A Study of Apomab in Combination With Rituximab in Patients With Non-Hodgkin's Lymphoma That Has Progressed Following Previous Rituximab Therapy

All patients will receive Rituximab once per week for up to 8 weeks in Cycles 1-3. The first dose of Rituximab will be administered between 24 and 120 hours prior to the first dose of Apomab in Cycle 1. In Cycles 2 & 3 on Day 1, Rituximab will be administered directly prior to Apomab, without a rest period between the two treatments. All patients will receive Apomab for a total of six cycles. Each cycle lasts 21 days with a resting period built into each cycle. The length of the resting period depends on the cycle. The Apomab dose will be based on the patient's body weight at screening. The rituximab dose will be based on the patient's body surface area at screening. Both Rituximab and Apomab are administered intravenously (IV).