Use of a Tc-99m labeled anti-TNF alpha monoclonal antibody in Crohn's disease: in vitro and in vivo studies

Aim. Crohn's disease (CD) is a chronic inflammatory bowel disease characterized by a cellular-mediated immune response driven by cytokines secreted mainly by T helper 1 cells (Th1). in active phases of the disease, an increased production and release of tumor necrosis factor alpha (TNF alpha) by macrophages and monocytes; of the lamina propria has been described. The aim of this study was to detect the presence of TNFa within the gut mucosa in patients with active CD by using Tc-99m-labelled chimeric human/mouse monoclonal antibody anti-TNF alpha (Infliximab, Remicade (R)). Methods. Infliximab has been labeled with Tc-99m after reduction of disulfide bound by 2-ME method. In vitro binding assay and biodistribution in animal of [Tc-99m]Infliximab has been performed to evaluate the retention of its biological activity. Ten patients with active CD refractory to conventional medical therapies were studied. images of the abdomen were acquired at 6 to 20 h after i.v. injection of about 10 mCi of [Tc-99m]Infliximab and a week later, all patients were also studied with [Tc-99m]HMPAO-labeled autologous white blood cells (WBC). Results. A product with high labeling efficiency (>95%) and stability has been obtained. In vitro tests with stimulated T-cells expressing TNFa indicated that [Tc-99m] Infliximab retains its binding activity to cell bound TNFa as compared to unlabelled Infliximab. The degree of [Tc-99m]Infliximab uptake by the inflamed bowel evaluated at 20 h postinjection was much less than that seen with labeled WBC and with a different distribution. Three of these patients received anti-TNF alpha (Infliximab) for therapeutic purposes with good clinical results despite the scintigraphy with Tc-99m-Infliximab was negative in 2 of them. Conclusion Scintigraphy with [Tc-99m]Infliximab shows the presence of little TNF alpha in the affected bowel of patients with active CD. Therefore, the clinical benefit that patients have from Infliximab therapy is unlikely die consequence of a local a reduction of TNF alpha and the mechanism of action of Infliximab, in therapeutic doses, deserves further investigations