BACKGROUND OF THE INVENTION

Cytokines are soluble, small proteins that mediate a variety of biological effects, including the induction of immune cell proliferation, development, differentiation, and/or migration, as well as the regulation of the growth and differentiation of many cell types (see, for example, Arai et al.,Annu. Rev. Biochem.59:783 (1990); Mosmann,Curr. Opin. Immunol.3:311 (1991); Paul et al.,Cell,76:241 (1994)). Cytokine-induced immune functions can also include an inflammatory response, characterized by a systemic or local accumulation of immune cells. Although they do have host-protective effects, these immune responses can produce pathological consequences when the response involves excessive and/or chronic inflammation, as in autoimmune disorders (such as multiple sclerosis) and cancer/neoplastic diseases (Oppenheim et al., eds.,Cytokine Reference, Academic Press, San Diego, Calif. (2001); von Andrian et al.,New Engl. J. Med.,343:1020 (2000); Davidson et al.,New Engl. J. Med.,345:340 (2001); Lu et al.,Mol. Cancer Res.,4:221 (2006); Dalgleish et al.,Cancer Treat Res.,130:1 (2006)).

IL-17A, IL-17F and IL-23 are cytokines involved in inflammation. IL-17A induces the production of inflammatory cytokines such as IL-1β, TNF-α, IL-6, and IL-23 by synovial fibroblasts, monocytes, and macrophages, all of which promote inflammation and Th17 development. IL-17A also induces an array of chemokines, including CXCL-1, CXCL-2, CXCL-5, CXCL-8, CCL-2, and CCL-20, leading to recruitment of T cells, B cells, monocytes, and neutrophils. Lundy, S. K.,Arthritis Res. Ther.,9:202 (2007). IL-17F shares the greatest homology (55%) with IL-17A and is also a proinflammatory cytokine. Both IL-17A and IL-17F are produced by Th17 cells, whereas the other IL-17 family members, IL-17B, IL-17C, and IL-17D, are produced by non-T cell sources. IL-17A and IL-17F can exist as IL-17A homodimers and IL-17F homodimers or as IL-17A/F heterodimers. Liang, S. C. et al.,J. Immunol.,179:7791-7799 (2007). IL-17A is increased in rheumatoid arthritis sera and synovial fluid, and is present in the T-cell rich areas of the synovium. Shahrara, S.,Arthritis Res. Ther.,10:R93 (2005). IL-17A can also orchestrate bone and cartilage damage. An effective blockade of IL-17 will need to neutralize IL-17A homodimers, IL-17F homodimers and IL-17A/F heterodimers.

IL-23 is a type-1 heterodimer, comprising a 19 kilodalton (kD) fourfold helical core α subunit (IL-23p19), disulfide linked to an additional 40 kD distinct β subunit (IL-12p40). IL-23 is a key cytokine in bridging the innate and adaptive arms of the immune response; it is produced early in response to an antigen challenge, and is essential for driving early local immune responses. Furthermore, IL-23 plays a central role in the activation of NK cells, the enhancement of T cell proliferation and the regulation of antibody production. IL-23 also regulates pro-inflammatory cytokines (e.g., IFN-γ), which are important in cell-mediated immunity against intracellular pathogens. Recent reports have indicated that in humans increased amounts of IL-23 have been associated with several autoimmune diseases including rheumatoid arthritis (RA), Lyme arthritis, inflammatory bowel disease (IBD), Crohn's disease (CD), psoriasis and multiple sclerosis (MS). IL-23p19 knock-out mice were resistant to autoimmune encephalomyelitis (EAE), collagen-induced arthritis (CIA) and central nervous system autoimmune induction. IL-23 is not essential for the development of human Th17 cells, but appears to be required for their survival and/or expansion. Paradowska-Gorycka, A.,Scandinavian Journal of Immunology,71:134-145 (2010). Genetic studies revealed an association between IL-23 receptor genes and susceptibility to several autoimmune diseases including CD, RA and Graves' ophthalmopathy. The IL-23-Th17 axis is crucial to autoimmune disease development. Leng et al.,Archives of Medical Research,41:221-225 (2010).

The demonstrated activities of IL-17A, IL-17F and IL-23p19 in mediating and promoting several autoimmune diseases illustrate the clinical potential of, and need for, molecules which can antagonize these targets. The present invention, as set forth herein, meets these and other needs.

