Mr. Alderson et al., MOLECULAR AND BIOLOGICAL CHARACTERIZATION OF HUMAN 4-1BB AND ITS LIGAND, European Journal of Immunology, 24(9), 1994, pp. 2219-2227
4-1BB was originally described as a cDNA expressed by activated murine
T cells and subsequently demonstrated to encode a member of the tumor
necrosis factor receptor family of integral membrane proteins. Recent
ly, we identified and cloned a murine ligand for 4-1BB (mu4-1BB-L) and
demonstrated it to be a member of an emerging family of ligands with
structural homology to tumor necrosis factor. To characterize further
the role of 4-1BB in the immune response we undertook to clone the hum
an homologue of 4-1BB-L. However, attempts to isolate a cDNA encoding
the human 4-1BB-L by cross-hybridization with the murine cDNA were uns
uccessful. Therefore we first utilized cross-species hybridization to
isolate a cDNA encoding human 4-1BB (hu4-1BB). A fusion protein consis
ting of the extracellular portion of hu4-1BB coupled to the Fc region
of human immunoglobulin G1 (hu4-1BB.Fc) was then used to identify and
clone a gene for human 4-1BB-L from an activated CD4(+) T cell clone u
sing a direct expression cloning strategy. Human 4-1BB-L shows 36% ami
no acid identity with its murine counterpart and maps to chromosome 19
p13.3. Scatchard analysis demonstrated high-affinity binding of hu4-1B
B.Fc to either native or recombinant human 4-1BB-L. Both monoclonal an
tibody to hu4-1BB and cells transfected with hu4-1BB-L induced a stron
g proliferative response in mitogen co-stimulated primary T cells. In
contrast, ligation of 4-1BB on T cell clones enhanced activation-induc
ed cell death when triggered by engagement of the TCR/CD3 complex.