CD4 and infection: To determine whether HIV+ naive CD4+ T cells identified in samples from participants in this study were the result of infection with R5-tropic virus or the less-abundant X4-tropic virus, we sequenced and analyzed the env V3 loop region amplified by PCR from RRE+ MDA products from participants 0444, 0555, and 1001 (GenBank accession numbers PV031992–PV031999).