An anti–PR1/HLA-A2 T-cell receptor–like antibody mediates complement-dependent cytotoxicity against acute myeloid leukemia progenitor cells

Abstract

PR1 (VLQELNVTV) is a human leukocyte antigen-A2 (HLA-A2)-restricted leukemiaassociated peptide from proteinase 3 (P3) and neutrophil elastase (NE) that is recognized by PR1-specific cytotoxic T lymphocytes that contribute to cytogenetic remission of acute myeloid leukemia (AML). We report a novel T-cell receptor (TCR)- IntroductionCD8 T cells specific for the human leukocyte antigen-A2 (HLA-A2)-restricted peptides WT1 and PR1, which are derived from the endogenous leukemia-associated antigens Wilms' tumor antigen [1][2][3] and proteinase 3 (P3), respectively, mediate cytotoxicity against acute myeloid leukemia (AML). PR1-specific T cells also contribute to cytogenetic remission of chronic myeloid leukemia (CML) in patients treated with interferon, 4,5 and vaccination with WT1 and PR1 6,7 can induce specific CD8 immunity in patients with myeloid malignancies. These results validate endogenous self-peptides as targets for immunotherapy, including vaccination, adoptive cell therapy, or antibodies that bind peptide/MHC. Such T-cell receptor (TCR)-like monoclonal antibodies (mAbs) may have selective activity against leukemia if target peptide/MHC complexes are aberrantly expressed on leukemia. Furthermore, mAbs are easy to administer and can be dosed frequently, which may increase their effectiveness against high leukemia burdens.Eliciting TCR-like mAbs has been technically challenging, 8 primarily because of the high immunogenicity of HLA molecules in mice. Phage-display libraries, 9 peptide/MHC immunization, 10,11 and the combination of both strategies 8,12 have been used to produce TCR-like mAbs targeting peptides derived from solid-tumor antigens (eg, MAGE, ␤-HCG, TARP, and NY-ESO-1) in the context of HLA-A1 or HLA-A2. [9][10][11]13,14 Although antibody activity against primary tumors has not been well studied, complement-dependent cytotoxicity (CDC) against tumor cell lines has been reported. 11 Some toxin-conjugated antibodies also show activity against tumor cells. 14-16 However, to eradicate cancer, these antibodies must be active against cancerinitiating cells, and TCR-like mAb-induced cytolysis of cancer stem cells has not been reported. Nevertheless, because PR1-specific CTLs suppress leukemia progenitor cells in vitro 17 and because Lin Ϫ CD34 ϩ CD38 Ϫ cells are enriched for leukemia stem cells (LSCs) 18 and can be easily studied, we hypothesized that if an anti-PR1/HLA-A2 antibody could be produced, it may be active against blasts and LSCs from HLA-A2 ϩ AML patients.We report the discovery of 8F4, a novel mAb that binds with high affinity to a conformational epitope of PR1/HLA-A2 and induces dose-dependent cytolysis of myeloid leukemia cells but not normal hematopoietic cells. 8F4 mediates CDC against Lin Ϫ CD34 ϩ CD38 Ϫ LSCs and preferentially inhibits the growth of leukemia progenitor cells. These results justify further study of TCR-like antibodies to verify the differential effects against normal stem cells and LSCs. Biologically significant differences may justify further study of a humanized form o...

CML patients with deep molecular responses to TKI have restored immune effectors and decreased PD-1 and immune suppressors

“…LAAs such as WT1, PRAME, PR3, and BMI-1 in CML patients represent attractive targets for immunotherapy, [23][24][25][26][27][28][29] with efficacy demonstrated in vaccination, including dendritic cell vaccination, [30][31][32][33] and, more recently, T-cell receptor-mimic antibodies. [34][35][36] In support of these studies, we observed maximal restoration of immune recovery, as demonstrated by increased effector NK cell and T-cell immune responses, reduced PD-1 inhibitory molecule expression on CD4 1 and CD8 1 T cells, and reduced numbers of Mo-MDSC in MR 4.5 only, suggesting DMR may be the preferred threshold for future TFR studies to benefit from the improved effector immune responses. Therapeutic methods to enhance NK cell function and immunogenic CTL responses early or blocking aberrant PD-1 signaling may result in greater rate of success in TKI cessation studies.…”

A therapeutic T cell receptor mimic antibody targets tumor-associated PRAME peptide/HLA-I antigens

“…Decrease in Pr20 binding was not due to instability of peptide/HLA-A2 complexes, as each peptide increased surface HLA-A2 over unpulsed T2 cells in the assay, indicating that the peptides complexed with and stabilized HLA-A2 ( Figure 1B). The data demonstrated that specific changes to the native peptide sequence can abrogate Pr20 binding, consistent with other reported TCRm (15,29). of leukemia in vivo (11).…”

A TCR-mimic antibody to WT1 bypasses tyrosine kinase inhibitor resistance in human BCR-ABL+ leukemias

“…23 Although T cell-based therapies have been attempted against WT1-expressing cancers, monoclonal TCRm antibodies have several advantages over vaccines, TCR constructs, and adaptive T cells: ESKM can be produced and administered easily; and it has greater potency, more predictable and simpler pharmacokinetics, and high efficacy. Although several TCRm antibodies have been developed for other antigens, 24 none has entered human trials.…”