Multiple vaccine-elicited nonneutralizing antienvelope antibody activities contribute to protective efficacy by reducing both acute and chronic viremia following simian/human immunodeficiency virus SHIV89.6P challenge in rhesus macaques

Abstract

We have shown that following priming with replicating adenovirus type 5 host range mutant (Ad5hr)-human immunodeficiency virus (HIV)/simian immunodeficiency virus (SIV) recombinants, boosting with gp140 envelope protein enhances acute-phase protection against intravenous simian/human immunodeficiency virus (SHIV)(89.6P) challenge compared to results with priming and no boosting or boosting with an HIV polypeptide representing the CD4 binding site of gp120. We retrospectively analyzed antibodies in sera and rectal secretions from these same macaques, investigating the hypothesis that vaccine-elicited nonneutralizing antibodies contributed to the better protection. Compared to other immunized groups or controls, the gp140-boosted group exhibited significantly greater antibody activities mediating antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cell-mediated viral inhibition (ADCVI) in sera and transcytosis inhibition in rectal secretions. ADCC and ADCVI activities were directly correlated with antibody avidity, suggesting the importance of antibody maturation for functionality. Both ADCVI and percent ADCC killing prechallenge were significantly correlated with reduced acute viremia. The latter, as well as postchallenge ADCVI and ADCC, was also significantly correlated with reduced chronic viremia. We have previously demonstrated induction by the prime/boost regimen of mucosal antibodies that inhibit transcytosis of SIV across an intact epithelial cell layer. Here, antibody in rectal secretions was significantly correlated with transcytosis inhibition. Importantly, the transcytosis specific activity (percent inhibition/total secretory IgA and IgG) was strongly correlated with reduced chronic viremia, suggesting that mucosal antibody may help control cell-to-cell viral spread during the course of infection. Overall, the replicating Ad5hr-HIV/SIV priming/gp140 protein boosting approach elicited strong systemic and mucosal antibodies with multiple functional activities associated with control of both acute and chronic viremia.

FIG. 1.

Immunization regimen, challenge outcome, and antienvelope binding titers (adapted from reference 49). (A) Three Ad5hr recombinants containing HIV_89.6Pgp140ΔCFI, SIV₂₃₉gag, and SIV₂₃₉nefΔ_1-14 were administered at 5 × 10⁸ PFU/recombinant/dose, a total of 1.5 × 10⁹ PFU/macaque either orally and intranasally (week 0) or intratracheally (week 12). Boosting immunogens were administered intramuscularly at weeks 24 and 36 at a dose of 100 μg/macaque, in either MPL-SE adjuvant or PBS as shown. All macaques were challenged intravenously at week 44 with 90 MID₅₀ of a SHIV_89.6P stock. (B) Summary of viral loads following SHIV_89.6P challenge. Significant differences were seen in peak acute viremia and in median chronic viremia (over weeks 8 to 40) between the gp140 group and controls. (C) Anti-Env binding titers against gp140 protein. Arrow indicates time of SHIV_89.6P challenge. The asterisks indicate statistically significant differences between the gp140 group and the nonboost and peptomer groups. The P values for weeks 26 and 38 (P < 0.0002 for both) were previously reported (49). The P value for week 44 is 0.0001.

FIG. 2.

Analysis of ADCC activity. (A) Geometric mean ADCC-mediating antibody titers of each immunization group. Arrow indicates time of SHIV_89.6P challenge. *, the ADCC titer of the gp140 group was significantly higher than those of the nonboost and peptomer groups at week 26 (P = 0.0007) and at weeks 38 and 44 (P < 0.0001 for both). (B) The mean percent ADCC killing of target cells, determined at a 1:100 serum dilution and following subtraction of background killing, was significantly higher at week 38 than those of the nonboost and peptomer groups (P = 0.0003). Error bars indicate the standard errors of the means. Arrow indicates time of SHIV_89.6P challenge. (C and D) The percent ADCC killing by the immunized macaques before challenge (week 38) was significantly correlated with both decreased peak acute viremia (panel C) and decreased median chronic phase viremia (panel D). The correlation coefficients (r) and P values are from Spearman rank analysis.

