Mouse anti-Human BTN3A1 monoclonal antibody, clone CU4.2 [PE]

Studies of aryl phosphonate derivatives of a butyrophilin 3A1 ligand have resulted in identification of a potent stimulant of V gamma 9 V delta 2 T cells. This compound, a mixed ester bearing one pivaloyloxymethyl substituent and one 1-naphthyl ester displayed an EC50 of 0.79 nM as a stimulant of T cell proliferation, and a 9.0 nM EC50 in an assay designed to measure interferon gamma production. In both assays, this is the most potent butyrophilin ligand prodrug yet reported, and thus it should be a valuable tool for studies of T cell function. Furthermore, mixed aryl/acyloxyalkyl esters may represent a new class of phosphonate prodrugs with high efficacy.

Human V gamma 9V delta 2 T cells are well known for their rapid and potent response to infection and tumorigenesis when in the presence of endogenous or exogenous phosphoisoprenoids. However, the molecular mechanisms behind the activation of this gamma delta T cell population remains unclear. Evidence pointing to a role for the CD277/butyrophilin-3 (BTN3A) molecules in this response led us to investigate the structures of these molecules and their modifications upon binding to an agonist antibody (20.1) that mimics phosphoisoprenoid-mediated V gamma 9V delta 2 activation and an antagonist antibody (103.2) that inhibits this reactivity. We find that the three BTN3A isoforms: BTN3A1, BTN3A2, and BTN3A3, have high structural homology to the B7 superfamily of proteins and exist as V-shaped homodimers in solution, associating through the membrane proximal C-type Ig domain. The 20.1 and 103.2 antibodies bind to separate epitopes on the BTN3A Ig-V domain with high affinity but likely with different valencies based on their binding orientation. These structures directly complement functional studies of this system that demonstrate that BTN3A1 is necessary for V gamma 9V delta 2 activation and begin to unravel the extracellular events that occur during stimulation through the V gamma 9V delta 2 T cell receptor.