AACR 2021: Double-humanized 4-1BB/4-1BBL mouse is an advanced model for liver toxicity and efficacy evaluation of 4-1BB therapeutic antibodies
4-1BB is an activation-induced costimulatory TNF receptor family member which is expressed on a variety of cell types such as activated T cells, NK cells, dendritic cells, B cells, monocytes and Neutrophils. 4-1BB/4-1BBL interaction leads to a series of activation effects including increased cytotoxic T lymphocytes (CTL) activity, cytokine induction, prevention of activation-induced cells death (AICD).
Agonistic monoclonal antibodies targeting 4-1BB have shown robust anti-tumor activity but have also caused substantial liver toxicity which hampered their clinical development. To better assist the efficacy and toxicity evaluation of anti-4-1BB antibodies, Biocytogen developed a 4-1BB/4-1BBL double humanized knock-in mice, which is the second generation of humanized 4-1BB mice.
In the double humanized mouse, the exons of mouse 4-1BBL and 4-1BB genes that encode the transmembrane domain and extracellular domain were replaced by human counterpart exons. The expression of knocked in exons was confirmed by both RT-PCR and Flow cytometry. In vivo efficacy study showed that 4-1BB antibodies significantly inhibited tumor growth in mice bearing the colon cancer cell line MC38 and this effect was dose-dependent. The tumor growth inhibition (TGI) reached approximately 70% in the mice group dosed 1mg/kg. More importantly, the Toxicity study showed that compared to the single humanized 4-1BB mice, double humanized 4-1BB/4-1BBL mice have higher sensitivity on liver toxicity testing, reflected by sera AST and ALT level as well as liver pathological analysis. These results indicate that the double humanized B-h4-1BB/h4-1BBL mouse model, by mimicking a more human-like 4-1BB and 4-1BBL interaction, has been proved to be a more advanced option for preclinical toxicity and efficacy evaluation for 4-1BB therapeutic antibodies compared to single humanized 4-1BB mice.