| Abstract: |
We studied the antigen density (B-max and binding affinity (K-a) of the monoclonal antibody (MAb) 3F8, a murine IgG3, selective for ganglioside GD(2), to the neuroblastoma tumor in order to further understand the influence of the above factors on the antibody-antigen systems. We compared the results of B-max and K-2 obtained from quantitative autoradiography (QAR) of xenografted NMB-7 tumors with competitive inhibition of in vitro binding assay (CIBA) using NMB-7 cell suspension, two situations with different cell growth characteristics. Both methods yielded a K-a value of 1 - 2 x 10(8) L M(-1), an antibody binding affinity which is not exceptional and shared by many murine anti-tumor antibodies. On the other hand, the mean maximal concentration, B-max, of GD(2) antigen in tumor tissue was 3423 +/- 357 picomols g(-1) by QAR. This value is approximately 10 fold higher than reported with other antigen systems such as p97 and the chondroitin sulfate proteoglycan. CIBA revealed a mean B-max of 15 +/- 2.8 x 10(6) sites of GD(2) antigen per cell (12534 +/- 2300 picomol g(-1)) assuming bivalent binding. |
