Background:  Protection from HIV-1 infection with a single dose of microbicide gel administered regardless of timing of coitus may be the optimal use for such products. Studies were undertaken in vitro to determine if a single dose of tenofovir (TDF) 1% gel could be effective when used independently of challenge.

Methods:  TDF 1% gel was applied either 24 hours pre- or 24 hours post-HIV-1_BaL challenge of cervical explant tissue. Cervical explants from 3 separate patients were established in duplicate, placed through a trans-well, and sealed with Matrigel to create a polarized system with the tissue at the air-liquid interface. The basolateral side received medium containing phytohemagglutinin (PHA) -p and interleukin (IL) -2 for the initial 48 hours; 24 hours pre- or post-challenge with 5x10⁴ TCID₅₀ of HIV-1_BaL, TDF 1% gel or placebo gel was applied to the explant for 1 hour, then washed off. The basolateral medium was collected and replenished every 3 to 4 days for 21 days. HIV-1 p24 was measured by ELISA and infection was confirmed by immunohistochemistry for HIV-1 p24-positive cells.

Results:  Control explant HIV-1_BaL growth in cervical tissue was similar to previous work in that viral peak replication occurred between days 10 and 18 of culture. For statistical analysis (Wilcoxon matched pairs test), day 14 was chosen to determine reduction of HIV-1 p24 by the TDF 1% gel or placebo gel. When applied 24 hours pre-challenge, TDF 1% gel reduced p24 levels by 6.5-fold compared to the control levels (p = .09) and by 6.4-fold (p = .03) compared to the placebo gel levels. When applied 24 hours post-challenge, TDF 1% gel reduced p24 levels by 32-fold compared to the control levels (p = 0.02) and by 58-fold compared to the placebo gel levels (p = 0.02). In either case, placebo gel did not reduce HIV-1 p24 levels when compared to the control levels. The efficacy was confirmed by immunohistochemistry showing TDF 1% gel-treated tissues were negative for p24-positive cells while control- and placebo-treated tissues were positive.

Conclusions:  TDF 1% gel was effective at preventing HIV-1_BaL infection of cervical explants up to 24 hours pre- or post-challenge, protecting the cervical tissues regardless of when the microbicide was applied. While these results are intriguing, they need to be confirmed by pharmacokinetic data quantifying the drug at these time points. Collectively, these data suggest that TDF 1% gel could be used independently of coitus.