Complications with current HIV antiretroviral therapy have left many children and adolescents with limited therapeutic options due to drug resistance. The purpose of this study is to test the effectiveness and safety of Vicriviroc (VCV), an HIV entry inhibitor and CCR5 co-receptor antagonist.

Highly active antiretroviral therapy (HAART) that includes a protease inhibitor (PI) or a non-nucleoside reverse transcriptase inhibitor (NNRTI) has become the standard treatment of HIV-infected adults and children. When effective, HAART decreases the viral population, increases the body's immune responses, and leads to decreased disease progression and increased survival. However, several factors including poor adherence, drug toxicities, and drug resistance complicate HIV management and allow for children and adolescents to develop resistance to multiple drug classes, leaving them with very limited therapeutic options. Fortunately, drugs with new mechanisms of action, such as HIV entry inhibitors, demonstrate activity even in people with resistance to the currently available reverse transcriptase and protease inhibitors.

The purpose of this study is to test the effectiveness and safety of Vicriviroc (VCV), an HIV entry inhibitor. Vicriviroc targets the CCR5 chemokine receptor, which HIV uses to bind and enter CD4+ cells.

This study is a two-stage, age-stratified, non-comparative study to explore the safety, tolerability, pharmacokinetic profile and antiviral activity of the investigational CCR5 inhibitor Vicriviroc in HIV-infected treatment experienced children and adolescents.

In Step I participants will be screened for the co-receptor CCR5 to assess whether they can enter Step II. Only participants with CCR5-tropic virus are eligible for Step II - the main portion of the study to evaluate the study outcome measures. Those participants who continue to Step II will be assigned to one of four age-stratifies cohorts which will receive varying forms, either liquid or tablet, of Vicriviroc:

Cohort I: 12 years to less than 19 years of age, to receive tablet formulation of VCV

Cohort II: 6 years to less than 12 years of age, to receive tablet formulation of VCV

Cohort III: 6 years to less than 12 years of age, to receive liquid formulation of VCV

Cohort IV: 2 years to less than 6 years of age, to receive liquid formulation of VCV

Dose strengths of 20 mg and 30 mg will be used, or in liquid formulation at a concentration of 1mg/mL.

Step II is composed of Stage I and Stage II. Stage I is a dose ranging study designed to explore how the body responds to different doses of vicriviroc, including safety factors associated with dosage. After optimal dosage information and safety measures have been assessed for the different cohorts in Stage I, Stage II will open. Stage II will evaluate the long term safety, tolerability and effectiveness of vicriviroc.

The study, including Steps I and II will last for approximately 48 weeks. Follow-up for all subjects exposed to vicriviroc will last for 5 years after initial exposure. Visits will be every 3 months for subjects on study provided vicriviroc and every 6 months for subjects who discontinue vicriviroc.

The study was terminated shortly after the initiation, when the drug company decided to discontinue development of the study drug. As of study termination, nine participants had enrolled under Cohort I in Step I, but only 4 participants had CCR5 tropism and received the study medication under Step II. All 4 participants had limited post-baseline data.

Inclusion Criteria:

• Confirmed HIV infection
• Treatment experienced subjects: Children or adolescents on an unchanged therapeutic regimen for at least 12 weeks and experiencing virologic failure OR participants on no treatment for 4 weeks or more but with history of virologic failure on a prior therapeutic regimen.
• Likely to have virus that is sensitive to at least one ritonavir boosted protease inhibitor
• HIV viral load greater than or equal to 1,000 copies/ml within 90 days prior to Step I entry
• Able to swallow study medication, in tablets or liquid form specific to age-assigned cohort
• Parent, legal guardian or participant able and willing to provide signed informed consent and to have the participant followed at the clinic site
• Willing to use effective methods of contraception

Inclusion Criteria for Step II (In addition to the inclusion criteria for Step I):

• Participant's plasma HIV tested at Step I must be R5 tropic
• Genotypic sensitivity enabling the participant to take optimized background therapy (OBT) consisting of at least a ritonavir-based protease inhibitor. More information on this criterion can be found in the study protocol.

Exclusion Criteria:

• Presence of any currently active AIDS defining illness or history of malignancy
• History of a seizure disorder that requires current anti-seizure medication for control or at risk for seizures. Those with a history of febrile seizures alone are not excluded.
• Certain abnormal laboratory values. More information on this criterion can be found in the protocol.
• Any vaccinations 14 days prior to Step I, or scheduled to occur within 14 days prior to entry into Step II, and the week 24 and 48 visits in Step II
• Allergy or sensitivity to study drug or its ingredients
• Taking any Step II disallowed medications (see protocol) and unable or unwilling to discontinue them at least one week prior to entering Step II
• Use of NNRTIs other than etravirine 21 days prior to Step II entry
• Pregnancy or breastfeeding. Infants who are receiving breastmilk are allowed to enroll.

Exclusion Criteria for Step II

• All exclusion criteria for Step I
• Participants harboring dual or mixed tropic virus (R5/X4) or X4 virus or non phenotypable virus
• Current or anticipated use of any disallowed medications
• Use of efavirenz, nevirapine, and delavirdine for 21 days prior to Step II entry
• Pregnant within 3 days of Step II entry

In accordance with the Clinical Trial Agreement between NIAID (DAIDS) and company collaborators, NIAID (DAIDS) provides companies with a copy of any abstract, press release, or manuscript prior to submission for publication with sufficient time for company review and comment. The publication/other disclosure can be delayed for up to 30 additional business days for manuscripts and five (5) business days for abstracts, to preserve U.S. or foreign patent or other intellectual property rights.