Suppression of HIV replication by CD8⁺cells from LTS and individuals who progressed to AIDS (Progressors). The ability of CD8⁺ cells from 14 LTS and 14 Progressors to suppress HIV-1_SF33 replication in CD4⁺cells was determined in an acute infection assay over a range of CD8⁺:CD4⁺ cell ratios of twofold dilutions ranging from 0.25:1 to 4:1. The level of antiviral activity of CD8⁺ cells shown represents the lowest CD8⁺:CD4⁺ cell ratio that achieved ≥90% reduction of RT activity relative to that observed in the fluid of CD4⁺ cells cultured alone. Each point represents the result from a different individual. A CD8⁺:CD4⁺ cell ratio greater than 2:1 was used in cases where the number of CD8⁺ cells from Progressors was limited such that the CD8⁺:CD4⁺ cell ratio of 4:1 could not be tested. For statistical analysis, the anti-HIV level was considered to be 3:1 (see Results). Bars represent the mean values of the data obtained for each group of individuals tested. The ratio of CD8⁺:CD4⁺ cells needed from LTS and Progressors to suppress HIV replication by 90% was statistically different (P < .01) using the Mann-Whitney U test.