Cancer drug may reveal HIV's secret brain hideout

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

* INCLUSION CRITERIA: * 18 years or older * Diagnosis of HIV-1 infection, with positive HIV 1 antibody testing * HIV RNA less than or equal to 40 copies/mL in plasma in the last 12 or greater months * CD4 count above 350 cells/uL * Antiretroviral therapy for 12 months prior to trial * Fully vaccinated against SARS-CoV-2. Fully vaccinated is defined as: * Two weeks out from the second dose of a two-dose vaccine series (Moderna, Pfizer-BioNTech); or * Two weeks out from a single-dose vaccine (Johnson \& Johnson/Janssen) * Patient must be willing and able to comply with all the aspects of trial design and follow-up. * Patients must be able to provide informed consent * Women of childbearing potential must agree to use contraception (defined as two forms of effective birth control), from the time of enrollment until 4 months after the last exposure to pembrolizumab * Participants who are physically able to father a child must agree to use 2 effective methods of contraception (birth control) from the time you enroll in the study until 4 months after your last exposure to pembrolizumab * Effective methods of contraception for this study include: * hormonal contraception (birth control pills, birth control patches, injected hormones, hormonal implants or vaginal ring), * Intrauterine device, * Barrier methods (condom or diaphragm) combined with spermicide, and * Surgical sterilization (hysterectomy, tubal ligation, or vasectomy). * If you have had a hysterectomy, tubal ligation, or vasectomy (or have a partner with a hysterectomy, tubal ligation or vasectomy), you do not have to use 2 methods of birth control. EXCLUSION CRITERIA: * Clinically significant medical disorders that might expose the patient to undue risk of harm confound study outcomes or prevent the patient from completing the study as identified on screening studies and by patient history. Examples of such conditions include known cardiac disease such as congestive heart failure, chronic obstructive pulmonary disease, uncontrolled hypertension, kidney disease, liver disease, endocrine disease, pulmonary disease, heart disease, progressive CNS disease such as Parkinson s disease, dementia, prior tuberculosis infection or ongoing CNS opportunistic infection. * Patient has received immunomodulatory/immunosuppressive therapy (including IV steroids but excluding local injections) in the preceding 6 months. * Patient with known autoimmunity that would include but is not limited to disorders such as hypo/hyperthyroidism, myasthenia gravis, diabetes mellitus type 1, hemolytic anemia, and immune mediated hepatitis (but excluding patients with hypothyroidism already on thyroid replacement therapy). * Prior history of cancer (excluding non-invasive squamous and basal cell carcinoma) * Any opportunistic infection in the prior 2 years (excluding thrush) including latent TB (or a positive TB Quantiferon Gold test) * Patient has received other investigational drugs within 3 months before enrollment * Positive serological or PCR evidence of active or prior infection with HTLV-1/II, Hepatitis B or C. Patients with hepatitis B core (+), surface antibody (+), surface antigen ( ) and hepatitis B DNA (-) eligible to participate in the study (provided they are on tenofovir, lamivudine or TAF). Participants with prior hepatitis C who are hepatitis C antibody (+) but hepatitis C RNA (-) with normal liver enzymes and no evidence of cirrhosis on clinical liver ultrasound are eligible to participate in the study. * Metal in the body which would make having an MRI scan unsafe, such as pacemakers, stimulators, pumps, aneurysm clips, metallic prostheses, artificial heart valves, cochlear implants or shrapnel fragments, or history of welding or metal worker * Claustrophobia * Inability to lie comfortably on the back for up to two hours. * Abnormal anti-thyroid panel (anti-TPO and anti-TG) test at screening visit. * Abnormal screening/baseline blood tests exceeding any of the limits defined below or as deemed exclusionary by the investigators on review: * AST and ALT values \>1.1 times ULN * Fasting triglyceride \> 300 mg/dL * Total bilirubin \>1.1 times ULN (unless participant is taking atazanavir or has Gilbert syndrome) * Creatinine Clearance or eGFR \<60 ml/minute (adjusted for race) * Hemoglobin \< 10 g/dL * Absolute neutrophil count \< 1000/microliter * Platelet count \<130,000/mm(3) (if platelet clumping is present on hematology slide review, platelet count \<100,000/mm3 is considered exclusionary to study) * Hemoglobin A1c greater than or equal to 6% * Thyroid-stimulating hormone (TSH) and adrenocorticotropic hormone (ACTH) within normal limits. If TSH is not within normal limits then the participant may be eligible if thyroxine (T4) is within normal limits. Participants are not excluded if they are on a stable dose of replacement thyroid medication; dose may be adjusted as needed. * An employee or staff of the NIH