Simple and highly sensitive assay system for TNFR2-mediated soluble- and transmembrane-TNF activity

An immunocytokine consisting of a TNFR2 agonist and TNFR2 scFv enhances the expansion of regulatory T cells through TNFR2 clustering

Regulatory T cells (Tregs) are lymphocytes that play a central role in peripheral immune tolerance. Tregs are promising targets for the prevention and suppression of autoimmune diseases, allergies, and graft-versus-host disease, and treatments aimed at regulating their functions are being developed. In this study, we created a new modality consisting of a protein molecule that suppressed excessive immune responses by effectively and preferentially expanding Tregs. Recent studies reported that tumor necrosis factor receptor type 2 (TNFR2) expressed on Tregs is involved in the proliferation and activation of Tregs. Therefore, we created a functional immunocytokine, named TNFR2-ICK-Ig, consisting of a fusion protein of an anti-TNFR2 single-chain Fv (scFv) and a TNFR2 agonist TNF-α mutant protein, as a new modality that strongly enhances TNFR2 signaling. The formation of agonist-receptor multimerization (TNFR2 cluster) is effective for the induction of a strong TNFR2 signal, similar to the TNFR2 signaling mechanism exhibited by membrane-bound TNF. TNFR2-ICK-Ig improved the TNFR2 signaling activity and promoted TNFR2 cluster formation compared to a TNFR2 agonist TNF-α mutant protein that did not have an immunocytokine structure. Furthermore, the Treg expansion efficiency was enhanced. TNFR2-ICK-Ig promotes its effects via scFv, which crosslinks receptors whereas the agonists transmit stimulatory signals. Therefore, this novel molecule expands Tregs via strong TNFR2 signaling by the formation of TNFR2 clustering.

Structural optimization of a TNFR1-selective antagonistic TNFα mutant to create new-modality TNF-regulating biologics

Excessive activation of the proinflammatory cytokine tumor necrosis factor-α (TNFα) is a major cause of autoimmune diseases, including rheumatoid arthritis. TNFα induces immune responses via TNF receptor 1 (TNFR1) and TNFR2. Signaling via TNFR1 induces proinflammatory responses, whereas TNFR2 signaling is suggested to suppress the pathophysiology of inflammatory diseases. Therefore, selective inhibition of TNFR1 signaling and preservation of TNFR2 signaling activities may be beneficial for managing autoimmune diseases. To this end, we developed a TNFR1-selective, antagonistic TNFα mutant (R1antTNF). Here, we developed an R1antTNF derivative, scR1antTNF-Fc, which represents a single-chain form of trimeric R1antTNF with a human IgG-Fc domain. scR1antTNF-Fc had properties similar to those of R1antTNF, including TNFR1-selective binding avidity, TNFR1 antagonistic activity, and thermal stability, and had a significantly extended plasma t _1/2 in vivo In a murine rheumatoid arthritis model, scR1antTNF-Fc and 40-kDa PEG-scR1antTNF (a previously reported PEGylated form) delayed the onset of collagen-induced arthritis, suppressed arthritis progression in mice, and required a reduced frequency of administration. Interestingly, with these biologic treatments, we observed an increased ratio of regulatory T cells to conventional T cells in lymph nodes compared with etanercept, a commonly used TNF inhibitor. Therefore, scR1antTNF-Fc and 40-kDa PEG-scR1antTNF indirectly induced immunosuppression. These results suggest that selective TNFR1 inhibition benefits the management of autoimmune diseases and that R1antTNF derivatives hold promise as new-modality TNF-regulating biologics.

