The biodistribution of radiolabeled antilymphocyte monoclonal antibody in the rat

The biodistribution of radiolabeled mouse anti-pan T monoclonal antibody (W3/13) against rat lymphocytes was examined in normal rats. Monoclonal antibody to human prostate-associated antigens (PAA) served as a control. In vitro studies demonstrated a 38% maximum binding of radiolabeled W3/13 to lymphocytes, which was significant (P less than 0.001) when compared with the control (PAA) value of 3.4%. In vivo, intravenously administered 111In labeled W3/13 and 131I labeled W3/13 exhibited similar tissue distribution patterns. The localization of W3/13 in lymphoid tissue was significantly greater than that achieved with PAA. W3/13, however, did not demonstrate significant localization in the intact thymus and accumulated to a higher degree (6-10% ID/g) than expected in bone marrow at 24 h. These findings suggest that radiolabeled anti-lymphocyte monoclonal antibodies may not be well suited for the treatment of lymphoreticular neoplasms and allograft rejection in patients.