Transient lymphocyte decrease due to adhesion and migration following catumaxomab (anti-EpCAM x anti-CD3) treatment...

Area of Science:

• Immunology
• Oncology
• Pharmacology

Background:

• A transient decrease in peripheral blood lymphocyte counts was observed in patients after intraperitoneal administration of the trifunctional monoclonal antibody catumaxomab (anti-EpCAM x anti-CD3).
• The underlying mechanism for this observed effect required further investigation.

Purpose of the Study:

• To investigate the effect of catumaxomab on lymphocyte counts in a preclinical mouse model.
• To elucidate the in vitro mechanism of action responsible for the observed lymphocyte redistribution.

Main Methods:

• Administration of a related antibody (BiLu) to mice to analyze blood leukocytes.
• In vitro studies using human peripheral blood mononuclear cells (PBMC) to assess T cell activation, cytokine secretion, and adhesion to endothelial cells.
• Flow cytometry was used to quantify adherent T cells.

Main Results:

• BiLu treatment in mice led to a dose-dependent, transient decrease in CD3+ T cells (CD4+ and CD8+), with counts normalizing within 48 hours.
• Catumaxomab induced T cell activation (CD69 expression) and cytokine release (TNFα, IFNγ) in vitro.
• Catumaxomab dose-dependently enhanced T cell adhesion to endothelial cells, further increased by TNFα-induced endothelial cell activation.

Conclusions:

• Catumaxomab enhances T cell adhesion to endothelial cells via antibody-mediated T cell activation and subsequent cytokine production.
• This mechanism, involving upregulation of endothelial cell adhesion molecules, explains the transient, reversible decrease in lymphocyte counts observed in patients.
• The findings suggest lymphocyte redistribution as the cause for the observed clinical effect.