Tc-Type II tumor necrosis receptor-Fc-interlukin-1 receptor antagonist fusion protein

Tumor necrosis factor (TNF) is a proinflammatory cytokine produced by macrophages, and it plays an important role in inflammation and immune response (1). There are two types of TNF (TNF-α, TNF-β). TNF-α is mainly responsible for initiating inflammatory responses by induction of several proinflammatory cytokines, chemokines, matrix metalloproteinases, and vascular endothelial adhesion molecules that attract leukocytes known to promote inflammation. There are two types of TNF receptors: TNFR1 and TNFR2. Soluble forms of TNF receptors are released upon proteolytic cleavage of the membrane-bound TNF receptors. Soluble TNF receptors participate in limiting the availability of TNF to bind to its receptors (2, 3). Several anti-TNF monoclonal antibodies (TNF blockers) to further reduce circulating TNF have been approved by the United States Food and Drug Administration (FDA) for the treatment of a variety of inflammatory diseases (4, 5). The interleukin-1 family consists of two proinflammatory cytokines, IL-1α and IL-1β, which bind to two IL-1 receptors (IL-1R1 and IL-1R2), and an IL-1R antagonist (IL-1ra), which is mainly produced by activated macrophages and tissue macrophages (6). IL-1α and IL-1β are important mediators of the inflammatory response and hematopoiesis, and they are involved in a variety of cellular activities, including cell proliferation, differentiation, and apoptosis. IL-1 is involved in chronic inflammatory diseases and in neuropathological conditions (7, 8). The balancing act of IL-1 and IL-1ra plays an important role in the regulation of inflammation and immune responses (9). IL-1ra has been shown to be effective as an anti-inflammatory treatment in several chronic inflammatory diseases and stroke (10, 11). A human recombinant, non-glycosylated form of the human IL-1ra (rhIL-1ra, Anakinra) has been approved by the FDA for the treatment of rheumatoid arthritis (12). IL-1β and TNF-α exhibit additive or synergistic effects in promoting pathophysiological processes observed in many inflammatory diseases (13). A dual domain TNFR2-Fc-IL-1ra fusion protein was constructed by joining TNFR2 and IL-1ra cDNA to the Fc fragment of human IgG cDNA in an expression plasmid (14). The amino-terminal segment binds to TNF, and the carboxyl-terminal sequence binds to the IL-1R. Liu et al. (14) radiolabeled TNFR2-Fc-IL-1ra with Tc 2-iminothiolane reduction to produce Tc-TNFR2-Fc-IL-1ra for use with single-photon emission computed tomography (SPECT) imaging of inflammation in mice.