Determination of tumor necrosis factor binding protein disulfide structure: deviation of the fourth domain structure from the TNFR/NGFR family cysteine-rich region signature

Complete mapping of disulfide linkages for etanercept products by multi-enzyme digestion coupled with LC-MS/MS using multi-fragmentations including CID and ETD

The disulfide linkages of two etanercept products, Enbrel® (innovator drug) and TuNEX®, were characterized and compared using a multi-fragmentation approach consisting of electron transfer dissociation (ETD) and collision induced dissociation (CID) in combination with multi-enzyme digestion protocols (from Lys-C, trypsin, Glu-C, and PNGase F). Multi-fragmentation approach allowed multi-disulfide linkages contained in a peptide to be un-ambiguously assigned based on the cleavage of both the disulfide and the backbone linkages in a MS³ schedule. New insights gained using this approach were discussed. A total of 29 disulfides, Cys18-Cys31, Cys32-Cys45, Cys35-Cys53, Cys56-Cys71, Cys74-Cys88, Cys78-Cys-96, Cys98-Cys104, Cys112-Cys121, Cys115-Cys139, Cys-142-Cys157, Cys163-Cys178 in TNFR portion and Cys240-Cys240, Cys246-Cys246, Cys249-Cys249, Cys281-Cys341, Cys387-Cys445 in IgG1 Fc domain, were completely assigned with the demonstration of the same disulfide linkages between the Enbrel® and TuNEX® products. The data showed the higher order structure was preserved throughout the recombinant manufacturing processes and consistent between the two products.

Comprehensive identification of protein disulfide bonds with pepsin/trypsin digestion, Orbitrap HCD and Spectrum Identification Machine

Disulfide bonds (SS) are post-translational modifications important for the proper folding and stabilization of many cellular proteins with therapeutic uses, including antibodies and other biologics. With budding advances of biologics and biosimilars, there is a mounting need for a robust method for accurate identification of SS. Even though several mass spectrometry methods have emerged for this task, their practical use rests on the broad effectiveness of both sample preparation methods and bioinformatics tools. Here we present a new protocol tailored toward mapping SS; it uses readily available reagents, instruments, and software. For sample preparation, a 4-h pepsin digestion at pH 1.3 followed by an overnight trypsin digestion at pH 6.5 can maximize the release of SS-containing peptides from non-reduced proteins, while minimizing SS scrambling. For LC/MS/MS analysis, SS-containing peptides can be efficiently fragmented with HCD in a Q Exactive Orbitrap mass spectrometer, preserving SS for subsequent identification. Our bioinformatics protocol describes how we tailored our freely downloadable and easy-to-use software, Spectrum Identification Machine for Cross-Linked Peptides (SIM-XL), to minimize false identification and facilitate manual validation of SS-peptide mass spectra. To substantiate this optimized method, we've comprehensively identified 14 out of 17 known SS in BSA. SIGNIFICANCE: Comprehensive and accurate identification of SS in proteins is critical for elucidating protein structures and functions. Yet, it is far from routine to accomplish this task in many analytical or core laboratories. Numerous published methods require complex sample preparation methods, specialized mass spectrometers and cumbersome or proprietary software tools, thus cannot be easily implemented in unspecialized laboratories. Here, we describe a robust and rapid SS mapping approach that utilizes readily available reagents, instruments, and software; it can be easily implemented in any analytical core laboratories, and tested for its impact on the research community.

Mass spectrometry profiles superoxide-induced intramolecular disulfide in the FMN-binding subunit of mitochondrial Complex I

Protein thiols with regulatory functions play a critical role in maintaining the homeostasis of the redox state in mitochondria. One major host of regulatory cysteines in mitochondria is Complex I, with the thiols primarily located on its 51 kDa FMN-binding subunit. In response to oxidative stress, these thiols are expected to form intramolecular disulfide bridges as one of their oxidative post-translational modifications. Here, to test this hypothesis and gain insights into the molecular pattern of disulfide in Complex I, the isolated bovine Complex I was prepared. Superoxide (O(2)(.-)) is generated by Complex I under the conditions of enzyme turnover. O(2)(.-)-induced intramolecular disulfide formation at the 51, kDa subunit was determined by tandem mass spectrometry and database searching, with the latter accomplished by adaptation of the in-house developed database search engine, MassMatrix [Xu, H., et al., J. Proteome Res. 2008, 7, 138-144]. LC/MS/MS analysis of tryptic/chymotryptic digests of the 51 kDa subunit from alkylated Complex I revealed that four specific cysteines (C(125), C(142), C(187), and C(206)) of the 51 kDa subunit were involved in the formation of mixed intramolecular disulfide linkages. In all, three cysteine pairs were observed: C(125)/C(142), C(187)/C(206), and C(142)/C(206). The formation of disulfide bond was subsequently inhibited by superoxide dismutase, indicating the involvement of O(2)(.-). These results elucidated by mass spectrometry indicate that the residues of C(125), C(142), C(187), and C(206) are the specific regulatory cysteines of Complex I and they participate in the oxidative modification with disulfide formation under the physiological or pathophysiological conditions of oxidative stress.

