Different evolutionary pathways of HIV-1 between fetus and mother perinatal transmission pairs indicate unique immune selection pressure in fetuses

Summary Study of evolution and selection pressure on HIV-1 in fetuses will lead to a better understanding of the role of immune responses in shaping virus evolution and vertical transmission. Detailed genetic analyses of HIV-1 env gene from 12 in utero transmission pairs show that most infections (67%) occur within two months from childbirth. In addition, e nv sequences from long-term infected fetuses were highly divergent and formed separate phylogenetic lineages from their cognate maternal viruses. Host selection sites unique to infant viruses were identified in regions frequently targeted by broadly neutralizing antibodies and T cell immune responses. The identification of unique selection sites in the env gene of fetal viruses indicates that the immune system in fetuses is capable of exerting selection pressure on viral evolution. Studying selection and evolution of HIV-1 or other viruses in fetuses can be an alternative approach to investigate adaptive immunity in fetuses.