The Compartmental Biology of HIV in the Male Genital Tract

8 HIV positive men taking TDF/FTC and 8 HIV negative men taking TDF/FTC as pre-exposure
prophylaxis will provide multiple semen and blood samples during a 48-hour inpatient visit.

Participants will take part in the study for approximately two months. After the screening
visit, there is one 2 day overnight visit for intensive PK/PD
(pharmacokinetic/pharmacodynamic) sampling. The investigators will study drug concentrations
and intracellular endogenous nucleotide concentrations (dATP and dCTP) in seminal plasma and
(where appropriate) seminal cells.

Samples will be analyzed through the use of novel laboratory methods to determine the
seminal plasma and seminal cell concentrations of tenofovir emtricitabine. New technologies
will be used to better understand compartmental and intracellular antiretroviral
pharmacology of nucleoside/tide reverse transcriptase inhibitors. Pharmacokinetic modeling
will be used to estimate the primary outcomes.

Inclusion Criteria:

- Born male between the ages of 18 and 60

- HIV positive taking TDF/FTC (and a third drug) as treatment; or HIV negative men
receiving TDF/FTC as pre-exposure prophylaxis

- if on routine treatment must have been taking medication for at least 3 months and
adherence to medication as assessed by blood plasma HIV RNA less than 50 copies per
mL.

- documentation of at least 80% adherence to ART regimen, through clinician or
self-report, with no missed doses in the 3 days prior to the inpatient visit.

- willing and able to comply with scheduled visits, treatment plan, laboratory tests,
and other trial procedures.

Exclusion Criteria:

- Evidence or history of clinically significant hematological, renal, endocrine,
pulmonary, gastrointestinal, cardiovascular, hepatic, psychiatric, or neurologic
disease that would pose unnecessary risk or interfere with study results.

- unwilling or unable to abstain from sexual activity 72 hours prior to overnight
sampling visit

- unlikely to remain on current drug regimen during study period

- anemia that precludes blood donation

- unable to provide semen specimen

- current receipt of other medications that may affect endogenous nucleotide
concentrations, such as additional HIV nucleoside reverse transcriptase inhibitors,
ribavirin, or adefovir