Direct stringency comparison of two macaque models (single-high vs. repeat-low) for mucosal HIV transmission using an identical anti-HIV chemoprophylaxis intervention.

BACKGROUND: In our previous work, oral chemoprophylaxis with tenofovir disoproxil fumarate (TDF) provided partial protection in rhesus macaques against repeated low-dose (RL) intrarectal SHIV162p3 exposure.
METHODS: Here, we make a direct comparison of these previous findings with data generated using a single high (SH)-dose challenge strategy.
RESULTS: All 5 (100%) control macaques were infected after a SH challenge and only three of five (60%) TDF-treated macaques became infected. The remaining two TDF-treated macaques remained virus-negative and were susceptible to virus infection upon re-challenge in the absence of oral TDF. Thus, two of five (40%) TDF-treated macaques were protected by the pre-exposure chemoprophylaxis regimen. By comparison with the RL challenge system, only one of four (25%) of TDF-treated macaques were protected from infection, whereas four of four (100%) control macaques became infected using RL challenges.
CONCLUSION: Taken together, these findings indicate that the stringency of the RL challenge model for testing antiretroviral interventions is not lower and possibly greater than that of the SH challenge model.