Pre-exposure prophylaxis (PrEP) is a method of preventing HIV infection through the use of antiretroviral (ARV) medications before exposure to HIV. This study will assess the potential of MVC as a "on demand" pre-exposure prophylaxis, within a strategy for the prevention of HIV infection in men who have sex with men (MSM).

Several clinical trials are currently under way evaluating the safety and effectiveness of ARV-based PrEP for preventing HIV infection. The results of the first efficacy trials of ARV-based PrEP showed fewer HIV infections among study participants receiving the study drugs compared to those receiving placebo. Although the results are promising, concerns about adherence, pharmacokinetics, and toxicity still needs further exploration so new and more effective preventive pharmacological approaches should be evaluated. This trial will evaluate the safety, pharmacokinetics and efficacy of ex vivo HIV infection of rectal mucosa by the CCR5 antagonist drug maraviroc (Selzentry) administered to healthy volunteers. This trial will last approximately one year. Twenty-one volunteers will receive MVC 300 mg orally in a single dose. Study visits will occur at enrollment and at days 0, 7, 9, 14 and 16. All study visits will include a physical examination, blood collection and storage and in the basal visit and a day 7 or 9 the participants will undergo a colonoscopy. Ex vivo HIV infectivity in rectal mucosa biopsies and plasma/mucosa MVC levels will be evaluated.

Inclusion Criteria:

1. Men who have sex with men (MSM)
2. Age 18 years or above
3. HIV negative at the time of inclusion 4. Signed informed consent

Exclusion Criteria:

1. Existence of sexually transmitted infection (STI) or active systemic infection
2. Submit a contraindication to rectal biopsy
3. Take any drugs concomitantly with interactions with the MVC
4. Subject unable to follow protocol