FIG. 3.

Vaccine-induced ADCVI activity. (A) Mean percent ADCVI activity of each immunization group at the indicated time points. Error bars indicate the standard errors of the means. Arrow indicates time of SHIV_89.6P challenge. *, inhibition by the gp140 group was significantly greater than that by the nonboost and peptomer groups at weeks 38 (P = 0.0001), 44 (P = 0.018), 48 (P = 0.0001), and 52 (P = 0.0001). (B) Significant inverse correlation between ADCVI activity at challenge (week 44) and week 4 postchallenge viremia in the gp140 group. (C) Inverse correlation between peak acute viremia and ADCVI activity 2 weeks postchallenge (week 46). (D) Inverse correlation between median chronic viremia and ADCVI activity 4 weeks postchallenge (week 48) in all macaques (solid line) as well as in immunized macaques only (dashed line). Open symbols represent control macaques; filled symbols represent immunized macaques. The correlation coefficients (r) and P values are from Spearman rank analysis.

FIG. 4.

Avidity of anti-Env antibody. (A) Mean of antibody avidity in each immunization group at the indicated time points. Error bars indicate the standard errors of the means. Arrow indicates time of SHIV_89.6P challenge. *, the antibody avidity of the gp140 group was significantly higher than those of the nonboost and peptomer groups at weeks 38 (P = 0.0007), 44 (P = 0.0019), 46 (P = 0.0001), and 48 (P = 0.0005). (B and C) Significant correlation between the antibody avidity and percent ADCC killing at week 38 (B) and at week 48 (C). (D to F) Significant correlation between the antibody avidity and ADCVI activity at week 38 in the gp140 group (D), at week 38 in all macaques (E), and at week 48 in all macaques (F). The correlation coefficients (r) and P values are from Spearman rank analysis.

FIG. 5.

Antibody avidity and viremia control. (A) Inverse correlation between antibody avidity 2 weeks postchallenge (week 46) and peak acute viremia. (B) Inverse correlation of antibody avidity 4 weeks postchallenge (week 48) and median chronic viremia in all macaques (solid line) and in immunized macaques only (dashed line). Open symbols represent control macaques; filled symbols represent immunized macaques. The correlation coefficients (r) and P values are from Spearman rank analysis.

FIG. 6.

Vaccine-induced mucosal antibody responses. (A) Means of Env-specific IgA in rectal secretions of each immunization group at the indicated time points. *, the level of mucosal IgA of the gp140 group was significantly higher than those of the nonboost and peptomer groups at week 48 (P = 0.0013). (B) Mean of Env-specific IgG in rectal secretions of each immunization group at the indicated time points. *, the level of mucosal IgG of the peptomer group was significantly higher than those of the nonboost and gp140 groups at week 46 (P = 0.0039). In panels A and B, error bars indicate the standard errors of the means. An arrow indicates time of SHIV_89.6P challenge. (C and D) Correlation between Env-specific serum IgG binding titer and rectal IgG specific activity (Env-specific IgG/total IgG) at week 38 (C) and lack of correlation at week 52 (D).

FIG. 7.

Inhibition of transcytosis. (A) Mean percent transcytosis inhibition of each immunization group at the indicated time points. Error bars indicate the standard error of the mean. Arrow indicates time of SHIV_89.6P challenge. *, inhibition by the gp140 group was significantly higher than that by the nonboost and peptomer groups at week 38 (P = 0.0047) and week 48 (P = 0.0001). (B) A significant correlation between transcytosis inhibition at week 48 and IgA specific activity (Env-specific IgA/total IgA) in the immunized macaques at week 48. (C) A marginally nonsignificant correlation between transcytosis specific activity (percent inhibition/total rectal IgA and IgG) prechallenge (week 38) and reduced peak acute viremia in the immunized macaques. (D) A significant correlation between median chronic viral loads (weeks 8 to 40) and transcytosis specific activity (percent inhibition/total rectal IgA and IgG) of the immunized macaques at week 48. The correlation coefficients (r) and P values are from Spearman rank analysis.