Kinetics of 99mTc-labelled antibodies against CD4 (T-helper) lymphocytes in man

The availability of radiolabeled anti-CD4 antibodies permitted the study of their kinetic behaviour. Four patients suffering from rheumatoid arthritis were investigated prospectively. Three of them received 250 micrograms of 99mTc-labelled anti-CD4 antibody (MAX.16H5). One patient received in vitro 99mTc-antibody-labelled lymphocytes. 4% of the activity was excreted by the kidneys. From 4 to 24 h the splenic uptake decreased from 7.5 to 4%, the liver uptake increased from 25 to 30% the bone marrow uptake remained about the same 50% and the uptake of a single diseased joint (2%) increased slightly to 2.5%. 15 to 30 min after injection of the antibody a redistribution of labelled cells or antibody from liver and spleen to the circulating blood seemed to occur. The recovery rate (0-1 h) of in vivo labelled cells amounted to 30%, that of in vitro labelled cells to 19%. One patient was examined with in vitro labelled CD4-expressing lymphocytes. There was no difference in the antibody kinetics between in vitro and in vivo labelled cells. The authors suggest that circulating CD4-lymphocytes can be labelled with monoclonal antibodies. The kinetics of these in vitro labelled cells and the injected labelled antibody itself resembles that of recirculating lymphocytes.