HUMANIZATION OF AN ANTIBODY AGAINST HUMAN PROTEIN-C AND CALCIUM-DEPENDENCE INVOLVING FRAMEWORK RESIDUES

A murine monoclonal antibody to the zymogen form of human protein C th at blocks protein C activation by thrombin-thrombomodulin both in vitr o and in vivo has been humanized using the consensus and resurfacing m ethods. While the binding of the parent murine antibody to protein C i s calcium-dependent (1.5-2-fold decrease in binding without calcium), the humanized antibody exhibited a significant increase in its calcium -dependence (5-fold decrease in binding without calcium). Two exposed human framework residues in the variable light domain of the humanized antibody, aspartic acid L1 and glutamine L3, are responsible for the increase in calcium-dependence.