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 encodingenvof 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.

Background: The majority of infants infected through maternal transmission acquire the virus during birth or postpartum through breastfeeding: mucosal exposure is considered to be a major route of infection. Objectives: To develop passive immunization with human neutralizing monoclonal antibodies (mAbs) against mother-to-child transmission of HIV during delivery and through breastfeeding. Design: An oral challenge model in newborn rhesus macaques mimicked peri- and postpartum virus transmission. Methods: Neonatal rhesus macaques were challenged orally with the highly pathogenic, chimeric simian–human immunodeficiency virus SHIV89.6P and given post-exposure prophylaxis with a quadruple combination of neutralizing human mAbs, IgG1b12, 2G12, 2F5, and 4E10, directed against conserved epitopes of HIV envelope glycoproteins. Control animals were virus challenged but left untreated. All infants were followed prospectively for signs of viremia and immunodeficiency. Results: Two out of four macaque infants treated with neutralizing mAbs showed no evidence of infection; the other two maintained normal CD4 T cell counts. In contrast, all control animals became highly viremic and had profound CD4 T cell losses; three out of four died from AIDS within 1.5–6 weeks of the challenge. Conclusions: Passive immunization with this quadruple neutralizing mAbs combination may represent a promising approach to prevent peri- and postnatal HIV transmission. Furthermore, the epitopes recognized by the four neutralizing mAbs are key determinants to achieve complete protection and represent important targets against which to develop active, antibody-response-based AIDS vaccines.

We recently proved that exosomes engineered in vitro to deliver high amounts of HPV E7 upon fusion with the Nef^mut exosome-anchoring protein elicit an efficient anti-E7 cytotoxic T lymphocyte immune response. However, in view of a potential clinic application of this finding, our exosome-based immunization strategy was faced with possible technical difficulties including industrial manufacturing, cost of production, and storage. To overcome these hurdles, we designed an as yet unproven exosome-based immunization strategy relying on delivery by intramuscular inoculation of a DNA vector expressing Nef^mut fused with HPV E7. In this way, we predicted that the expression of the Nef^mut/E7 vector in muscle cells would result in a continuous source of endogenous (ie, produced by the inoculated host) engineered exosomes able to induce an E7-specific immune response. To assess this hypothesis, we first demonstrated that the injection of a Nef^mut/green fluorescent protein-expressing vector led to the release of fluorescent exosomes, as detected in plasma of inoculated mice. Then, we observed that mice inoculated intramuscularly with a vector expressing Nef^mut/E7 developed a CD8⁺ T-cell immune response against both Nef and E7. Conversely, no CD8⁺ T-cell responses were detected upon injection of vectors expressing either the wild-type Nef isoform of E7 alone, most likely a consequence of their inefficient exosome incorporation. The production of immunogenic exosomes in the DNA-injected mice was formally demonstrated by the E7-specific CD8⁺ T-cell immune response we detected in mice inoculated with exosomes isolated from plasma of mice inoculated with the Nef^mut/E7 vector. Finally, we provide evidence that the injection of Nef^mut/E7 DNA led to the generation of effective antigen-specific cytotoxic T lymphocytes whose activity was likely part of the potent, therapeutic antitumor effect we observed in mice implanted with TC-1 tumor cells. In summary, we established a novel method to generate immunogenic exosomes in vivo by the intramuscular inoculation of DNA vectors expressing the exosome-anchoring protein Nef^mut and its derivatives.