Characterization of polyvalent allogeneic vaccines

Allogeneic polyvalent vaccines have significant therapeutic and manufacturing advantages including: (i) the presence of multiple tumour-associated antigens; (ii) the potential benefit of viable but non-replicating cells which can provide persistent antigen presentation to the patient, and (iii) the ability to be consistently manufactured in large lots that can be used to treat multiple patients and be fully tested before release. Canvaxin is an example of a multi-cell allogeneic, polyvalent active immunotherapy and has been extensively tested in phase I and II clinical trials. Results of these clinical studies show a statistically significant increase in median and five-year survival of stage III and stage IV surgically resected patients with melanoma as compared to matched historical controls. Phase III randomized double-blind trials in both stage III and stage IV patients with melanoma are in progress. Manufacture of allogenic whole cell vaccines requires identity testing and assurance that the vaccine is replication-incompetent. Since allogeneic whole-cell vaccines contain multiple antigens and patient immune responses may occur to several different antigens, it may be essential to test-for multiple antigens on the cells in the vaccine. This can be accomplished using quantitative flow cytometry to assess cell-surface antigens on viable cells and intracellular antigens on fixed and permeablilized cells. In addition, multi-cell allogeneic vaccines may also be assessed for content using PCR assays to identify unique cell line-associated DNA microsatellites to verify that each of the cell lines is present in the final product. Finally, a critical issue with allogeneic tumour cell vaccines is the assurance that irradiation of the final product is effective and that cells have been rendered replication-incompetent. This can be achieved using both high sensitivity visual assessment of the vaccine following extended culture and comparing cell cultures from irradiated vaccine and irradiated vaccine spiked with replication competent vaccine cells. This approach has been shown to have a limit of detection of one replication-competent cell in one million non-replicating, irradiated vaccine cells. DNA-based assays such as BrdU incorporation can also be used to assess cell replication, but in our hands these assays are generally less sensitive. Phase I/II data with Canvaxin are encouraging and support the further testing and extension of this approach to other tumour vaccines. In addition, the manufacture, testing, and release of whole cell active immunotherapies can be achieved using quantitative antigen testing and proliferation assays to ensure the consistent manufacturing necessary to produce a commercial product.