Successful in vivo immunolocalization of langerhans cell histiocytosis with use of a monoclonal antibody, NA 1/34

The antibody NA 1/34 is a murine monoclonal antibody directed against the CD1a surface antigen expressed on normal Langerhans cells, cortical thymocytes, and on lesional cells in Langerhans cell histiocytosis (LCH). Our hypothesis was that NA 1/34 would localize sites of disease activity in patients with multisystem LCH. To test this hypothesis, indium 111-labeled NA 1/34 was administered to five patients with multisystem LCH and serial gamma scans were obtained for up to 120 hours. Serial serum samples were obtained from one patient for analysis of anti-mouse lg antibody and NA 1/34 levels. Direct and indirect immunofluorescence staining for CD1a and NA 1/34 were performed on a tissue biopsy specimen from one patient after administration of the antibody. The 1-and 4-hour scans showed distribution of antibody in the blood pool, but in later scans localization of the antibody was noted in areas of known disease activity in all five patients. Bony lesions, previously seen on skeletal radiographs, were especially well identified. Serum kinetics studies showed clearance of the antibody from the blood pool within 12 hours of administration. Direct binding of NA 1/34 to lesional cells was demonstrated by direct immunofluorescence. The only adverse effect was urticaria in one patient. We conclude that NA 1/34 localizes disease activity in vivo in bones of patients with LCH with minimal toxic effects. An evaluation of its role in determining disease extent ("staging") and in treatment is now needed.