Functional Characterization of Antibodies Neutralizing Soluble Factors In Vitro and In Vivo

Functional characterization of antibodies that inhibit soluble cytokines or chemokines requires robust, sensitive in vitro and in vivo bioassays. Testing an antibody in vitro requires consideration of antigen source, integrity, and concentration, as well as the magnitude of the biologic response and assay interference by components in the antibody test sample. This chapter describes several exemplary in vitro bioassays, including an assay to determine species cross-reactivity of an anti–tumor necrosis factor antibody and a whole blood assay for interleukin–18 (IL–18) to determine neutralization of native antigen. Testing an antibody in vivo requires consideration of species cross-reactivity, selection of the dose range and the route of administration, analyses of the pharmacokinetics and tissue distribution of the antibody, and evaluation of host antibody responses. An example of an in vivo bioassay, in which human peripheral blood mononuclear cells are injected into severe combined immunodeficient mice and activated in vivo to produce human IL–18, is provided.