Postnatal passive immunization of neonatal macaques with a triple combination of human monoclonal antibodies against oral simian-human immunodeficiency virus challenge

Abstract

To develop prophylaxis against mother-to-child human immunodeficiency virus (HIV) transmission, we established a simian-human immunodeficiency virus (SHIV) infection model in neonatal macaques that mimics intrapartum mucosal virus exposure (T. W. Baba et al., AIDS Res. Hum. Retroviruses 10:351-357, 1994). Using this model, neonates were protected from mucosal SHIV-vpu(+) challenge by pre- and postnatal treatment with a combination of three human neutralizing monoclonal antibodies (MAbs), F105, 2G12, and 2F5 (Baba et al., Nat. Med. 6:200-206, 2000). In the present study, we used this MAb combination only postnatally, thereby significantly reducing the quantity of antibodies necessary and rendering their potential use in humans more practical. We protected two neonates with this regimen against oral SHIV-vpu(+) challenge, while four untreated control animals became persistently infected. Thus, synergistic MAbs protect when used as immunoprophylaxis without the prenatal dose. We then determined in vitro the optimal MAb combination against the more pathogenic SHIV89.6P, a chimeric virus encoding env of the primary HIV89.6. Remarkably, the most potent combination included IgG1b12, which alone does not neutralize SHIV89.6P. We administered the combination of MAbs IgG1b12, 2F5, and 2G12 postnatally to four neonates. One of the four infants remained uninfected after oral challenge with SHIV89.6P, and two infants had no or a delayed CD4(+) T-cell decline. In contrast, all control animals had dramatic drops in their CD4(+) T cells by 2 weeks postexposure. We conclude that our triple MAb combination partially protected against mucosal challenge with the highly pathogenic SHIV89.6P. Thus, combination immunoprophylaxis with passively administered synergistic human MAbs may play a role in the clinical prevention of mother-to-infant transmission of HIV type 1.

FIG. 1

Experimental design of the in vivo oral challenge studies with SHIV-vpu⁺ (A and B) and SHIV89.6P (C and D). (A) Two neonatal rhesus monkeys (P1 and P2) were infused twice i.v. with human MAbs F105, 2G12, and 2F5 (10 mg/kg; solid black arrows). d0 and d8, days 0 and 8. (B) Four neonates (R9C, R10C, R11C, and R16C) served as untreated control animals. All six animals were challenged orally with 10 oral AID₅₀ of SHIV-vpu⁺ 1 h after the first MAb treatment on the day of birth (open arrows). Treated animals were observed for 31 months, and serial blood samples were collected. Control animals were sacrificed 6 to 12 months after virus challenge. (C) Four neonatal rhesus monkeys (RCh-7, RFh-7, RIh-7, and RWg-7) were infused i.v. twice with human MAbs IgG1b12, 2G12, and 2F5 (10 mg/kg; solid black arrows). (D) Four neonates (REh-7, RHh-7, RJh-7, and RUg-7) served as untreated control animals. All eight animals were challenged orally with SHIV89.6P (15 oral AID₅₀) 1 h after the first MAb treatment or at the corresponding time point (3 days after birth) (open arrows). Animals were observed for 12 months, and serial blood samples were collected. †, animals RWg-7, RHh-7, RJh-7 were sacrificed 10, 7, and 9 weeks postexposure, respectively.

FIG. 2

Human MAb neutralization of SHIV89.6P in MT-2 cells. Neutralization was measured colorimetrically by the percentage of viable cells after incubation with the virus-antibody mixture (y axis). The antibody concentration (x axis) in combinations of two or more MAbs is the sum of the concentrations of each MAb with the exception of IgG1b12 and F105. When used in combinations, MAbs IgG1b12 and F105 were at 50 μg/ml; as potentiators, these amounts are not included in the total antibody concentration indicated on the x axis. In addition, when MAbs 2G12 and 2F5 were tested alone or in combination with other antibodies, the concentration of each was identical. Results are representative of two or three separate experiments for each antibody.

FIG. 3

Plasma viral RNA load (A to D), virus isolation by coculture (E and F), and peripheral absolute CD4⁺ T-cell counts (G and H) of neonatal macaques challenged orally with SHIV-vpu⁺ (A and B) or SHIV89.6P (C to H). P1 and P2 (B) received MAbs F105, 2G12, and 2F5. No RT-PCR data were obtained for the fourth SHIV-vpu⁺ control animal, R16C (not shown in panel A), because sodium citrate-anticoagulated blood samples were not available. RCh-7, RFh-7, RIh-7, and RWg-7 (D, F, and H) received MAbs IgG1b12, 2G12, and 2F5. The sensitivity of the RT-PCR assay is 50 copies/ml (A to D, dotted line). CD4⁺ T-cell counts were not available for animal RCh-7 between weeks 9 and 43 (H). A dotted line is drawn in panels G and H to indicate 750 CD4⁺ T cells/μl, which defines severe T-cell depletion in human infants less than 12 months of age. †, animals RWg-7, RHh-7, and RJh-7 were sacrificed 10, 7, and 9 weeks postexposure, respectively, due to progressed disease.

FIG. 4

Western blot analysis of plasma collected from SHIV89.6P-exposed animals. Serial samples were analyzed using HIV-2 strips. The number of weeks after challenge is indicated. Migration of HIV-2 proteins is shown on the left. The arrow on the right indicates migration of Gag antigen. Plasma from SIV-free macaques or normal human serum and plasma from SIV-infected macaques or human anti-HIV-2 serum were negative and positive controls, respectively (leftmost 4 lanes). †, sacrificed animal.