Rectal Safety and Acceptability Study of Tenofovir 1% Gel

Inclusion Criteria: 1. ≥ Age of 18 at screening, verified per site SOP 2. Willing and able to provide written informed consent for screening and enrollment 3. HIV-1 uninfected at screening 4. Willing and able to communicate in English 5. Willing and able to provide adequate locator information, as defined in site SOP 6. Availability to return for all study visits, barring unforeseen circumstances 7. Per participant report at screening, a history of consensual receptive anal intercourse (RAI) at least once in the prior year (Required to assure that participants have a context for the acceptability assessments). 8. Willing to abstain from insertion of anything rectally, including sex toys, other than the study gel for the duration of study participation 9. Willing to abstain from RAI for the duration of study participation 10. Must agree to use study provided condoms for the duration of the study for vaginal and insertive anal intercourse 11. Must be in general good health 12. At Screening and Enrollment, must agree not to participate in other research studies involving drugs, medical devices, or genital products for the duration of study participation (until all follow-up visits are completed) In addition to the criteria listed above, female participants must meet the following criteria: 13. Postmenopausal or using (or willing to use) an acceptable form of contraception (e.g., barrier method, intrauterine device (IUD), hormonal contraception, surgical sterilization, or vasectomization of male partner). If the female participant has female partners only, the method of contraception will be noted as a barrier method in the study documentation. Exclusion Criteria: 1. Abnormalities of the colorectal mucosa, or significant colorectal symptom(s), which in the opinion of the clinician represents a contraindication to biopsy (including but not limited to presence of any unresolved injury, infectious or inflammatory condition 2. At screening: participant-reported symptoms, and/or clinical or laboratory diagnosis of active rectal or reproductive tract infection requiring treatment per current Centers for Disease Control (CDC) guidelines or symptomatic urinary tract infection (UTI). Infections requiring treatment include symptomatic bacterial vaginosis, symptomatic vaginal candidiasis, other vaginitis, trichomoniasis, Chlamydia (CT), gonorrhea (GC), syphilis, active herpes simplex virus (HSV) lesions, chancroid, pelvic inflammatory disease, genital sores or ulcers, cervicitis, or symptomatic genital warts requiring treatment. Note that an HSV-1 or HSV-2 seropositive diagnosis with no active lesions is allowed, since treatment is not required Note: In cases of non-anorectal GC/CT identified at screening, one re-screening 2 months after screening visit will be allowed 3. Anorectal sexually transmitted infections (STI) within six months prior to the Screening Visit 4. At screening: Positive for hepatitis B surface antigen Hemoglobin \< 10.0 g/dL Platelet count less than 100,000/mm3 White blood cell count \< 2,000 cells/mm3 or \> 15,000 cells/mm3 For females: calculated creatinine clearance less than 60 mL/min by the Cockcroft-Gault formula where creatinine clearance in mL/min (140- age in years) x (weight in kg) x (0.85 for female)/72 x (serum creatinine in mg/dL) For males: calculated creatinine clearance less than 60 mL/min by the Cockcroft-Gault formula where creatinine clearance in mL/min = (140 - age in years) x (weight in kg) x (1 for male)/72 x (serum creatinine in mg/dL) Serum creatinine \> 1.3× the site laboratory upper limit of normal (ULN) Alanine transaminase (ALT) and/or aspartate aminotransferase (AST) \> 2.5× the site laboratory ULN +1 glucose or +1 protein on urinalysis (UA) History of bleeding problems 5. History of significant gastrointestinal bleeding in the opinion of the investigator 6. Allergy to methylparaben, propylparaben, sorbic acid, and components of N-9 7. Known HIV-infected partners 8. By participant report at enrollment, history of excessive daily alcohol use (as defined by the CDC as heavy drinking consisting of an average consumption of more than 2 drinks per day for men, and more than 1 drink per day for women), frequent binge drinking or illicit drug use that includes any injection drugs, methamphetamines (crystal meth), heroin, or cocaine including crack cocaine, within the past 12 months 9. Per participant report at screening, anticipated use and/or unwillingness to abstain from the following medications during the period of study participation: Heparin, including Lovenox® Warfarin Plavix® (clopidogrel bisulfate) Rectally administered medications (including over-the-counter products) Aspirin Non-steroidal anti-inflammatory drugs (NSAIDS) Any other drugs that are associated with increased likelihood of bleeding following mucosal biopsy 10. By participant report at screening, use of post-exposure prophylaxis for HIV exposure, systemic immunomodulatory medications, rectally administered medications, rectally administered products (including condoms) containing N-9, or any investigational products within the 4 weeks prior to the Enrollment/Baseline Evaluation Visit and throughout study participation 11. History of recurrent urticaria 12. Any other condition or prior therapy that, in the opinion of the investigator, would preclude informed consent, make study participation unsafe, make the individual unsuitable for the study or unable to comply with the study requirements. Such conditions may include, but are not limited to, current or recent history of severe, progressive, or uncontrolled substance abuse, or renal, hepatic, hematological, gastrointestinal, endocrine, pulmonary, neurological, or cerebral disease In addition to the criteria listed above, female participants will be excluded if they meet any of the following criteria: 13. Pregnant at the Enrollment/Baseline Visit 14. Breastfeeding at screening or intend to breastfeed during study participation per participant report.