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Genetically Modified Vaccines, 2005

Friday 25 May 2007

 

Such vaccines carrying chimerical organisms have also been designed for man. A vaccine against rotaviruses, that are responsible for large numbers of diarrhoea cases worldwide, has been obtained by associating human genes with a simian rotavirus strand. Marketed in the United-States, it was about to be commercialized in Europe, when it was hastily withdrawn in July 1999, only a few months after it had been authorized, because some of the newborns vaccinated were suffering from diverticulosis. 

 

For these vaccines based on Chimeric organisms, the same problems than those encountered with plants occur: the dissemination of genes within a human or animal population with the risk of uncontrollable recombinations.

Obtaining antigenic proteins 

The most well known recombinant vaccine is the anti-hepatitis B type (GenHevac B®, Engerix B®, HBVax DNA® or Recombivax®). In that case, the genetically modified micro-organism is not directly used, but the product it generates is. The technique consists in making the cellular system express the surface protein of the virus of hepatitis B (HBs) thanks to a recombinant plasmid introduced in its cells.

In the case of GenHevac B®, the consecutive operations are the following:

 

  • Creation of two recombinant plasmids from Escherichia coli plasmids (colon bacillus) including an ampicillin-resistant gene and in which an S gene of the hepatitis B is inserted for one, and a methotrexate-resistant gene (dhfr) for the other. Each of these genes is then placed under the control of a viral promoter coming from the simian virus SV40 for the gene S and the MMTV virus (Mouse Mammary Tumour Virus) for the dhfr-resistant gene. SV40 regulator sequences complete these assemblies. - The fusion between the two plasmids gives the “pSVS dhfr” recombinant plasmid which is cloned in bacteria, the ampicillin-resistant gene making it possible to sort out the bacteria that have incorporated the plasmids.
  • The plasmids are then transfected into the continuous cell lines CHO (Chinese hamster ovary lacking dhfr). After transfection, the cell cultures are treated with methotrexate: the cultures /the cells that have incorporated pSVS dhfr plasmids can resist to this poison, and are capable of translating the S gene into an HBs protein. 

 

 

The other anti-hepatitis B vaccines are obtained on the same principle, but with a few differences, the main one being the cellular system of expression of the S gene which is based on yeast. 

 

What are the risks of these vaccines? 

In a  dossier from the French Centre for Information on Hospital Drugs (CNIMH) devoted to the vaccines against hepatitis B, it appears that the vaccines contain between 1 and 30 picograms of residual DNA. This DNA comes both from the cell cultures (some of which, like the CHO cells, have characteristics of cancer cells) and the necessary manipulations for manufacturing recombinant plasmids. Such DNA impurities constitute an appreciable amount since one picogram of DNA represents one a billion of basic pairs. The main risk is for the DNA to incorporate itself into the genetic inheritance of the recipients, and therefore to induce insertion-based mutations than can take part in the onset of cancers. This risk was already mentioned as early as 1987 by WHO in an expert report on the “acceptability of cell cultures for the production of biological substances”, a report in which one can read: 

 

“One of the major issues is, in the long term, a risk of malignancy of an heterogeneous DNA contaminant, in particular if it turns out to contain coding sequences or potentially oncogenous regulator sequences. This is really preoccupying as hundreds of thousands of healthy people, mostly newborns, may be vaccinated with products born from continuous cell lines, or will receive them anyway.” […]


“Several points must be taken into account when assessing the risks”: 


First of all calculations are based on the premise that the tumoral induction factor risk decreases linearly with the DNA concentration. The premise is not necessarily true, since a given quantity of DNA that has no measurable biological effect during standard trails/experiments because its concentration is too low, may still have some effect in certain conditions or on certain organs or tissues.


Secondly, we do not know whether the risk associated to repeated expositions to DNA will have a cumulative effect or not.


Thirdly, one must consider the possibility that DNA preparations that do not induce tumours in experimental systems could, in man, induce modifications that are likely to increase the incidence of the onset of tumours after long periods of latency .


Fourthly, the experiments conducted on small lifespan animals do not make it possible to assess the long term effects of acquired DNA sequences”.

 

What was the purpose with these anti-hepatitis B vaccines? To curb a widespread disease? There is no such thing according to a clinical hepatology work: In low endemic countries (including France) “hepatitis B is essentially an adult disease, typically occurring in specific high risk groups. In such countries the prevalence of chronic carriers is low, cirrhosis and hepatocellular carcinoma associated to hepatitis B virus are rare and the mother-to-child transmission very unusual.”

 

The French health authorities have let themselves be seduced by the pharmaceutical industry, but thatwas not the case for Great-Britain, which has the same prevalence of hepatitis B than France, but where the authorities do not consider hepatitis B to be a major public health issue.