Objectives: Establishment of an in vitro model to evaluate rectal safety and the efficacy of microbicide candidates. Design: An investigation and characterization of human colorectal explant culture for screening candidate microbicides to prevent rectal transmission of HIV-1 infection. Methods: Human colorectal explants were cultured at the liquid-air interface on gelfoam rafts. Phenotypic characterization of HIV-1 target cells was performed by fluorescence-activated cell sorter analysis. HIV-1 infection was determined by the measurement of p24 antigen release, viral RNA, and proviral DNA accumulation. Results: Colorectal explant CD4 T cells expressed higher CCR5 and CXCR4 levels compared with blood. Minor differences between the rectal and sigmoid colon were observed with a trend for slightly higher CCR5 and HLA-DR expression in cells from the sigmoid colon. Favourable culture conditions were established for colorectal tissue. Although tissue structure degenerated with time, CD4: CD8 cell ratios remained constant, and tissue supported productive HIV-1 infection. The ability of candidate microbicides to inhibit R5 HIV-1 infection was evaluated. Polyanion candidates, PRO2000 and dextrin sulphate, provided 99% protection at 1 [mu]g/ml and 1 mg/ml, respectively, equivalent to 1/5000 and 1/40 of the vaginal formulations. The nucleotide reverse transcriptase inhibitor (NRTI) 9-[2-(phosphonomethoxy)propyl]adenine (PMPA) provided protection at concentrations 1000-fold lower (10 [mu]g/ml) than the proposed vaginal formulation (1%). Furthermore, non-NRTI UC-781 and TMC-120 provided greater than 99% inhibition at 3.3 or 0.33 [mu]g/ml, respectively. No products demonstrated toxicity to rectal mucosa at inhibitory concentrations. Conclusion: Colorectal explant culture was shown to be a useful tool for the preclinical evaluation of potential microbicides. The data suggest that rectally applied microbicides might provide protection from HIV-1 transmission.
AIDS (2006) 20 (9) pp. 1237-1245.