RATIONALE: Biological therapies, such as antithymocyte globulin, may stimulate the immune system in different ways and stop cancer cells from growing.

PURPOSE: This phase II trial is studying how well antithymocyte globulin works in treating patients undergoing stem cell transplant for multiple myeloma.

OBJECTIVES:

Primary

• Determine the response rate at 4 weeks in patients with multiple myeloma treated with anti-thymocyte globulin at least 4 to 6 weeks prior to undergoing conditioning therapy for allogeneic or autologous stem cell transplantation.

Secondary

• Determine the toxicity of this drug, in terms of formation of antirabbit antibodies, in these patients.

OUTLINE: This is an open-label, multicenter study.

Patients receive anti-thymocyte globulin IV over 6 hours on day 1 and over 4 hours on days 3 and 5. Treatment begins 4 to 6 weeks prior to undergoing conditioning therapy for autologous or allogeneic stem cell transplantation.

After completion of study treatment, patients are followed at 28 days.

PROJECTED ACCRUAL: A total of 12 patients will be accrued for this study.

DISEASE CHARACTERISTICS:

• Histologically confirmed multiple myeloma
• Candidate for autologous or allogeneic stem cell transplantation within 1 to 3 months after study treatment
• Measurable disease, defined as serum monoclonal protein ≥ 1 g/dL OR urinary light chain excretion = 500 mg/24 hours
• No malignant CNS disease

PATIENT CHARACTERISTICS:

• Life expectancy ≥ 6 months
• Absolute neutrophil count ≥ 1,000/mm³
• Platelet count > 50,000/mm³
• Creatinine ≤ 2 mg/dL
• Hepatic function ≤ 2 times upper limit of normal
• DLCO ≥ 50%
• No active infection
• No hypersensitivity to rabbit proteins
• No symptomatic hyperviscosity syndrome
• Negative pregnancy test

PRIOR CONCURRENT THERAPY:

• More than 28 days since prior chemotherapy, including prednisone (20 mg equivalent/day)
• No prior anti-thymocyte globulin
• No concurrent radiotherapy