Monospecific and Polyreactive Monoclonal Antibodies against Human Leukocyte Antigen-E: Diagnostic and Therapeutic Relevance

Abstract

A monoclonal antibody (mAb) binds to an antigen recognizing an epitope (a sequence of amino acids). A protein antigen may carry amino acid sequence unique to that antigen as well as sequences found in other proteins. Human leukocyte antigens (HLA), a family of proteins expressed by the Major Histocompatibility Complex gene family represent a special case, in that it displays a high degree of polymorphism. Every HLA molecule possesses both specific (private) epitopes and epitopes shared (public) with other HLA class Ia and class Ib molecules. HLA-E is overexpressed in cancer cells more than any other HLA Class I molecules. Therefore specific localization of HLA-E with mAbs is pivotal for developing targeted therapy against cancer. However, the commercially available mAbs for immunodiagnosis are polyreactive. We have developed anti-HLA-E mAbs and distinguished monospecific from polyreactive mAbs using Luminex multiplex single antigen bead (SAB) assay. HLA-E-binding of monospecific-mAbs was also inhibited by E-restricted epitopes. The amino acid sequences in the region of the epitopes bind to CD94/NKG2A receptors on CD8+ T cells and NK cells and block their antitumor functions. Monospecific-HLA-E mAbs recognizing the epitopes sequences can interfere with the binding to restore the anti-tumor efficacy of NK cells. Also, monospecific-mAbs augment the proliferation of CD4-/CD+ cytotoxic T-lymphocytes. Therefore, anti-HLA-E monospecific-mAb can serve as a double-edged sword for eliminating tumor cells.