Therapeutic window of an EpCAM/CD3-specific BiTE antibody in mice is determined by a subpopulation of EpCAM-expressing lymphocytes that is absent in humans

Cancer Immunol Immunother. 2009 Jan;58(1):95-109. doi: 10.1007/s00262-008-0529-y. Epub 2008 Jul 2.


MuS110 is a BiTE antibody bispecific for murine EpCAM (CD326) and murine CD3. A recent study has shown that microS110 has significant anti tumor activity at well-tolerated doses as low as 5 microg/kg in orthotopic breast and lung cancer models (Amann et al. in Cancer Res 68:143-151, 2008). Here, we have explored the safety profile of microS110 at higher doses. Escalation to 50 microg/kg microS110 caused in mice transient loss of body weight, and transient piloerection, hypomotility, hypothermia and diarrhoea. These clinical signs coincided with serum peaks of TNF-alpha, IL-6, IL-2, IFN-gamma and IL-4, and an increase of surface markers for T cell activation. Because activation of T cells in response to BiTE antibodies is typically dependent on target cells, we analyzed mouse blood for the presence of EpCAM(+) cells. Various mouse strains presented with a subpopulation of 2-3% EpCAM(+) blood cells, mostly B and T lymphocytes, which was not detected in human blood samples. In vitro experiments in which the number of EpCAM(+) cells in blood samples was either reduced or increased suggested that both T cell activation and cytokine release in response to microS110 was dependent on the number of target-expressing cells. In support for a role of EpCAM(+) lymphocytes in the observed side effects, reduction of EpCAM(+) blood cells in mice via a low-dose pre treatment with microS110 dramatically increased the tolerability of animals up to at least 500 microg/kg of the BiTE antibody. This high tolerability to microS110 occurred in the presence of non-compromised T cells. No damage to EpCAM(+) epithelial tissues was evident from histopathological examination of animals daily injected with 100 microg/kg microS110 for 28 days. In summary, these observations suggest that side effects of microS110 in mice were largely caused by an acute T cell activation that was triggered by a subpopulation of EpCAM(+) lymphocytes. Because humans have extremely low numbers of EpCAM(+) cells in blood, this toxicity of an EpCAM-specific BiTE may be specific for mice.

MeSH terms

  • Animals
  • Antigens, Neoplasm / blood*
  • Antigens, Neoplasm / genetics
  • Antigens, Neoplasm / metabolism
  • CHO Cells
  • Cell Adhesion Molecules / blood*
  • Cell Adhesion Molecules / genetics
  • Cell Adhesion Molecules / metabolism
  • Cell Line, Tumor
  • Cricetinae
  • Cricetulus
  • Epithelial Cell Adhesion Molecule
  • Epitopes, T-Lymphocyte / blood*
  • Female
  • Humans
  • Lymphocyte Activation
  • Lymphocyte Subsets* / metabolism
  • Mice
  • Mice, Inbred BALB C
  • Mice, Inbred C57BL
  • Recombinant Proteins / genetics
  • Species Specificity


  • Antigens, Neoplasm
  • Cell Adhesion Molecules
  • Epithelial Cell Adhesion Molecule
  • Epitopes, T-Lymphocyte
  • Recombinant Proteins