T-cell engagers (TCEs), i.e., bispecific antibodies targeting CD3 and a tumor-associated antigen, have ignited a lot of excitement in the immuno-oncology field. These compounds have often proved efficient in preclinical studies, but their translatability to the clinic strongly depends on the experimental settings, and the preclinical models used. To best assess TCEs’ efficacy and toxicity, the immune system needs to be intact and functional, making immunocompetent mice expressing a human CD3 an attractive choice.
The challenges of expressing human CD3 in mice
Several groups have generated mouse models expressing a human, or a mouse/human chimeric form of, CD3ε, the CD3 chain required for TCR-CD3 complex formation and T-cell activation. However, these models presented T-cell deficiencies (in counts and/or function), or even showed thymic dysplasia.1,2 These observations underline the utmost importance of genetic design when generating a genetically humanized model. In the case of CD3ε, the “humanized” CD3ε chimeric protein must preserve its capacity to interact with other CD3 chains to form the TCR-CD3 complex, and thus activate T cells.
Minimal humanization of CD3epsilon preserves T-cell development and function
A recent paper published in Scientific Reports3 showed that, by replacing 5 amino acids of murine CD3 with 11 amino acids of its human counterpart, mice maintained normal T cell development, frequencies, and function.
The authors also tested the ability of these T cells to mediate cytotoxic killing of murine B cells upon treatment with a TCE. Finally, CD3ε humanized mice were treated with this same TCE to test B cell depletion in vivo. A single dose of the hCD3-mCD20 bispecific antibody resulted in the complete depletion of CD19-positive B cells. These data show that this novel hCD3ε mouse model can be used to assess TCE in vivo, while preserving functional antibody-dependent cellular cytotoxicity.
Of note, the hCD3ε mouse model described in this publication was designed and generated by genOway, a designer and provider of numerous physiologically relevant preclinical models in multiple research areas, including immuno-oncology, metabolism, cardiovascular diseases, and neuroscience. A similar hCD3ε mouse model for assessment of TCE efficacy is available off the shelf at genOway.
Wang, B. et al. A block in both early T lymphocyte and natural killer cell development in transgenic mice with high-copy numbers of the human CD3E gene. Proc. Natl. Acad. Sci. U.S.A. 91, 9402–9406.
Ueda, O. et al. Entire CD3epsilon, delta, and gamma humanized mouse to evaluate human CD3-mediated therapeutics. Sci. Rep.7, 45839.
Zorn JA, et al. Humanization of a strategic CD3 epitope enables evaluation of clinical T-cell engagers in a fully immunocompetent in vivo model. Sci Rep. 2022 Mar 3;12(1):3530. .
hCD3ε immunocompetent mice enable the preclinical in vivo efficacy assessment of T-cell engagers, to study cancer cell recognition, immunosuppressant therapies, etc.