title: Measurement and biological correlates of antibody bioactivity during antibody immunotherapies.
abstract: An important factor in the effectiveness of antibody immunotherapies is the antibody bioactivity, or the availability of free binding sites. Bioactivity may be decreased in settings where the target antigen exists in a soluble form capable of binding to circulating antibody. Because many antigens have soluble forms, we developed a method for determining if antibody is bound by soluble antigen in vivo. As a model system, we studied the interaction of soluble interleukin-2 receptor alpha (Tac; IL2R alpha; CD25) and anti-Tac antibody. We show first that HPLC readily separates free antibody from antibody which is monovalently or bivalently bound by soluble antigen. Further, we demonstrate that the distribution of the three forms of antibody accords with predictions of mass action and the binomial probability distribution. These methods were used to examine the bioactivity and concentration of free antibody in 14 patients undergoing therapeutic trial with Humanized anti-Tac antibody in leukemia and lymphoma. Results of two contrasting patients are highlighted. Low bioactivities correlated with reduced targeting of tumor cells and reduced therapeutic effectiveness. This report highlights the importance of soluble antigen in antibody therapies and demonstrates a simple method for evaluating in vivo bioactivity of antibody after therapeutic administration.
authors.affiliation: Biotherapeutics Development Lab, Harvard Institutes of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center, Boston, MA 02215, USA.
authors.forename: D S
authors.initials: DS
authors.lastname: Hagg
authors.forename: R P
authors.initials: RP
authors.lastname: Junghans
mesh_terms: D000328:Adult; D000906:Antibodies / Q000097:blood / Q000276:immunology* / Q000302:isolation & purification / Q000627:therapeutic use; D000937:Antigen-Antibody Reactions; D000941:Antigens / Q000276:immunology / Q000378:metabolism; D001666:Binding Sites, Antibody; D016010:Binomial Distribution; D002452:Cell Count; D002845:Chromatography; D002851:Chromatography, High Pressure Liquid; D005434:Flow Cytometry; D006689:Hodgkin Disease / Q000097:blood / Q000628:therapy*; D006801:Humans; D007167:Immunotherapy; D008297:Male; D008875:Middle Aged; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000097:blood / Q000628:therapy*; D015375:Receptors, Interleukin-2 / Q000276:immunology*; D012995:Solubility; D013816:Thermodynamics; D013997:Time Factors
chemical_list: D000906:Antibodies; D000941:Antigens; D015375:Receptors, Interleukin-2