IL2 and lymphopenia: - Multi-modal mechanism of action where Fc-portion mediates ADCC and CDC while IL-2 moiety activates NK cells and T cells- hu14.18-IL2 peak serum levels similar for responders and nonresponders- Transient lymphopenia followed by lymphocytosis consistent with immune activation- Transiently increased serum sIL2R, no association with DLT- 13-16 patients developed anti-drug antibodies, not associated with drug serum levels or responses- No association between factors at diagnosis and responses