Memory and Vaccination

A booster dose of a vaccine is sometimes required to maintain sufficient immunity. The immune system has a memory and when the vaccinated individual is later exposed to the actual pathogen, the body can mount a rapid immune response and prevent the disease. This is called artificially acquired immunity. 

The award of a Beit Memorial Fellowship for medical research in 1933 provided him with more financial security and independence. Stacey moved to London and for the next 3 years worked full-time in Raistrick s laboratory. He was given the task of working on vaccines against typhoid fever. The work was successful eventually and the vaccines were used by the Royal Air Force and also were sent to the Air Force in New Zealand. Also, some advances were made in studies of the carbohydrate components of the vaccines. In addition to this research, he completed, by part-time study, the diploma course in bacteriology. 

The ideal of any vaccine is to provide life-long protection to the individual against disease. Immunological memory (Chapter 14) depends upon the survival of cloned populations of small B and T lymphocytes (memory cells). These small lymphocytes have a lifespan in the body of ca. 15-20 years. Thus, if the immune system is not boosted, either by natural exposure to the organism or by re-immunization, then immunity gained in childhood will be attenuated or lost completely by the age of 30. Those vaccines which provide only poor protection against disease have proportionately reduced time-spans of effectiveness. Yellow fever vaccination, which is highly effective, must therefore be repeated at 10-year intervals, whilst typhoid vaccines are only effective for 1-3 years. Whether or not immunization in childhood is boosted at adolescence or in adult life depends on the relative risks associated with the infection as a function of age. 

CpG ODNs are also effective as vaccine adjuvants to enhance adaptive TH1 cellular immune responses.104 In mice, CpG ODNs can trigger strong TH1 responses,105 enhancing the number and function of tumor-specific Cytotoxic T lymphocytes (CTLs) and IFN-y secreting T cells.106 This has resulted in therapeutic vaccines in mouse tumor models where no other approach has shown comparable efficacy, even with large (1 cm) established tumors.107 108 Even without a vaccine, CpG ODNs can induce CD8+ T cell-mediated regression of established tumors with durable memory responses.109... 

The process is as follows a piece of DNA, which encodes a gene for a surface protein of the virus, is incorporated into a plasmid. From a suitable vector, DNA is taken up by host cells and incorporated into their DNA. A large amount of viral protein is produced within the host cell, hydrolysed and the resultant peptide complexed with MHC class I molecules presented on the cell surface. This is then seen and responded to by the Th cells which proliferate and form memory cells that will result rapidly in the death of host cells infected by the virus in subsequent infections. DNA vaccines are safer than live-virus vaccines and, furthermore, several genes that produce different viral antigens can be constracted on the same piece of DNA. 

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