RATIONALE: Vaccines may make the body build an immune response to kill tumor cells. Biological therapies, such as QS21, use different ways to stimulate the immune system and stop cancer cells from growing.

PURPOSE: Phase II trial to study the effectiveness of vaccine therapy plus QS21 in treating patients who have small cell lung cancer that has responded to initial therapy.

OBJECTIVES: I. Compare the antibody response after immunization with polysialic acid keyhole limpet hemocyanin (PSA-KLH) conjugate or N-propionylated PSA-KLH conjugate plus immunological adjuvant QS21 in patients with small cell lung cancer. II. Assess the clinical toxicities resulting from these regimens and from the immune response in this patient population.

OUTLINE: Patients receive polysialic acid keyhole limpet hemocyanin (PSA-KLH) conjugate or N-propionylated PSA-KLH conjugate plus immunological adjuvant QS21 subcutaneously weekly on weeks 1-4 and on weeks 8 and 16 for a total of 6 vaccinations. Patients are followed at 2 weeks, and then every 3 months for up to 1 year.

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

DISEASE CHARACTERISTICS: Histologically confirmed small cell lung cancer Must have completed initial therapy with or without radiotherapy and have achieved a complete response or partial response to therapy without subsequent evidence of disease progression Must have completed any radiotherapy including prophylactic cranial radiotherapy as part of the planned primary therapy

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: Karnofsky 70-100% Life expectancy: Not specified Hematopoietic: WBC at least 3,000/mm3 Lymphocyte count at least 500/mm3 Hepatic: Bilirubin no greater than 1.5 mg/dL SGOT no greater than 1.5 times upper limit of normal (ULN) Alkaline phosphatase no greater than 1.5 times ULN Renal: Not specified Cardiovascular: No New York Heart Association class III or IV heart disease Other: No known immunodeficiency or autoimmune disease No other active malignancies within the past 5 years except nonmelanoma skin cancer No clinically significant peripheral neuropathy Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY: Biologic therapy: See Disease Characteristics At least 4 weeks but no more than 12 weeks since prior initial therapy and recovered Chemotherapy: See Disease Characteristics At least 4 weeks but no more than 12 weeks since prior initial therapy and recovered Endocrine therapy: See Disease Characteristics At least 4 weeks but no more than 12 weeks since prior initial therapy and recovered No concurrent corticosteroids Radiotherapy: See Disease Characteristics At least 4 weeks but no more than 12 weeks since prior initial therapy and recovered No prior radiotherapy to the spleen Surgery: No prior splenectomy