Immunological changes in the ascites of cancer patients after intraperitoneal administration of the bispecific antibody catumaxomab (anti-EpCAM × anti-CD3)

• The intraperitoneal infusion of catumaxomab activates T cells, NK cells and macrophages in the ascites of tumour patients.
• The intraperitoneal infusion of catumaxomab favours CD8+ T cell accumulation in ascites.
• The pervasive immunosuppressive ability of ascites is neutralised when both catumaxomab Fab arms bind their cognate antigens (EpCAM and CD3).

ObjectiveTo explore the effects of intraperitoneal (i.p.) infusion of catumaxomab, a bispecific monoclonal antibody (anti-EpCAM × anti-CD3), on T cells, NK cells and macrophages in ascites of cancer patients and to understand how ascitic immune cells can be activated despite the pervasive immunosuppressive ability of ascites microenvironment.MethodsSix patients with malignant ascites received i.p. catumaxomab infusion. Ascitic immune cells were profiled by flow cytometry and gene expression at baseline and after i.p. catumaxomab infusion. In vitro experiments enabled investigations on the adverse effect of ascites microenvironment on catumaxomab-stimulated immune cells.ResultsI.p. catumaxomab infusion enhanced the expression of the CD69 and CD38 activation molecules in CD4+ and CD8+ T cells, NK cells and macrophages, and favoured CD8+ T cell accumulation into the peritoneal cavity. An analogous immune cell activation as well as IFN-γ and IL-2 production were induced by catumaxomab in vitro. In vitro experiments showed that the immunosuppressive milieu of ascites abrogated all the immunostimulatory activities of catumaxomab. Adding EpCAM+ tumour cells to the culture permitted both catumaxomab Fab regions to engage cognate antigens and restored immunostimulatory catumaxomab activity.ConclusionsThis is the first demonstration in a clinical setting that i.p. catumaxomab infusion activates NK cells and macrophages in addition to T cells in ascites and favours CD8+ T cell accumulation into the peritoneal cavity. Moreover, our findings indicate that the concomitant binding of both catumaxomab Fab regions delivers an activation signal that is strong enough to activate immune cells despite the prevailing immunosuppressive environment of malignant ascites.