Phase II Study of Aldesleukin (IL-2) Following the Administration of Zanolimumab (Anti-CD4mAb) in Metastatic Melanoma and Metastatic Renal Cancer

Background: * Aldesleukin (IL-2) is a drug that can help to shrink tumors in some patients with metastatic renal cancer and metastatic melanoma. It is possible that removing certain white blood cells (known as CD4 cells) before IL-2 treatment may improve the treatment effects. * Zanolimumab is an antibody that works by destroying CD4 cells in the blood. Researchers are interested in determining whether zanolimumab can improve the results of IL-2 treatment if it is given before, during, and after IL-2 treatment. In addition, further research with zanolimumab may provide more information on how IL-2 treatment causes tumors to stop growing or shrink. Objectives: \- To evaluate the effectiveness of IL-2 treatment in conjunction with zanolimumab in individuals with metastatic cancer. Eligibility: \- Individuals at least 18 years of age who have been diagnosed with metastatic melanoma or metastatic kidney cancer. Design: * Eligible participants will be screened with a full physical examination and medical history, imaging studies, and blood samples, including leukapheresis, to remove a sample of white blood cells for testing purposes. Participants may also have a colonoscopy and biopsies if they have received previous treatments that have been known to cause colon damage. * Participants will be treated with zanolimumab and IL-2 treatment for 9 weeks. * Zanolimumab will be given on an outpatient basis during weeks 1 through 4, 6, 8, and 9. In weeks 5 and 7, participants will receive zanolimumab as an inpatient in addition to IL-2 therapy. * Inpatient IL-2 treatment will be given during weeks 5 and 7. Up to 15 doses of IL-2 treatment will be given over a maximum of 5 days, followed by inpatient recovery time. * During week 5, participants will have tumor imaging studies prior to receiving zanolimumab and IL-2 treatment. * About 2 weeks after the treatment period, participants will return to the clinical center for a 2-day evaluation with a physical examination, imagi