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.
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.
Amann
Maria
M
Micromet AG, Munich, Germany. Maria.Amann@Micromet.de
Friedrich
Matthias
M
Lutterbuese
Petra
P
Vieser
Eva
E
Lorenczewski
Grit
G
Petersen
Laetitia
L
Brischwein
Klaus
K
Kufer
Peter
P
Kischel
Roman
R
Baeuerle
Patrick A
PA
Schlereth
Bernd
B
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
D000951:Antigens, Neoplasm; D015815:Cell Adhesion Molecules; D000071858:Epithelial Cell Adhesion Molecule; D018984:Epitopes, T-Lymphocyte; D011994:Recombinant Proteins