Safety & Immunogenicity of 426c.Mod.Core-C4b Vaccine With 3M-052-AF+Alum in Infants Perinatally Exposed to HIV But Uninfected

The purpose of this study is to evaluate the safety and immunogenicity of 426c.Mod.Core-C4b vaccine adjuvanted with 3M-052-AF + Alum in infants with perinatal HIV exposure who are without HIV at birth

This study will compare the safety and immunogenicity of an experimental HIV vaccine in infants with perinatal HIV exposure who are without HIV at birth. The study vaccine is called 426c.Mod.Core-C4b. The vaccine is mixed with an adjuvant called 3M-052-AF + Alum. This study is divided into 2 parts: Part A and B. Part A has 4 groups, while Part B has 2 groups. Part A of the study is testing the vaccine alone or in combination with different doses of adjuvant. Part B is testing study vaccine and the safest dose of adjuvants from Part A versus placebo. Depending on their group, participants will receive 426c.Mod.Core-C4b, 426c.Mod.Core-C4b vaccine adjuvanted with 3M-052-AF + Alum, or a placebo by injection at Months 0, 3, and 7. Additional study visits will occur at Day 1, Week 2, Month 3 1/2, Month 7 1/2, Month 10, Year 1, Year 1 1/2, and Year 1 3/4. Study visits may include physical exams, blood and saliva collection for the infants and questionnaires, counselling, blood, and optional breastmilk collection for the mothers of infants.