Maternal plasma and breastmilk viral loads are associated with HIV-1-specific cellular immune responses among HIV-1-exposed, uninfected infants in Kenya

Abstract

Infants exposed to maternal HIV-1 provide an opportunity to assess correlates of HIV-1-specific interferon (IFN)-γ responses and may be informative in the development of HIV-1 vaccines. HIV-1-infected women with CD4 counts 200-500 cells/mm(3) were randomized to short-course zidovudine/nevirapine (ZDV/NVP) or highly active anti-retroviral therapy (HAART) between 2003 and 2005. Maternal plasma and breastmilk HIV-1 RNA and DNA were quantified during the first 6-12 months postpartum. HIV-1 gag peptide-stimulated enzyme-linked immunospot (ELISPOT) assays were conducted in HIV-1-exposed, uninfected infants (EU), and correlates were determined using regression and generalized estimating equations. Among 47 EU infants, 21 (45%) had ≥1 positive ELISPOT result during follow-up. Infants had a median response magnitude of 177 HIV-1-specific spot-forming units (SFU)/106 peripheral blood mononuclear cells (PBMC) [interquartile range (IQR)=117-287] directed against 2 (IQR = 1-3) gag peptide pools. The prevalence and magnitude of responses did not differ by maternal anti-retroviral (ARV) randomization arm. Maternal plasma HIV-1 RNA levels during pregnancy (P=0.009) and breastmilk HIV-1 DNA levels at 1 month (P=0.02) were associated with a higher magnitude of infant HIV-1-specific ELISPOT responses at 1 month postpartum. During follow-up, concurrent breastmilk HIV-1 RNA and DNA (cell-free virus and cell-associated virus, respectively) each were associated positively with magnitude of infant HIV-1-specific responses (P=0.01). Our data demonstrate the importance of antigenic exposure on the induction of infant HIV-1-specific cellular immune responses in the absence of infection.

Keywords: HIV-1-EU; interferon gamma; paediatric immunity.

Fig 1

Detection of negative and positive HIV-1-gag-specific interferon (IFN)-γ responses in HIV-1-exposed, uninfected (EU) infants during the first year postpartum. The detection of HIV-1-specific IFN-γ responses is shown for 47 EU infants born to mothers randomized to either short-course ZDV/NVP or HAART. Filled circles = detectable response; open circles = undetectable response; no circle = not tested.

Fig 2

Infant HIV-1-specific peptide responses and maternal viral loads. Interferon (IFN)-γ enzyme-linked immunospot (ELISPOT) assays were conducted on freshly isolated peripheral blood mononuclear cells (PBMC) samples from HIV-1-exposed, uninfected infants using 2 × 10⁵ PBMC per well with two wells per peptide pool. Data from assays with background spot-forming units (SFU) ≤ 100/10⁶ PBMC are depicted. Pools with ≥ 50 HIV-1-specific SFU/10⁶ PBMC and > ×2 the background response were defined as positive ELISPOT responses. Magnitude of HIV-1-specific peptide responses (stacked bar), plasma HIV-1 RNA (open squares, dashed line), breastmilk HIV-1 RNA (closed circles, solid line) and breastmilk HIV-1 DNA (open triangles, solid line) are shown for all infants with positive ELISPOT responses. Months −1 and 0 refer to 32 weeks gestation (initiation of antitetroviral regimen) and delivery, respectively. The mean days to delivery after the 32 weeks gestation visit was 39 (median 39 days, range 2–82 days). Data points marked NT indicate time-points when infants were not tested for ELISPOT responses. Black reference lines indicate the lower limits of detection for HIV-1 RNA/ml in plasma (200 copies/ml, dashed line) and breastmilk (100 copies/ml, solid line) and red reference lines indicate threshold for a positive HIV-1-specific IFN-γ response (50 HIV-1-specific SFU/10⁶ PBMC).