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.