Fig. 1. Study design, vaccine efficacy, and monocytes.

a, b Age of vaccinated (a; p = 0.00000002) and control (b; p = 0.0000000017) animals. c Schematic study design of Study 1 with immunization schedule (weeks 0–12) and SIV_mac251 challenges (weeks 17–27). d, e SIV_mac251 acquisition. The number of intravaginal exposures before infection was assessed in (d) n = 13 young and (e) n = 17 old animals relative to their n = 27 young and n = 11 old control animals (Log-rank Mantel-Cox test). f, g Log₁₀ of SIV-DNA copies in vaginal mucosa at 2–3 weeks after infection in (f) n = 7 vaccinated and n = 15 control young animals; and (g) n = 11 vaccinated and n = 9 control old animals. h Correlation between the frequency of classical monocytes (CD14⁺CD16⁻HLA-DR⁺ in live cells) at week 13 and the time of acquisition (TOA) in n = 13 young animals. i Frequency of classical monocytes in n = 13 young and n = 11 old vaccinated animals (week 13). j Classical monocytes expressing CCR2 (CCR2⁺ in CD14⁺CD16⁻ cells) in n = 13 young and n = 13 old vaccinated animals (week 13). k Serum CCL2 levels (pg/ml) in n = 13 young and n = 17 old vaccinated animals (average weeks 10 and 14; p = 0.0000001). l Correlation between the arginase activity measured in plasma at week 13 and the average of the serum CCL2 levels (pg/ml) at weeks 10 and 14 in n = 13 young vaccinated animals. m, n Correlations between (m) the average of adjusted specific ADCC killing of SIV_mac251-infected cells at week 14 assessed at different plasma dilutions and the TOA, or (n) the average of the serum CCL2 levels (pg/ml) at weeks 10 and 14 in n = 13 young vaccinated animals. o Correlation between the frequency of intermediate monocytes (CD14⁺CD16⁺HLA-DR⁺ in live cells) at week 13 and the TOA in n = 13 young animals. Comparisons: a, b, f, g, i–k Two-tailed Mann–Whitney t-test with median. Correlation analyses: h, l–o two-tailed Spearman correlation test and simple linear regression. Displayed p values are unadjusted. Source data are provided in the Source Data file.