Early short-term treatment with neutralizing human monoclonal antibodies halts SHIV infection in infant macaques

Abstract

Prevention of mother-to-child transmission (MTCT) of HIV remains a major objective where antenatal care is not readily accessible. We tested HIV-1-specific human neutralizing monoclonal antibodies (NmAbs) as a post-exposure therapy in an infant macaque model for intrapartum MTCT. One-month-old rhesus macaques were inoculated orally with the simian-human immunodeficiency virus SHIVSF162P3. On days 1, 4, 7 and 10 after virus exposure, we injected animals subcutaneously with NmAbs and quantified systemic distribution of NmAbs in multiple tissues within 24 h after antibody administration. Replicating virus was found in multiple tissues by day 1 in animals that were not treated. All NmAb-treated macaques were free of virus in blood and tissues at 6 months after exposure. We detected no anti-SHIV T cell responses in blood or tissues at necropsy, and no virus emerged after CD8(+) T cell depletion. These results suggest that early passive immunotherapy can eliminate early viral foci and thereby prevent the establishment of viral reservoirs.

Figure 1. NmAb cocktail dosing and kinetics in plasma

(a) Experimental design of the early NmAb therapy experiment is shown and symbols are defined. (b) VRC07-523 and PGT121 were combined in a 1:1 mass ratio (μg/ml) to generate a cocktail for s.c. injection at doses of 10 mg/kg and 40 mg/kg. (b, top) Recombinant proteins RSC3 and ST09AA were used in ELISA for specific detection of VRC07-523 and PGT121 (5 mg/kg and 20 mg/kg each NmAb, respectively), and (b, bottom) the NmAb cocktail was assayed by an SF162 gp140 ELISA (left: 10 mg/kg cocktail; right: 40 mg/kg). Data shown are NmAb concentrations in the plasma of twelve macaques. Concentrations were determined using non-linear regression and the EC₅₀ of the NmAb cocktail or the individual NmAb and were graphed in GraphPad Prism. Error bars indicate Standard Deviation (SD). Individual NmAbs and NmAb cocktail served as standard curves.

Figure 2. Viral kinetics and tissue distribution during the first two weeks after oral SHIV exposure

SHIV_SF162P3 viremia was quantified in eight male and female treated and untreated control animals. (a) Plasma viral loads assessed by measurements of SIV viral RNA in blood using a quantitative reverse-transcription PCR (QRT-PCR) assay and in (b) PBMC by quantitative PCR (QPCR). (c) Anatomic locations of tissues collected at necropsy following oral inoculation. (d–g) Viral DNA in tissues was detected by ultrasensitive nested quantitative PCR and RT-PCR targeting a highly conserved region in SIV and SHIV gag. Each sample was assayed in 12 replicates (5 μg each). Virus copy numbers were derived from the frequency of positive replicates using the Poisson distribution and calculated as copies per μg of DNA or copies per 10⁶ cell equivalents using the input nucleic acid mass and by assuming a DNA content of 6.5 μg per million cells. Infected tissues are colored to indicate quantified virus according to the scale shown in SIV gag copies/μg of DNA.

Figure 3. SHIV_SF162P3-associated viremia is not established in plasma or PBMC of NmAb-treated infants

(a,c) Quantified virus in blood and (b,d) peripheral blood cells in both NmAb dosing groups of male and female infant rhesus macaques (n = 10). Plasma viral loads were assessed by measurements of SIV viral RNA in blood using a quantitative reverse-transcription PCR (QRT-PCR) assay and in (b) PBMC by quantitative PCR (QPCR). CD8⁺ T cell depletion study timeline is shown in red. Data shown in gray indicate mean plasma virus (+/− SD) from eight historical controls from an earlier study^,.

Figure 4. NmAb cocktail lowers tissue-associated viremia within 24 h after s.c. delivery

SHIV DNA quantified by ultrasensitive nested quantitative PCR and RT-PCR in each tissue sample shown in four control animals (Table 1, Groups 1 and 2a) at either 1 day after SHIV exposure with No NmAb treatment or 1 day after s.c. injection of 10 mg/kg NmAb cocktail and 2 days after SHIV inoculation. Wilcoxon signed rank test (statistics performed in SAS 9.4 software).