Challenge
One of our sponsors requested GLP mAb bioanalysis to measure a humanized therapeutic monoclonal antibody fragment (Fab) that inhibits a human growth factor involved in the pathogenesis of a common degenerative disease of aging. Several considerations come into play to deisgn and execute a high performing PK ELISA assay for this crucial mAb bioanalytical testing.
Monoclonal antibody fragments offer numerous advantages over full-length antibodies in terms of production cost, increased penetration into the target tissue, and reduced potential for inappropriate activation of immune effector mechanisms. However, because monoclonal antibody fragments lack many common domains typically targeted (e.g., Fc regions) by immunoassay reagents for binding and detection, they may also present unique challenges for bioassay design, potentially impacting sensitivity since fewer antigens/antibodies can bind to each fragment.
We could try to optimize the concentration of coating and detection reagents to improve sensitivity. Still, this strategy risks increasing background noise due to specific and nonspecific interactions within the various assay components (e.g., the therapeutic molecule, the blocking agents, and/or the coating antigen). The potential for off-target specific interactions is especially concerning when the matrix belongs to a closely related species, in this case, a non-human primate.
The development and validation of immunoassays for mAb bioanalysis require careful consideration of various factors, including the unique properties of monoclonal antibody fragments, optimization of assay components for sensitivity and specificity, and mitigation of risks associated with off-target interactions. Through meticulous mAb bioanalytical testing, optimal assay performance can be achieved to meet the sponsor’s requirements for measuring the therapeutic efficacy of the monoclonal antibody fragment.