• Maximum tolerated dose (Phase I) [ Designated as safety issue: Yes ]
  
• Toxicity (Phase I) [ Designated as safety issue: Yes ]
  
• Proportion of patients who receive 2 sequential doses of Y2B8 immunotherapy and are progression-free at 3 years (Phase II) [ Designated as safety issue: No ]
  

• Association between the amount of tumor radiation indicated by the In2B8 scan and tumor response (Phase I) [ Designated as safety issue: No ]
  
• Association between In2B8 scan and positron emission tomography scan results (Phase I) [ Designated as safety issue: No ]
  
• Appearance of tumor and normal organ images on the second In2B8 scan (Phase I) [ Designated as safety issue: No ]
  
• Survival (Phase II) [ Designated as safety issue: No ]
  
• Time to disease progression (Phase II) [ Designated as safety issue: No ]
  
• Tumor response rate (Phase II) [ Designated as safety issue: No ]
  

OBJECTIVES:

• Determine the maximum tolerated dose (MTD) of yttrium Y 90 ibritumomab tiuxetan (IDEC-^90Y2B8) administered with rituximab with and without filgrastim (G-CSF) and interleukin-11 (IL-11) in patients with relapsed low-grade or follicular CD20+ non-Hodgkin's lymphoma. (Phase I)
• Determine the toxicity of this regimen in these patients.
• Determine the response rate in patients treated with this regimen.
• Compare tumor and normal organ dosimetry with positron emission tomography and computerized tomography scans, subsequent tumor response, and normal organ toxicity by utilizing indium In 111 ibritumomab tiuxetan radioimmunoconjugate scans before each IDEC-^90Y2B8 dose in these patients. (Phase I)
• Determine the immune response to this regimen, in terms of human anti-mouse and human anti-chimeric antibody formation, in these patients. (Phase I)
• Determine whether G-CSF and IL-11 can ameliorate the effect of the MTD of IDEC-^90Y2B8 on bone marrow function in these patients. (Phase I)
• Determine progression-free survival at 3 years. (Phase II)

OUTLINE: This is a phase I dose-escalation study of yttrium Y 90 ibritumomab tiuxetan (IDEC-^90Y2B8) followed by a phase II open-label study.

• Phase I: Patients receive rituximab IV on days 1 and 8, indium In 111 ibritumomab tiuxetan IV over 10 minutes on day 1 (for radioimaging), and IDEC-^90Y2B8 IV over 10 minutes on day 8. Treatment repeats 24-36 weeks later for a total of 2 courses in the absence of disease progression or unacceptable toxicity. Once the maximum tolerated dose (MTD) of IDEC-^90Y2B8 is determined, patients also receive filgrastim (G-CSF) subcutaneously (SC) daily beginning when absolute neutrophil count is less than 1,500/mm^3 and continuing until blood counts recover. Patients also receive interleukin-11 (IL-11) SC beginning when platelet count is less than 75,000/mm^3 and continuing until blood counts recover. Patients undergo PBSC transplantation only if marrow recovery is inadequate. Cohorts of 3-6 patients receive escalating doses of IDEC-^90Y2B8 until the MTD is determined. The MTD is defined as the dose preceding that at which at least 2 of 6 patients experience dose-limiting toxicity.

Once the MTD is determined, additional patients are accrued to determine the MTD of this radioimmunotherapy with the addition of the prophylactic cytokines, G-CSF and IL-11.

• Phase II: Patients receive rituximab, indium In 111 ibritumomab tiuxetan, and IDEC-^90Y2B8 IV as determined at the MTD in phase I. Treatment repeats 24-36 weeks later for a total of 2 courses in the absence of disease progression or unacceptable toxicity.

After completion of study treatment, patients are followed every 3 months for 1 year, every 4 months for 1 year, every 6 months for 1 year, and then annually for 2 years.

PROJECTED ACCRUAL: A total of 73 patients will be accrued for this study.