Tag Archives: blindness

Visionary Science: Gene therapy saves sight thanks to animal research

Yesterday the BBC News and Guardian Newspaper reported that a team led by surgeon Professor Robert Maclaren at the Oxford Eye Hospital had succeeded in using gene therapy to halt the decline in vision in six patients with the progressive eye disorder choroideremia.

All six patients were taking part in a clinical trial, and what was especially exciting was the sustained improvement in vision in the two patients whose vision had deteriorated the most. This is great news for the patients themselves, and as the technique is likely to be applicable to many different genetic eye disorders it is also good news for many millions of people who may benefit in future. It is also an excellent example of how years of research in mice, dogs and monkeys can lead to an important clinical advance.

Choroideremia is caused by a defect in the CHM gene, which encodes the Rab escort protein 1 (REP1), and lack of this protein leads to gradual degeneration of the retinal epithelium layer  (RPE) and rod photoreceptor cells in the eye, causing a progressive decline in vision that usually starts with night blindness and loss of peripheral vision, and eventually leads to total blindness.

To halt this decline Professor Maclean’s team used a vector  based on a modified adeno-associated virus serotype 2 (AAV2) which could express the healthy CHM gene in the eye and produce REP1.  Why did they choose AAV2 out of all the potential virus vectors available? The Lancet paper reporting on this trial cites a key study published in the Journal of Molecular Medicine in  2013* by Professor Maclaren and colleagues, which describes the development and evaluation of the vector used in the trial. In their introduction and discussion they discuss the rational for choosing the AAV2 vector:

With a functional fovea, safety with regard to avoiding a vector-related inflammatory reaction is of paramount importance. Two recent clinical trials had demonstrated that serotype 2 adeno-associated viral (AAV2) vectors have no long-term retinal toxicity when administered at the dose range 1010–1011 genome particles [12, 13]. Importantly, in addition to transducing the RPE, AAV2 is also known to target rod photoreceptors efficiently in the non-human primate [14], providing the ideal tropism for a CHM gene therapy strategy.

… Although one might argue that other serotypes such as AAV8 may be more efficient in targeting photoreceptors, AAV2 with the CBA promoter remains the gold standard for retinal transduction as evidenced by the sustained vision in Briard dogs treated with AAV2 vector over a decade ago [35].

12. Cideciyan AV, Aleman TS, Boye SL, Schwartz SB, Kaushal S, Roman AJ, Pang JJ, Sumaroka A, Windsor EA, Wilson JM, et al. Human gene therapy for RPE65 isomerase deficiency activates the retinoid cycle of vision but with slow rod kinetics. Proc Natl Acad Sci U S A. 2008;105:15112–15117. doi: 10.1073/pnas.0807027105.  13. Jacobson SG, Cideciyan AV, Ratnakaram R, Heon E, Schwartz SB, Roman AJ, Peden MC, Aleman TS, Boye SL, Sumaroka A, et al. Gene therapy for Leber congenital amaurosis caused by RPE65 mutations: safety and efficacy in 15 children and adults followed up to 3 years. Arch Ophthalmol. 2011;130:9–24. doi: 10.1001/archophthalmol.2011.298.  35. Bennicelli J, Wright JF, Komaromy A, Jacobs JB, Hauck B, Zelenaia O, Mingozzi F, Hui D, Chung D, Rex TS, et al. Reversal of blindness in animal models of Leber congenital amaurosis using optimized AAV2-mediated gene transfer. Mol Ther. 2008;16:458–465. doi: 10.1038/sj.mt.6300389.

So which two clinical trials are they referring to? Well, as you can see from the references they are referring to the successful trials of gene therapy for Leber Congenital Amaurosis (LCA)whose development we discussed on this blog back in 2009. As McLaren and colleagues point out, the sustained expression of RPE65 and long-term recovery of vision in the Briard dog model of LCA was a key factor in their decision.  The observation that AAV2 could be used to drive gene expression in rod photoreceptors was also important, as Maclaren and colleagues had previously generated a genetically modified mouse model of Choroideremia by knocking out CHM expression in the eye, and established that in Choroideremia the degeneration of rod photoreceptors is independent of the degeneration of the RPE, so it is crucial that the vector can drive healthy gene expressed in both the rods and RPE.

