Schematic model of mucosal MTCT of HIV-1. After oral ingestion at birth or breastfeeding, HIV-1 enters the intestinal lumen of the infant. In the epithelium and just under it, CD4⁺ T cells expressing CCR5 are present, which are accessible targets for HIV-1. These memory CD4⁺ T cells were further characterized by prototypic nuclear transcription factors for the Th subsets T-bet, Gata-3, RORγt, and FoxP3, indicating a predominance of Th1 and Th17 cells of activated CD4⁺ T cells in the infant gut mucosa.