Background: IgG4 antibodies are able to undergo a process termed Fab arm exchange (FAE). Results: A novel method for quantifying FAE in physiologically relevant matrices was developed. Conclusion: A hinge mutation in IgG4 antibodies inhibits FAE to undetectable levels in the immunoassays described herein. Significance: These methods are valuable for investigating and assessing the factors affecting and controlling IgG4 FAE.

Administration of antibodies to sclerostin (Scl-Ab) has been shown to increase bone mass, bone mineral density (BMD) and bone strength by increasing bone formation and decreasing bone resorption in both animal studies and human clinical trials. In these studies, the magnitude and rate of increase in bone formation markers is attenuated upon repeat dosing with Scl-Ab despite a continuous and progressive increase in BMD. Here, we investigated whether the attenuation in the bone formation response following repeated administration of Scl-Ab was associated with increased expression of secreted antagonists of Wnt signalling and determined how the circulating marker of bone formation, P1NP, responded to single, or multiple doses, of Scl-Ab four days post-dosing. Female Balb/c mice were treated with Scl-Ab and we demonstrated that the large increase in serum P1NP observed following the first dose was reduced following administration of multiple doses of Scl-Ab. This dampening of the P1NP response was not due to a change in the kinetics of the bone formation marker response, or differences in exposure to the drug. The abundance of transcripts encoding several secreted Wnt antagonists was determined in femurs collected from mice following one or six doses of Scl-Ab, or vehicle treatment. Compared with vehicle controls, expression of SOST, SOST-DC1, DKK1, DKK2, SFRP1, SFRP2, FRZB, SFRP4 and WIF1 transcripts was significantly increased (approximately 1.5-4.2 fold) following a single dose of Scl-Ab. With the exception of SFRP1, these changes were maintained or further increased following six doses of Scl-Ab and the abundance of SFRP5 was also increased. Up-regulation of these Wnt antagonists may exert a negative feedback to increased Wnt signalling induced by repeated administration of Scl-Ab and could contribute to self-regulation of the bone formation response over time. After an antibody-free period of four weeks or more, the P1NP response was comparable to the naïve response, and a second phase of treatment with Scl-Ab following an antibody-free period elicited additional gains in BMD. Together, these data demonstrate that the rapid dampening of the bone formation response in the immediate post-dose period which occurs after repeat dosing of Scl-Ab is associated with increased expression of Wnt antagonists, and a treatment-free period can restore the full bone formation response to Scl-Ab.

1 The aims of the present study were to determine the profile of tumour necrosis factor (TNF) release, and the effect of monoclonal antibodies to TNF, on the changes in regional haemodynamics and the responses to vasodilator and vasoconstrictor challenges, during a continuous 24 h low dose infusion of lipopolysaccharide (LPS) in conscious rats. 2 Male Long Evans rats were chronically instrumented for measurement of regional haemodynamics (renal, superior mesenteric and hindquarters) and were challenged with 3 min infusions of acetylcholine (22 nmol min-'), methoxamine (120 nmol min-'), salbutamol (0.83 nmol min-') and bradykinin (14.4 nmol min-'). The rats were given either saline, or the TNF antibodies, TN3gl or TN3g2a, 1 h before the start of a continuous infusion of LPS (150 pg kg -' h -') and were subsequently re-tested with the vasodilator and vasoconstrictor challenges 2, 6 and 24 h after the start of the LPS infusion. 3 Prior to infusion of LPS, TNF was not detectable in the plasma. During continuous infusion of LPS there was a transient elevation in plasma TNF levels, reaching a maximum (-2300 pg ml-') after approximately 1 h, and returning to undetectable levels after approximately 3 h of LPS infusion. 4 In the saline pretreated group, after 1-2 h of LPS infusion, there was a small hypotension and a marked renal vasodilatation; 6 h after the start of LPS infusion there was a minor elevation in MAP above control levels, renal vasodilatation was maintained and a hindquarters vasoconstriction occurred; after 24 h of LPS infusion, there was a hypotension and renal and hindquarters vasodilatation. There were significant reductions in the tachycardic and renal vasodilator responses and an enhanced depressor response to acetylcholine after 24 h of LPS infusion. LPS infusion also caused a generalized hyporesponsiveness to the cardiovascular effects of methoxamine and salbutamol. The major changes in response to bradykinin were reduced tachycardic and enhanced depressor responses throughout the LPS infusion, a biphasic decrease and increase in renal conductance and enhanced hindquarters vasodilatation at 24 h. 5 Pretreatment with either TN3gl or TN3g2a antibodies had no major effects on the changes in resting haemodynamics, or on the changes in response to methoxamine, salbutamol or bradykinin challenges during LPS infusion. However, the tachycardic responses to acetylcholine were generally preserved, and its hypotensive effect after 24 h of LPS infusion was not enhanced after TN3gl or TN3g2a pretreatment. Thus, despite substantial, but transient, elevation of plasma TNF levels during continuous LPS infusion, it appears that the majority of cardiovascular changes were dependent on factors other than plasma TNF.

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Interleukin-6 (IL-6) is implicated in the pathophysiology of several inflammatory conditions. Olokizumab, a humanized anti-IL-6 monoclonal antibody, selectively blocks the final assembly of the IL-6 signaling complex. A randomized, doubleblind, placebo-controlled, phase I dose-escalation study assessed the safety and tolerability of escalating single doses of olokizumab administered intravenously (iv) or subcutaneously (sc) to 67 healthy male volunteers. The pharmacokinetics, pharmacodynamics and immunogenicity of olokizumab were also assessed. Olokizumab was tolerated at doses up to 3.0 mg/kg sc and 10.0 mg/kg iv; the maximum tolerated dose was not reached. No serious adverse events or withdrawals as a result of treatment-emergent adverse events were reported. Pharmacokinetic analysis showed that both maximum serum concentration and area under the concentration-time curve increased linearly with increasing dose. Mean terminal half-life was 31.5 days (standard deviation 12.4 days). The bioavailability of the sc doses ranged from 84.2% to 92.5%. Rapid decreases in C-reactive protein concentrations were observed, with no dose dependency.