To develop the vector Maclaren and colleagues first compared the efficiency of 3 different promoters (promoters are sections of DNA that promote gene expression) -AAV2/2-EFS, AAV2/5-EFS and AAV2/2-CBA  – in driving expression of the CHM gene when added in vitro in a variety of dog and human fibroblast (connective tissue cell)  lines in an AAV2 vector, and then when injected in vivo in the retinas of healthy mice. These studies demonstrated that the most efficient AAV2 vector – named AAV2/2-CBA-REP1 – could drive expression of high levels of REP1 in both the RPE and rod photoreceptors of mice. After identifying the most effective AAV2 vector for expressing REP1  they assessed whether it was capable of expressing REP1 in isolated human retina’s obtained post-mortem from human donors, which it did. They then evaluated whether there as any toxicity associated with expressing REP1 in vivo in the retina of healthy mice, finding that AAV2/2-CBA-REP1 was non-toxic even when injected into the retina at high doses, and that it did not adversely affect vision.

Following these studies the question remained; would injection of AAV2/2-CBA-REP1 stop deterioration of vision in choroideremia?

To address this Maclaren and colleagues turned again to the genetically modified mouse model of choroideremia thay they had created earlier. Injection of the vector into the retinas of these CHM mice:

Subretinal injections of AAV2/2-CBA-REP1 into CHM mouse retinas led to a significant increase in a- and b-wave of ERG responses in comparison to sham injected eyes confirming that AAV2/2-CBA-REP1 is a promising  vector suitable for choroideremia gene therapy in human clinical trials.”

In other words the therapy worked in the mouse model of choroideremia, paving the way for the successful clinical trial reported this week.

This new therapy is another example of the importance of animal studies to the development of new clinical techniques and therapies, but also highlights the fact that medical science is a long game, with basic and applied research conducted more than a decade, even two decades,  ago being crucial to this week’s exciting announcement. This is something policy makers would do well to remember!

Paul Browne

* While this paper was published in 2013, the work it reports was completed several years earlier, before the clinical trial was launched in 2011.

1) Tanya Tolmachova, Oleg E. Tolmachov, Alun R. Barnard, Samantha R. de Silva, Daniel M. Lipinski, Nathan J. Walker, Robert E. MacLaren,corresponding author and Miguel C. Seabra “Functional expression of Rab escort protein 1 following AAV2-mediated gene delivery in the retina of choroideremia mice and human cells ex vivo”  J Mol Med (Berl). 2013 July; 91(7): 825–837. PMCID: PMC3695676

Interfacing with the nervous system: Studies in mice and rats show the way.

As fundamental scientific knowledge about how the nervous system works has increased over the past few decades, the possibility has emerged that we may one day be able to use electrical stimulation (or inhibition) to treat – even to functionally cure – conditions where it has been damaged by disease or injury.  Scientists are now working hard to make this dream a reality, indeed we have recently discussed the role of animal research in developing deep brain stimulation to treat Parkinson’s disease, and in the work being done to enable quadriplegic patients to operate robotic limbs, and even to restore voluntary control of their own limbs.

But these are not the only examples of how animal research is advancing the use of neural interfaces in medicine, today Nature News carries two articles on how groundbreaking research is paving the way for advances in optical prosthesis and the treatment of epilepsy.

Recent years have seen a number of innovative treatments for different types of blindness move from the lab to the clinic, including monoclonal antibodies, gene therapy and embryonic stem cells, Another approach that has been studied in patients for some time, and which may be useful in patients whose retina is too badly damaged to benefit from the techniques mentioned above,  is the use of neural prosthesis which replace damaged photoreceptor cells in the retina and directly stimulate the optic nerve, an approach discussed by Speaking of Research committee member Dario Ringach on his blog in 2010.

A prosthetic retina that can translate an image into neural signals was tested using a picture of a baby’s face. A is the original image. B is the image after it passes through the coding software. C is after it has been processed by the mouse retinal ganglion cells. D is the processed image without coding. Credit: Sheila Nirenberg, Nirenberg, S. & Pandarinath, C. Proc. Natl Acad. Sci. USA http://dx.doi.org/10.1073/pnas.1207035109 (2012).

