A neonatal oral Mycobacterium tuberculosis-SIV prime/intramuscular MVA-SIV boost combination vaccine induces both SIV and Mtb-specific immune responses in infant macaques

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Mother-to-child-transmission of HIV by breast-feeding remains a major obstacle in the eradication of HIV infection. Compared to adults, HIV-infected infants have more rapid disease and show higher susceptibility to co-infections like tuberculosis (TB). Although the Bacille Calmette–Guérin vaccine can be administered at birth to protect against TB, BCG can disseminate in HIV-infected infants and increase mortality. Thus, a pediatric combination vaccine to stop both HIV and TB infection in infants is urgently needed.Towards the goal of developing a pediatric combination HIV-TB vaccine to prevent both oral HIV acquisition by breast-feeding and TB infection, we tested and optimized an immunization regimen using a novel live attenuated Mycobacterium tuberculosis vaccine engineered to express simian immunodeficiency (SIV) antigens followed by heterologous MVA-SIV boosting in the infant macaque model. A single oral dose of the attenuated Mtb-SIV vaccine strain mc26435 during the first week of life was sufficient to induce persistent TB-specific immune responses. SIV-specific immunity was induced at low but comparable magnitudes after oral or intradermal priming, and was enhanced following MVA-SIV boosts. T cell responses were most pronounced in intestinal tissues and oral lymph nodes. Importantly, in addition to plasma SIV-specific IgG and IgA antibodies, infant macaques developed mucosal SIV-specific IgA in saliva and intestinal IgA and IgG. While future SIV and Mtb challenge studies will be needed to determine the protective efficacy of the Mtb-SIV/MVA-SIV vaccine, infants at high risk for oral HIV acquisition by breast-feeding and TB infection could profoundly benefit from an effective combination vaccine.