Low and undetectable breast milk interleukin-7 concentrations are associated with reduced risk of postnatal HIV transmission

Objective: To investigate if breast milk interleukin [IL]-7 concentrations are associated with postnatal HIV transmission. Design: A case-control study nested within a cohort of women recruited in Lusaka, Zambia. Methods: IL-7 breast milk concentrations were measured in samples from 24 HIV infected breast-feeding women who transmitted HIV to their child after the neonatal period and from 47 women who did not transmit. Samples were frequency-matched by the time of sample collection (1 week and 1 month postpartum). Logistic regression was used to adjust for possible confounders. For comparison, samples from 18 HIV uninfected women from the same community were included in the analysis, and plasma IL-7 was determined. Results: Breast milk IL-7 concentrations were significantly higher than plasma IL-7 concentrations in all 3 groups. In contrast to levels among transmitters and HIV uninfected women, breast milk IL-7 concentrations exhibited a bimodal distribution among nontransmitters. Breast milk IL-7 concentrations undetectable or less than 30 pg/mL were significantly associated with less HIV transmission (odds ratio = 0.13, 95% confidence interval: 0.03 to 0.64). The association remained strong after adjustment for breast milk viral load and sodium, maternal CD4 cell counts, parity, and time of sample collection. Conclusion: Breast milk IL-7 may be necessary for effective HIV transmission.