Kinetic analysis of unpurified native antigens available in very low quantities and concentrations

Affinity measurements of antigen–antibody interactions are generally performed using known concentrations of purified or recombinant materials. In addition, many technologies that measure affinity require the interacting components to be present in at least microgram quantities. Specifically, if the antigen is either available only in low quantities or unable to be purified, or if the quantity is unknown, then the measurement of affinity can be very difficult. Using the Kinetic Exclusion Assay (KinExA) technology, here we describe a method that overcomes the requirement for large amounts of purified and known quantities of antigen. We used this method to precisely measure the affinity of fully human anti-human interleukin 13 (IL13) monoclonal antibodies to IL13 produced in native form from primary T cells derived from a variety of species, including human. These antigens were available only in the limited quantities present in the conditioned cell culture medium, and the affinity was measured directly without further purification.