Identification and characterization of disulfide bonds in proteins and peptides from tandem MS data by use of the MassMatrix MS/MS search engine

A new database search algorithm has been developed to identify disulfide-linked peptides in tandem MS data sets. The algorithm is included in the newly developed tandem MS database search program, MassMatrix. The algorithm exploits the probabilistic scoring model in MassMatrix to achieve identification of disulfide bonds in proteins and peptides. Proteins and peptides with disulfide bonds can be identified with high confidence without chemical reduction or other derivatization. The approach was tested on peptide and protein standards with known disulfide bonds. All disulfide bonds in the standard set were identified by MassMatrix. The algorithm was further tested on bovine pancreatic ribonuclease A (RNaseA). The 4 native disulfide bonds in RNaseA were detected by MassMatrix with multiple validated peptide matches for each disulfide bond with high statistical scores. Fifteen nonnative disulfide bonds were also observed in the protein digest under basic conditions (pH = 8.0) due to disulfide bond interchange. After minimizing the disulfide bond interchange (pH = 6.0) during digestion, only one nonnative disulfide bond was observed. The MassMatrix algorithm offers an additional approach for the discovery of disulfide bond from tandem mass spectrometry data.

Requirement of Oxidation-dependent CD40 Homodimers for CD154/CD40 Bidirectional Signaling

It is well established that the CD154/CD40 interaction is required for T cell-dependent B cell differentiation and maturation. However, the early molecular and structural mechanisms that orchestrate CD154 and CD40 signaling at the T cell/APC contact site are not well understood. We demonstrated that CD40 engagement induces the formation of disulfide-linked (dl) CD40 homodimers that predominantly associate with detergent-resistant membrane microdomains. Mutagenesis and biochemical analyses revealed that (a) the integrity of the detergent-resistant membranes is necessary for dl-CD40 homodimer formation, (b) the cytoplasmic Cys(238) of CD40 is the target for the de novo disulfide oxidation induced by receptor oligomerization, and (c) dl-CD40 homodimer formation is required for CD40-induced interleukin-8 secretion. Stimulation of CD154-positive T cells with staphylococcal enterotoxin E superantigen that mimics nominal antigen in initiating cognate T cell/APC interaction revealed that dl-CD40 homodimer formation is required for interleukin-2 production by T cells. These findings indicate that dl-CD40 homodimer formation has a physiological role in regulating bidirectional signaling.

Tumor Necrosis Factor (TNF)-Soluble High-Affinity Receptor Complex as a TNF Antagonist

A novel high-affinity inhibitor of tumor necrosis factor (TNF) is described, which is created by the fusion of the extracellular domains of TNF-binding protein 1 (TBP-1) to both the alpha and beta chains of an inactive version of the heterodimeric protein hormone, human chorionic gonadotropin. The resulting molecule, termed TNF-soluble high-affinity receptor complex (SHARC), self-assembles into a heterodimeric protein containing two functional TBP-1 moieties. The TNF-SHARC is a potent inhibitor of TNF-alpha bioactivity in vitro and has a prolonged pharmacokinetic profile compared with monomeric TBP-1 in vivo. Consistent with the long half-life, the duration of action in an lipopolysaccharide-mediated proinflammatory mouse model is prolonged similarly. In a collagen-induced arthritis mouse model, this molecule demonstrates improved efficacy over monomeric TBP-1. Based on these results, we demonstrated that inactivated heterodimeric protein hormones are flexible and efficient scaffolds for the creation of soluble high-affinity receptor complexes.