A trimeric structural fusion of an antagonistic tumor necrosis factor-α mutant enhances molecular stability and enables facile modification

Tumor necrosis factor-α (TNF) exerts its biological effect through two types of receptors, p55 TNF receptor (TNFR1) and p75 TNF receptor (TNFR2). An inflammatory response is known to be induced mainly by TNFR1, whereas an anti-inflammatory reaction is thought to be mediated by TNFR2 in some autoimmune diseases. We have been investigating the use of an antagonistic TNF mutant (TNFR1-selective antagonistic TNF mutant (R1antTNF)) to reveal the pharmacological effect of TNFR1-selective inhibition as a new therapeutic modality. Here, we aimed to further improve and optimize the activity and behavior of this mutant protein both in vitro and in vivo Specifically, we examined a trimeric structural fusion of R1antTNF, formed via the introduction of short peptide linkers, as a strategy to enhance bioactivity and molecular stability. By comparative analysis with R1antTNF, the trimeric fusion, referred to as single-chain R1antTNF (scR1antTNF), was found to retain in vitro molecular properties of receptor selectivity and antagonistic activity but displayed a marked increase in thermal stability. The residence time of scR1antTNF in vivo was also significantly prolonged. Furthermore, molecular modification using polyethylene glycol (PEG) was easily controlled by limiting the number of reactive sites. Taken together, our findings show that scR1antTNF displays enhanced molecular stability while maintaining biological activity compared with R1antTNF.

Creation of mouse TNFR2-selective agonistic TNF mutants using a phage display technique

Tumor necrosis factor-α (TNF), which is an immuno-modulatory cytokine, has been suggested to cause inflammatory responses as well as protection against tissue dysfunction by binding two types of TNF receptor (TNFR1/TNFR2). However, the physiological effects of TNFR2-specific activation remain unclear. We therefore aimed to generate a TNF mutant with full TNFR2-selective agonist activity as a functional analytical tool. In this study, we utilized a phage display technique to create mouse TNFR2 (mTNFR2)-selective TNF mutants that bind specifically to mTNFR2 and show full bioactivity compared with wild-type TNF. A new phage library displaying TNF mutants was created, in which nine amino acid residues at the predicted receptor-binding site were randomized. From this library, an agonistic TNF mutant exhibiting high binding selectivity and bioactivity to mTNFR2 was isolated. We propose that this TNF mutant would be a powerful tool with which to elucidate the functional roles of mTNFR2.

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We generated a TNF mutant with full TNFR2-selective agonist activity.

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This mutant was identified using a phage display technique.

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This agonist exhibited high binding selectivity and bioactivity to mouse TNFR2.

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This would be a powerful tool to elucidate the functional roles of mouse TNFR2.

[Development of New Biologics through Creation of a Functional Cytokine Mutant]

The clinical use of cytokines is fairly limited because of their characteristics of having significant bioactivity and low stability, although some are useful biopharmaceuticals, such as interferon. Cytokines, which are secreted from various immune cells, show many kinds of bioactivities including unexpected activities; thus it would be desirable to regulate cytokine activity. Recently, we have developed a new drug delivery system (DDS) to create structural mutant cytokines using a phage display system. This system can produce functional mutant proteins that can bind their objective targets specifically. In this study, tumor necrosis factor (TNF) was used as a model cytokine to create agonist and antagonist activities against two TNF receptors TNFR1 and TNFR2, respectively. We created a phage library expressing mutant TNF, where the amino acids in the binding interface between TNF and TNF receptors were alternately exchanged. Affinity panning was performed at the optimum condition and the bioactivities of these mutant TNFs were analyzed to obtain the objective agonists or antagonists. The pharmacological activity and toxicity of these engineered TNF mutants could indicate their potential use as novel biopharmaceutical agents.

Mutants of lymphotoxin-α with augmented cytotoxic activity via TNFR1 for use in cancer therapy

The cytokine lymphotoxin-α (LTα) is a promising candidate for use in cancer therapy. However, the instability of LTαin vivo and the insufficient levels of tumor necrosis factor receptor 1 (TNFR1)-mediated bioactivity of LTα limit its therapeutic potential. Here, we created LTα mutants with increased TNFR1-mediated bioactivity by using a phage display technique. We constructed a phage library displaying lysine-deficient structural variants of LTα with randomized amino acid residues. After affinity panning, we screened three clones of lysine-deficient LTα mutant, and identified a LTα mutant with TNFR1-mediated bioactivity that was 32 times that of the wild-type LTα (wtLTα). When compared with wtLTα, the selected clone showed augmented affinity to TNFR1 due to slow dissociation rather than rapid association. In contrast, the mutant showed only 4 times the TNFR2-mediated activity of wtLTα. In addition, the LTα mutant strongly and rapidly activated caspases that induce TNFR1-mediated cell death, whereas the mutant and wtLTα activated nuclear factor-kappa B to a similar extent. Our data suggest that the kinetics of LTα binding to TNFR1 play an important role in signal transduction patterns, and a TNFR1-selective LTα mutant with augmented bioactivity would be a superior candidate for cancer therapy.

