Before beginning GLP expensive TCR study, it is interesting to unrisk a development project during its phase of research and development.
Tissue Cross Reactivity studies (TCR) may be conducted from the first lead candidates to direct development strategic choices and enhance the chance of success.
“TCR are screening assays conducted with monoclonal antibody and related antibody-like pharmaceuticals primarily to identify off-target binding and, secondarily, to identify sites of on-target binding that were not identified.” (1) They involve the immunohistochemical staining of a panel of frozen tissues from humans and animals.
As they are recommended by both European Medical Agency (EMA) and Federal Drug Agency (FDA) in their guidelines to support the Investigational New Drug application (IND), they are a key step in the development process of a therapeutic antibody. According to EMA and FDA, TCR have to be conducted following the Good Laboratory Practices (GLP), on a minimum of 33 human organs from at least three different donors, at two different concentrations levels of antibody.
Non GLP preliminary TCR on restraint panels with only one donor are also very useful to un-risk the cost and time of developments allocated to the antibody until the GLP TCR.
Performed on key organs, they help identify candidates having the less expressed off target binding and provide an important overview on unexpected binding. As such they enable to promote the antibody with the less potential toxicity and adverse events.
Pre-TCR studies can also be performed on animal tissues. They represent a useful tool to select the most appropriate animal model that will be used for the in vivo toxicology study. Tissues from several animal species are exposed to the monoclonal antibody in order to identify the one which has a similar cross reactivity profile observed
Additionally TCR studies can be combined with deeper investigations based on immunohistochemistry. It is for instance necessary to validate candidates with the highest on target binding. Pathological tissues from a large cohort of patients can be confronted and compared according to the activity of the antibody.
All TCR require conception and validation steps for the immunostaining protocols in order to demonstrate the specificity, repeatability, reproducibility and robustness of the experimental conditions. Standard quality procedures must be strictly followed.
The use of preliminary experiments during the discovery phase will support the proof of concept, optimize the resource allocation, and improve wised decisions because they avoid to go too far with a candidate which has a bad cross reactivity profile. These studies are also a scientific and strategic advantage when it comes to convince strategic partners like investors.
(1) Michael W. LEACH & AL., 2010, « Use of Tissue Cross-reactivity Sudies in the development of Antibody-based Biopharmaceuticals : History, Experience, Methodology, and Future Directions », Toxicologic Pathology, 38 : 1138-1166.