Intervention: Tenofovir
Trial phase: Phase 1
SMILES: C[C@H](Cn1cnc2c(N)ncnc21)OCP(=O)(O)O
Sex: Male
Age groups: Adult
Healthy volunteers: No
Participants at risk: 48
Group description: Participants will receive Truvada once daily for ten days. Participants will be asked to provide blood and urine samples and undergo penile, urethral, and rectal swabs. Up to 12 rectal biopsies will be taken.
Eligibility criteria:
Inclusion Criteria:

HIV-negative man who reports receptive anal sex with another man in the last 6 months
Male to female transgender women who have sex with men who report receptive anal intercourse with another man in the last 6 months and are not currently taking hormonal therapy or plan to take hormonal therapy for the duration of the study
Not currently taking PrEP and no plans to initiate during study
Able to provide informed consent in English
No plans for relocation in the next 3 months
Willing to undergo peripheral blood and rectal biopsy sampling
Willing to use study products as directed
Willing to abstain from receptive anal intercourse 3 days prior to starting study product and for the duration of the study and for 7 days after any rectal biopsy procedure.

Exclusion Criteria:

History of inflammatory bowel disease or other inflammatory, infiltrative, infectious or vascular condition involving the lower gastrointestinal tract that, in the judgment of the investigators, may be worsened by study procedures or may significantly distort the anatomy of the distal large bowel

Significant laboratory abnormalities at baseline visit, including but not limited to:

Hgb ≤ 10 g/dL
PTT > 1.5x ULN or INR > 1.5x ULN
Platelet count <100,000
Creatinine clearance <60

Any known medical condition that, in the judgment of the investigators, increases the risk of local or systemic complications of endoscopic procedures or pelvic examination, including but not limited to:

Uncontrolled or severe cardiac arrhythmia
Recent major abdominal, cardiothoracic, or neurological surgery
History of uncontrolled bleeding diathesis
History of colonic, rectal, or vaginal perforation, fistula, or malignancy
History or evidence on clinical examination of ulcerative, suppurative, or proliferative lesions of the anorectal or vaginal mucosa, or untreated sexually transmitted disease with mucosal involvement

Continued need for, or use during the 14 days prior to enrollment, of the following medications:

Aspirin or more than 4 doses of NSAIDs
Warfarin, heparin (low-molecular weight or unfractionated), platelet aggregation inhibitors, or fibrinolytic agents
Any form of rectally administered agent besides products lubricants or douching used for sexual intercourse

Continued need for, or use during the 90 days prior to enrollment, of the following medications:

Systemic immunomodulatory agents
Supraphysiologic doses of steroids
Experimental medications, vaccines, or biologicals
Intent to use HIV antiretroviral pre-exposure prophylaxis (PrEP) during the study, outside of the study procedures
Symptoms of an untreated rectal sexually transmitted infection (e.g. rectal pain, discharge, bleeding, etc.)
Current use of hormonal therapy
Any other clinical condition or prior therapy that, in the opinion of the investigator, would make the patient unsuitable for the study or unable to comply with the study requirements.