title: 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.
abstract: 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.
authors.affiliation: Micromet AG, Munich, Germany. Maria.Amann@Micromet.de
authors.forename: Maria
authors.initials: M
authors.lastname: Amann
authors.forename: Matthias
authors.initials: M
authors.lastname: Friedrich
authors.forename: Petra
authors.initials: P
authors.lastname: Lutterbuese
authors.forename: Eva
authors.initials: E
authors.lastname: Vieser
authors.forename: Grit
authors.initials: G
authors.lastname: Lorenczewski
authors.forename: Laetitia
authors.initials: L
authors.lastname: Petersen
authors.forename: Klaus
authors.initials: K
authors.lastname: Brischwein
authors.forename: Peter
authors.initials: P
authors.lastname: Kufer
authors.forename: Roman
authors.initials: R
authors.lastname: Kischel
authors.forename: Patrick A
authors.initials: PA
authors.lastname: Baeuerle
authors.forename: Bernd
authors.initials: B
authors.lastname: Schlereth
mesh_terms: D000818:Animals; D000951:Antigens, Neoplasm / Q000097:blood* / Q000235:genetics / Q000378:metabolism; D016466:CHO Cells; D015815:Cell Adhesion Molecules / Q000097:blood* / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D006224:Cricetinae; D003412:Cricetulus; D000071858:Epithelial Cell Adhesion Molecule; D018984:Epitopes, T-Lymphocyte / Q000097:blood*; D005260:Female; D006801:Humans; D008213:Lymphocyte Activation; D016131:Lymphocyte Subsets / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D011994:Recombinant Proteins / Q000235:genetics; D013045:Species Specificity
chemical_list: D000951:Antigens, Neoplasm; D015815:Cell Adhesion Molecules; D000071858:Epithelial Cell Adhesion Molecule; D018984:Epitopes, T-Lymphocyte; D011994:Recombinant Proteins