Project Info.

Abstract

Background

Objective

Hypothesis

Procedures

Results

Future Work

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Acknowledgements

References

Type 1 diabetes (T1D), also known as juvenile diabetes mellitus or insulin-dependent diabetes mellitus, is a serious life-threatening autoimmune disease (Bach, 1994). T1D is considered the third most prevalent chronic disease for children. T1D occurs when T lymphocytes of the host immune system become activated and destroy the insulin-producing cells of the pancreas, resulting in the body’s failure to produce insulin, the hormone that allows glucose to enter the cells of the body to provide fuel. There is no effective therapy for T1D. While daily insulin injection saves the lives of diabetic patients, it cannot cure the disease. Treatment with immunosuppressive drugs such as steriod or cyclosporine has showed some effects. However, such drugs often produce serious side effects due to global suppression. Therefore there is a strong demand for new therapies. Accumulated evidence suggests that T lymphocytes play a crucial role in T1D development (Rochen et al., 1996). There are two subsets of helper T lymphocytes: T helper 1 (Th1) and T helper 2 (Th2). The disease is primarily mediated by the Th1 lymphocytes that produce interferon γ (INF-γ), whereas Th2 cells have a beneficial, protective role in T1D development since they produce anti-inflammatory cytokines such as IL-4, IL-10 and IL-13. Cytokines are the dominant factors guiding the development of Th1 and Th2 cells (Slavin et al., 2001). For instance, IL-4 directs the differentiation of precursor T cells to become Th2 cells while INF-γ stimulates T cell maturation towards Th1 cells (Le Gros et al., 1990). Thus, induction of selective deviation of harmful Th1 responses towards an anti-inflammatory Th2 phenotype using Th2 cytokines such as IL-13 represents the most promising immune-based therapeutic approach to T1D. This strategy has been termed “immune deviation” (Rochen et al., 1996). Indeed, prolonged treatment with cytokines IL-13, (also IL-10) has found to be effective in preventing T1D in the nonobese diabetic (NOD) mice (Zaccone et al., 1999). However, like IL-4 and IL-10, systemic injection of IL-13 leads to severe side effects that may limit its use in clinical practice. Localized oral delivery of IL-13 will eliminate or reduce the side effects associated with its systemic administration. However, for orally administered IL-13 to take effect, large amounts of IL-13 are required, which may be unaffordable unless a new low-cost expression system is developed.

Recently, genetically engineered (transgenic) plants have emerged as an ideal expression system or “bioreactor” for the production of pharmaceutical proteins in large quantities at low cost (Jani et al., 2002; Ma et al., 2004; Ma et al., 2005). In this study, I propose to produce large amounts ofIL-13 or an IL-13-containing fusion protein in transgenic plants for oral administration to prevent or treat T1D. I cloned the human IL-13 gene and the chimeric gene CTB-IL-13 where IL-13 was fused with the CTB gene encoding the non-toxic subunit B of cholera toxin, CTB, a mucosal carrier molecule. Agrobacterium-mediated transformation was used to generate low-nicotine transgenic tobacco plants expressing CTB-IL-13 and IL-13. The availability of large amounts of recombinant proteins of IL-13 and CTB-IL-13 produced by transgenic plants in this study provides a solid foundation for the development of a plant-derived oral cytokine (plantikine) for treatment of T1D.