SUCCESSFUL IN-VIVO IMMUNOLOCALIZATION OF LANGERHANS CELL HISTIOCYTOSIS WITH USE OF A MONOCLONAL-ANTIBODY, NA1 34/

The antibody NA1/34 is a murine monoclonal antibody directed against t he CD1a surface antigen expressed on normal Langerhans cells, cortical thymocytes, and on lesional cells in Langerhans cell histiocytosis (L CH). Our hypothesis was that NA1/34 would localize sites of disease ac tivity in patients with multisystem LCH. To test this hypothesis, indi um 111-labeled NA1/34 was administered to five patients with multisyst em LCH and serial gamma scans were obtained for up to 120 hours. Seria l serum samples were obtained from one patient for analysis of anti-mo use Ig antibody and NA1/34 levels. Direct and indirect immunofluoresce nce staining for CD1a and NA1/34 were performed on a tissue biopsy spe cimen from one patient after administration of the antibody. The 1- an d 4-hour scans showed distribution of antibody in the blood pool, but in later scans localization of the antibody was noted in areas of know n disease activity in all five patients. Bony lesions, previously seen on skeletal radiographs, were especially well identified. Serum kinet ics studies showed clearance of the antibody from the blood pool withi n 12 hours of administration. Direct binding of NA1/34 to lesional cel ls was demonstrated by direct immunofluorescence. The only adverse eff ect was urticaria in one patient. We conclude that NA1/34 localizes di sease activity in vivo in bones of patients with LCH with minimal toxi c effects. An evaluation of its role in determining disease extent ('' staging'') and in treatment is now needed.