Cancer vaccines: an update with special focus on ganglioside antigens.

Vaccine development is one of the most promising and exciting fields in cancer research; numerous approaches are being studied to developed effective cancer vaccines. The aim of this form of therapy is to teach the patient's immune system to recognize the antigens expressed in tumor cells, but not in normal tissue, to be able to destroy these abnormal cells leaving the normal cells intact. In other words, is an attempt to teach the immune system to recognize antigens that escaped the immunologic surveillance and are by it, therefore able to survive and, in time, disseminate. However each research group developing a cancer vaccine, uses a different technology, targeting different antigens, combining different carriers and adjuvants, and using different immunization schedules. Most of the vaccines are still experimental and not approved by the US or European Regulatory Agencies. In this work, we will offer an update in the knowledge in cancer immunology and all the anticancer vaccine approaches, with special emphasis in ganglioside based vaccines. It has been demonstrated that quantitative and qualitative changes occur in ganglioside expression during the oncogenic transformation. Malignant transformation appears to activate enzymes associated with ganglioside glycosylation, resulting in altered patterns of ganglioside expression in tumors. Direct evidence of the importance of gangliosides as potential targets for active immunotherapy has been suggested by the observation that human monoclonal antibodies against these glycolipids induce shrinkage of human cutaneous melanoma metastasis. Thus, the cellular over-expression and shedding of gangliosides into the interstitial space may play a central role in cell growth regulation, immune tolerance and tumor-angiogenesis, therefore representing a new target for anticancer therapy. Since 1993 researchers at the University of Buenos Aires and the University of Quilmes (Argentina), have taken part in a project carried out by the <Centro de Inmunologia Molecular> (CIM) from La Havana, Cuba, to developed new strategies for specific active immunotherapy. The project included two ganglioside based vaccines and one anti-idiotypic vaccine. We focused on two antigens: first GM3, an ubiquitous antigen which is over-expressed in several epithelial tumor types; and a second one, N-Glycolyl-GM3 a more <tumor specific> molecule, not being expressed in normal tissues and recently found in several neoplastic cells, in particular breast, melanoma and neuroectodermal cancer cells. We developed two vaccines, one with each antigen, both using proteins derived from the outer membrane proteins (OMP) of Neisseria Meningitidis B, as carriers. We developed also the 1E10 vaccine; an anti-idiotype vaccine designed to mimic the N-Glycolyl-GM3 gangliosides. This monoclonal antibody is an Ab2-type-antibody which recognizes the Ab1 antibody called P3, the latter is a monoclonal antibody that specifically recognizes gangliosides as antigens. Since 1998 we initiated a clinical development program for these three compounds. Results of the phase I clinical trials proved that the three vaccines were safe and able to elicit specific antibody responses. In addition we were able to demonstrate the activation of the cellular arm of the immune response in patients treated with the GM3 vaccine. Although phase I trials are not designed to evaluate antitumor efficacy, it was encouraging to observe tumor shrinkage in some patients treated both with the GM3 and N-Glycolyl-GM3 vaccines. We have already begun a phase II program in several neoplastic diseases, with all three vaccines.