Nature news reports that scientists at Cornell University have solved one of the greatest challenges facing this technology, how to encode the electrical signal so that the light hitting the prosthesis is turned into a signal that the brain can understand. This problem has meant that current retinal prosthesis only allow patients to discern edges or lines, but not to be able to see movement or recognize faces. Now Sheila Nirenberg and her colleagues report the development of a code that enables mice that are blind due to severe retinal degeneration to see with far greater acuity than was possible with earlier prosthesis, the Nature News article noting that:

After receiving the encoded input, the mice were able to track moving stripes, something that they hadn’t been able to do before. The pair then looked at the neural signals that the mice were producing and used a different, ‘untranslate’, code to figure out what the brain would have been seeing. The encoded image was clearer and more recognizable than the non-encoded one”

It’s an exciting discovery that combines advanced visual prosthetic technology – which converted the light into a pattern that the brain can understand –  and genetic modification to introduce the Channelrhodopsin-2 gene into the retinal ganglion cells of the optic nerve, thus enabling them to respond to the light pattern emitted by the prosthetic and pass it to the brain. They hope to take into clinical trials in the near future, and may well do so as variations on the techniques required for this approach – including gene therapy of the eye – are already well developed, and several have already proven successful when evaluated in human patients.

The second item in Nature news is a very interesting discussion of the potential to use of a different technology – transcranial electrical stimulation (TES) – to stimulate neurons using electrodes implanted in the skull of epilepsy patients. Deep Brain Stimulation has been used to treat patients with epilepsy who don’t respond to anti-epileptic drugs, but while it has proven to be effective in many cases its use has been limited by the risks inherent in the surgery required to implant the electrodes, and the side effects due to the electrodes being continually on.

In an article published this week in the journal Science, György Buzsáki and colleagues at the New York University School of Medicine reported the development of a TES implant that was able to detect epileptic seizures in rats and then turn on to limit the reduce the duration of the seizure. Dr. Buzsáki and his colleagues have so far only studies this technique in “petit mal” or absence seizures, and are now planning to study its effectiveness for other types of epileptic seizures, but the potential of an electrostimulation technique that can control epileptic seizures but requires less invasive surgery than DBS and turns on only when requires is great.

All in all, they are two articles that highlight both the advances being made in this field, and how those advances depend on animal research.

Paul Browne

Restoring vision in night blindness: Mice point way to stem cell therapy

Impaired vision and blindness are leading causes of disability, affecting over 3 million people in the USA today, so it’s no surprise that biomedical scientists are working hard to develop therapies to improve and restore vision.  Over the past few years we have discussed several therapies that have been developed to treat different types of vision loss, including anti-angiogenic therapies to treat wet age related macular degeneration, a leading cause of severe, irreversible vision loss in the elderly,  and gene therapy to treat Leber congenital amaurosis, an inherited disease characterised by progressive degeneration of the retina. Speaking of Research committee member Dario Ringach has also written on the Opposing Views website on the very promising research now underway to develop electronic prosthesis to restore vision in blind people.

In another important development in this field Professor Robin Ali* and his team at the UCL Institute of Ophthalmology have announced the first demonstration that transplanted retinal rod cells can improve vision in mice with night-blindness, publishing the results of their study in the prestigious science journal Nature1. Rod cells are photoreceptor cells in the retina of the eye that function well in low light conditions, and an absence of rod cells leads to night blindness. Mutations in the gene GNAT1 cause congenital night blindness in humans, and mice in which the Gnat1 gene has been knocked out are night blind.  In the video below Professor Ali show that by transplanting rod cell precursors into the retina of Gnat1 knockout mice his team was able to restore vision – albeit  not fully.

It’s a fascinating piece of work, though as Professor Ali makes clear in comments to the Guardian newspaper last week there is still a lot of work to do before this can be evaluated in humans.

Now we’ve discovered we can restore vision, it gives us impetus to go on and make the process better”

As both the video and Guardian article indicate an important step will be identifying suitable sources of cells for transplantation, with both embryonic stem cells and induced pluripotent stem (iPS) cells under consideration.  This may not take as long as one might think, as we discussed last November a clinical trial was recently launched to assess the potential for transplantation of another retinal cell type, retinal epithelial cells derived from human embryonic stem cells , to improve vision in patients with  Stargart’s Macular Dystrophy, an inherited form of blindness.

The work of Professor Ali and his colleagues at UCL is moving us closer to an effective treatment – and perhaps it is not unrealistic to talk about a cure – for night blindness. Their work will also no doubt drive research on protoreceptor cell transplantation in other forms of blindness, such as dry age related macular degeneration – the most common cause of vision loss in people aged over 50 – which is characterised by loss of both rod and cone photoreceptor cells.

