Differential neutralization sensitivities of the wild-type and CT-truncated SIVsmE660 clones. (A) Serially diluted sera of a rhesus macaque infected with a SIVsmE660 tier 1 virus collected at different time points, 4 weeks postinfection (4w), 40 weeks postinfection, and 80 weeks postinfection, were tested in duplicate against the tier 1, tier 2, and tier 3 viral clones in a TZM-bl neutralization assay. The percentages of neutralization by sera at different dilutions are shown. (B) Virus clones with truncated cytoplasmic tails are less sensitive to neutralization by rhesus sera. A neutralization assay was performed on tier 1, tier 2, and tier 3 mutant viral clones in duplicate in a TZM-bl neutralization assay as described above for panel A. The percentages of neutralization by sera at different dilutions are shown.