Disulfide bond cleavages observed in SORI-CID of three nonapeptides complexed with divalent transition-metal cations

Tandem MS sequencing of peptides that contain a disulfide bond is often hampered when using a slow heating technique. We show that complexation of a transition-metal ion with a disulfide-bridge-containing nonapeptide yields very rich tandem mass spectra, including fragments that involve the cleavage of the disulfide bond up to 56% of the total product ion intensity. On the contrary, MS/MS of the corresponding protonated nonapeptides results predominantly in fragments from the region that is not involved in the disulfide bond. Eleven different combinations of three nonapeptides and three metal ions were measured using Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) combined with sustained off-resonance irradiation collision induced dissociation (SORI-CID). All observed fragments are discussed with respect to four different types of product ions: neutral losses, b/y-fragmentation with and without the disulfide bond cleavage, and losses of internal amino acids without rupture of the disulfide bridge. Furthermore, it is shown that the observed complementary fragment pairs obtained from peptide-metal complexes can be used to determine the region of the binding site of the metal ion. This approach offers an efficient way to cleave disulfide-bridged structures using low energy MS/MS, which leads to increased sequence coverage and more confidence in peptide or protein assignments.

Reversed-phase liquid chromatography in-line with negative ionization electrospray mass spectrometry for the characterization of the disulfide-linkages of an immunoglobulin gamma antibody

In this report, we present a new approach for the determination of the disulfide bond connectivity in proteins using negative ionization mass spectrometry of nonreduced enzymatic digests. The mass spectrometric analysis in negative ion mode was optimized to allow in-line analysis coupled directly to the HPLC system used for the separation of the peptides resulting from enzymatic digestion. We determined the disulfide structure of a human immunoglobulin gamma 2 (IgG2) antibody containing 18 unique cysteine residues linked via 11 unique disulfide bonds. The efficiency of the gas-phase dissociation of disulfide-linked peptides using negative electrospray ionization was evaluated for an ion trap mass spectrometer and an orthogonal acceleration time-of-flight mass spectrometer. Both mass spectrometry techniques provided efficient in-source fragmentation for the identification of the disulfide-linked peptides of the antibody. Both instruments were limited in the number of disulfide bonds that could be dissociated. Seven of the 11 unique disulfide linkages have been determined, including the linkage of the light chain to the heavy chain. Only the disulfide connectivity of the hinge peptide H6H7H8H9 (C6C7VEC8PPC9PAPPVAGPSVFLFPPKPK) could not be determined (numbering the cysteine residues sequentially from the N-terminus and labeling the heavy chain cysteines "H" and the light chain cysteines "L"). However, we identified the dimer of peptide C6C7VEC8PPC9PAPPVAGPSVFLFPPKPK linked via four disulfide bonds based on the unique molecular weight of this dipeptide. The established linkages were H1 to H2, H10 to H11, H12 to H13, L1 to L2, L3 to L4, and L5 to H3H4. The intrachain linkages of the light chain (L1 to L2, L3 to L4), and heavy chain (H10 to H11, H12 to H13) domains were identical to the linkages found in IgG1 antibodies.

Trap for MAbs: characterization of intact monoclonal antibodies using reversed-phase HPLC on-line with ion-trap mass spectrometry

For the first time, the characterization of intact 150-kDa monoclonal antibodies (MAbs) using a commercially available three-dimensional ion-trap mass spectrometer (IT-MS) is reported. The IT-MS analysis was performed on-line with reversed-phase high performance liquid chromatography (RP-HPLC) on a POROS column using a nontraditional solvent system of acetonitrile, isopropanol, ethanol, and water in formic acid. The operating parameters of the IT-MS were optimized by extending the mass range to m/z 4000 and elevating the tube lens offset voltage value to around -100 V. Mass accuracy better than 300 ppm (+/-40 Da) has been routinely achieved for these macromolecules. Multiple peaks 162 Da apart due to the hexose variants of the monoclonal IgG antibodies were partially resolved in mass spectra. Several commercial and chimeric antibodies have been investigated in this study.

