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Reprinted with permission from Peter Zhou at https://www.nature.com/articles/6605530, Yadi & Zhou, Peter (2010).

its infancy (7). Researchers at Centacor had created a chimeric TNF antibody called infliximab (Remicade®) by attaching the variable region of the mouse TNF antibody to the Fc region of human IgG1 (12). Taking advantage of the Gillis-authorized sandbox, Smith, in his spare evenings, began expressing and purifying recombinant forms of TNF (7). Then, he used radiolabeled TNF to isolate, clone, and express the TNF receptor (13).

Craig Smith

Cindy Jacobs

TNF signaling pathways

TNF binds to two receptors: TNFR-1 and TNFR2. The extracellular (i.e., the binding site) portion of these membrane-bound receptors is functional, like the intact receptors. Extracellular TNFR-1 (p55) and TNFR-2 (p75) circulate as “soluble receptors” and can bind to TNF everywhere in the body (13, 14). In a similar manner, the soluble (extracellular) portion of the IL-1 receptor specifically binds to IL-1 (15). The soluble TNF receptors expressed by Smith and his colleague, Ray Goodwin, bound to TNF with relatively low affinity (14). TNF is a homo-trimer, and on the cell surface it normally binds to 2-3 receptor molecules. This multiplicity increases receptor affinity for TNF through interlocking “cooperative binding” (7). Smith aimed to construct a molecule that mimicked the membrane-bound receptor configuration and would have much higher affinity for TNF than the monomeric soluble receptor. Smith clipped human IgG1, leaving just the Fc stem and a portion of the two hinge regions. He then fused a human p75 soluble TNF receptor to each of the hinges and called the resulting molecule a “TNFR:Fc fusion protein” (11, 16). The two soluble receptors in this configuration accommodated 1-2 binding domains of the TNF molecule (7). As predicted, TNFR:Fc had up to a 1000-fold greater affinity for TNF than the monomeric p75 soluble receptor and was equivalent to the interlocking membrane-bound receptors’ affinity for TNF (7, 14).

Craig Smith (left) and Raymond Goodwin

Reprinted from The Pharmacologist • December 2017

Cindy Jacobs

Profile for ASPET

2018 Special Compilation Issue of The Pharmacologist  

ASPET is pleased to present the second in a series of special editions of our quarterly news magazine, The Pharmacologist. This special com...

2018 Special Compilation Issue of The Pharmacologist  

ASPET is pleased to present the second in a series of special editions of our quarterly news magazine, The Pharmacologist. This special com...