Generation of mouse macrophages expressing membrane-bound TNF variants with selectivity for TNFR1 or TNFR2

Tumor necrosis factor-alpha (TNF) is expressed on the cell surface as a transmembrane form (tmTNF), that can be released as a soluble form (solTNF) via proteolytic cleavage. These two types of TNF exert their biological functions by binding to one of two TNF receptors, TNFR1 or TNFR2. However, the biological function of tmTNF through these two receptors remains to be determined. Here, we generated macrophages that expressed tmTNF mutants with selectivity for either TNFR1 or TNRF2 as a tool to evaluate signaling through these receptors. Wild-type TNF (wtTNF), TNFR1-selective mutant TNF (mutTNF-R1) or TNFR2-selective mutant TNF (mutTNF-R2) were individually expressed on the TNFR1(-/-)R2(-/-) mouse macrophages (Mphi) as the tmTNF forms. tm-mutTNF-R1-expressing Mphi exhibited significant selectivity for binding to TNFR1, whereas tm-mutTNF-R2-expressing Mphi only showed a slight selectivity for binding to TNFR2. Signaling by tm-mutTNF-R1-expressing Mphi through the hTNFR2 was weaker than that of tm-wtTNF-expressing Mphi, suggesting that the binding selectivity correlated with functional selectivity. Interestingly, signaling by tm-mutTNF-R2-expressing Mphi through TNFR2 was much stronger than signaling by tm-wtTNF-expressing Mphi, whereas signaling by the corresponding soluble form was weaker than that mediated by wtTNF. These results indicate tmTNF variants might prove useful for the functional analysis of signaling through TNF receptors.

Structure-function relationship of tumor necrosis factor (TNF) and its receptor interaction based on 3D structural analysis of a fully active TNFR1-selective TNF mutant

Tumor necrosis factor (TNF) is an important cytokine that suppresses carcinogenesis and excludes infectious pathogens to maintain homeostasis. TNF activates its two receptors [TNF receptor (TNFR) 1 and TNFR2], but the contribution of each receptor to various host defense functions and immunologic surveillance is not yet clear. Here, we used phage display techniques to generate receptor-selective TNF mutants that activate only one TNFR. These TNF mutants will be useful in the functional analysis of TNFR. Six amino acids in the receptor binding interface (near TNF residues 30, 80, and 140) were randomly mutated by polymerase chain reaction. Two phage libraries comprising over 5 million TNF mutants were constructed. By selecting the mutants without affinity for TNFR1 or TNFR2, we successfully isolated 4 TNFR2-selective candidates and 16 TNFR1-selective candidates, respectively. The TNFR1-selective candidates were highly mutated near residue 30, whereas TNFR2-selective candidates were highly mutated near residue 140, although both had conserved sequences near residues 140 and 30, respectively. This finding suggested that the phage display technique was suitable for identifying important regions for the TNF interaction with TNFR1 and TNFR2. Purified clone R1-6, a TNFR1-selective candidate, remained fully bioactive and had full affinity for TNFR1 without activating TNFR2, indicating the usefulness of the R1-6 TNF mutant in analyzing TNFR1 receptor function. To further elucidate the receptor selectivity of R1-6, we examined the structure of R1-6 by X-ray crystallography. The results suggested that R31A and R32G mutations strongly influenced electrostatic interaction with TNFR2, and that L29K mutation contributed to the binding of R1-6 to TNFR1. This phage display technique can be used to efficiently construct functional mutants for analysis of the TNF structure-function relationship, which might facilitate in silico drug design based on receptor selectivity.