Collision-activated cleavage of a peptide/antibiotic disulfide linkage: possible evidence for intramolecular disulfide bond rearrangement upon collisional activation

Ceftiofur is an important veterinary beta-lactam antibiotic whose bioactive metabolite, desfuroylceftiofur, has a free thiol group. Desfuroylceftiofur (DFC) was reacted with two peptides, [Arg8]-vasopressin and reduced glutathione, both of which have cysteine residues to form disulfide-linked peptide/antibiotic complexes. The products of the reaction, [vasopressin + (DFC-H) + (DFC-H) + H]+, [(vasopressin+H) + (DFC-H) + H]+ and [(glutathione-H) + (DFC-H) + H]+, were analyzed using collision-activated dissociation (CAD) with a quadrupole ion trap tandem mass spectrometer. MS/MS of [vasopressin + (DFC-H) + (DFC-H) + H]+ resulted in facile dissociative loss of one and two covalently bound DFC moieties. Loss of one DFC resulted from either homolytic or heterolytic dissociation of the peptide/antibiotic disulfide bond with equal or unequal partitioning of the two sulfur atoms between the fragment ion and neutral loss. Hydrogen migration preceded heterolytic dissociation. Loss of two DFC moieties from [vasopressin + (DFC-H) + (DFC-H) + H]+ appears to result from collision-activated intramolecular disulfide bond rearrangement (IDBR) to produce cyclic [vasopressin + H]+ (at m/z 1084) as well as other cyclic fragment ions at m/z 1084 +/- 32 and +64. The cyclic structure of these ions could only be inferred as MS/MS may result in rearrangement to non-cyclic structures prior to dissociative loss. IDBR was also detected from MS(3) experiments of [vasopressin + (DFC-H) + (DFC-H) + H]+ fragment ions. MS/MS of [(glutathione-H) + (DFC-H) + H]+ resulted in cleavage of the peptide backbone with retention of the DFC moiety as well as heterolytic cleavage of the peptide/antibiotic disulfide bond to produce the fragment ion: [(DFC-2H) + H]+. These results demonstrate the facile dissociative loss by CAD of DFC moieties covalently attached to peptides through disulfide bonds. Published in 2004 by John Wiley & Sons, Ltd.

Biotinylation sites of tumor necrosis factor-alpha determined by liquid chromatography-mass spectrometry

Tumor pretargeting with biotinylated antibody/avidin complexes improves the therapeutic index of systemically administered biotin-tumor necrosis factor (TNF) conjugates. Since the number of biotins in this conjugate is known to be critical for activity, we have characterized the structure of different biotin-TNF conjugates, prepared by reaction with d-biotinyl-6-aminocaproic acid N-hydroxysuccinimide ester and identified the biotinylation sites by trypsin digestion, reverse-phase chromatography, and electrospray mass spectrometry analyses. The results have shown that N-terminal valine is a preferential biotinylation site at pH 5.8, half of biotins being located on the alpha-amino group of this residue in a conjugate bearing one biotin/trimer (on average). Moreover, evidence has been obtained to suggest that the remaining part of biotins are linked to the epsilon-amino group of lysine 128, 112, and 65, while lysine 11, 90, and 98 were practically unmodified. No evidence of O-biotinylation of serine, threonine and tyrosine was obtained.

Determination of disulfide bond assignments and N-glycosylation sites of the human gastrointestinal carcinoma antigen GA733-2 (CO17-1A, EGP, KS1-4, KSA, and Ep-CAM)

The GA733-2 antigen is a cell surface glycoprotein highly expressed on most human gastrointestinal carcinoma and at a lower level on most normal epithelia. It is an unusual cell-cell adhesion protein that does not exhibit any obvious relationship to the four known classes of adhesion molecules. In this study, the disulfide-bonding pattern of the GA733-2 antigen was determined using matrix-assisted laser desorption/ionization mass spectrometry and N-terminal sequencing of purified tryptic peptides treated with 2-[2'-nitrophenylsulfonyl]-3-methyl-3-bromoindolenine or partially reduced and alkylated. Numbering GA733-2 cysteines sequentially from the N terminus, the first three disulfide linkages are Cys1-Cys4, Cys2-Cys6, and Cys3-Cys5, which is a novel pattern for a cysteine-rich domain instead of the expected epidermal growth factor-like disulfide structure. The next three disulfide linkages are Cys7-Cys8, Cys9-Cys10, and Cys11-Cys12, consistent with the recently determined disulfide pattern of the thyroglobulin type 1A domain of insulin-like growth factor-binding proteins 1 and 6. Analysis of glycosylation sites showed that GA733-2 antigen contained N-linked carbohydrate but that no O-linked carbohydrate groups were detected. Of the three potential N-linked glycosylation sites, Asn175 was not glycosylated, whereas Asn88 was completely glycosylated, and Asn51 was partially glycosylated. These data show that the extracellular domain of the GA733-2 antigen consists of three distinct domains; a novel cysteine-rich N-terminal domain (GA733 type 1 motif), a cysteine-rich thyroglobulin type 1A domain (GA733 type 2 motif), and a unique nonglycosylated domain without cysteines (GA733 type 3 motif).