Paul Browne

*        Professor Ali also played a leading role in the development of gene therapy for Leber congenital amaurosis, and led the first clinical trial of this technique.

1)      Pearson RA, Barber AC, Rizzi M, Hippert C, Xue T, West EL, Duran Y, Smith AJ, Chuang JZ, Azam SA, Luhmann UF, Benucci A, Sung CH, Bainbridge JW, Carandini M, Yau KW, Sowden JC, Ali RR. “Restoration of vision after transplantation of photoreceptors.Nature. 2012 Apr 18. doi: 10.1038/nature10997.

Trachea Transplant Makes History: Part 2

It’s been a little while since I’ve had much free time to devote to blog writing, and I’m only too aware of all the exciting examples of how animal research is advancing medicine. These have ranged from successful development of  bronchial thermoplasty for treating severe asthma thanks to studies in dogs,  to the  launch of clinical trials of embryonic stem cells in the eye disease dry AMD and Stargardt’s macular dystrophy following promising results in mice and rats, to the development in mice of artificial intestines for transplants, among many others.

This morning my attention was caught by an exciting report on the BBC this morning about the first successful transplant of a synthetic windpipe, developed by seeding a scaffold made from a novel nanocomposit polymer with stem cells taken from the patient himself.

This operation was performed by Professor Paolo Macchiarini, who has already performed several successful trachea transplants using a scaffold manufactured from decellularised donor tracheas, a technique that was developed through careful research on animals, as Bianca Summons discussed on this blog back in 2008.

A new bioengineered trachea developed by scientists at UCL. Image courtesy of UCL.

The latest transplant is a further development of that technique, but uses a scaffold constructed from the novel nanocomposit polymer polyhedral oligomeric silsesquioxane-poly(carbonate-urea)urethane (POSS-PCU), developed by a team at University College London led by Professor Alex Seifalian, in place of the decellularised donor trachea. This novel polymer was thoroughly evaluated in sheep over a three year period, where it was found to be biocompatible and non-toxic, showing no evidence of degradation or inflammation, and superior to other polymers used for tissue engineering purposes. This has led to the novel polymer’s evaluation in a range of applications, including heart valves, blood vessels and the artificial trachea reported this morning.

Avoiding a reliance on the availability of a suitible donor trachea gives this new technique a significant advantage over the decellularised trachea approach, and is another great example of how fast the field of tissue engineering is moving.

I do have one complaint, it would have been better if the BBC report and UCL Press release had acknowledged the role of animal research in making this advance possible. Clearly even in the UK there is still some work to be done on that front!

Paul Browne

Open your eyes: go blind for a day!

May is “Healthy Vision Month,” a good time to celebrate the past accomplishments of scientists and clinicians in advancing vision health and to draw attention to the importance of the sense of sight.

The occasion also brings back memories of animal right activists distributing pamphlets at UCLA declaring that “blindness is not a life threatening disease” and that,  in their opinion, “animal research in this field is not justified.”  (Of course they don’t approve of any research at all, but that’s a different story.)

Here is a simple exercise for activists with such shortsighted beliefs — one that I hope will help open their eyes.  Simply blindfold yourself for one day and go about your daily routine (but please, don’t drive).  I am not asking for much; go blind for just one day in your life.  In the process, you will surely learn what is that you take for granted every day and gain a deeper understanding of the impairments that come with vision loss.

The UCLA mobile eye clinic screens thousands of children for vision problems at schools every year.

So take good care of your vision and that of your family.   How?   To celebrate “Healthy Vision Month”, the National Eye Institute Director issued the following press release that includes some very good recommendations:

During Healthy Vision Month, the National Eye Institute (NEI), part of the National Institutes of Health, encourages people and organizations around the world to recognize the value of the sense of sight and make vision health a priority.

In focus groups conducted by NEI in 2005, the majority of participants reported that though they consider eyesight to be important, they take it for granted. In surveys conducted the same year by the NEI’s National Eye Health Education Program and the Lions Club International Foundation, American adults noted that the loss of eyesight would have an extreme impact on their daily lives — though more than 25 percent said their last eye examination was more than two years prior, and 9 percent had never had an eye exam.

