The Changing Landscape of Global Vaccine Development and Market Potential - - BioPharm International

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The Changing Landscape of Global Vaccine Development and Market Potential


BioPharm International
Volume 20, Issue 10

Tumor cell vaccines can be generated from either the patients' own tissues (autologous) or other sources (allogeneic). An autologous tumor cell-based vaccine against melanoma, conjugated to a hapten (dinitrophenyl), demonstrated improved disease-free and overall survival as compared to historical controls.28 It is currently undergoing Phase 1 and 2 clinical studies. Canvaxin has been one of the most promising allogeneic melanoma vaccines investigated to date. It is an irradiated whole-cell vaccine derived from three different melanoma cell lines, and administered with BCG as adjuvant. These cell lines were screened to ensure the greatest likelihood that the vaccine would contain an antigen common to each recipient's tumor. Canvaxin was shown to express at least 20 distinct melanoma associated antigens, immune responses to which have been associated with survival in vaccine recipients.29

Dendritic cell based vaccines are under active development. Once dendritic cells are generated, they can be loaded with tumor antigens through the addition of tumor antigens to the culture media, through incubation with autologous or allogeneic tumor lysate, through gene modification with tumor antigen cDNA or autologous tumor mRNA, or through creation of tumor cell–dendritic cell hybrids. Provenge, a vaccine against prostate cancer developed by Dendreon, is prepared from a patient's own monocytes and then loaded with a tumor antigen (a fusion protein of full-length PAP and GM-CSF). In hormone-refractory prostate cancer patients treated with the vaccine, the median survival was significant longer than placebo.30

Plasmid DNA and viral vector based vaccines have been actively tested in clinical trials. Intramuscular or intradermal plasmid DNA administration is attractive because gene-transduction of the recipient's cells will result in continuous production of the tumor antigen. Recombinant viral vectors are commonly used to enhance gene transduction efficiency over plasmid DNA. A significant challenge of this strategy is the presence of pretreatment antiviral antibodies, which can neutralize the effects of subsequent treatment.

Preventive cancer vaccines are mostly in the early research stage. New breakthroughs will depend on an increased understanding of what tumor-specific antigens are expressed during the initial tumor development stage.

Malaria Vaccines

Malaria infection occurs in more than 30% of the world's population, almost exclusively in developing countries, and results in one million deaths annually. Most cases of the disease in humans are caused by four different species of the malarial parasite. There is currently no vaccine available for the parasite pathogens that infect humans, despite extensive efforts. The complex lifecycle of the malaria parasite contributes to the complexity of developing an effective vaccine. The parasite is spread by insect vectors that go through different stages and forms (intracellular, extracellular, sexual, and asexual) as they grow in the blood and tissues (primarily the liver) of the human hosts. Malaria is difficult to grow in large quantities outside the natural host.3

Malaria vaccine development has been focused on subunit vaccines targeting either the pre-erythrocytic or erythrocytic stage of the parasite lifecycle.31 The vaccine that is currently most advanced in development is the RTS,S vaccine in an AS02 adjuvant. It comprises portions of the circumsporozoite protein (CSP) linked to components of the hepatitis B surface antigen such that immunogenic particles are formed. The vaccine (given three doses over several months) provided protection in 41% of the individuals in sporozoite challenge studies. Subsequent field trials showed significant protection in adults and recently in children. This vaccine is believed to act mainly through antisporozoite antibodies, but perhaps also through T-cells that target infected hepatocytes.


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