Immunogenicity can obscure efficacy
Biologic drugs such as monoclonal antibodies or RNA therapies can trigger immune reactions (immunogenicity) upon treatment. Such immune reactions can result in toxicity. Aside from potential safety problems, the immune reaction can also reduce the efficacy of the biologic drug. Production of neutralizing anti-drug antibodies (ADA) in small animal models used for efficacy testing can result in decreased circulating levels of the drug and reduced efficacy. This process can be a major roadblock during early stage drug discovery. Although immunogenicity must be carefully monitored during drug development, neutralizing antibody response during the efficacy determination phase of early screening can confound identification of lead antibody candidates. Given that compensatory changes to reduce or eliminate immunogenicity can be further engineered onto highly efficacious candidates at later stages in the development process, it may be important a select an early screening animal model in which immunogenic responses do not occur.
Researchers have often used scid mice, which lack T and B cells, as a tool to assess in vivo
efficacy in a mouse model which cannot produce neutralizing antibodies.1,2
However the severe immune deficiency of a scid background mouse may not be desirable for drug discovery platforms aimed at T cell specific molecules and pathways. One example is the rise of immunotherapies to develop new immuno-oncology drug candidates, which has driven increased use of syngeneic tumor models. Syngeneic tumor models are immunocompetent mice implanted with tumor cell lines derived from the same background strain. For example, the B16 melanoma tumor cell line was derived from the C57BL/6 inbred mouse strain, and B16 cells can be easily engrafted in C57BL/6 mice. The C57BL/6 mice are immunocompetent and are therefore useful to evaluate immunotherapy approaches to engage immune cells and target or attack the engrafted tumor. If the immunotherapy being tested requires the participation of mouse T cells, a mouse model which lacks T and B cells cannot be employed. Yet, as mentioned, the consequence of immune competence can result in immunogenicity that undermines efficacy studies. In that case, a mouse model with targeted mutations affecting only the adaptive antibody response by disrupting B cell development but not impacting T cell development may be the appropriate alternative.
Taconic Biosciences offers the Jh mouse
, in which targeted disruption of the Igh-J gene results in a mouse model that cannot produce neutralizing antibodies due to inhibition of the first critical stage of B cell receptor rearrangement. Without passing this critical early checkpoint, pre B cells arrest, resulting in attenuation of B cell lineage commitment. It can serve as an effective model for efficacy testing in a mouse which has most other components of the murine immune system, but which will not produce an efficacy-limiting ADA response. For use in syngeneic experiments, the Jh mouse is 96% congenic to the BALB/c background, and may successfully engraft some cell lines of BALB/c origin.
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1. McCaffrey AP, Nakai H, Pandey K, Huang Z, Salazar FH, Xu H, Wieland SF, Marion PL, Kay MA. (2003) Inhibition of hepatitis B virus in mice by RNA interference. Nat Biotechnol. 21(6):639-44.
2. Sun B, Zhang H, Franco LM, Young SP, Schneider A, Bird A, Amalfitano A, Chen YT, Koeberl DD. (2005) Efficacy of an adeno-associated virus 8-pseudotyped vector in glycogen storage disease type II. Mol Ther. 11(1):57-65.