Monoclonal antibody therapeutics: history and future.

Over the last three decades, monoclonal antibodies have made a dramatic transformation from scientific tools to powerful human therapeutics. At present, approximately 30 therapeutic monoclonal antibodies are marketed in the United States and Europe in a variety of indications, with sales in the US alone reaching approximately $18.5 billion in 2010. This review describes how antibody engineering has revolutionized drug discovery and what are considered the key areas for future development in the monoclonal antibody therapy field.

Study of the sequence of events involved in nevirapine-induced skin rash in Brown Norway rats.

Nevirapine, used for the treatment of HIV infection, is associated with development of skin rash and liver toxicity. The mechanism of these idiosyncratic reactions is unknown. We have previously reported the discovery of a new animal model of nevirapine-induced skin rash in rats. When treated with nevirapine, Brown Norway rats developed red ears on about day 7 and skin rash on about day 21. On rechallenge, ears turn red within 24 h, and skin lesions develop by day 9. In the current study, we analyzed the time course of the sequence of events involved in the development of skin rash. Rats were treated with nevirapine for 7, 14, or 21 days or rechallenged with it for 0, 1, or 9 days. This treatment led to an increase in the total number of auricular lymph node T, B, and macrophage cells. There was also an increase in the activation/infiltration marker ICAM-1 and activation/antigen presentation marker MHC II in these cells compared with those from control rats. Immunohistochemistry analysis showed macrophage infiltration and ICAM-1 expression in the ears of treated rats as early as day 7 of treatment. Macrophage infiltration preceded T cell infiltration, which was not apparent until the onset of rash. Both MHC I and MHC II expression increased in the skin of nevirapine-treated rats that developed rash. A major inducer of MHC is IFNgamma. Although rechallenge with nevirapine led to a large increase in serum levels of IFNgamma, this was not observed during the treatment of naïve rats with nevirapine. These observations provide further clues to the mechanism of nevirapine-induced skin rash.

Evidence of an immune-mediated mechanism for an idiosyncratic nevirapine-induced reaction in the female Brown Norway rat.

Previously, we reported a new animal model of an idiosyncratic drug reaction in which nevirapine causes a skin rash in some rats that has characteristics similar to the reaction that occurs in humans. Strong evidence that the reaction is immune-mediated was found; specifically, low-dose pretreatment induced tolerance, while with rechallenge, the time to onset decreased and the severity increased. Furthermore, splenocytes from rechallenged rats transferred rash susceptibility to naïve recipients. We now report the results of studies to explore the immune aspects of this reaction. T cells were found to play an important role, as demonstrated by their ability to adoptively transfer susceptibility to the skin reaction. Of these T cells, CD4+ cells are the likely effectors because they were capable of transferring susceptibility and the reaction was delayed in rats partially depleted of CD4+ T cells. In contrast, it appears that CD8+ T cells are not essential, as CD8+ T cells were unable to transfer sensitivity to a naïve animal and rats depleted of CD8+ T cells still developed skin rash. Unlike the penicillamine model, where we have demonstrated that the tolerance induced by low-dose treatment is immune-mediated, tolerance induced by low-dose nevirapine appears to be largely due to induction of metabolism as it can be overcome by inhibition of cytochrome P450. Pretreatment with the immunosuppressants, cyclosporine and tacrolimus, prevented the rash and even led to resolution of the rash during nevirapine treatment. These studies reinforce the hypothesis that the reaction in this model is similar to that which occurs in humans. In particular, the finding that CD4+ T cells may play a central role in this model fits with the observation that the incidence of idiosyncratic reactions to nevirapine in humans appears to be lower in patients with low CD4+ counts.

Animal models of idiosyncratic drug reactions.

Idiosyncratic drug reactions represent a major problem. In most cases the mechanisms of these reactions are unknown, but circumstantial evidence points to the involvement of reactive metabolites and the characteristics of the reactions suggest involvement of the immune system. If progress is to be made in dealing with these adverse reactions it is essential that we have a better understanding of their mechanisms, and it is hard to imagine testing mechanistic hypotheses without good animal models. Unfortunately, idiosyncratic reactions are also idiosyncratic in animals so few good models exist. The best models, in which a rodent develops a clinical syndrome similar to that which occurs in humans, appear to be penicillamine-induced autoimmunity in Brown Norway rats and nevirapine-induced skin rash in rats. Sulfamethoxazole-induced hypersensitivity in dogs and propylthiouracil-induced autoimmunity in cats are also similar to adverse reactions that occur in people, but they have practical limitations. Halothane-induced liver toxicity in guinea pigs and amodiaquine-induced bone marrow and liver toxicity in rats represent models in which there is an immune response and mild, reversible toxicity. It is possible that the development of immune tolerance is what limits the toxicity in these models, and if this is true, interventions that prevent tolerance might lead to good models. Although the history of developing animal models of idiosyncratic drug reactions is mostly one of failure, such models are essential. A better understanding of immune tolerance may greatly facilitate the development of better models; transgenic technology may also provide an important tool.

