CHARACTERIZATION OF IMMUNOLOGICAL AND MOLECULAR-PROPERTIES OF AN ANTI-HUMAN 4-1BB MONOCLONAL-ANTIBODY

4-1BB was first identified to be expressed on activated murine T cells as a 55 kDa homodimer and to belong to the tumor necrosis factor rece ptor family of integral membrane proteins. The ligand for 4-1BB (4-1BB L) was found on activated macrophages and mature B cells. 4-1BB and 4- 1BBL interaction may be important in costimulation of T lymphocyte act ivation. The gene encoding human 4-1BB (h4-1BB) was recently isolated from a cDNA library of activated human peripheral T cells. In this stu dy, we generated a monoclonal antibody (MAb) against h4-1BB and charac terized its immunological and molecular properties. MAbs generated aga inst recombinant h4-1BB protein were assayed by ELISA for affinity to 4-1BB, and one of the clones with the highest affinity was designated 4B4-1-1. Using now cytometry, we found that 4B4-1-1 had a high affinit y to 4-1BB on phytohemagglutinin-activated human CD4(+) and CD8(+) T c ells. The 4B4-1-1 heavy chain variable region (V-H) and light chain va riable region (VL) genes were cloned using PCR. The cloned V-H gene co ded for 118 amino acid residues and the deduced amino acid sequence sh ared the highest homology with that of rheumatoid factor-binding antib ody (A5'CL) (86. 2% identity, 90.5% similarity). The V-H segment belon ged to the subgroup II (B) and the D and J(H) segments originated from DFL16.2 and the J(H3) gene, respectively. The V-L gene coded for 107 amino acids and the deduced amino acid sequence was very similar to VK -23.32'CL (93.8% identity, 94.8% similarity). The V-L segment and J(K) segment of the 4B4-1-1 V-L gene belonged to the subgroup V and MUSJK1 gene, respectively. Since Mab 4B4-1-1 has been shown to have immunosu ppressive properties, information and materials obtained in this study will be valuable in development of chimeric and humanized antibodies for the treatment of autoimmune diseases.