A recent study has reported the use of tattoo in boosting immune response to DNA vaccines. Pokorna et al1 revealed this startling discovery in their recent paper published in the online open access journal Genetic Vaccines and Therapy. At last, tattoo which used to be mere fashion is now synonymous with medicine and tattooists are now taking the centre stage in science. The emergence of deoxyribonucleic acid (DNA) vaccines over the past decade appeared to be a promising approach for inducing better and lasting immune responses as compared to traditional vaccines e.g. sub-unit, live, attenuated vaccines etc2. A DNA vaccine contains a nucleotide sequence encoding a key antigenic determinant from a given pathogen, which is then injected into a host, then transcribed and translated by host cells into protein which is degraded into peptides that are foreign to the host3. The essence of this is to produce protein that induces immune response in the host against a given pathogen and therefore confers immunity on the host. DNA vaccine technology offers considerable promise for the improvement of existing immunisation strategies. In 1990, Jon Wolff 4 and colleagues found that intramuscular injection of naked DNA into mice could be taken up by the cell and expressed in minute amount. Since it had been shown that simple injection of plasmid DNA vectors or naked DNA could stimulate both cellular (cell-mediated) and humoral (antibodies) responses, various studies have come up on how to optimise the efficacy of DNA vaccination. It is assumed that the slow development of immune responses after DNA vaccination is due to the fact only a small number of cells take up the injected, foreign DNA. In a recent study by Pokorna et al.1, they were able to show that vaccination via tattooing could induce stronger humoral and cellular immune responses than intramuscular delivery supported by molecular adjuvants. This discovery has opened door for better understanding on how to boost the efficacy of DNA vaccines for better preventive and therapeutic immunization. This discovery has shown that tattoos are not just for fashion but an important phenomenon in medicine and this may cause “attention shift to the tattooists”

Tattooing is an invasive procedure involving a solid vibrating needle that repeatedly punctures the skin, causing wound both to the epidermis and the upper dermis in the process and results in cutaneous (skin) inflammation and healing5.

Picture showing human skin being tattooed with the tattoo device (Not able to load picture)

Modified tattooing devices have been used in medical research for delivery of various materials into the skin such as viruses to induce papillomas in mice and rabbits, pigments to study processes associated with cosmetic tattooing and DNA for prospective gene therapy of skin disorder. Although DNA delivery by tattooing seems to produce better humoral and cellular immune response as compared to other methods of DNA vaccines delivery, Pokorna and others are able to show through comparison that the immune response generated by tattooing even produces better immune response than DNA vaccines plus adjuvants delivered intramuscularly. They compared DNA immunisation protocols using different routes of administration (intramuscular injection versus intradermal tattoo) and two types of molecular adjuvants (cardiotoxin pretreatment versus granulocyte macrophage colony-stimulating factor (GM-CSF) DNA co-delivery) using mouse model. Gene encoding the L1 major capsid protein of the human papilloma-virus type 16 (HPV 16) was used as the model antigen. This had been shown to be highly immunogenic in previous experiment using intramuscular administration of DNA in combination with cardiotoxin pre-treatment.  PUF3L1h and pBSC/GM-CSF plasmids were used for the induction of antigen-specific immune responses and as adjuvant respectively.

To evaluate immune response upon DNA vaccination using the different protocols, the authors immunised anaesthetised mice with DNA four times. Each of them received 50 micrgrams of pUF3L1h plasmid (six groups) or pBSC/GM-CSF plasmid (control group) as a single immunisation dose (Days 0, 14, 28 and 98). Another two groups of mice were given a mixture of 50 microgram of pUF3L1h DNA and 50 microgram pBSC/GM-CSF DNA each in a single dose. The tattooed DNA was delivered in a 10 microlitre TE (Tween 80 and diethyl ether) buffer for single plasmid administration or a 20 microlitre TE buffer for the mixture of plasmids in one or two drops to the shaved skin, this was followed by tattooing with a 7-linear needle using a commercial tattoo machine. Although the procedure was well tolerated, swelling and reddening of the skin was observed. In addition, some mice were pretreated with 50 microlitres of cardiotoxin five days prior to the first DNA immunisation.

Blood collection from these immunised mice was done 10 days after the third and nine days after the fourth DNA immunisation. An antigen capture ELISA (enzyme-linked immunosorbent) assay was used for detection and end point titration assays of HPV 16 L1-specific antibodies, and an ELISPOT assay to measure L1-specific cellular immune responses.

The researchers found that efficacy of DNA vaccine delivered intramuscularly was substantially enhanced with cardiotoxin pretreatment or GM-CSF DNA co-delivery but had virtually no effect on the intradermal tattoo vaccination. Both adjuvants had better effect after three rather than four immunisations. However, three immunisations using tattooing method without an adjuvant induced significantly higher L1-specific humoral immune responses than three or four intramuscular DNA injections supported by molecular adjuvants. Tattooing also triggered significantly higher L1-specific cellular immune responses than DNA combined with adjuvants and delivered intramuscularly.

