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Exploiting the power of a patient’s immune system has brought a breakthrough in terms of specificity and efficacy in cancer therapy, significantly improving therapy success and quality of life for patients. While much more specific in their mode of action and frequently more potent than small molecules, immunomodulatory antibody therapeutics bring about new challenges for their preclinical development. For example, most animal models cannot be used to reliably determine human antibodies’ pharmacodynamic (PD) and pharmacokinetic (PK) properties. Also, the majority of antibodies are precise for their human targets, and their efficacy cannot be tested in traditional models such as mice and rats.
"Unleashing the power of the immune system is efficacious to kill tumors, but its over-activation can lead to serious adverse events"
For years, The Jackson Laboratory (JAX) has been leading the development, validation, and application of new preclinical tools for the successful selection of the antibody variants with the best PK/PD, efficacy, and safety profiles.
Therapeutic antibody PK determination
Pioneering work by Derry Roopenian of JAX showed that, due to the different affinities of the human antibody Fc portion for the murine and human neonatal Fc receptors (FcRn - the major component of the machinery that keeps recycling antibodies in circulation),wild type mice are not suitable to predict human antibody half-life. Roopenian’s team developed transgenic mice lacking murine FcRn and express ingits human orthologue. These mouse models show an excellent correlation of the half-lives of therapeutic antibodies with humans. Furthermore, they are successfully used by antibody developers to test the effects of modifications in the Fc portion on the antibody’s pharmacokinetic properties. Importantly, allometric scaling can be used to extrapolate half-life in humans and inform clinical trial decisions on dosing. Due to its reliability and relatively low cost, this platform has become an integral part of the early antibody drug development pipeline of major pharmaceutical companies. Also, many pharma and biotech companies routinely outsource the half-life determination of their drug candidates to the expert team at JAX.
Testing immunotherapy efficacy
the significant benefit for their use in immunotherapy, but they also bring about challenges to evaluate their efficacy pre-clinically. Most lead molecules will be specific to human targets and thus cannot be efficiently tested in non-human models. Therefore, preclinical models must carry human targets on cancer cells AND immune cells. At JAX, professor Lenny Shultz pioneered the development of immune system-humanized mice by developing the NSG™ mouse model, the most immune deficient mouse to date. Dr. Shultz demonstrated that the NSG™ mouse could be engrafted with human hematopoietic stem cells, which then develop into various hematopoietic lineages that constitute a human-like immune system. In the past few years, the Schultz group and their collaborators have developed different variants of the NSG™ mouse, all expressing human cytokines, which allow the development of more “complete” human immune systems featuring human T-cells, myeloid cells, NK cells, and so forth. These mice with humanized immune systems can be co-engrafted with human tumors, establishing sophisticated preclinical models allowing the evaluation of immunotherapies relying on human-specific compounds such as bi- or multi-specific immune cell engagers and other modalities. Humanized mice have already proven to be valuable tools in IND filings to bring novel therapies to the clinic. Building on Dr. Schultz’s experience, the JAX team routinely runs studies for antibody developers.
Preclinical toxicity assessment of immunotherapies
Unleashing the power of the immune system is efficacious to kill tumors, but its over-activation can lead to serious adverse events. Infamously, the CD28 super-agonist TGN1412 caused a life threatening cytokine release syndrome (CRS) when first infused into healthy volunteers. However, the drug was innocuous when tested in in vitro assays using human peripheral blood mononuclear cells (PBMCs) and in vivo using mice, rats, and monkeys. Other immune cell engagers, either alone or in combination, have led to severe CRS in patients as well. Until recently, adequate preclinical tools that can predict CRS quickly, sensitively, and reliably have been missing. Dr. James Keck’steam at JAXemploys the engraftment of human PBMCs into immunodeficient mice to assess the propensity of immunomodulatory molecules that cause CRS. The platform can detect TGN1412 toxicity, unlike any of the assays used in the past. The assay can predict how an antibody lead behaves across a panel of distinct PBMC donors to understand donor-specific differences in response, allowing the selection of antibody candidates early in development based on their safety profile. Due to its sensitivity and specificity, the model can also be employed to estimate the safe dose on a new investigational drug before going first in man.
In summary, the development of new treatment paradigms, such as antibody immunotherapies, require appropriate preclinical in vivo tools. In the past few years, the development of innovative mouse models has proven highly successful in de-risking the preclinical PK/PD, efficacy and safety phases of the therapeutic antibody development pipeline, and drug developers now have access to a new generation of sophisticated tools that can guide them in the intricate path that leads to the successful development of a novel therapeutic antibody.