Breast milk cellular HIV-specific interferon γ responses are associated with protection from peripartum HIV transmission

Abstract

Objective: Breast milk is a major route of infant HIV infection, yet the majority of breast-fed, HIV-exposed infants escape infection by unknown mechanisms. This study aimed to investigate the role of HIV-specific breast milk cells in preventing infant HIV infection.

Design: A prospective study was designed to measure associations between maternal breast milk HIV-specific interferon-γ (IFN-γ) responses and infant HIV-1 detection at 1 month of age.

Methods: In a Kenyan cohort of HIV-infected mothers, blood and breast milk HIV-gag IFN-γ ELISpot responses were measured. Logistic regression was used to measure associations between breast milk IFN-γ responses and infant HIV infection at 1 month of age.

Results: IFN-γ responses were detected in breast milk from 117 of 170 (69%) women. IFN-γ responses were associated with breast milk viral load, levels of macrophage inflammatory protein (MIP) 1α, MIP-1β, regulated upon activation, normal T-cell expressed, and secreted and stromal-cell derived factor 1 and subclinical mastitis. Univariate factors associated with infant HIV infection at 1 month postpartum included both detection and breadth of breast milk IFN-γ response (P = 0.08, P = 0.04, respectively), breast milk MIP-1β detection (P = 0.05), and plasma (P = 0.004) and breast milk (P = 0.004) viral load. In multivariate analyses adjusting for breast milk viral load and MIP-1β, breast milk IFN-γ responses were associated with an approximately 70% reduction in infant HIV infection [adjusted odds ratio (aOR) 0.29, 95% confidence interval (CI) 0.092-0.91], and each additional peptide pool targeted was associated with an approximately 35% reduction in infant HIV (aOR 0.65, 95% CI 0.44-0.97).

Conclusion: These data show breast milk HIV-gag-specific IFN-γ cellular immune responses are prevalent and may contribute to protection from early HIV transmission. More broadly, these data suggest breast milk cellular responses are potentially influential in decreasing mother-to-child transmission of viruses.

Fig. 1. Participant flow

Cohort numbers are based on available test results, focusing on breastfeeding women whose infants were HIV uninfected at birth. Chemokine and mastitis data are reported in [25]. BMCs, breast milk cells; PBMCs, peripheral blood mononuclear cells.

Fig. 2. HIV-specific interferon-γ responses and viral replication

Scatter plots show the correlation between (a) plasma and breast milk HIV viral load, (b) plasma viral load and HIV-specific IFN-γ responses in peripheral blood mononuclear cells (PBMCs), and (c) breast milk viral load and HIV-specific IFN-γ responses in breast milk cells (BMCs). Correlation coefficients and P values were generated using Spearman’s correlation. IFN, interferon.

Fig. 3. Stratified analysis of early peripartum transmission and breast milk HIV-specific interferon-γ responses

Markers show the proportion of infants with HIV infection at 1 month of age, stratified by breast milk viral load and (a) HIV-gag-specific response detected in breast milk and (b) the number of peptide pools eliciting a positive HIV-gag-specific response in breast milk. Bars show exact 95% confidence intervals calculated from the binomial distribution. The number of mother–child pairs is shown for each category (n). No confidence intervals are shown for categories where no transmission occurred. P values are shown for logistic regression within strata.