CD4+ T-cells and the immune function in the context of paediatric HIV-1 infection.