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Infants who are exposed to HIV but uninfected (iHEU) have higher risk of infectious morbidity than infants who are HIV-unexposed and uninfected (iHUU), possibly due to altered immunity. As infant gut microbiota may influence immune development, we evaluated the effects of HIV exposure on infant gut microbiota and its association with tetanus toxoid vaccine responses. We evaluated the gut microbiota of 82 South African (61 iHEU and 21 iHUU) and 196 Nigerian (141 iHEU and 55 iHUU) infants at <1 and 15 weeks of life by 16S rRNA gene sequencing. Anti-tetanus antibodies were measured by enzyme-linked immunosorbent assay at matched time points. Gut microbiota in the 278 included infants and its succession were more strongly influenced by geographical location and age than by HIV exposure. Microbiota of Nigerian infants, who were exclusively breastfed, drastically changed over 15 weeks, becoming dominated by Bifidobacterium longum subspecies infantis . This change was not observed among South African infants, even when limiting the analysis to exclusively breastfed infants. The Least Absolute Shrinkage and Selection Operator regression suggested that HIV exposure and gut microbiota were independently associated with tetanus titers at week 15, and that high passively transferred antibody levels, as seen in the Nigerian cohort, may mitigate these effects. In conclusion, in two African cohorts, HIV exposure minimally altered the infant gut microbiota compared to age and setting, but both specific gut microbes and HIV exposure independently predicted humoral tetanus vaccine responses.IMPORTANCEGut microbiota plays an essential role in immune system development. Since infants HIV-exposed and uninfected (iHEU) are more vulnerable to infectious diseases than unexposed infants, we explored the impact of HIV exposure on gut microbiota and its association with vaccine responses. This study was conducted in two African countries with rapidly increasing numbers of iHEU. Infant HIV exposure did not substantially affect gut microbial succession, but geographic location had a strong effect. However, both the relative abundance of specific gut microbes and HIV exposure were independently associated with tetanus titers, which were also influenced by baseline tetanus titers (maternal transfer). Our findings provide insight into the effect of HIV exposure, passive maternal antibody, and gut microbiota on infant humoral vaccine responses., Competing Interests: The authors declare no conflict of interest.

Differences in Bacille Calmette-Guérin (BCG) immunogenicity and efficacy have been reported, but various strains of BCG are administered worldwide. Since BCG immunization may also provide protection against off-target antigens, we sought to identify the impact of different BCG strains on the ontogeny of vaccine-specific and heterologous vaccine immunogenicity in the first 9 months of life, utilizing two African birth cohorts. A total of 270 infants were studied: 84 from Jos, Nigeria (vaccinated with BCG-Bulgaria) and 187 from Cape Town, South Africa (154 vaccinated with BCG-Denmark and 33 with BCG-Russia). Infant whole blood was taken at birth, 7, 15, and 36 weeks and short-term stimulated (12 h) in vitro with BCG, Tetanus and Pertussis antigens. Using multiparameter flow cytometry, CD4+ T cell memory subset polyfunctionality was measured by analyzing permutations of TNF-α, IL-2, and IFN-γ expression at each time point. Data was analyzed using FlowJo, SPICE, R, and COMPASS. We found that infants vaccinated with BCG-Denmark mounted significantly higher frequencies of BCG-stimulated CD4+ T cell responses, peaking at week 7 after immunization, and possessed durable polyfunctional CD4+ T cells that were in a more early differentiated memory stage when compared with either BCG-Bulgaria and BCG-Russia strains. The latter responses had lower polyfunctional scores and tended to accumulate in a CD4+ T cell naïve-like state (CD45RA+CD27+). Notably, BCG-Denmark immunization resulted in higher magnitudes and polyfunctional cytokine responses to heterologous vaccine antigens (Tetanus and Pertussis). Collectively, our data show that BCG strain was the strongest determinant of both BCG-stimulated and heterologous vaccine stimulated T cell magnitude and polyfunctionality. These findings have implications for vaccine policy makers, manufacturers and programs worldwide and also suggest that BCG-Denmark, the first vaccine received in many African infants, has both specific and off-target effects in the first few months of life, which may provide an immune priming benefit to other EPI vaccines., (Copyright © 2019 Kiravu, Osawe, Happel, Nundalall, Wendoh, Beer, Dontsa, Alinde, Mohammed, Datong, Cameron, Rosenthal, Abimiku, Jaspan and Gray.)

Objective: The effects of in-utero HIV-exposure on infectious morbidity and mortality in settings with universal maternal treatment and high breastfeeding rates are unclear. Further, the benefits of exclusive feeding options have not been assessed in the Option B+ era. We investigated these in two African settings with high breastfeeding uptake and good HIV treatment infrastructure during the first year of life., Methods: Cox regression with time-changing variables in a birth cohort of 749 HIV-exposed uninfected and HIV-unexposed uninfected infants from Cape Town, South Africa and Jos, Nigeria., Results: There was no difference in infectious morbidity incidence between HIV-exposed uninfected and HIV-unexposed uninfected infants (hazard ratio 1.01; 95% CI 0.78-1.32) after adjusting for confounding variables. Formula-fed infants had significantly higher infectious morbidity incidence when compared with exclusively breastfed infants (hazard ratio 1.64; 95% CI 1.03-2.63) and mixed-breastfed infants (hazard ratio 1.42; 95% CI 1.00-2.02) after adjusting for potential confounding variables. There was no significant difference in mortality among HIV-exposed infants and HIV-unexposed infants during the first year of life in this cohort (2.04 versus 0.94%, P = 0.38). Notably, exclusive breastfeeding for only 4 months had protective effects on morbidity up to 1 year., Conclusion: In settings with universal antiretroviral coverage and high breastfeeding rates, breastfeeding mitigates the effects of in-utero HIV exposure among infants during the first year of life. These findings support previous recommendations for exclusive breastfeeding among HIV-infected women and highlight the role that breastfeeding plays on the health of infants in settings where exclusive breastfeeding is not always feasible or where replacement feeding is recommended.