Importance of pH in defining the specificity and clinical utility of monoclonal antibodies--an evaluation of two anti-CA 19-9 monoclonal antibodies.
The effect of pH on the binding characteristics of monoclonal antibodies against tumor associated antigens has been studied, using anti-CA 19-9 monoclonal antibodies as an example. The 1116-NS-19-9 monoclonal antibody is used in several commercially available two-step sandwich IRMAs for the measurement of the CA 19-9 antigen in cancer patient sera (Centocor CA 19-9 RIA, Malvern, PA, U.S.A., or similar kits by Centocor licensees). The B25.10 monoclonal antibody is in use in the Truquant GITM RIA (Biomira Inc., Edmonton, Alberta, Canada), a competitive inhibition assay measuring the CA 19-9 antigen. We determined the Ka value of the B25.10 and the 1116-NS-19-9 antibodies at pH 4.5 and 7.3 on a solid phase coated with CA-19-9 bearing mucin. The 1116-NS-19-9 antibody had a Ka value of 4.1 x 10(8) at pH 4.5 and approximately 0.3 x 10(8) at pH 7.3. The Ka value of B25.10 was in the range of 0.7-4.1 x 10(9) at either pH, but somewhat lower at pH 4.5. At pH 4.5 (the pH optimum for binding of 1116-NS-19-9 to the CA 19-9 antigen Del Villano, B.C., 1984]) the binding of 125I-labeled B25.10 to the solid phase was comparably inhibited by 1116-NS-19-9 and B25.10. However, at neutral pH (pH 7.2) the apparent affinity of the 1116-NS-19-9 antibody for the CA 19-9 antigen is significantly diminished [Del Villano, B.C., 1984] while that of B25.10 is slightly higher. Consequently, the ability of the 1116-NS-19-9 to inhibit the binding of the B25.10 antibody to the CA 19-9 solid phase is greatly reduced in the physiological pH range. The consequences of these findings for in vivo applications are discussed.
van Heel
A
A
Biomira Inc; Edmonton, Alberta, Canada.
Suresh
M R
MR
D000911:Antibodies, Monoclonal / Q000276:immunology*; D000912:Antibodies, Neoplasm / Q000276:immunology*; D000915:Antibody Affinity; D000918:Antibody Specificity; D015295:Antigens, Tumor-Associated, Carbohydrate / Q000276:immunology*; D001667:Binding, Competitive; D006801:Humans; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques
D000911:Antibodies, Monoclonal; D000912:Antibodies, Neoplasm; D015295:Antigens, Tumor-Associated, Carbohydrate