Determination of the disulfide bond pattern of a novel C-type lectin from snake venom by mass spectrometry

The disulfide bond pattern of Trimeresurus stejnegeri lectin (TSL), a new member of the C-type lectin family, was determined by mass spectrometry. Four intrachain disulfide bonds of TSL, Cys(3)-Cys(14), Cys(31)-Cys(131), Cys(38)-Cys(133) and Cys(106)-Cys(123), and two interchain linkages, Cys(2)-Cys(2) and Cys(86)-Cys(86), were determined. Three strategies were used in this work. One intrachain (Cys(106)-Cys(123)) and one interchain (Cys(86)-Cys(86)) disulfide linkages were detected by standard MS methods. The disulfide bonds Cys(2)-Cys(2) and Cys(3)-Cys(14) were analyzed using a modified partial reduction procedure and MS/MS. The last two disulfide bonds were characterized by a MS/MS/MS technique. The strategies developed in this work could be applied more generally to detection of disulfide bond patterns.

Expression and characterization of a recombinant soluble form of bovine tumor necrosis factor receptor type I

A recombinant soluble bovine tumor necrosis factor receptor type I (sboTNF-RI) was expressed in the methylotrophic yeast Pichia pastoris and evaluated for its ability to inhibit bovine tumor necrosis factor alpha (TNF-alpha) cytotoxicity. A cDNA encoding the extracellular domain of bovine TNF-RI was placed under the control of the powerful and tightly regulated alcohol oxidase1 (AOX1) gene promoter of the pPICZa A vector and the resulting construct integrated into the 5' region of the alcohol oxidase genes of GS115 and KM71 strains of Pichia. Soluble bovine TNF-RI was secreted into the medium following induction of the AOX1 gene promoter with methanol, and purified to greater than 95% purity by ion-exchange chromatography. In in vitro assays, the purified recombinant sboTNF-RI will block the cytolytic activity of bovine TNF-alpha on WEHI 164 cells clone 13 by 50% when used at a concentration of 170 microg/ml, and by nearly 90% when used at a concentration of 310 microg/ml. Results of this study suggest that recombinant sboTNF-RI may have therapeutic value as a TNF inhibitor in cattle with coliform mastitis.

A novel missense mutation (C30S) in the gene encoding tumor necrosis factor receptor 1 linked to autosomal-dominant recurrent fever with localized myositis in a French family

OBJECTIVE

To characterize both phenotypic (clinical features and magnetic resonance imaging [MRI] findings) and genotypic aspects of autosomal-dominant recurrent fever, also known as tumor necrosis factor receptor (TNFR)-associated periodic syndrome (TRAPS), in a French family and to investigate the role of the mutated 55-kd tumor necrosis factor alpha (TNFalpha) receptor (TNFR1) in the pathogenesis of the disease.

METHODS

The coding region of TNFR1 was sequenced in 2 individuals with TRAPS (the propositus and her grandfather) and in 3 clinically unaffected relatives. Expression of soluble TNFR1 (sTNFR1) was investigated in 3 of the family members carrying a C30S mutation in TNFR1, and was compared with the levels of soluble TNFR2 (sTNFR2) by enzyme-linked immunosorbent assay. The membrane TNFR1 expression was then compared with membrane TNFR2 levels at the surface of peripheral blood mononuclear cells by flow cytometric analysis. The clinical heterogeneity in this French family was investigated by searching polymorphic variants in the TNFalpha promoter by DNA sequencing.

RESULTS

Both the disease course and the clinical presentation in the propositus were highly indicative of TRAPS. MRI study of the segmental inflammatory process in the limbs showed abnormal signals in the muscle and subcutaneous tissue without involvement of adjacent joints or fascia. A novel missense mutation, C30S, in the first extracellular N-terminal cysteine-rich domain (CRD1) of TNFR1 was characterized in the propositus, her affected grandfather, and her clinically unaffected father. Expression of membrane TNFR1 at the surface of monocytes and polymorphonuclear leukocytes, as well as the levels of sTNFR1 in serum when the disease was not active were not modified in the 3 individuals carrying the TNFR1 C30S mutation. In contrast, during attacks, sTNFR1 levels remained abnormally low, as compared with the levels in unrelated patients with active adult-onset systemic Still's disease. The clinical heterogeneity could not be explained by a polymorphic variant in the TNFalpha promoter.

