MINIMAL TUMOR-NECROSIS-FACTOR RECEPTOR-BINDING PROTEIN - OPTIMUM BIOLOGICAL-ACTIVITY OF A TRUNCATED P55 SOLUBLE TUMOR-NECROSIS-FACTOR RECEPTOR IGG FUSION PROTEIN

We have previously demonstrated, using expressed deletion constructs, that the fourth membrane proximal cysteine-rich repeat of the p55 TNF receptor (TNF-R) is not required for binding of tumour necrosis factor -alpha (TNF) or lymphotoxin-alpha (LT; tumour necrosis factor-beta), W e and others have also shown that the soluble p55 TNF-R, rendered dime ric by fusion to an Ige backbone is extremely effective at neutralizin g the harmful effects of TNF overproduction, such as in toxic shock. H ere we address the question of how the TNF binding properties of the t runcated TNF-R comprising the three distal cysteine-rich repeats (Delt a 4 TNF-R), when fused with an IgG backbone, compare with those of the full length soluble receptor. We constructed several versions of the soluble Delta 4 TNF-R, on a complete IgG heavy chain backbone and on a n IgG lacking the CH1 (first constant region) domain. The constructs w ere expressed with an Ig or native TNF receptor leader sequence and al tered or native N terminal sequence, to compare efficiency of expressi on. When compared with a full length, soluble receptor Ig fusion prote in, the affinity of all for TNF was identical, as were their activitie s in in vitro binding and cytotoxicity assays. III vivo studies showed that the Delta 4 and wild type fusion proteins afforded equivalent pr otection against LPS-induced lethality. However, the Delta 4 proteins exhibited a significantly lower affinity for LT, and reduced activity in LT binding and cytotoxicity assays. We conclude that the truncated TNF receptor IgG fusion protein is as effective at neutralizing TNF ac tivity as the full length soluble receptor fusion protein, Its lower a ffinity for LT may make it a more selective agent in blocking the acti on of TNF, while causing less interference with the action of LT, Also its smaller size may make it a more useful therapeutic agent as it ma y be less immunogenic than the full length receptor.