Relationship of Tenofovir With HIV-1 Suppression in ex Vivo Tissue in Adolescents

Inclusion Criteria: 1. Age \>/= 10 years and \</= 14 years and age \</= 18 years and \</= 21 years. 2. Willing and able to communicate in English. 3. Willing and able to provide written informed consent or assent to take part in the study (where required, parent/guardian must provide consent). 4. Willing and able to provide adequate information for locator purposes. 5. Understand and agree to local sexually transmitted infections (STI) reporting requirements. 6. HIV-negative or -positive as documented in prior serologic testing or per report, and willing to undergo repeat HIV testing. 7. Willing and able to not take aspirin, any aspirin containing medications, or non-steroidal anti-inflammatory drugs for at least 72 hours before and 72 hours after flexible sigmoidoscopy. 8. All female patients of childbearing potential (post-menarche) must be willing to undergo urine pregnancy testing at screening. 9. Must be in general good health, including normal renal function. 10. Subjects \<18 years old must be scheduled for a clinically indicated colonoscopy or flexible sigmoidoscopy with biopsies. 11. HIV-positive participants only (Aim 1): * Must have recent HIV polymerase chain reaction (PCR) documented in the last 6-12 months by verbal report * Must have tenofovir in chronic cART regimen (\>/= 1 month). * Be reportedly compliant. * CD4 T cells \>250/cmm Exclusion Criteria: 1. Known history of inflammatory bowel disease. 2. 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, inflammatory condition of the local mucosa, and presence of symptomatic external hemorrhoids). 3. Evidence of any known enteric infection at the time of study visit. 4. Participant-reported symptoms and/or clinical or laboratory diagnosis of active and symptomatic rectal infection (gonorrhea, Chlamydia, syphilis, clinically active perineal HSV). * Note: Allow one re-screening after documented treatment (30 days) in cases of gonorrhea/chlamydia (GC/CT) identified at screening. 5. Pregnancy. 6. Subjects with other poorly controlled medical conditions (e.g. diabetes, congestive heart failure). 7. Chronic renal disease (BUN and serum creatinine \>1.5 times the upper normal limit). 8. History or presence of impaired gastrointestinal motility, or history of extensive small bowel resection (greater than half the length of the small intestine). 9. Use of warfarin or heparin. 10. Use of systemic immunomodulatory medications within 4 weeks of screening. 11. Use of any investigational products within 4 weeks of screening. 12. Fever at time of endoscopy. Subjects can be re-scheduled at a later point after the fever is resolved. 13. 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. Such conditions may include, but are not limited to, current or recent history of sever, progressive, or uncontrolled renal, hepatic, hematological, gastrointestinal, endocrine, pulmonary, neurological, or cerebral disease.