CHIMERIZATION OF LL2, A RAPIDLY INTERNALIZING ANTIBODY SPECIFIC FOR B-CELL LYMPHOMA

LL2 is a murine monoclonal antibody (MAb) that has been shown to be ef fective for the diagnosis and treatment of patients with non-Hodgkin's B cell lymphoma. Studies have also shown that radiolabeied murine LL2 (mLL2) or mLL2 and fragments thereof coupled to Pseudomonas exotoxin (PE) can effectively target human B cell lymphoma in mice. We have obt ained the DNA sequences encoding the V-K and V-H domains of mLL2, an I gG(2a) MAb, which were combined with their respective human K and IgG( 1) constant region domains and expressed in SP2/0 cells. Like its muri ne counterpart, the chimeric LL2 (cLL2) antibody is glycosylated in th e light chain variable region. Chimerization did not interfere with th e immunoreactivity of the antibody, as determined by a competitive bin ding assay, where either antibody shows equivalent inhibition of the b inding of its counterpart to the Raji cell membrane surface antigen, C D22. Both antibodies bind and are rapidly internalized by Raji cells, whereas an irrelevant humanized antibody did not bind and was not inte rnalized under similar conditions. The internalization rates of the bo und murine or chimeric antibodies were nearly identical, with K-2 valu es of 0.106 and 0.118 min(-1) for mLL2 and cLL2, respectively. The obs erved close equivalence between the murine and chimeric antibodies sug gests potential advantages of the latter as a less immunogenic agent. Studies are currently underway to evaluate the chimeric antibody as a potential therapeutic immunoconjugate.