A Phase I Study of the Safety and Pharmacokinetics of Recombinant CD4 (rCD4) in Infants and Children Infected With or at Risk for HIV Infection

rCD4 may be an effective treatment for HIV infection, based on its ability to block infection of human cells by HIV in laboratory tests. However, the activity of rCD4 still needs to be confirmed in clinical trials. It is hoped that these tests will show that rCD4 is both safe and effective in treating children who are infected with or who are at risk for infection with HIV. Children have preliminary testing and evaluation to determine eligibility and health. The dosage schedule varies with the dose. During the course of the study, children are monitored for safety through physical exams and blood tests. They have blood withdrawn to study the response to rCD4 and measure the activity of rCD4 in the body. Children may receive immunization of DPT (diphtheria, pertussis, tetanus) or DT and a polio vaccine to measure their antibody response. If the rCD4 is beneficial, children may continue treatment. The study is conducted in four parts: * Part A: Children 13 to 18 years old. * Part B: Children 3 months to less than 13 years old. * Part C: Full-term infants over 3 months old. * Part D: Preterm infants less than 3 months old. Parts C and D are not started until parts A and B have been completed.