The human fetal immune system begins to develop early during gestation, however, factors responsible for fetal immune-priming remain elusive. Dr Florent Ginhoux from A*STAR's Singapore Immunology Network, Professor Jerry Chan from KK Women's and Children's Hospital, Professor Salvatore Albani from SingHealth Duke-NUS Translational Immunology Institute, and Cambridge University explored potential exposure to microbial agents in-utero. They identified live microbes across fetal organs that stimulate activation of fetal T-cells during the second trimester of gestation.