As explained in detail in a recently published hypothesis article (Hladik F. A new hypothesis on HIV cure. F1000Research, 4:77 (2015)), the investigators hypothesize that NRTI drugs may reduce the likelihood of HIV eradication by promoting the survival of cells with integrated provirus. In this study, the investigators will test whether daily oral use of two NTRI drugs, tenofovir and emtricitabine (Truvada Pill), induces changes in the upper and lower gut mucosa that are congruent with supporting this hypothesis.

Inclusion Criteria:

• • HIV-negative

  • Male gender at birth
  • Age ≥18 years old
  • Intent to initiate PrEP in the next 1-2 months.
  • Willingness and ability to provide informed consent for study participation
  • Willingness to undergo all required study procedures

Exclusion Criteria:

• Creatinine clearance < 60mL/min

• Platelet count below the normal reference

• Coagulation (PT/PTT) tests above the normal reference

• Any prior use of PrEP

• Use of PEP within 30 days prior to study entry

• Receipt of

  • anti-coagulant medications (e.g. warfarin). Aspirin is allowable.
  • Systemic corticosteroid medications
  • Non-steroidal anti-inflammatory drug (NSAID) use >2 days/week

• Signs or symptoms of acute HIV infection within 14 days of study entry

• No availability of another person who will drive participant home on days of entry and follow-up procedures.

• Plan to leave the Seattle area in the subsequent 2.5 months

• Any condition or substance use that, in the opinion of the study investigator, would interfere with study participation.

The study population is a prospective observational study of cis-gender male persons initiating HIV pre-exposure prophylaxis.

Duration of study enrollment, approximately 2 months

Serious adverse events would have been collected as part of the protocol, however, given that this was not an intervention study, only adverse events that might have been attributed to study procedures (i.e. specimen collection) would have been reported, had any occurred.