7 Novel Formulation Strategies For Influenza Vaccine.#MedTech #Biopharmaceutical #Manufacturing #Flu
1. Use of recombinant antigens
Recombinant DNA technology has enabled the production of several influenza virus antigens that are highly immunogenic. The immune responses include not only against HA but towards M2 ectodomains and HA stalk, that are cross reactive as well. Recombinant antigens are designed particularly to activate HA-stalk specific antibodies. Headless recombinant HA2 proteins are expressed on virus like particles which are able to induce immunogenic response. Virus like particles are also used to present the A-helix of HA2 that was able to activate stalk reactive antibodies. These antibodies were able to recognize many groups of influenza 1 and 2, HA subtypes. After recombinant VLP antigens, nanoparticles were utilized to increase immunogenicity of ectodomains of recombinant HA. Ectodomains of HA were fused to ferritin nanoparticles that induced high antibody titers against both the stalk as well as globular head domain.
Recombinant proteins are also being used to induce M2e specified immune response. Purified recombinant M2e proteins were joined with many adjuvants that induced M2e specific antibodies. Vaccines having covalently bound M2e antigen to an adjuvant or carrier protein, induce potent cross reactive immune response observed in mice. A shift to IgG2a was also reported which indicated skewing towards TH1, which induces cytotoxic T lymphocytes. Such additional immune responses widen the protection of these vaccine concepts.
2. Use of viral vectors
Engineered replication deficient viral vectors are now being used to produce influenza vectors when introduced in to the host cells. These immunogenic vectors can display multiple antigens. Modified Vaccinia Virus Ankara is one of the most widely studied viral vectors. This vector is used to display several influenza virus antigens such as M2e, HA, NP and M1. The most promising influenza vector vaccine is MVA-NP+M1, which is able to activate potent T-cell response. This vaccine did not cause any adverse effects related to vector vaccines. It is therefore, likely to become a universal influenza vaccine in near future.
Adenovirus has also been used as successful viral vectors. The adenoviruses with expressed HA or NP+M1 showed successful clinical studies.
Antivector immunity is one of the possible risks against vector based vaccines. This could induce tolerance to the vaccines. Adenovirus vector based HIV vaccines efficacy was negatively responded by both humoral and cell mediated immune responses.
3. Use of peptides
Peptides are able to induce both, B-cell and T-cell response against conserved epitopes. Peptide antigens can be long with multiple epitopes or minimal, which cause less immunogenicity. Liposomes are proven to be affective adjuvants for such peptides. These conjugates were remarkably able to induce CD8 memory T cells without contribution of CD4 T-cells. Aside from liposome, virosome have also been proven to be effective delivery systems. Virosomes along with the antigen are able to induce cytotoxic T cell response.
4. DNA & RNA based vaccines
DNA vaccines, unlike protein antigen, are able to produce antigen by the host itself. DNA copy is made of viral RNA of antigen of interest. This DNA copy is inserted into plasmid which is than inserted into bacteria for culturing. The plasmid is then purified and inserted into host for its expression. The concept was analyzed by epidermal administered vaccines having HA gene. Plasmid coated gold particles were applied on epidermis using gene gun. The vaccine was able to protect the individuals from influenza.
5. Adjuvant for influenza vaccine
Addition of adjuvant in vaccines has several advantages including induction of specific type of immune response like cell mediated, increased efficacy in elderly, dose sparing etc. Aluminum salt is one of the commonly used adjuvant along with influenza vaccine.
6. Improvement of stability in vaccines
Influenza vaccine shelf life is one year if stored refrigerated. Therefore, there is need of refrigeration during distribution and storage. This is costly yet not reliable. Therefore, there is a need to improve vaccines stability.
Liquid antigen stabilization is generally achieved by making it dry. But drying methods also have stress effects. Excipients addition such as sugars can stabilize influenza vaccines. During drying process, sugars form a glassy matrix which can protect the antigen by giving a physical barrier. Such glass matrix sometimes possesses high transition temperatures. This increase stability of vaccine against heat.
The aforementioned formulations are all novel and universal as they should be able to protect against all types of influenza strains. Many of such vaccines have entered clinical trials. Nonetheless, HA stalk reactive antibodies have yet not entered into clinical trials.