Lecture 9 Recombinant and Synthetic Vaccines II PDF

Lecture 9: Recombinant and synthetic Vaccines II  A RECOMBINANT SUBUNIT VACCINE FOR HEPATITIS B The hepatitis B virus, transmitted through contaminated needles and sexual contact Infects an estimated 200,000 Americans every year Of the 20,000 who subsequently b...

Lecture 9: Recombinant and synthetic Vaccines II  A RECOMBINANT SUBUNIT VACCINE FOR HEPATITIS B The hepatitis B virus, transmitted through contaminated needles and sexual contact Infects an estimated 200,000 Americans every year Of the 20,000 who subsequently become carriers, one in five dies of cirrhosis of the liver and one in 20 develops liver cancer  RECOMBINANT SUBUNIT VACCINE FOR HEPATITIS B Hepatitis B is a viral infection that attacks the liver and can cause both acute and chronic disease Hepatitis B is an important occupational hazard for health workers However, it can be prevented by currently available safe and effective vaccine RECOMBINANT SUBUNIT VACCINE FOR HEPATITIS B RECOMBINANT SUBUNIT VACCINE FOR HEPATITIS B  RECOMBINANT SUBUNIT VACCINE FOR HEPATITIS B Does not grow in tissue culture cells -only from the plasma of carriers Vaccines - by purifying the viral surface antigen or by inactivating living virus through chemical treatment (e.g., with formaldehyde) This source - quite limited use of the killed vaccine always carried the risk that not all the particles were inactivated  RECOMBINANT SUBUNIT VACCINE FOR HEPATITIS B The surface antigen (the surface glycoprotein) - an effective vaccine Clone the gene for this protein from the viral genome Genome consists of largely double-stranded DNA - codes for a core protein as well as for the major surface protein (S protein) Most of the protein subunits making up the viral envelope are S protein molecules (226 residues) RECOMBINANT SUBUNIT VACCINE FOR HEPATITIS B  RECOMBINANT SUBUNIT VACCINE FOR HEPATITIS B The DNA coding for the S protein was inserted into a YEp plasmid vector behind an effective yeast promoter and before a terminator (the construction of the first-generation recombinant plasmid) Yeast was chosen as the host was the expectation that it would glycosylate the envelope protein It did not do so, but the protein seemed to have folded properly Self-assembled -resembled an empty virus envelope 22 nm in diameter - indistinguishable from those found in the plasma of patients RECOMBINANT SUBUNIT VACCINE FOR HEPATITIS B  RECOMBINANT SUBUNIT VACCINE FOR HEPATITIS B Yeast-produced vaccine, although lacking the oligosaccharides, was as effective as the vaccine derived from human plasma In 1986, it became the first recombinant DNA–based vaccine licensed for use in the United States With earlier methodologies, about 40 L of infected human serum were required to produce a single dose of hepatitis B vaccine  RECOMBINANT SUBUNIT VACCINE FOR HEPATITIS B Now we can obtain many doses of the recombinant vaccine from the same volume of yeast culture A newer generation of vaccines is now produced using DNA that codes for PreS2 and PreS1 regions N-terminal parts of the protein appear to help in the build-up of immunity  RECOMBINANT SUBUNIT VACCINE FOR HEPATITIS B The plasmid also contains a promoter effective in animal cells and is introduced into a mammalian cell line the translation occurs on ribosomes attached to the endoplasmic reticulum protein products are exported - through the natural secretion pathway of the endoplasmic reticulum–Golgi apparatus glycosylated in the normal manner and enter the medium as empty vesicles These vaccines can produce immunity even in the 5% to 10% of the population - not respond to the older vaccines produced in yeast  POTENTIAL PROBLEMS OF RECOMBINANT SUBUNIT VACCINES Recombinant DNA subunit vaccines, when they are effective, have many advantages over traditional vaccines They can be produced easily safely inexpensively and are devoid of all the extraneous components of the pathogen that may cause undesirable side effects Furthermore, there is absolutely no possibility that a living pathogen will be present in the subunit vaccine  POTENTIAL PROBLEMS OF RECOMBINANT SUBUNIT VACCINES If subunit vaccines produced by recombinant DNA technology are really so effective and advantageous, why have they not yet replaced the traditional vaccines? Reason 1: Economic When a traditional vaccine – chemically inactivated diphteria toxoid - is effective and causes no major adverse reactions no vaccine manufacturer will be interested in spending the necessary funds to develop and test a recombinant DNA–derived substitute even though “genetically inactivated” toxins are known to be safer and usually more effective  POTENTIAL PROBLEMS OF RECOMBINANT SUBUNIT VACCINES Reason 2: Scientific Some genes have a low level of expression Some proteins fold improperly in a non-mammalian host, or when they are produced in unusually large amounts Many viral proteins, including proteins from the viruses that cause fowl plague, vesicular stomatitis, and herpes viruses, have been expressed successfully in E. coli; unfortunately, improper folding apparently prevents the production of many others  POTENTIAL PROBLEMS OF RECOMBINANT SUBUNIT VACCINES Cultured mammalian cells have been used to express genes for protective antigens - induce tumors when injected into appropriate hosts In order to prevent the introduction of any tumor-causing DNA - all of the host cell DNA must be removed from the vaccine, and this can be a difficult process Immunity produced is weak and of short duration