Most rhesus macaques infected with the CCR5-tropic SHIV(AD8) generate cross-reactive antibodies that neutralize multiple HIV-1 strains

Abstract

The induction of broadly reacting neutralizing antibodies has been a major goal of HIV vaccine research. Characterization of a pathogenic CCR5 (R5)-tropic SIV/HIV chimeric virus (SHIV) molecular clone (SHIV(AD8-EO)) revealed that eight of eight infected animals developed cross-reactive neutralizing antibodies (NAbs) directed against an envelope glycoprotein derived from the heterologous HIV-1(DH12) strain. A panel of plasmas, collected from monkeys inoculated with either molecularly cloned or uncloned SHIV(AD8) stocks, exhibited cross-neutralization against multiple tier 1 and tier 2 HIV-1 clade B isolates. One SHIV(AD8)-infected animal also developed NAbs against clades A and C HIV-1 strains. In this particular infected macaque, the cross-reacting anti-HIV-1 NAbs produced between weeks 7 and 13 were directed against a neutralization-sensitive virus strain, whereas neutralizing activities emerging at weeks 41-51 targeted more neutralization-resistant HIV-1 isolates. These results indicate that the SHIV(AD8) macaque model represents a potentially valuable experimental system for investigating B-cell maturation and the induction of cross-reactive NAbs directed against multiple HIV-1 strains.

Fig. 1.

Virus replication and CD4⁺ T-cell dynamics in rhesus macaques inoculated i.v. or intrarectally with the molecularly cloned SHIV_AD8-EO. The levels of plasma viremia (A), percentage of BAL fluid CD4⁺ T cells (B), and absolute numbers of circulating CD4⁺ T cells (C) are shown.

Fig. 2.

Autologous and cross-reacting NAbs produced by animals infected with the molecularly cloned SHIV_AD8-EO. Plasma samples from the indicated SHIV_AD8-EO–infected macaques were collected at different times post infection, diluted 1:20, and assayed for neutralizing activity against the autologous SHIV_AD8 (A) or the heterologous SHIV_DH12 (B). The dashed line in each panel at 50% neutralization represents the threshold of virus suppression in the TZM-bl cell assay. The IC₅₀ neutralization titers determined for plasmas collected from macaques DC6W (week 52), DCF1 (week 40), and JG7 (week32) were determined by reciprocal dilution and assay in TZM-bl cells. Asterisks indicate NAbs detected at week 95. nd: not done.

Fig. 3.

Macaques infected with uncloned or molecularly cloned SHIV_AD8 viruses develop cross-reacting NAbs against multiple HIV-1 strains. IC₅₀ neutralization titers against the highly sensitive SHIV_DH12 (A), the indicated clade B (B) and clade A and C (C) HIV-1 isolates in plasmas of a cohort of 11 SHIV_AD8–infected animals were determined by reciprocal dilution and assay in TZM-bl cells. Values represent reciprocal serum dilution required to achieve 50% neutralization. The previously reported (12) neutralizing activity of week 100 plasma from animal CE8J is shown at the bottom of each panel. Value between 20 and 99, green; value between 100 and 999, yellow; value ≥1,000, red. Blank cell indicates that value was not determined.

Fig. 4.

Rhesus monkeys generate cross-reactive NAbs during two phases of the SHIV_AD8 infection. (A) The IC₅₀ neutralization titers in plasma samples collected at various times from macaque CL5E against the indicated HIV-1 strains were determined by reciprocal dilution and assay in TZM-bl cells. Values represent reciprocal serum dilution required to achieve 50% neutralization. Value between 20 and 99, green; value between 100 and 999, yellow; value ≥1,000, red. (B) Cross-reactive anti-SHIV_DH12 NAbs rapidly develop in two representative SHIV_AD8–infected animals. Plasma samples, collected from SHIV_AD8–infected macaques DCF1 or CL5E at the indicated times, were diluted 1:20 and assayed for neutralizing activity against pseudovirions carrying the SHIV_DH12-CL-7 (15) envelope glycoprotein in TZM-bl cells.

Fig. 5.

SHIV_AD8 is far superior to SHIV_DH12 in eliciting potent cross-reactive NAbs during infections of rhesus macaques. Anti–HIV-1_SS1196.1 IC₅₀ neutralizing titers in plasma collected from the indicated infected monkeys were determined by reciprocal dilution and assay in TZM-bl cells. Values represent reciprocal serum dilution required to achieve 50% neutralization. Value between 20 and 99, green; value between 100 and 999, yellow; value ≥1,000, red.