An Evaluation of Immunogenicity and Safety of Two Doses of MVA-nef vs. MVA-BN in HIV-1 Infected Patients

Inclusion Criteria: * Ages 18-60 * HIV-1 infection, as documented by any licensed PCR kit or ELISA (confirmed by an complementary assay e.g. Western blot HIV-1 culture, HIV-1 antigen, plasma HIV-1 RNA, or a second antibody test by a method other than ELISA) at any time prior to study entry. * Stable on HAART for at least 6 consecutive months prior to study entry (changes of one drug for the another drug due to reasons other than virologic failure are allowed) * Plasma HIV-1 RNA levels of \< 50 copies/ml for at least 6 months prior to study entry (two single blips of up to 200 HIV-1 RNA copies/ml are acceptable if they resolve spontaneously without a change in HAART) * Plasma HIV-1 RNA levels of \< 50 copies/ml at study entry * CD4 nadir \>100 * CD4+ cell counts \> 250/µl (one measurement within 4 months prior to study entry and one measurement within screening phase) * For women, negative serum pregnancy test at screening and negative urine or serum pregnancy test within 24 hours prior to vaccination. * If the volunteer is female and of childbearing potential, she agrees to use an acceptable method of contraception, and not become pregnant for at least 56 days after the last vaccination. A woman is considered of childbearing potential unless post-menopausal or surgically sterilized. (Acceptable contraception methods are restricted to intrauterine contraceptive device; oral contraceptives; diaphragm or condom in combination with contraceptive jelly, cream or foam; Norplant® or DepoProvera®) with use of method for a minimum of 30 days prior to vaccination). * ALT/SGPT, AST/SGOT, and alkaline phosphatase \< 3 times institutional upper limit of normal (ULN). * Urine protein by dipstick or urinalysis \< 100mg/dl or \<2+ proteinuria * CBC: Haemoglobin \>8 g/dl; White blood cells greater than 2,500 and less than 11,000/mm3; Platelets greater than or equal to 100,000/mm3 * Read, signed and dated informed consent document after being advised of the risks and benefits of the study in a language able to understand, and prior to performance of any study specific procedure * Cardiac enzymes: within normal range. Exclusion Criteria: * Pregnant or breast-feeding women. * Administration of any HIV nef vaccine or vaccinia immunization within the past 5 years. * Uncontrolled serious infection i.e. not responding to antimicrobial therapy. * History of any serious medical condition, which in the opinion of the investigator would compromise the safety of the subject. * History of or active autoimmune disease. Persons with vitiligo or thyroid disease on thyroid replacement are not excluded. * History of malignancy, other than squamous cell or basal cell skin cancer, unless there has been surgical excision that is considered to have achieved cure. * History or clinical manifestation of clinically significant mental illness or haematological, renal, hepatic, pulmonary, central nervous, cardiovascular or gastrointestinal disorders. * Any condition which might interfere with study objectives or would limit the subject's ability to complete the study in the opinion of the investigator. * ECG with clinical significance (complete left or right bundle branch block, or sustained ventricular arrythmia, or 2 PVCs in a row, or ST elevation consistent with ischemia). * History of myocardial infarction, angina, congestive heart failure, cardiomyopathy, stroke or transient ischemic attack, or other heart condition under the care of a doctor. * 3 or more of the following risk factors: 1. High blood pressure requiring therapy. 2. High blood cholesterol (\> 300 mg/dl or ratio LDL/HDL ≥ 3) not induced by the HIV therapy. 3. Diabetes mellitus or high blood sugar. 4. He/she has a first degree relative (for example mother, father, brother, or sister) who had a heart condition before the age of 50. 5. Smoking cigarettes now. * History of chronic alcohol abuse (40g / day for at least 6 month) and/or intravenous drug abuse (within the past 6 month). * History of allergic disease or reactions likely to be exacerbated by any component of the vaccine. * History of anaphylaxis or severe allergic reaction. * Acute disease (a moderate or severe illness with or without a fever) at the time of enrolment. * Any vaccinations with active vaccines within a period starting 30 days prior to administration of the vaccine and ending 30 days after administration of the study vaccine. Any vaccinations with inactive vaccines within a period starting 14 days prior to administration of the vaccine and ending 14 days after administration of the study vaccine. * Chronic administration (defined as more than 14 days) of immuno- suppressant or immune-modifying drugs during the study period (Corticosteroid nasal sprays are permissible. Subjects who have used topical and inhaled steroids can be enrolled after their therapy is completed). * Administration or planned administration of immunoglobulins and/or any blood products during a period starting from 3 months prior to administration of the vaccine and ending at study conclusion. * Use of any investigational or non-registered drug or vaccine other than the study vaccine within 30 days or 7 half-lives (whichever is longer) preceding the first dose of the study vaccine, or planned administration of such a drug during the study period.