Background B-cells expressing B-cell receptors (BCRs) specific for self-antigens are normally eliminated, or made anergic, through negative selection during B-cell development. VH4-34 is an intrinsically autoreactive antibody (and BCR) heavy chain variable region that includes a hydrophobic patch in framework region 1 (FR1). Autoantigens recognized by VH4-34-encoded antibodies include N-acetyl lactosamine chains displayed on red blood cells. In healthy individuals, <1% of B cells express VH4-34-encoded BCRs but during the loss of self-tolerance, the hydrophobic region in FR1 reacts to self-antigen, erroneously driving B-cell activation and expansion.
Expansion of VH4-34+ B cells and increased serum concentrations of auto-reactive VH4-34 antibodies have been reported in autoimmune disorders, including systemic lupus erythematosus (50%) and virtually all cases of cold agglutinin disease. To date, there have been no successful therapies against VH4-34 due to challenges of specifically targeting VH4-34 while avoiding other VH regions.
Methods We applied Hummingbird Bioscience’s Rational Antibody Discovery approach to develop anti-VH4-34 antibodies that bind to a computationally predicted and lineage conserved epitope in the FR1 of VH4-34 antibodies. In vitro, the ability of HMBD-011 to specifically bind VH4-34+ cell lines was determined using flow cytometry. Potency of HMBD-011, to eliminate circulating VH4-34 antibodies and VH4-34+ cells in vivo, was measured using serum ELISA and IVIS Spectrum In Vivo Imaging System respectively.
Results The lead antibody, HMBD-011, demonstrates selective and high affinity binding to tested VH4-34 antibodies, with no off-target binding to a panel of other VH antibodies. The binding epitope of HMBD-011 was confirmed by mutagenesis to be within the FR1 of VH4-34. Further, HMBD-011 shows selective binding to cells that endogenously and exogenously express VH4-34 BCRs. In vivo, HMBD-011 treatment results in specific elimination of VH4-34 auto-antibodies and depletion of VH4-34+ B cells.
Conclusions HMBD-011 represents a promising new precision therapy for patients with VH4-34 autoimmune disorders.
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