Effect of Leflunomide on T Cell Proliferation in HIV-Infected Patients

* INCLUSION CRITERIA: * Age greater than or equal 18 and less than or equal to 65 years. * HIV infected. * CD4+ cell count greater than or equal to 350 cells/mm(3) at screening and historical nadir (since diagnosis of HIV) of greater than or equal to 200 cells/mm(3). * Plasma HIV viral load greater than or equal to 1,000 copies/mL at screening. * Ability to understand and sign informed consent and willingness to comply with the study requirements and clinic policies. * Must have a primary care physician who will be taking care of patients for their HIV infection. * Female study subjects of reproductive potential (defined as girls who have reached menarche or women who have not been post-menopausal for at least 24 consecutive months, i.e., who have had menses within the preceding 24 months or have not undergone a sterilization procedure (hysterectomy or bilateral oophorectomy), must have a negative serum or urine pregnancy test. * Agreement not to participate in a conception process (eg. active attempt to become pregnant or impregnate, sperm donation, or in vitro fertilization) and to follow strict contraceptive measures while on study. * If participating in sexual activity that could lead to pregnancy, the study volunteer must agree that two reliable methods of contraception will be used simultaneously during the entire study. Acceptable forms of contraception include: Condoms (male or female) with or without a spermicidal agent. Condoms are recommended because their appropriate use is the only contraception method effective for preventing HIV transmission. Diaphragm or cervical cap with spermicide. IUD. Hormonal-based contraception. Study subjects who are not of reproductive potential (women who have been post-menopausal for at least 24 consecutive months, women who have undergone hysterectomy or bilateral oophorectomy, or prepubescent boys or men who have documented azoospermia) are eligible without requiring the use of contraception. Written or oral documentation communicated by clinician or clinician's staff of one of the following: Physician report/letter. Operative report or other source documentation in the patient record (a laboratory report of azoospermia is required to document successful vasectomy). Discharge summary. Laboratory report of azoospermia. FSH measurement elevated into the menopausal range as established by the reporting laboratory. EXCLUSION CRITERIA: * Current treatment with antiretrovirals or use of antiretrovirals within 12 weeks of screening. * Intention of start antiretroviral regimen within 64 day study period. * Previous treatment with leflunomide. * Previous treatment with IL-2. * Treatment with immunomodulatory agents (including hydroxyurea, mycophenolate, cyclosporine, rapamycin, anti-HIV vaccines, interleukins other than IL-2, interferons) within 60 days of study. * Treatment with systemic corticosteroids within 30 days of study. * Inability or unwillingness to discontinue drugs (except NSAIDS) that are metabolized by P450 2C9 isoenzyme (see Appendix A- Medications Metabolized by CYP 2C9 and Contraindicated During Treatment Period). * Inability or unwillingness to discontinue hepatotoxic drugs (eg. isoniazid, rifampin, HMG CoA reductase inhibitors). * Inability or unwillingness to discontinue drug that interact with cholestyramine (eg. have diminished absorption with cholestyramine) (see Appendix B- Medications that have Interactions with Cholestyramine). * Current use of or known intolerance of cholestyramine or bile acid sequestering resins. * History of familial hyperlipoproteinemia type III, IV or V. * Active bacterial infection within 4 weeks of screening. * History of AIDS-defining illness (category C) (see Appendix C - CDC AIDS Classification Criteria). * Hepatitis B or C infection. * Acute or chronic liver disease from any cause (eg. alcoholic hepatitis or alcohol induced cirrhosis, autoimmune hepatitis, primary biliary cirrhosis, sclerosing cholangitis, Wilson's disease, hemochromatosis) which the investigator feels would compromise the subject's safety. * History of biliary obstruction. * Current alcohol abuse or unwillingness to abstain from alcohol use for study period. * History of hypertension that is not controlled (less than 140/80 mm/Hg) on a single antihypertensive agent. * Abnormal laboratory findings: hemoglobin less than 10 g/dL; ANC less than 1000/mm(3); platelets less than 100,000/mm(3); creatine above the upper limit of normal; ALT or alkaline phosphatase greater than 1.25 times the upper limit of normal; AST greater than 1.25 times the upper limit of normal (subjects with isolated AST elevation, higher than normal CPK values in the absence of liver disease and compatible history such as intense exercise will be allowed to re-screen if the study investigators suspect that the elevated AST is of muscular origin) direct bilirubin greater than 1.5 times the upper limit of normal; total bilirubin greater than 2 times the upper limit of normal lipase greater than 1.5 times the upper limit of normal; PT greater than 1.1 times the upper limit of normal; PTT greater than 1.5 times the upper limit of normal. * History of malignant neoplasm except in situ anogenital carcinoma, adequately treated basal or squamous cell carcinoma of the skin or solid tumors treated with curative therapy and disease free for at least five years. * Significant medical or psychiatric disorder which the investigator feels would interfere with the subject's ability to participate or would compromise safety. * Women who are currently pregnant or breast-feeding. * History of interstitial lung disease.