Other methods such as in vivo electroporation (Mechanical method used to introduce polar molecules into a host cell through the cell membrane) and gene gun delivery are used to deliver DNA vaccines into the host cells. However, intramuscular administration of DNA vaccine by simple injection is considered to be one of the less effective routes of DNA vaccination6, 7. Although intramuscular DNA immunisation has the potential to result in conventional priming as well as cross priming both at the protein and nucleic acid levels, effort is being geared towards improving uptake  and the expression of plasmid in professional antigen presenting cells8. What brought tattooing to limelight in science is the recent knowledge about its usefulness in generating better immune response upon DNA vaccination. Several groups have been working on how to trigger better immune response upon DNA vaccination9, 10. They combined their knowledge of immunology and DNA technology to explain what happen upon delivery of DNA into the host cells. They found that when the DNA vaccine is introduced into the cell through intramuscular injection, the genes are transcribed and there will be protein production in the cytoplasm. The secreted proteins induce cytokines, T helper cells and antibodies that will react and eliminate the pathogen. These cytokines or the DNA itself in the immune cascade activates natural killer cells leading to killing of virus infected cells8. It is conceivable that tattooing generates robust local tissue injury which attracts leukocytes and this leads to local release of cytokines.

2. Mechanism of action of DNA vaccines in a muscle cell (Not able to load picture).

The plasmid DNA is introduced into the nucleus of the cell. It is transcribed and translated to make pathogen-derived protein in the cytoplasm. Some of this protein moves outside of the cell, where it is either bound by antibody molecules on B cells or phagocytosed by macrophages. Either way, the protein gets digested inside these cells into small peptides and placed in the binding groove of a cell surface protein called the class II major histocompatibility complex (MHC II), much like a hot dog fits into a bun. T cell receptors (TCRs) on the surface of helper T cells can recognize these peptides as being foreign to the body, and therefore from an invading pathogen. Once the peptides are bound and recognized as foreign by the TCR, the helper T cell releases a variety of interleukin (IL) proteins to stimulate both arms of the immune system (humoral and cellular) to kick into action. (Brookscole)

The next task for Pokorna and colleagues was to determine the mechanism by which DNA tatto0ing in mouse model induces superior immune response to intramuscular injection. They could only speculate that this may be due to:(a) better uptake of the DNA by non-antigen presenting cells (b) better uptake of DNA by antigen-presenting cells (c) the duration of [removed]d) the induced traumata(pain) accompanying the tattooing (causing sufficient inflammation to prime the immune system). The larger surface area available for transfection of DNA into cells when using tattooing method may as well substitute for the role of GM-CSF and cardiotoxin (adjuvants), which is to attract antigen-presenting cells to the application site when using intramuscular delivery method. Taking these facts into account, it may be appropriate to say that the larger the surface area cover by DNA vaccines, the better the immune response (humoral and cellular) induced.

Although this study is an eye opener and provides startling revelation as to the importance of tattoo to science, the social and ethical aspects of this study are too important to be neglected. Despite the fact that tattooing method of DNA delivery is cost effective and the method of application is standardised, the major disadvantages are (1) the local traumata (pain) induced and (2) the procedure is somewhat cumbersome. These were also noted by the researchers. The implication of this is that this wonderful method that is assumed to be the much needed solution to the elusive approach at inducing better immune response upon DNA vaccination may end up not being useful for prophylactic vaccination in humans. Though it may be useful for routine vaccination in animals such as cattle and therapeutically in humans says the researchers. The pain that may accompany this method of DNA delivery is an issue to be considered critically. The researchers suggested a role for tattoo delivery in therapeutic vaccination for humans because of the faster and stronger immune response it induces. However, the benefit-risk ratio has to be considered before it can be generally accepted as a method of DNA vaccines delivery. Scientists may be left with little or no option as it stands now than to embrace tattooing as a way of getting out the best from DNA vaccines. The many advantages of DNA vaccines include: (1) rapid and large scale vaccine production is much cheaper than for traditional vaccines (2) these vaccines are also temperature stable; in contrast many traditional vaccines require cold storage and have a limited lifetime. This study may have provided solution to the technical hurdle faced by scientists in finding a way to efficiently deliver DNA into human cells and making sure the gene is expressed once it is inside the cell etc.

I wonder if anyone would want to have DNA vaccine delivered by tattoo machine for infections such as common cold. However, for HIV/AIDS people would dare to queue to have the tattoo because its benefit outweighs its pains. A very important question still begging for answer is: How ethical is DNA vaccines delivery by tattooing?

This study establishes a strategy for generating robust humoral and cellular immune responses in mice using DNA vaccine. Further work will be required to establish the efficacy of this straightforward and inexpensive strategy in humans.

References

1. Pokorna D. et al (2008). Genetic Vaccines and Therapy 6:4 (doi:10.1186/1479-0556-6-4)

2. Bin A.D. et al. (2005) Nature med. 11:899-904

3 .McDonnell and Askari (1999) Medscape General Medicine at http://www.medscape.com/viewarticle/408733

4. Wolff J.A. et al. (1990) Science 247:1465-1468

5. Gopee N.V. et al. (2005) Toxicol. Appl. Pharmacol. 209: 145-158

6. Reuter J.D. et al (2001) J. Virol. Methods 98: 127-134

7. Corder W.T. et al. (1996) Ann Allergy Asthma Immunol. 77: 222-226

8. Donnelly J.J. et al. (2005) J. Immunol. 175: 633-639

9.  Davis H. L. and McCluskie M.J. (1999) Microbes and Infection 1: 7-21

10. Rice J. et al. (2008) Nature Reviews 8:108-120

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