Serial passage of SHIV-1157i in rhesus monkeys for viral adaptation. The first animal was inoculated i.v. with cell-free supernatant from 293T cells transfected with the infectious molecular clone SHIV-1157i; subsequent animals were inoculated i.v. through serial blood transfer. The neonatal period comprises birth to one month; infancy the period up to one year, and juvenile monkeys are aged between one and five years.