Introduction: Mechanisms facilitating mother-to-child transmission (MTCT) of HIV have not been elucidated. Small quantities of blood pass from mother to infant during childbirth, termed 'microtransfusion'; this is one possible mechanism for HIV entry into the infant's circulation. HIV-specific cellular immune responses have been detected in some uninfected infants born to HIV-infected women, indicating transient virus exposure or replication in these infants. Both microtransfusion and HIV-specific immune responses in infants born to HIV-infected women has not previously been investigated. Methods: 46 uninfected infants born to HIV-infected women were included in this study. Infants were grouped according to interventions utilised by the mother: none or antiretroviral therapy (ART; group A, n = 16), ART with elective caesarean section (elCS; group B, n = 12), highly active antiretroviral therapy (HAART) only (group C, n = 7), and HAART with elCS (group D, n = 11). HLA-A and -B alleles were typed for all mother-baby pairs to identify the non-inherited maternal allele (NIMA). Microtransfusion was detected using flow cytometry or by qPCR targeting the NIMA. HIV-specific immune responses were detected using 51Cr-release and IFN-?????? ELISpot assays. Results: Microtransfusion was detected in umbilical cord blood of 9 of 11 infants, and in peripheral blood of 4 of 11 infants up to 1 week old. One infant without detectable microtransfusion in umbilical cord blood had detectable maternal cells in peripheral blood. 8/46 infants had HIV-specific T cell responses, 5 were in group A, 2 in group B, and 1 in group C, while no infants in group D had detectable responses (p = 0.04). Blood samples from 2 of these 8 infants were also available for the analysis of microtransfusion. Microtransfused maternal cells were present in the umbilical cord blood of both infants. Conclusion: In this study, the number of infants with HIV-specific immune responses decreased with the use of MTCT interventions, indicating reduced exposure to HIV in these infants. This is the first study to demonstrate both microtransfusion and HIV-specific immune responses in uninfected infants. Microtransfusion may facilitate viral exposure, resulting in the development of potentially protective immune responses in infants born to HIV-infected women.

Introduction: Mechanisms facilitating mother-to-child transmission (MTCT) of HIV have not been elucidated. Small quantities of blood pass from mother to infant during childbirth, termed 'microtransfusion'; this is one possible mechanism for HIV entry into the infant's circulation. HIV-specific cellular immune responses have been detected in some uninfected infants born to HIV-infected women, indicating transient virus exposure or replication in these infants. Both microtransfusion and HIV-specific immune responses in infants born to HIV-infected women has not previously been investigated. Methods: 46 uninfected infants born to HIV-infected women were included in this study. Infants were grouped according to interventions utilised by the mother: none or antiretroviral therapy (ART; group A, n = 16), ART with elective caesarean section (elCS; group B, n = 12), highly active antiretroviral therapy (HAART) only (group C, n = 7), and HAART with elCS (group D, n = 11). HLA-A and -B alleles were typed for all mother-baby pairs to identify the non-inherited maternal allele (NIMA). Microtransfusion was detected using flow cytometry or by qPCR targeting the NIMA. HIV-specific immune responses were detected using 51Cr-release and IFN-?????? ELISpot assays. Results: Microtransfusion was detected in umbilical cord blood of 9 of 11 infants, and in peripheral blood of 4 of 11 infants up to 1 week old. One infant without detectable microtransfusion in umbilical cord blood had detectable maternal cells in peripheral blood. 8/46 infants had HIV-specific T cell responses, 5 were in group A, 2 in group B, and 1 in group C, while no infants in group D had detectable responses (p = 0.04). Blood samples from 2 of these 8 infants were also available for the analysis of microtransfusion. Microtransfused maternal cells were present in the umbilical cord blood of both infants. Conclusion: In this study, the number of infants with HIV-specific immune responses decreased with the use of MTCT interventions, indicating reduced exposure to HIV in these infants. This is the first study to demonstrate both microtransfusion and HIV-specific immune responses in uninfected infants. Microtransfusion may facilitate viral exposure, resulting in the development of potentially protective immune responses in infants born to HIV-infected women.