DNA Vaccines

LIMITATIONS OF TRADITIONAL VACCINES
Despite the best efforts of researchers around the globe, many dangerous diseases have evaded a suitable vaccine solution. In particular, vaccines against malaria and HIV remain intractable. One problem is that experimental vaccines may elicit an immune response inappropriate to the disease itself. Most vaccines preferentially induce the formation of antibodies rather than cell-mediated immunity. This is well suited for those diseases caused by toxins (e.g., diphtheria and tetanus), extra-cellular bacteria (e.g., pneumonia-causing agents), or even viruses that must pass through the blood to reach the tissue that is the target of infection (e.g., polio). However, some viruses act as an intracellular parasite and are out of the reach of antibodies, while they reside within their target cells. These infections must be addressed by the cell-mediated branch of the immune system, such as by cytotoxic T-lymphocytes (CTLs).

Yet, many vaccines do a poor job of eliciting cell-mediated immunity. An example is HIV, where much of the early work on developing a vaccine has focused on the antibody response in test animals. Antibodies may have a role in preventing infection or minimizing its spread, but cell-mediated responses are now recognized as being more important for pathogens that function by living in cells. There are thousands of patients dying of AIDS despite their high levels of anti-HIV-1 antibodies. (The most widespread test for HIV-1 infection does not detect the presence of the virus in cells, but the presence of antibodies against the virus). An additional obstacle in vaccine development is that some pathogens, such as influenza, HIV, West Nile, and many other viruses, evade the immune response system by rapid mutation of the specific pathogen proteins.

DNA VACCINES: ADVANTAGES AND LIMITATIONS
An alternative to conventional vaccines is DNA vaccines, an expanding area of vaccine development with a growing portfolio of candidates entering clinical trials. With DNA vaccines the individual is not injected with the viral antigen, but with DNA encoding the antigen. DNA vaccines are injected into patients either as “naked” DNA or DNA carried by a non-pathogenic virus vector. In either case, the DNA gains access to cells where the antigen protein is synthesized by normal cell mechanisms and presented to the immune system to stimulate the immune response to it. Because DNA can be synthesized to encode many different elements, there are many alternative ways to build a DNA vaccine.

As illustrated in the diagram below, nucleic acid is delivered to the cells either as DNA, RNA or as part of a specially modified virus that acts only as a carrier of the target DNA. It does not cause an infection because the DNA is selectively made to encode only the immune elements of the pathogen.

Once the nucleic acid is inside the cell, it uses the cell’s own biochemistry to make the protein coded in the vaccine nucleic acid (the “red diamonds” inside the cell in step 2). The cell then processes this protein, as it does all proteins, by digesting it into small pieces. A certain number of these pieces attach to specialized MHC proteins, and move to the outside of the cell. (In the diagram, the grossly exaggerated piece of the protein is represented in orange.) The protein is now free to interact with the outside world, and in particular the immune system. Depending on the type of cell that received the DNA, the antigenic protein will follow either MHC I or MHC II presentation. Class I MHCs are found in all cells; the MHC-IIs are only found in specialized “antigen presenting cells” (APCs) such as dendritic cells (“DCs”)

DNA vaccines have several distinct advantages: ease of manipulation, use of a genetic technology, simplicity of manufacture, and chemical and biological stability. However, the majority of work to date has been performed using laboratory animals, through which these vaccines have been able to protect against tuberculosis, SARS, smallpox, and other intracellular pathogens. Further, the recent approval of Vical’s melanoma vaccine for dogs validates the commercialization of DNA vaccines for use in large mammals.

DNA vaccines have been under development for approximately 15 years and have shown signs of real opportunity and promise to deal with many challenges in human health. Indeed, ITI’s own LAMP Technology has been incorporated in vaccines for cancer (prostate, AML, HPV), infectious diseases (influenza, dengue, West Nile, yellow fever), allergy (dust mite) and HIV.

With the many positive results, however, the DNA vaccine community remains confronted by the fact that commercialization of DNA-based vaccines through the FDA has been a difficult process and has yet to have a product reach the market in the US for humans. Why? We believe that there are two primary causes for the delay in DNA vaccines reaching the doctor’s office: first, most of the work has focused on applying the technology on diseases that present immense immunological challenges. Diseases such as cancer, HIV and hepatitis C have evaded traditional and non-conventional approaches alike and may never be successfully addressed through any type of vaccine. More recently, efforts have shifted to influenza, but again there is a concerted effort to focus on pandemic influenza rather than annual, seasonal influenza, which is still problematic for the conventional vaccine. However, the recent Vical DNA-based Phase I study for their pandemic influenza vaccine demonstrated an immune responses consistent with the development of protective antibodies.

The second reason that we believe DNA vaccines have yet to be commercialized is related to biology. Standard DNA vaccines result in the antigen being synthesized in the cytoplasm of the cells and access the immune system through MHC-I presentation. While this method is effective in eliciting a cellular immunity response, it is far less so with respect to antibody production and immunological memory, two key elements of a successful vaccine formulation.

ITI’s approach to commercializing a DNA vaccine addresses these two shortcomings by selecting a disease target in allergy that is highly problematic and has enormous market potential yet is in most cases not life threatening. Further, it is a simple matter of a skin test or of following symptom reduction to provide an easily monitored response in patients receiving therapy. The second problem – how antigens from DNA vaccines access the immune system – is addressed through the application of ITI’s LAMP-vax Technology which specifically directs the immune target antigen to the MHC-II compartment in the cell resulting in a more complete immune response.

