Ethics of Research involving animals
New therapeutic strategies for rheumatoid arthritis
6.4 RA is one of the most common human autoimmune diseases, affecting up to 600,000 individuals in the UK. It is a crippling disease resulting primarily in a chronic inflammation of joints of the hands, feet, knees, vertebrae or hips. It typically leads to progressive degeneration of the joint tissues with consequent disability and premature death. Although the exact cause of RA is unknown, in the last ten years there have been very considerable advances in the understanding of the molecular and cellular basis of the disease process. Animal models of arthritis have been used to study these processes and to devise and test new treatments. A successful treatment for RA has been developed, which has also led to therapeutic interventions for other chronic inflammatory conditions (see paragraph 6.10).3
6.5 There has been some debate about the relative relevance and contributions of in vitro and in vivo animal work to the study of RA. A review of the literature reveals that both animal models of arthritis and in vitro studies with human RA joint tissue have been used simultaneously and often by the same researchers. It would therefore be wrong to describe particular significant steps in the understanding of RA as having relied only on in vitro or in vivo methods. Experiments using both approaches relied on the results of previous experiments with animal and human tissue, live animals and human volunteers.
6.6 RA in humans is characterised by a chronic inflammation of the lining of the joint capsule (synovium). Inflammatory cells invade the synovial membrane of the joint, and there is excessive local secretion of molecules (cytokines) that produce inflammation. In the late 1980s, several groups of researchers started to examine the possible role of these molecules in RA after various cytokines were detected in the synovial fluid of patients.4 It became clear by the early 1990s from studies on human tissue5 and, later, in animal models of arthritis that the inflammatory process depends on a cytokine known as tumour necrosis factor alpha (TNFα).6 Enhanced TNF production in the affected joints results in release of other cytokines and of growth factors that cause abnormal growth of new blood vessels, increased blood flow and destruction of cartilage. Once the crucial role of TNF became clear, it was proposed that neutralising TNF or switching off its production in the joint might reverse joint inflammation. Researchers were able to test the usefulness of neutralising TNF with anti-TNF antibodies,7 both in in vitro studies with human joint tissue and in an arthritis model in rodents. In both cases, the antibodies reduced inflammation in joint tissue by binding specifically to the TNF molecules.8 Thus, researchers used in vivo studies of rodent arthritis models to complement in vitro studies of human RA joint tissue to understand the pathogenesis of immune arthritis.
The rodent model for arthritis
6.7 The rodent arthritis model is produced by the injection of bovine or chicken collagen,9 together with a chemical that increases the resulting immune reaction, into inbred strains of mice or rats. Swollen joints and arthritis appear within 20–40 days. Although collageninduced arthritis in the mouse does not exactly mimic RA in humans, it has a number of similarities. For example, the model allowed the primary role of TNF in joint inflammation to be examined, as it is common to both forms of arthritis. The mouse model for arthritis played a significant role in the development of the current and successful therapeutic intervention of blocking TNF to alleviate RA in humans.
6.8 Once arthritis develops, a painful swelling of the paws occurs, accompanied by erosions of the joint cartilage. In humans, painful swelling is accompanied by pain in the extremities. Similar effects resulting from the inflammation occur in mice, which may affect the welfare of the animal considerably since rodents use their front feet extensively for grooming, holding food, eating and moving around. Severely affected animals are usually euthanised before the end of the experiments.
Human clinical trials
6.9 It had been demonstrated in vitro that antibodies against TNF (anti-TNF) reduced the production of other cytokines involved in the inflammatory response.10 Subsequent animal experiments established that anti-TNF could be used to reduce the symptoms of inflammatory joint disease without seriously impairing the function of other tissues and organs. Clinical trials to assess the effect of anti-TNF reagents in humans began in 1992. Infliximab, a monoclonal antibody against human TNF, was used in a series of trials in patients to test the safety, efficacy and pharmocokinetics of anti-TNF therapy. The therapeutic dose used for the human trials was based on the mouse studies.11 The clinical results in RA patients treated with infliximab demonstrated substantial benefits: patients reported alleviation of symptoms such as swelling, pain, stiffness, tiredness and lethargy a short time after being treated with the medicine. The first study was carried out in RA
patients in which all other available therapies had failed. Following the success of this initial trial, larger studies were performed at four European centres.12 These were followed by successful repeated-dose studies, which showed a long-term therapeutic benefit of the treatment.
6.10 Several types of anti-TNF treatments have now been approved by regulatory authorities in the USA and Europe and represent a major advance in the treatment of RA.13 So far, more than 200,000 patients have been successfully treated, with marked improvement in their physical activity and quality of life. Anti-TNF therapy has now been adapted successfully to treat other chronic inflammatory conditions including inflammatory bowel disease (Crohn’s disease), the rheumatic disease ankylosing spondylitis, psoriasis and psoriatic arthritis.14
Footnotes3 Vilcek and Feldmann M (2004) Historical review: cytokines as therapeutics and targets of therapeutics Trends Pharmacol Sci 25:
201–9.
4 For example, see Hopkins SJ and Meager A (1988) Cytokines in synovial fluid: II The presence of tumour necrosis factor and
interferon Clin Exp Immunol 73: 88–92.
5 A seminal discovery was made by Brennan FM, Chantry D, Jackson A, Maini R and Feldmann M (1989) Inhibitory effect of TNF
alpha antibodies on synovial cell interleukin-1 production in rheumatoid arthritis Lancet 2: 244–7, who concluded that TNF plays a pivotal role in arthritis using inflamed tissues from patients of the disease; described later in Higgs G (2004) Molecular genetics: the Emperor’s clothes of drug discovery? Drug Discov Today 9: 727–9.
6 The abnormal synthesis of TNF by cells invading the joint capsule amplifies the inflammatory cell cascade, triggering the release
of other inflammatory cytokines which cause tissue damage when present in excess.
7 Anti-TNF antibodies bind specifically to TNF molecules. For a description of the function of antibodies, see paragraphs 5.24-5.25.
8 Williams RO, Feldmann M and Maini RN (1992) Anti-tumor necrosis factor ameliorates joint disease in murine collagen-induced
arthritis Proc Natl Acad Sci USA 89: 9784–8. For a review and references to simultaneous work, see Vilcek and Feldmann M
(2004) Historical review: cytokines as therapeutics and targets of therapeutics Trends Pharmacol Sci 25: 201–9.
9 Collagen is a tough, fibrous protein that forms a major component of skin, tendons, bones, cartilage and other connective
tissues. It helps to hold cells and tissues together.
10 Brennan FM, Chantry D, Jackson A, Maini R and Feldmann M (1989) Inhibitory effect of TNF alpha antibodies on synovial cell
interleukin-1 production in rheumatoid arthritis Lancet 2: 244–7.
11 Vilcek and Feldmann M (2004) Historical review: cytokines as therapeutics and targets of therapeutics Trends Pharmacol Sci 25:
201–9.