EDIBLE VACCINES :
What is Vaccine?
A vaccine is a biological preparation which is responsible to improves immunity to a particular disease. It contains an agent that resembles a disease causing micro organism and if often made from weakened or killed forms of the microbe, its toxins or one of its surface proteins. The process of disturbing and administrating vaccines is referred to as vaccination., vaccination is a form of immunization. Immunization science of prophylaxis.
Jenner in 1796 studied that inoculation of virus prevents small pox in human.
Routes of administration including oral, nasal, intramuscular, subcutaneous & intradermal.
Types of vaccines:-
Prophylactic vaccines (Inactivate pathogens):
Prophylactic vaccines are responsible for stimulates an individual person’s immune response to protect from the effects of a future infections by Pathogens.
Ex:- To prevent the effects of a future infection by any natural or wild pathogen.
Therapeutic vaccine is one which is used to induce antiviral immunity. It stimulates the immune system to target an infected cell. Generally Therapeutic vaccines are used after infection occurs.
Ex:- vaccines against cancer
In the edible vaccine production transgenic plants and animals are used as vaccine production system. Edible vaccines are effective as a delivery vehicle for immunization. Edible vaccines are currently being developed for a number of human and animal diseases.
Concept of edible vaccine:
This is Developed by amtzen in 1990
Introduce genes of interest in to plants (transformation)
Genes expressed in the plant tissues edible plants (transgenic plants)
Genes encode putatively protective vaccine antigens from viral, bacterial & parasitic pathogens that cause disease in humans and animals
Ingestion of the edible part of the transgenic plant (oral delivery of vaccine).
- It should be effective in affordable.
- Vaccination should be simple.
- Should not contaminate the environment.
- Long lasting humoral and cellular immunity
- It should not cause problems in individuals with impaired immune system.
- It should have very lower levels of side effects.
- It should be non toxic or non pathogenic.
Mechanism of action :-
The goal of oral vaccination is to stimulate the tissue layer and general immunity against microorganism.
Edible immunogen once taken orally undergoes the manduction method and also the majority of plant cell degradation occur within the bowel as a results of action of organic process or microorganism catalyst on edible vaccine.
Peyer’s patches (pp) are enriched source of IgA producing plasma cell and have the potential to populate mucosal tissue and serves as mucosal immune effector side.
The breakdown of edible immunogen close to pp, consisting of the 30-40 lymphoid nodules on the outer surface of intestine and contain follicles.
These follicles acts as the site from which antigen penetrates the intestinal epithelium there by accumulating antigen with in organised lymphoid structure.
The antigen then comes in contact with M-cell.
M-cells passes the antigen to macrophages and B cell.
These B lymphocyte activates the lymph cell to produce response.
In this way the immunity if activated by the edible vaccine.
Developing an edible vaccine :-
Case – 1 :-
The entire structural gene is inserted in to plant transformation vector between 5’ and 3’ regulatory element.
This will allow the transcription and accumulation of encoding sequence in the plant.
Case – 2:-
Epitope with in the antigen are identified DNA fragment encoding these can be used to construct gene by fusion with a coat protein gene from plant virus.
Ex:-Tobacco Mosaic Virus or Cucumber Mosaic Virus
Method for transformation of DNA/ gene in to plant :-
- Plasmid vector carrier system :- Agrobacterium tumefaciens method
- Micro projectile bombardment method / gene gun method.
- Electroporation method.
1) Gene gun method :-
- Selected DNA sequences are precipitated on to metal (ex:- gold, tungsten) micro particles.
- Bombarded against the vegetable tissue with a particle gunat an accelerated speed.
- Micro particles penetrate the walls and release the exogenous DNA inside the cell where it will be integrated in the nuclear genome
- Produce large number of genetically identical crop.
2) Electroporation method :-
- Introduction of DNA in to cells by exposing them for brief period to high voltage electrical impulse which is thought to induce transient pores in the plasma lemma.
- The cell wall presents an effective barrier to DNA. Therefore it has to be weakened by mild enzymatic treatment so as to allow the entry in to cell cytoplasm.
Factors affecting efficacy of edible vaccines :-
- Antigen selection (safe, suitable, stable)
- Efficacy in model systems (small quantity)
- Choice of plant species (suitable, easy grown, storage, cost)
- Delivery and dosing issues.
- Safety issues (allergic toxic potential)
- Public prescriptions and attitudes to genetic modification.
- Quality control & licensing (constituent)
Candidate plants :-
- Banana–easily transformation
- Tomato–grow quickly
- Rice – high expectation of proteins
- Maize -cheaper non need to be refrigerated
- Potato– easily transformed
These antigens are currently being investigated for the development of a plant based malaria vaccine, merozoite surface protein MSP 4 & MSP 5 from plasmodium falciparum and MSP 4/5 from P. Yoelliwang et al have demonstrated that oral immunization of mice with recombinent MSP 4, MSP 4/5 and MSPI, co-administered with CTB as a mucosal adjuvant induced antibody responses effective against blood stage parasite.
Mice fed with tobacco expressing MV-H (measels virus heamogluttinin from edmonston strain) could attain antibody titers five times the level considered protective for humans and they also demonstrated secretory IgA in their faeces. Carrot, banana and rice are the potential candidates.
3) Hepatitis B
Significantly exceeded the protective level of 10 MIU/ml in humans. Potato based vaccine against hepatitis B have reported. The amount of hepatitis B Ag needed for one dose could be achieved in a single potato.
Plants are transformed with the gene encoding B sub unit of the E coli heat liable enterotoxin (LT-B). Transgenic potatoes expressing LT-B were found to induce both serum and Secretary antibodies when fed to mice., these antibodies were protective in bacterial toxin assay in-vitro., this is the first “proof of concept” for the edible vaccine.
Edible vaccines are going to be the effective and safer immunization of future generations. However edible vaccines need to overcome some obstacles.These vaccines would certainly overcome the side effects of present vaccines.
Padma malini, Prasanna lakshmi