Since CD4 is the high-affinity receptor for HIV-1, molecules such as CD4-IgG2, which incorporate the gp120 binding region of CD4, have the potential to bind and neutralize all strains of the virus. [AS PER AMENDMENT 4/25/00: Study results have demonstrated that the product is safe in children, well tolerated, and may have antiviral properties. With these encouraging results in hand, an extra cohort has been added using twice the dose of rCD4-IgG2 as in Cohort I.]

The study is conducted in two parts. In Part 1 patients receive a single dose of CD4-IgG2 intravenously at 1 of 4 dose levels. A minimum of 3 patients are treated at a given dose level. If none of these 3 patients experience Grade 3 or 4 toxicity, patients are escalated to the next dose level. If any of these 3 patients have life-threatening toxicities or if more than 1 of these 3 patients experience non-life-threatening Grade 3 or 4 toxicities, escalation stops and the prior dose (if any) is considered the maximum tolerated dose (MTD). If 1 of these 3 patients experiences non-life-threatening Grade 3 or 4 toxicities, 3 additional patients are treated at this dose level. If 1 or more of these 3 additional patients has Grade 3 or 4 toxicity, escalation stops. If none of these 3 additional patients has Grade 3 or 4 toxicity, patients are escalated to the next dose level.

Part 2 provides additional data on the safety, toxicity and pharmacokinetics of CD4-IgG2 when given in multiple doses. Patients receive the highest safe dose (MTD) as established in Part 1. Treatment is given intravenously once weekly at Weeks 0, 1, 2, and 3. If insufficient activity is seen at this dose level, 6 additional patients will be enrolled at a higher dose level. Patients who participate in Part 1 may enroll in Part 2 provided they are followed for at least 3 months and meet inclusion criteria for Part 2. If any patient experiences a life-threatening condition due to CD4-IgG2, the study will stop. [AS PER AMENDMENT 4/25/00: Cohort II receives twice the dose of Cohort I intravenously once weekly at Weeks 0, 1, 2 and 3. Pharmacokinetic samples are obtained at pre-dose and 1 hour after the doses are administered at Weeks 0, 1, and 2; and pre-dose, 1 hour, 24 hours, and Days 3, 7, and 14 after the dose are administered at Week 3. An overnight stay in the hospital is recommended for the first 24 hours. At Weeks 0, 1, 2, and 3, virology testing including HIV-1 RNA is performed with each infusion of CD4-IgG. Follow-up monitoring of patients is done once a month for 4 months for patients in Cohort II.]