Box 1

- How Do Viral and Host Factors Modulate the Sexual Transmission of HIV? Can Transmission Be Blocked?

Box 1. Future Directions for Research

• Study transmission risk and viral load in plasma and genital secretions.

• Correlate cell-free and cell-associated viral load in genital secretions to risk of transmission.

• Investigate effect of vaccines on peak viral loads.

• Define the impact of co-pathogens (especially STDs) and hormones on vaccine and/or microbicide effectiveness in efficacy trials.

• Weigh the contribution of HIV–DC interaction to transmission in animal experiments.

• Isolate HIV from genital secretions.

• Identify mechanisms that restrict HIV replication in genital tract explants, including innate immunity.

• Evaluate mucosal boosting after systemic priming in order to induce genital immune responses.

• Evaluate inclusion of HIV-1 antigens, especially Env protein, as immunogens in microbicides.

• Improve mucosal immunogenicity—e.g., by incorporating Toll-like receptor ligands in vaccines/microbicides.