Anti-CD4 therapy in recent-onset IDDM

Induction of dominant tolerance using monoclonal antibodies

Monoclonal antibodies (MAb) have been shown to be effective in inducing immune tolerance in transplantation and autoimmunity. Several different MAb have tolerogenic properties and their effect has been studied in a range of experimental animal models and, in some cases, in clinical trials. The tolerant state seems to be maintained by CD4+ regulatory T cells (Treg), induced in the periphery, capable of suppressing other T cells specific for the same antigens or antigens presented by the same antigen presenting cells. Furthermore, following the initial induction of Treg cells under MAb treatment, Treg cells themselves can maintain the tolerant state in a dominant way in the absence of the therapeutic MAb or other immunosuppressive agents, and are able to recruit other T cells into the regulatory pool--a process named infectious tolerance.

Immunomodulatory effects of anti-CD4 antibody in host resistance against infections and tumors in human CD4 transgenic mice

Anti-CD4 antibodies, which cause CD4(+) T-cell depletion, have been shown to increase susceptibility to infections in mice. Thus, development of anti-CD4 antibodies for clinical use raises potential concerns about suppression of host defense mechanisms against pathogens and tumors. The anti-human CD4 antibody keliximab, which binds only human and chimpanzee CD4, has been evaluated in host defense models using murine CD4 knockout-human CD4 transgenic (HuCD4/Tg) mice. In these mice, depletion of CD4(+) T cells by keliximab was associated with inhibition of anti-Pneumocystis carinii and anti-Candida albicans antibody responses and rendered HuCD4/Tg mice susceptible to P. carinii, a CD4-dependent pathogen, but did not compromise host defense against C. albicans infection. Treatment of HuCD4/Tg mice with corticosteroids impaired host immune responses and decreased survival for both infections. Resistance to experimental B16 melanoma metastases was not affected by treatment with keliximab, in contrast to an increase in tumor colonization caused by anti-T cell Thy1.2 and anti-asialo GM-1 antibodies. These data suggest an immunomodulatory rather than an overt immunosuppressive activity of keliximab. This was further demonstrated by the differential effect of keliximab on type 1 and type 2 cytokine expression in splenocytes stimulated ex vivo. Keliximab caused an initial up-regulation of interleukin-2 (IL-2) and gamma interferon, followed by transient down-regulation of IL-4 and IL-10. Taken together, the effects of keliximab in HuCD4/Tg mice suggest that in addition to depleting circulating CD4(+) T lymphocytes, keliximab has the capability of modulating the function of the remaining cells without causing general immunosuppression. Therefore, keliximab therapy may be beneficial in controlling certain autoimmune diseases.

New therapeutic options in uveitis

Most patients with sight-threatening posterior uveitis eventually end up on systemic medication to control their disease. Although the more aggressive approach to the use of these drugs does offer the patient a better chance of significant visual improvement at least in the short term, this is often associated with severe systemic side-effects in both the young and older patient. Cyclosporin has become a very useful second-line agent as a steroid sparer in those patients who can tolerate it. However, it is not suitable for or effective in everyone and the other currently available drugs are often of limited effectivity or associated with major systemic sequelae. This paper summarises the therapeutic approaches currently being examined to define whether they have a role in the better management of these patients in the future. Particularly exciting is the potential for sustained intraocular drug delivery so that adequate drug levels are achieved inside the eye without the necessity for systemic administration.

Immunotherapies in diabetes

Insulin-dependent diabetes (IDD) is a serious, life-long disease replete with life-threatening complications that are not preventable through conventional insulin replacement therapies. The prolonged prodromal period of autoimmunity to beta cell antigens offers multiple intervention opportunities. These can target different steps that precede final destruction of insulin-secreting beta cells and clinical onset of the disease. All current and proposed immunotherapies are experimental procedures that have proven to be protective in animal models, especially the nonobese diabetic (NOD) mouse. This brief review deals with a selected list of nonspecific and autoantigen-specific immunotherapies that may bring hope in the near future to individuals at risk of developing the disease. None are yet proven to be effective in humans.