Monoclonal antibodies as agents for selective radiolabeling of human neutrophils.

Ten monoclonal antibodies (MAbs) have been evaluated as agents for selective radiolabeling of human neutrophils (PMNs). Four bifunctional chelating agents (BFCA) have been compared in order to determine the one that gives the best labeling of MAbs with radionuclides. Of these, the cyclic anhydride of diethylenetriaminepentaacetic acid (DTPA) has been chosen for routine use since it incorporated 111In efficiently, and only minimally altered the immunoreactivity of the MAb. Two [111In]DTPA MAbs (1 microgram or less, anti-SSEA-1 and B.37.2.1) incorporated 80 +/- 5% and 72 +/- 6% of the added radioactivity with 10(7) separated PMNs in 0.5 ml plasma. In whole blood these values were 27 +/- 5% and 38 +/- 9%, respectively. Using the other three BFCAs with anti-SSEA-1, the corresponding values of 70%-80% and 3%-5%, respectively were obtained. Polyacrylamide gel electrophoretic examinations of the radioactivity that did not bind to blood cells revealed that when DTPA was used as the BFCA, 21% of the radioactivity was associated with a plasma protein of mol wt 60-80 kD and 57% remained bound to the MAb (mol wt 900 kD). When the other three BFCAs were employed, these values were greater than 42% and less than 19%, respectively. When up to 4% of the PMN surface antigens were MAb bound, the PMNs physiologic function remained unaltered. For two MAbs, anti-SSEA-1, and B 37.2.1, the PMN specificity was found to be 1.6 X 10(-11) M and 2 X 10(-11) M, respectively, and the number of cell surface antigens was estimated to be 5.1 X 10(5) and 7.8 X 10(5), respectively. For 99mTc labeling of MAbs, the use of four different reducing agents were examined. One agent, sodium-dithionite (Na2S2O4), at a concentration of 0.2 mg/ml reaction mixture and with a molar ratio 3 X 10(3):1 to the MAb, gave us results that were comparable to those obtained with [111In]MAb. We conclude that at least two of the ten MAbs, anti-SSEA-1 and B.37.2.1 are worthy of evaluation in humans.