THE EFFECT OF AGLYCOSYLATION ON THE IMMUNOGENICITY OF A HUMANIZED THERAPEUTIC CD3 MONOCLONAL-ANTIBODY

The factors affecting the immunogenicity of a humanized gamma 1 CD3 mo noclonal antibody (mAb) were investigated in transgenic mice that expr ess the human CD3 antigen epsilon polypeptide (the mAb target antigen) . Two derivatives of the mAb were employed, one with a normal, glycosy lated Fc region (gamma 1 CD3 mAb), and the other with an aglycosylated Fc region (aglycosyl gamma 1 CD3 mAb). Comparisons of the antiglobuli n responses elicited by the two derivatives in transgenic and nontrans genic mice demonstrated that Fab-mediated cell binding activity, depen dent on target antigen expression, was a major positive determinant of CD3 mAb immunogenicity. A second positive factor was mAb Fc region gl ycosylation. At low dose levels the gamma 1 CD3 mAb consistently produ ced a higher antiglobulin response than the aglycosyl gamma 1 CD3 mAb. This was probably a result of the nonspecific, in vivo T cell activat ing property of the gamma 1 CD3 mAb, a consequence of its ability to c ross-link T cells to Bey receptor-bearing cells. (The aglycosyl gamma 1 CD3 mAb has a reduced Fe binding affinity for Fc gamma receptors and so does not activate T cells in vivo.) In support of this hypothesis, the gamma 1 CD3 mAb was able to nonspecifically enhance humoral immun ity to an unrelated, coadministered antigen, whereas the aglycosyl gam ma 1 CD3 mAb was not. The lower immunogenicity of the aglycosyl gamma 1 CD3 mAb correlated with a longer in vivo half-life and an improved c apacity to block the target CD3 antigen. These results suggest that, a s well as reducing the cytokine-induced side effects normally associat ed with CD3 mAb therapy, the nonactivating aglycosyl gamma 1 CD3 mAb w ill be less likely than the activating gamma 1 CD3 mAb to stimulate a neutralizing antiglobulin response.