Significance HIV transmission to infants by breast feeding after maternally acquired anti-HIVantibodies decline is well documented. Neonatal vaccination may reduce HIV transmission to children in developing nations where safe alternatives to breast feeding are not available. However, a safe and economical anti-HIV vaccine for neonates must also elicit immunity in the presence of maternal anti-HIV antibodies. Objectives Infection of newborn rhesus macaques with simian immunodeficiency virus is a well-established model for pediatric HIV infection and AIDS. This small pilot study evaluated whether a live-attenuated SHIV-33 (virus derived from a molecular clone that consists the HIV-1 SF-33 envelope gene in an otherwise SIV genome) could establish infection in neonates with transplacentally acquired anti-SIV antibodies. Results Two pregnant rhesus macaques were immunized twice intramuscularly during pregnancy with whole-inactivated SIV in adjuvant. After boosting, both dams produced high titer SIV-specific serum antibodies which were transferred to their infants. Four neonates with no anti-SIV antibodies served as controls. All six infants were inoculated intravenously with a high dose of SHIV-33 within 3 days of birth and all six neonates became infected. Virus levels remained low in all animals and none developed any clinical signs of disease by 24 weeks of age. Thus, transplacentally acquired anti-SIV antibodies did not interfere with infection by a live-attenuated vaccine in rhesus neonates. These results suggest that a live-attenuated HIV vaccine might be developed that could establish infection even in infants with maternally-derived anti-HIV antibodies. Future Directions At 1 year of age each of the six animals infected with live-attenuated SHIV-33 will be inoculated orally with SIVmac239 to determine whether neonatal vaccination can provide long-term protection against virulent SIV. KEYWORDS Pediatric simian AIDS, oral SIV transmission, perinatal HIV transmission, neonatal immunization, live-attenuated vaccine
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