A press release from Advaxis, Inc., a North Brunswick, New Jersey company, says that the firm has filed an investigational new drug application with the FDA “to assess the safety, efficacy, and immunogenicity of vaccination with Listeria monocytogenes expressing human papilloma virus Type 16 E7 (Lovaxin C) for the treatment cervical intraepithelial carcinoma stage 2/3.”
So, let us get it straight. Now we have a company that tries to utilize a bacterium responsible for a common food poisoning to fight a common cancer? Indeed, and the reason is the strong T cell mediated immune response that the human body mounds against Listeria, hence the organism could potentially be used as a vaccine vehicle. According to Advaxis, the firm holds the rights to a portfolio of patents based on the work of Dr. Yvonne Paterson from the University of Pennsylvania, protecting its use of Listeria and listerial products in hopes of developing vaccines against a variety of diseases.
Advaxis, on its technology page, explains how it plans to exploit the pathogen:
Listeria has a unique life cycle. It infects Antigen Presenting Cells (APC), which are the cells that activate immune cells and tell them what to attack. Because of this, Listeria becomes perfectly positioned to have the maximum effect on the immune system in terms of directing it against specific targets. Even more unusual is Listeria‘s ability to stimulate both helper T cells (CD4+) and killer T cells (CD8+), since both are necessary for an antitumor response and it is unusual for a single pathogen to stimulate both in the way Listeria does.
Antigen Processing Cells normally engulf foreign elements to remove them from the body and present them to the immune system.
Following their ingestion, they are encapsulated and digested in a phagolysosome. Fragments of the digested invader are used to stimulate the immune system through the exogenous pathway (exogenous; since the invader came from outside the cell).
This pathway is associated with the formation of MHC class II complexes and the activation of specific CD4+ helper T cells directed against the invader. This is the most common response to a foreign invader.
A certain percentage of Listeria, however, are able to break out of the phagolysosomes and enter into the cytoplasm of the cell, where they are safe from lysosomal destruction. After escaping from the phagolysosome, the bacteria multiply in the cell. Additionally, Listeria is able to migrate into neighboring cells and spread without entering the extracellular space.
Once in the cytoplasm, Listeria is capable of stimulating the immune system via the endogenous pathway (endogenous; because Listeria is now living within the cell). The endogenous pathway is associated with MHC class I complex formation and resultant CD8+ killer T cells.
Listeria also has other effects; such as the maturation of dendritic cells, which is most powerful APC and is essential for a strong antitumor response.
Thus, Listeria has the ability to stimulate multiple limbs of the immune response simultaneously and in an integrated way that serves to bring a number of immune mechanisms together to attack cancer…
The details of Listeria intracellular activity are important for understanding Advaxis technology. Inside the phagolysosome, Listeria produces and secretes the virulence factor listeriolysin O (“LLO”), a protein that generates a hole in the membrane of the phagolysosome and allows the bacteria to escape into the relatively safe cytoplasm. Once in the cytoplasm, however, LLO still retains some activity and is also capable of creating a hole in the cell membrane. This would destroy the host cell, and spill the bacteria back out into the intercellular space where it would be exposed to more immune cell attacks and destruction. To prevent this, a sequence of approximately 30 amino acids is present in the LLO protein, called the PEST sequence (for the predominant amino acids it contains). This PEST sequence is recognized by the host cells and targets the LLO protein for rapid digestion, thus giving LLO a very short life span. The benefit for the Listeria is that the LLO is neutralized and the bacteria can continue to prosper inside the cell, which also remains alive.
Since the activation of the immune system is also dependent upon the digestion of antigens and the creation of small fragments that can be used as recognition sites for an immune attack, Advaxis reasoned that we might use this mechanism that rapidly breaks down LLO to also break down antigens, which are released in both the phagolysosome and in the cytoplasm of the APC. To do so, we created a proprietary method in which we engineer Listeria to secrete a “fusion protein” which is comprised of a specific antigen that we wish to use as the focus for an immune attack fused to a segment of LLO. In this way, we can accelerate the breakdown of antigens into immuno-active fragments because the PEST sequence of the fusion protein is recognized and the secreted antigen fusion protein is routed for rapid degradation, thus accelerating both the rate at which antigen fragments are created and the speed with which they are delivered to the immune system for use in the creation of recognition molecules that activate T cells. Furthermore, the fusion of the antigen to LLO is essential to promote the secretion of the antigen, because the signal sequence needed for LLO secretion is kept intact in the fusion protein.
To read more, head on to Advaxis technology page…
Press release: Advaxis Files Investigational New Drug Application with U.S. Food and Drug Administration…
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