CONCLUSION

TRAPS is a distinct clinical and radiologic disease entity that is responsible for recurrent fever and migratory cellulitis-like processes with localized myositis. We have identified a novel TNFR1 mutation, C30S, that is located in the CRD1 domain in a French family affected by the disease. This mutation seems to affect the level of sTNFR1, which did not increase in the propositus during inflammatory attacks.

Development of disulfide peptide mapping and determination of disulfide structure of recombinant human osteoprotegerin chimera produced in Escherichia coli

Recombinant human osteoprotegerin chimera is a 90-kDa protein containing a human IgG Fc domain fused to human osteoprotegerin. The molecule is a dimer linked by two intermolecular disulfide bonds and contains eleven intramolecular disulfide bonds per monomer. A cysteine-rich region in osteoprotegerin contains nine disulfide bridges homologous to the cysteine-rich signature structure of the tumor necrosis factor receptor/nerve growth factor receptor superfamily. In this report, we have developed peptide mapping procedures suitable to generate disulfide-containing peptides for disulfide structure assignment of the fusion molecule. The methods employed included proteolytic digestion using endoproteinases Glu-C and Lys-C in combination followed by LC-MS analyses. Disulfide linkages of peptide fragments containing a single disulfide bond were assigned by sequence analysis via detection of (phenylthiohydantoinyl) cystine and/or by MS analysis. Disulfide bonds of a large, core fragment containing three peptide sequences linked by four disulfides were assigned after generation of smaller disulfide-linked peptides by a secondary thermolysin digestion. Disulfide structures of peptide fragments containing two disulfide bonds were assigned using matrix-assisted laser desorption ionization mass spectrometry with postsource decay. Both the inter- and intramolecular disulfide linkages of the chimeric dimer were confirmed.

Strategies for locating disulfide bonds in a monoclonal antibody via mass spectrometry

The location of the disulfide bonds in a recombinant monoclonal antibody was confirmed by matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF) and electrospray ionization (ESI) mass spectrometry (MS). A non-reduced Endoproteinase Lys-C (Endo Lys-C) digest of the antibody was analyzed directly by MALDI-TOFMS. The sample was then reduced on-plate by depositing dithiothreitol (DTT) on the sample spot and re-analyzed by MALDI-TOFMS. The disulfide bonds were assigned based on the disappearance of certain mass ions in the non-reduced digest and the appearance of product ions in the reduced digest. A rapid LC/ESI-MS protocol was also developed to determine the location of the disulfide bonds. The peptides generated from the Endo Lys-C digest of the antibody were partially separated on a high performance liquid chromatography (HPLC) column by utilizing a steep gradient and analyzed by ESI-MS. The masses of the partially resolved peptides were determined by deconvoluting the mass spectra.

Pharmacokinetics, immunogenicity, and efficacy of dimeric TNFR binding proteins in healthy and bacteremic baboon

Immunogenicity, pharmacokinetics, and therapeutic efficacy of three novel dimeric soluble tumor necrosis factor (TNF)-receptor I constructs [TNF-binding protein (bp)] were evaluated in 28 baboons, 12 of which were healthy and 16 were challenged with a lethal Escherichia coli bacteremia. The three constructs differed only in the number of extracellular domains of the TNF receptor I and were dimerized with polyethylene glycol. Although all three constructs had generally similar pharmacokinetics when administered to a naive animal, they differed quantitatively in their immunogenicity. Antibodies were detected more frequently, and titers were significantly higher (P < 0.05) in both healthy and septic baboons that received the 4.0-domain TNF-bp construct, compared with animals receiving the 2.6-domain construct. When the TNF-bp constructs were administered a second time (21 days later), the half-lives of the three constructs were significantly shorter in animals that had an antibody response after the first injection. In contrast, all three TNF-bp constructs were equally effective at improving outcome, blocking a systemic TNF-alpha response, and attenuating the cytokine responses when administered at a dose of 1.0 mg/kg body wt 1 h before a lethal E. coli infusion. The findings suggest that immunogenicity of TNF-bp constructs can be altered by changing the number of functional domains, without affecting their capacity to neutralize TNF-alpha and to abrogate TNF-mediated pathology.