Adjuvant active specific immunotherapy for human colorectal cancer: 6.5-year median follow-up of a phase III prospectively randomized trial.

PURPOSE: Patients with colon or rectal cancer were entered onto a prospectively randomized, controlled clinical trial of active specific immunotherapy (ASI) with an autologous tumor cell-bacillus Calmette-Guérin (BCG) vaccine. We investigated whether ASI could improve disease-free status and survival. PATIENTS AND METHODS: Ninety-eight patients with Dukes' stage B2-C3 colon or rectal cancer were randomized into groups treated by resection alone or resection plus ASI. Eighty patients met all eligibility criteria. All patients with rectal cancer were to receive 50 Gy of pelvic irradiation. Analysis of distribution of survival and disease-free survival was made on all eligible patients until December 31, 1990. RESULTS: As a single study, no statistically significant differences were detected in survival or disease-free survival for all 80 eligible patients. However, since it was recognized at the outset that there were treatment differences, in that rectal cancer patients were to receive postimmunotherapy radiation, it was considered that a cohort analysis of the colon and rectal cancer patients might be informative. With a median follow-up of 93 months, there is a significant improvement in survival (two-sided P = .02; hazards ratio, 3.97) and disease-free survival (two-sided P = .039; hazards ratio, 2.67) in all eligible colon cancer patients who received ASI. With a median follow-up of 58 months, no benefits were seen in patients with rectal cancer who received ASI. CONCLUSION: This study suggests that ASI may be beneficial to patients with colon cancer.

More on the relevance of animal tumor models: immunogenicity of transplantable leukemias of recent origin in syngeneic strain 2 guinea pigs.

The immunogenicity of four transplantable leukemias was evaluated in syngeneic Sewall-Wright strain 2 guinea pigs. The L76 and KSL leukemias are considered appropriate models for the assessment of immunogenicity because of their recent origin and unknown (natural) etiology. The chemically induced K77 leukemia of recent origin and the long-passaged L2C leukemia of unknown etiology could be classified as experimental tumors prone to artifactual immunogenicity. Our studies clearly show that naturally occurring guinea pig leukemias are potentially immunogenic, although to a lesser degree than experimental leukemias. These findings are in contrast to previous studies in mouse and rat tumor models, which showed that naturally occurring tumors were essentially nonimmunogenic, thereby raising questions about the relevance of animal tumor models to human cancer.

Development of a model of chronic lymphocytic leukemia in inbred strain 2 guinea pigs.

A new transplantable leukemia (KSL) of unknown etiology that arose in a female Sewall-Wright strain 2 guinea pig is described. KSL cells morphologically resembled medium to large lymphocytes, displayed surface Ia antigen and receptors for complement and for the Fc portion of immunoglobulin, and synthesized surface immunoglobulin (IgM). These characteristics suggest a leukemia of B-lymphocyte origin. KSL cells were shown to be sensitive in vivo to both cyclophosphamide and 1,3-bis(2-chloroethyl)-1-nitrosourea; however, neither drug effectively prevented eventual recurrence of the disease. KSL leukemia was also shown to be distinct from another guinea pig lymphatic leukemia (L2C) with respect to cell morphology, antigenicity, and in vivo growth rate. In this last respect, KSL appeared more closely related to the chronic lymphocytic leukemias. Thus KSL is the first chronic lymphocytic leukemia in the guinea pig to be characterized; it is also the only guinea pig model of lymphatic leukemia that is distinct from L2C leukemia currently available for study.

Synergistic effects of active specific immunotherapy and chemotherapy in guinea pigs with disseminated cancer.

Sewall Wright strain 2 guinea pigs bearing pulmonary metastases of the syngeneic line 10 (L10) hepatocarcinoma were treated with a vaccine composed of 10(7) bacillus Calmette-Guérin admixed with 10(7) x-irradiated L10 tumor cells beginning 10 days after tumor inoculation. Although this treatment failed to cure most of the guinea pigs of their metastatic disease, histologic examination of the pulmonary tumors in the vaccinated guinea pigs provided evidence of a cell-mediated hypersensitivity response that disrupted the normally compact architecture seen in control tumors. When a monoclonal antibody against the L10 tumor was injected i.v. to evaluate the vascular permeability of the tumors, significantly more antibody localized in tumors of vaccinated guinea pigs than in tumors of untreated controls. These results suggested that blood-borne substances could be delivered more efficiently to L10 metastases after the tumor-bearing guinea pigs had been treated with vaccine. To determine whether such increased vascular permeability would enhance the antitumor effects of chemotherapeutic agents, combined immunotherapy and chemotherapy studies were performed. Although cyclophosphamide treatment by itself did not cure L10-bearing guinea pigs, cyclophosphamide used in conjunction with prior immunotherapy increased the survival rate of animals to more than twice that of animals treated with immunotherapy alone (74 vs 33%). These results suggest that one mechanism by which active specific immunotherapy enhances chemotherapy of disseminated tumors is by rendering tumor foci more permeable to subsequently administered cytotoxic drugs.

Separation of guinea pig peripheral blood lymphocytes by discontinuous density gradient centrifugation using Ficoll-metrizoate.

We present a simple method for the recovery of lymphocytes from guinea pig peripheral blood by discontinuous density gradient centrifugation using Ficoll-metrizoate solutions. This technique is formulated specifically for the routine preparation of guinea pig lymphocytes for in vitro cultivation and is capable of recovering 40-60% of available lymphocytes. Whole, heparinized (10-100 U/ml) blood was drawn from strain 2 guinea pigs by cardiac puncture, diluted 1 : 4 with Ca2,Mga free Hanks' balanced salt solution (CMF-HBSS) containing EDTA (5 mM) and gentamicin (50 microgram/ml), and incubated at room temperature for 30-60 min to promote leukocyte disaggregation. Five volumes of diluted blood were layered onto 2 vol of Ficoll-metrizoate adjusted to a density of 1.107 g/ml with sodium metrizoate solution. A band of mononuclear cells (80-90% lymphocytes, 10-20% monocytes, and less than 2% granulocytes) formed at the interface after centrifugation (400 X g, 20-40 min, room temperature). More than 95% of the cells were viable by trypan blue exclusion. Lymphocytes recovered from as little as 3-5 ml whole blood were more sensitive to antigen- or mitogen-activated transformation than leukocyte suspensions obtained by dextran-citrate sedimentation with or without nylon column filtration.