Unfortunately, an estimated 14 million Americans are currently visually impaired due to eye diseases and disorders, and this number continues to grow as the population ages. Of adults aged 40 and older, more than 4 million currently have diabetic eye complications, more than 2 million have glaucoma, and more than 1.75 million have age-related macular degeneration. Millions of Americans have common, correctible vision problems such as nearsightedness, farsightedness, presbyopia, and astigmatism. The prevalence of nearsightedness alone has increased 66 percent in the past 30 years, according to a 2009 NEI study.

Recent investigations by NEI scientists have indicated that many eye diseases impact certain races and ethnicities more often, a key observation for eye care professionals and for members of the general public who have the ability to take charge of their eye health. For example, African-Americans have about a 12 percent risk of glaucoma, which affects peripheral vision. This is more than twice the risk of non-Hispanic white Americans. Both Asian-Americans and Hispanics have a risk of about 6.5 percent.

Another major NEI-supported study recently determined the first estimates of visual impairment and eye disease development in Latinos, the largest and fastest-growing minority population in the United States. Researchers found that Latinos have higher incidence rates of visual impairment, blindness, diabetic eye disease, and cataracts than non-Hispanic whites. The same scientists previously showed that more than 60 percent of eye disease in Latinos remains undiagnosed.

The best way for any person, regardless of their ethnicity, to detect vision problems at the earliest, most treatable stages, is through a comprehensive dilated eye exam. This simple, painless procedure allows an eye care professional to examine the eye through an enlarged pupil and gain a more complete look at any changes in eye health.

Comprehensive dilated eye exams can reveal common and correctable refractive errors as well as eye diseases that have no or few early warning signs, including diabetic retinopathy, glaucoma, and age-related macular degeneration. Early detection of risk factors for these and other blinding eye conditions can lead to earlier treatment with vision-saving therapies that NEI researchers have developed over the past decades.

For example, scientists have shown that laser therapy is effective in preserving sight in those with diabetic eye disease, and recent studies indicate that additional drugs may lead to even better vision. Another study revealed that high levels of antioxidant vitamins plus zinc reduce the risk of the progression of and vision loss from age-related macular degeneration. Researchers also found that eye drops used to treat high eye pressure reduced the development of glaucoma by more than 50 percent in people who are at a high risk for the condition.

Join NEI in making vision a health priority for the nation. To find more information about Healthy Vision Month and resources for raising eye health awareness, including e-cards, educational handouts, and teaching tools, visit <http://www.nei.nih.gov/hvm>. For additional information on eye diseases and disorders, visit <http://www.nei.nih.gov/health>.

As you might expect animal research plays a key role in the development new treatments for blindness,  recent examples include the use of gene therapy to reverse a form of childhood blindness called Leber congenital amaurosis and the development of the monoclonal antibody treatment lucentis for wet age related macular degeneration.

Happy Healthy Vision Month everyone!

Breakthrough of the Year (almost!)

As the year draws to a close it’s time to reflect on an exciting year of animal research, and there seems no better place to start than with the top 10 breakthroughs of the year as selected by the prestigious scientific journal Science. Science is of course a general science magazine, and the choices reflect this with research in diverse fields ranging from astronomy to paleontology.

Last year our sister organization in the United Kingdom reported that Science had selected cell reprogramming to produce induced pluripotent stem cells (iPS cells) as their breakthrough of the year.  Since then we have reported how the safety of iPS technology continues to improve while others have discussed exciting research which shows just how powerful the technique is by reprogramming fibroblast cells to generate healthy mice that can themselves produce offspring.

This year the top slot went to the discovery and study of Ardi, a 4.4 million year old ape who promises to shed a great deal of light on early human evolution, though it remains to be seem if she and her kind are a direct ancestor of modern humans.

We did have the consolation that one of the nine runner ups is an area of medicine to which animal research has made an enormous contribution , the return of gene therapy with Science claiming that  this year “… gene therapy turned a corner, as researchers reported success in treating several devastating diseases”. These diseases include X-Linked adrenoleukodystrophy, a usually fatal disease of the brain and nervous system, Leber’s congenital amaurosis, an inherited eye disorder that leads to blindness, and severe combinedimmunodeficiency (SCID)due to a lack of an enzyme called adenosinedeaminase.

Only last month I wrote about the crucial role of research with mice in developing the gene therapy for X-Linked adrenoleukodystrophy, while both Anna Matynia and I have written about Leber’s congenital amaurosis.  However,  we have not yet had an opportunity to discuss the therapy developed for treating SCID  in patients whose immune system has collapsed because they lack an enzyme named adenosine deaminase (ADA) which is crucial for removing toxic metabolites from cells.

