Vaccines

Vaccines

Vaccines
Viral vaccines consist of either virulent virus particles that have been inactivated, or of live particles of virus strains that have been weakened or attenuated, so that they no longer cause disease but immunize against the disease causing virulent strains.

The disadvantage of such conventionally made vaccines is that there is a small chance, that one or more virus particles have survived inactivation and vaccination with such a vaccine could therefore lead to isolated cases of disease.

Such accidents have indeed happened more than once, for example in cowherds vaccinated against foot (hoof) and mouth-disease virus.

A. Callus	B. Callus showing profuse rooting	C. Callus with many shoot buds

D. Same as after another three weeks. Note that the shoot buds have grown into plants	E. The Plant formed in cultures has developed a floral spike

Moreover, the viruses used to make vaccines are grown in animal cells and therefore the vaccines are very often contaminated with cellular material that can cause adverse immunological reactions in certain people.

Diagram of steps involved in micropropagation (aseptic multiplication) of plants. shoot multiplication is achieved through forced axillary branching adventitious budding from pieces of plants parts or callused tissue

Diagram of Steps Involved in Micropropagation (aseptic Multiplication) of Plants. Shoot Multiplication is Achieved Through Forced Axillary Branching Adventitious Budding From Pieces of Plants Parts or Callused Tissue

Since the proteins forming the coat of virus are the major antigens that induce antibody formation, it should be possible to use only the protein part and not the whole virus (which contains the genetic material, capable of causing the disease), to make a vaccine. This is where recombinant DNA techniques could be used by producing viral proteins from genetically engineered yeast and E. coli which in principle should be less expensive and might lead to the production of safer vaccines.

In this regard much work has been done on the cloning of the major antigenic viral protein (VPI) of the foot- and mouth-disease virus (FMDV) of cattle. The complementary DNA (cDNA) copies of the single-stranded genomic RNA (MW 2.6 x 108) of FMDV have been cloned in plasmid vectors of E. coli and synthesis of the VPI has been achieved in quantity of 1 to 5 million molecules per bacterial cell.

In addition to FMDV, there is also intensive work going on to use this technology to make vaccines for flu causing influenza virus (G.D. Searle), hepatitis B virus (Biogen/Merck) and Herpes simplex virus not only using E. coli but also potato tubers. One hurdle that has to be overcome in this approach is that the purified protein vaccines may be less immunogenic than the macromolecular assemblies of the same protein on the intact virus. Recent work on the expression of surface antigen particles in yeast has been promising in overcoming the above mentioned deficiencies in the E. coli expression of the antigenic protein.

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