and insertions any such modifications are within the scope of the present invention so long as the resulting cdr grafted antibody maintains the ability to bind to and inhibit human tissue factor the ordinarily skilled artisan can assess the activity of the cdr grafted antibody with reference to the functional assays described herein below the human constant region of the cdr grafted antibodies of the present invention is selected to minimize effector function the intended use of the cdr grafted antibodies of the present invention is to block the coagulation cascade by inhibition of tissue factor and thus antibody effector functions such as fixation of complement are not desirable antibodies with minimal effector functions include igg2 igg4 iga igd and ige in a preferred embodiment of the present invention the heavy chain constant region is the human igg4 kappa constant region and the light chain constant region is the human igg4 kappa constant region in that effector functions may not be desirable for therapeutic uses the present invention further contemplates active fragments of the cdr grafted antibodies and in particular fab fragments and f ab u2032 2 fragments active fragments are those fragments capable of inhibiting human tissue factor fab fragments and f ab u2032 2 fragments may be obtained by conventional means for example by cleavage of the cdr grafted antibodies of the invention with an appropriate proteolytic enzyme such as papain or pepsin or by recombinant production the active fragments maintain the antigen binding sites of the cdr grafted antibodies.