Cover photograph (Copyright © 2006, American Society for Microbiology. All Rights Reserved.): Neighbor-joining tree. Human immunodeficiency virus type 1 envelope gene sequences isolated from maternal peripheral blood mononuclear cells (PBMC) at time of delivery (blue), autologous neutralizing antibody cells infected with maternal virus (red), and infant PBMC at the first positive time point (green) were aligned and subjected to phylogenetic tree reconstruction. Nucleotide sequences were initially aligned using HMMER, then codon aligned using GeneCutter, and manually adjusted. Phylogenetic relationships were estimated using the F84 evolutionary model implemented in the Phylip Neighbor program. The branch lengths are drawn to scale. The neighbor-joining tree verified separate clustering of the nine mother-infant pairs. (See related article on page 6525.)