The Company’s focus on allergy includes intense regulatory and clinical efforts to reach the market in about 4 years. Our FDA strategy is designed to move rapidly from initial clinical study that answers the key safety and clinical design questions into a Phase III within 18 months of first dosing. Our study approach also incorporates exploration of alternate routes of administration (e.g. transdermal, sublingual or intranasal delivery) to supplement or replace traditional intramuscular delivery. We believe the alternate routes of delivery will facilitate acceptance and be a key value driver into the doctor’s office while maintaining highly reimbursable and profitable allergy vaccine products.

Japanese Red Cedar Allergy

ITI is developing a therapeutic allergy vaccine, JRC-LAMP-vax, for Japanese red cedar pollen, a major environmental allergen in Japan and an industrial threat at saw mills in the United States and abroad. The Japanese cedar, also called Sugi tree, is an evergreen growing 30 to 50 meters tall. Its needles shift from a pale opal in the summer to a bright red toward the autumn. Japanese cedar is native to Japan and the coastal provinces of China, and is often cultivated in Europe and North America. The male Japanese cedar tree flowers between February and April. As male Sugi flowers disperse a small amount of pollen in early January, some Japanese cedar pollinosis patients will experience allergic symptoms as early as January.

Japanese cedar pollen is the most common allergen causing seasonal pollen allergy in Japan. It is the most common cause of seasonal allergic rhinitis and contributes significantly to sinusitis and rhinoconjunctivitis during spring. It is a risk factor for bronchial asthma in Japanese adult asthmatics. Pollen from this tree also affects the severity of atopic dermatitis and is an important factor in oral allergy syndrome. Population-based surveys in Japan in 2004 yielded a prediction that the prevalence of Japanese cedar pollen allergy among adolescents was 28.7% in metropolitan areas and 24.5% in the general population of urban areas. The prevalence increased 2.6-fold between 1980 and 2000.

LAMP-vax DNA Vaccines As Immunotherapy For Allergy
The underlying rationale is that allergen proteins encoded in a LAMP-vax DNA vaccine will preferentially activate allergen-specific T-helper type 1 (Th1) cellular responses with the production of interferons by antigen presenting cells (APC), natural killer cells (NK), and T cells, rather than the characteristic Th2-type responses, such as secretion of interleukin (IL) -4, -5, and -13, and the formation of immunoglobulin E (IgE) by B lymphocytes and the maturation and recruitment of eosinophils in late-phase reactions. It has been demonstrated that LAMP-encoded allergen- DNA vaccine that will facilitate trafficking into the MHC II processing and presentation pathway of APCs is critical for optimal and precise expression of Th1 immune responses.

Lysosomal Associated Membrane Protein or “LAMP” is a protein that localizes in antigen presenting cells (APC) to the same compartment as the Major Histocompatibility Complex Type II (MHC-II). The work in the laboratory of Dr. J. Thomas August at Johns Hopkins University showed that, when the protein sequence that would otherwise be expressed in the cytoplasm of the cell, was linked to the protein sequence of LAMP, the chimeric protein (LAMP-antigen) will migrate to the MHC-II lysosomes in APC’s. ITI’s LAMPvax vaccine formulations utilize this intra-cellular trafficking function to access the MHC-II pathway and in the case of allergy vaccines, convert the immune system response from an IgE allergen response to an IgG antigen response with the concomitant elimination of allergy symptoms. This conversion of the patient antibody responses from IgE to IgG is the principle therapeutic paradigm that allergist try to achieve with either sublingual exposure or intradermal injections of allergens during desensitization therapy; thus, we are not changing the current allergy therapeutic paradigm.

As shown in the figure below, the ITI approach to allergy immunotherapy involves attacking the problem using a traditional method – converting the immune response from an IgE mediated response to allergen to an IgG mediated response. LAMP-vax Allergy vaccines introduce the allergen (antigen) to the immune system through the MHC-II / Th1 pathway which favors the generation of an IgG response (see diagram below).

A Key Safety Advantage – No Free Allergen is Present in the Therapy
The structure of the LAMP-allergen chimera offers a unique safety feature that is not present in any other allergy vaccine formulation: the allergen is isolated in a specific cellular compartment (i.e., the lysosome) and is “encased” in LAMP. The diagram to the right shows the lysosome in a cell expressing allergen. The allergen is anchored in the lysosome with the tail of LAMP and then is linked to the remaining sequence of LAMP. Work with dust mite allergen showed that the LAMP sequence eliminates circulating free allergen; thus, allows patient exposure to allergens without the fear of atopic reactions during sensitization therapy with DNA-based vaccines. To see how this works, view the PowerPoint Presentation.

Short Ragweed Allergy

ITI is also developing a therapeutic vaccine for short ragweed, SRW-LAMP-vax. "Ragweed" refers to a group of approximately 40 species of annual weed plants belonging to the Asteraceae (Compositae) family. Most Ragweed species are native to North America. Ragweed pollinosis was absent in Europe, but following the importation of Short Ragweed onto the continent during World War I as a result of contaminated seed shipments, the plant has become a major source of pollinosis in areas in Europe where the plants grow. Short Ragweed (see below) is also a serious source of pollinosis in Japan.

Ragweed, and in particular Short Ragweed (Ambrosia artemisiifolia), is clinically the most important source of seasonal aeroallergens, as it is responsible for both the majority of cases and the most severe cases of allergic rhinitis. Ragweed pollen also contributes significantly to exacerbation of asthma and allergic conjunctivitis. Ragweed pollen has also been implicated in Eustachian tube dysfunction in patients with allergic rhinitis and contact dermatitis.