Figure 6. Neutralization and ADCC on the day of high-dose vaginal challenge with SIV_mac251_UCD.

At 5, 20, or 40 weeks after inoculation with SIV_mac239Δnef, groups of 6 macaques each were challenged by high-dose vaginal inoculation with SIV_mac251_UCD. Serum collected the day of challenge was evaluated for neutralization of SIV_mac251_UCD (A–C) and ADCC against SIV_mac251_UCD-infected cells (D–F). Symbols appear in color for immunized macaques that remained uninfected by SIV_mac251_UCD, and in black for the immunized animals that became infected. Target cells infected with SHIV_SF162P3 served as a negative control for ADCC assays (gray). Dashed lines indicate 50% activity. The groups challenged on weeks 5, 20, and 40 were combined for statistical analysis (G–J). The SIV_mac239Δnef-immunized macaques remaining uninfected by SIV_mac251_UCD had higher 50% ADCC titers than those that became infected (2-tailed Mann-Whitney U test, P = 0.0487) (G). A similar but non-significant trend was observed in AUC values for ADCC (2-tailed Mann-Whitney U test, P = 0.0761) (H). Non-significant trends were in the direction of lower peak SIV_mac251_UCD viral loads for animals with higher 50% ADCC titers (R_S = −0.4615, P = 0.1124) (I) and higher AUC measurements of ADCC activity (R_S = −0.4560, P = 0.1173) (J). Linear regression lines are shown. The macaque with the lowest ADCC titers among those remaining uninfected was the only animal possessing the protective combination of MHC class I alleles Mamu-A*01 and -B*17 [70].