Measurement of Nef effects on the antiviral activities of CTL clones. CTL clones 42758-RL10-3.22 (Rev specific, B*07 restricted) and S16-RY11-10.41 (Nef specific, C*07 restricted) were tested for inhibition of NL4-3–based viruses containing wild-type Nef or Nef with the M20A mutation (rendering it unable to down-regulate HLA class I) in parallel. The target cells were acutely infected Jurkat cells (expressing both B*07 and C*07). Replication as assessed by measuring supernatant p24 antigen (log units picograms/milliliter) is plotted over time. (A) For clone 42758-RL10-3.22, inhibition of the wild-type virus at day 6 was 0.8 log₁₀ units (6.3-5.5) and inhibition efficiency was 0.13 (0.8 ÷ 6.3). Inhibition of the M20A virus at day 6 was 5.4 log₁₀ units (6.3-0.9) and inhibition efficiency was 0.86 (5.4 ÷ 6.3). Thus, the Nef effect ratio of wild-type to defective Nef virus inhibition was 0.15 (0.13 ÷ 0.86). (B) Similarly for clone S16-RY11-10.41, inhibition efficiency of the wild-type and M20A viruses were 0.49 and 0.59, respectively, yielding a Nef effect ratio of 0.83.