A clinical trial published in January by the New England Journal of Medicine (1) reported how an Italian team had successfully treated  children with SCID by harvesting bone marrow stem cells from the boys and treating these cells with a retroviral vector containing the ADA gene that produces adenosine deaminase, and then transplanting the modified cells back into them.  In 5 of the boys the therapy restored normal function and significant improvements in the function of the immune system were observed in the other 5.  This therapy has been a couple of decades in development and one of the key investigators involved in this effort, and indeed in the recent clinical trial,  has been Dr. Claudio Bordignon of the University of Milan. Dr. Bordignon developed techniques that enabled scientists to study the ability of retrovirus transformed bone marrow cells from patients with ADA-SCID  to restore immune function in  the NOD/SCID mice that lack a functioning immune system (2).  This enabled him and his team to develop retroviral vectors that could safely drive the production of adenosine deaminase in bone marrow stem cells that survived for long periods after transplantation and are suitable for use in ADA-SCID patients where they need to function for many years.

It’s great to see an area of medical research that we’ve been following closely over the past year receive this recognition from Science, and we hope that as with iPS cells in 2009 gene therapy continues to show what it can do in 2010.

Paul Browne

1)      Aiuti A. et al.”Gene therapy for immunodeficiency due to adenosine deaminase deficiency.” N Engl J Med. Volume 360(5), Pages 447-458 (2009) DOI:10.1056/NEJMoa0805817

2)      Ferrari G. et al “An in vivo model of somatic cell gene therapy for human severe combined immunodeficiency.” Science. Volume 251(4999), Pages 1363-1366 (1991) PubMed:1848369

Gene therapy for blindness – when dogged determination pays off!

Leber’s congenital amaurosis is a progressive disorder that affects about 3,000 Americans, and hundreds of thousands worldwide, and causes a progressive loss of vision that usually results in blindness. The disease, for which there has until now been no effective treatment, is caused by a mutation in the encoding RPE65, an enzyme which is crucial to the production of the chemical 11-cis retinal that photoreceptor cells in the eye need so that they can respond to light.

In one of my first posts for Speaking of Research last year I discussed on this blog how two teams of scientists at Moorfields hospital in the UK and the University of Pennsylvania had used gene therapy to introduce a functioning RPE65 gene into the eye of patients with Leber’s congenital amaurosis, and only last month Anna Matynia discussed how this treatment employs adenovirus-based vectors that have been developed through years of research in rodents and dogs. While the results of those trials were promising the benefits to most of the patients were modest, which was not all that surprising since the scientists doing the trials knew from their studies of Briard dogs with naturally occurring mutations in the RPE65 gene that the therapy needed to begin early in the course of the disease for maximum benefit. For this reason, and because the therapy appeared safe in the first adult human trials, the team at Pennsylvania decided to include children with Leber’s congenital amaurosis in their next study group.


Briard Dog

The early results of that study have been announced following publication in the medical journal The Lancet, and as expected the greatest benefits have been seen in the children, one of whose eyesight improved to nearly normal, though adults in the study also experienced significant improvement. While this particular therapy will benefit a relatively small number of patients its success and that of early trials of gene therapy for Parkinson’s disease are an indication how gene therapy, a field of medicine that has seen its fair share of hope and disappointment over the past couple of decades, is maturing as scientists have learned from both animal studies and human trials about how to harness this powerful therapeutic approach.

The insights gained through the study of the Briard dog with naturally occurring mutations in the RPE65 gene are a good example of the increasingly close ties between clinical and veterinary medicine, a collaboration that is exemplified by the Comparative Oncology Trials Program which brings together veterinary and clinical oncologists under the leadership of the National Cancer Institute to study cancers that affects both dogs and humans, with a dozen trails of new anti-cancer medications already underway. In the future such trials may play an important role bridging the gap between in vitro and rodent studies in the lab that rely on a relatively limited range of cancer cell lines and the far more diverse cancers seen in the clinic. It is hardly surprising that antivivisectionist groups are opposed to these trials, as our colleagues at Understanding Animal Research point out they are quite happy to put dogma ahead of dogs, but fortunately the majority of veterinarians have a much more positive attitude to animal research.


Paul Browne