Investigation of the involvement of macrophages and T cells in D-penicillamine-induced autoimmunity in the Brown Norway rat.

The initiating events in drug-induced autoimmunity are poorly understood and difficult to study. We examined the role of macrophages and T-cells in the Brown Norway rat model of D-penicillamine-induced autoimmunity. When activated, macrophages can act as both antigen presenting cells, initiating immune responses, and as phagocytic cells mediating systemic tissue damage. We found that B7(+) macrophages are the major antigen-presenting cell type infiltrating the spleen and caecum early in the response to Dpenicillamine. As well, the increase in splenic B7(+) macrophages correlates with the incidence of autoimmune disease. Treatments that increase the incidence of disease accentuate the increase in splenic B7(+) macrophages, and treatments that prevent disease also prevent the increase in B7(+) macrophages. In vivo depletion of macrophages appeared to decrease, but not totally prevent, autoimmune disease. The role of T-cells in D-penicillamine-induced autoimmunity was also examined using the T-cell inhibitor tacrolimus. Short-term treatment with tacrolimus not only prevented disease onset but also reversed ongoing disease and prevented disease relapse upon re-challenge with D-penicillamine. The results of this study indicate that both macrophages and T-cells could be important immune cell types involved in D-penicillamine-induced autoimmunity. Furthermore, the effects of tacrolimus in this model suggest that short-term tacrolimus treatment may be an effective way to prevent or treat IDRs in high-risk patients.

Characterization of a potential animal model of an idiosyncratic drug reaction: nevirapine-induced skin rash in the rat.

Idiosyncratic drug reactions are difficult to study in humans due to their unpredictability. Unfortunately, this characteristic also hinders the development of animal models needed for mechanistic studies. Nevirapine, used to treat human immunodeficiency virus (HIV) infections, results in a severe idiosyncratic skin rash in some patients. We found that nevirapine can also cause a significant rash in some strains of rats. At a dose of 150 mg/kg/day, the incidence in female Sprague-Dawley rats was 6/28 (21%), in female Brown Norway rats 32/32 (100%), and in female Lewis rats 0/6 (0%) while no male Sprague-Dawley or Brown Norway rats developed a rash. Female SJL mice 0/7 also did not develop nevirapine-induced skin lesions. The first sign of a reaction in Brown Norway rats was red ears at days 7-10 followed by a rash with scabbing mainly on the back; this was a shorter time to onset than in Sprague-Dawley rats. Light microscopy of the skin revealed a primarily mononuclear inflammatory infiltrate and lesions typical of self-trauma. Immunohistochemistry results suggest that the infiltrate was composed of CD4 and CD8 T cells as well as macrophages. A lower dose of either 40 or 75 mg/kg/day did not lead to a rash and, in fact, 2 weeks of the lower doses induced tolerance to the 150 mg/kg/day dose in female Brown Norway rats. A dose of 100 mg/kg/day resulted in rash in 2/4 (50%) of female Brown Norway rats. Rechallenge of Brown Norway rats that had been allowed to recuperate after a nevirapine-induced rash led to red ears in less than 24 h followed by hair loss and occasional skin lesions. Although the skin rash was less evident on rechallenge, microscopically, the cellular infiltrate was more prominent, especially surrounding the hair follicles. Moreover, there were lesions of interface dermatitis with apoptosis and satellitosis, indicative of a cell-mediated immune attack on the epidermis. While systemic signs of illness did not accompany the rash on primary exposure, on rechallenge, the animals appeared generally unwell and this forced sacrifice after 2 weeks or less of treatment. Importantly, splenocytes isolated from rechallenged animals were able to transfer susceptibility to nevirapine-induced skin rash to naïve female Brown Norway recipients, which was illustrated by a faster time to onset of rash in the recipients. The characteristics of this adverse reaction are similar to that seen in humans; that is, it is idiosyncratic in that it only occurs in some strains of animals, is delayed in onset, is more common in females, is dose-dependent, and appears to be immune-mediated. Therefore, it may represent a good animal model for the study of idiosyncratic drug reactions.