Infant mortality remains significantly higher in HIV-exposed but uninfected (HEU) children compared to their HIV-unexposed counterparts, even with widespread access to maternal antiretroviral therapy (ART). This disparity suggests potential immune abnormalities stemming from maternal viremia, immune dysfunction, and co-infections during pregnancy. The Sanitation Hygiene Infant Nutrition Efficacy (SHINE) trial in rural Zimbabwe provided a unique dataset to explore these underlying mechanisms. Previous analysis of the SHINE trial demonstrated that despite high maternal ART coverage and exclusive breastfeeding rates, mortality among HEU infants was 41% higher than in HIV-unexposed infants. This study aimed to delve deeper into the biological pathways linking maternal HIV exposure to adverse infant outcomes, particularly focusing on the roles of inflammation and CMV co-infection and exploring potential sex-differentiated effects.

Existing literature highlights increased infectious mortality and atypical pathogen spectra in HEU infants, suggesting immune system compromise. Studies have shown that maternal HIV infection, even with ART, is associated with adverse infant outcomes including mortality and impaired growth. Previous research has explored the association between maternal HIV and inflammatory biomarkers, including C-reactive protein (CRP) and soluble CD14 (sCD14), and their potential impact on infant health. The role of co-infections, especially cytomegalovirus (CMV), which frequently reactivates during pregnancy and is linked to immune activation, also needed further investigation. Prior studies have indicated a potential link between CMV co-infection and adverse outcomes in both HIV-infected and HIV-unexposed populations. The study built upon this existing knowledge to further elucidate the complex interplay between maternal factors, infant immunity, and mortality outcomes in HEU children.

This secondary analysis utilized data from the SHINE trial conducted in rural Zimbabwe. The study population included 726 pregnant women with HIV and a control group of HIV-unexposed women. Maternal blood samples were collected during the second and third trimesters to measure HIV viral load, CRP, sCD14, and CMV viral load. Infant blood samples were collected at one month of age to assess systemic inflammation (sCD14, CRP, IL-6) and immune cell populations (CD4+ and CD8+ T cells, monocytes) by flow cytometry. Mortality data were collected through 18 months of age. Statistical analyses included Cox proportional hazards models to assess associations between maternal biomarkers and infant mortality, and generalized estimating equations (GEE) to compare immune biomarkers between HEU and HIV-unexposed infants. Adjustments were made for confounding variables, including maternal age, education, socioeconomic status, gestational age at sampling, and trial arm assignment. The analysis incorporated sex stratification to investigate potential differences in mortality and immune development between male and female HEU infants.

Maternal systemic inflammation, as reflected by elevated CRP levels during pregnancy, was strongly associated with infant mortality in HEU infants (adjusted hazard ratio (aHR) 2.09; 95% CI 1.33–3.27). Each log10 rise in maternal CRP doubled the risk of infant death. A similar relationship was observed for maternal CMV viremia (aHR 1.62; 95% CI 1.11–2.36). Interestingly, sex-specific effects were observed. In girls, the association between mortality and maternal CRP was stronger than that with CMV, whereas in boys, mortality was more strongly linked to CMV than CRP. HEU infants at one month showed a distinct immune profile compared to HIV-unexposed infants: significantly higher sCD14 levels and altered CD8 T-cell subsets (higher activation and proliferation markers, lower naïve cells, and higher proportions of memory and effector memory cells). These immune alterations were generally more pronounced in boys. Maternal CMV viremia during pregnancy was more common among women with HIV and was independently associated with increased infant mortality. There was a dose-response relationship between maternal CMV viral load and infant mortality. The study also found associations between maternal CMV viremia and altered CD8+ T-cell subsets in infants.

The findings strongly implicate maternal inflammation and CMV viremia as independent risk factors for infant mortality among HEU infants. The sex-differentiated effects suggest distinct biological mechanisms at play for males and females, highlighting the need for sex-specific interventions. The observed alterations in the infant immune system, particularly the increased sCD14 and the distinct CD8+ T-cell profile, may be consequences of the altered in utero immune environment and represent a persistent vulnerability to infection. The study's findings suggest that targeting maternal inflammation and CMV infection during pregnancy may be effective strategies to improve survival rates in HEU infants. Future research could focus on developing interventions targeting specific inflammatory pathways or antiviral strategies to mitigate the risks associated with CMV infection in pregnant women with HIV.

This study demonstrates that maternal inflammation and CMV viremia during pregnancy are significant risk factors for mortality and immune dysregulation in HEU infants, with sex-specific effects. Targeting these factors through interventions may improve outcomes for this vulnerable population. Future studies should investigate the underlying mechanisms driving these associations and explore targeted interventions tailored to each sex.

The study's limitations include its observational design, which limits causal inference. The reliance on a single trial setting in rural Zimbabwe may limit the generalizability of the findings to other contexts. Residual confounding may exist despite adjusting for several variables. Finally, some data were missing, potentially introducing bias into the analyses.