Targeting the Intracellular WT1 Oncogene Product with a Therapeutic Human Antibody

Abstract

The Wilms tumor 1 (WT1) oncoprotein is an intracellular, oncogenic transcription factor that is overexpressed in a wide range of leukemias and solid cancers. RMFPNAPYL (RMF), a WT1-derived CD8+ T cell human leukocyte antigen (HLA)–A0201 epitope, is a validated target for T cell–based immunotherapy. Using phage display technology, we discovered a fully human “T cell receptor–like” monoclonal antibody (mAb), ESK1, specific for the WT1 RMF peptide/HLA-A0201 complex. ESK1 bound to several leukemia and solid tumor cell lines and primary leukemia cells, in a WT1-and HLA-A0201–restricted manner, with high avidity [dissociation constant (Kd) = 0.1 nM]. ESK1 mediated antibody-dependent human effector cell cytotoxicity in vitro. Low doses of naked ESK1 antibody cleared established, disseminated, human acute lymphocytic leukemia and Philadelphia chromosome–positive leukemia in nonobese diabetic/severe combined immunodeficient γc−/− (NSG) mouse models. At therapeutic doses, no toxicity was seen in HLA-A0201 transgenic mice. ESK1 is a potential therapeutic agent for a wide range of cancers overexpressing the WT1 oncoprotein. This finding also provides preclinical validation for the strategy of developing therapeutic mAbs targeting intracellular oncogenic proteins.

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

“…ESKM is also a therapeutically effective antibody in mouse models of other human leukemias and solid tumors. 23 However, as monotherapy, the antibody was unable to achieve cures in these models. In combination, TKIs and ESKM did not exhibit enhanced toxicity, had at least an additive therapeutic effect, and resulted in molecular cures of Ph 1 ALL in mice.…”

“…Before its use in vivo, stock solutions of TKIs were prepared in dimethyl sulfoxide (DMSO), with the scheduled dose of TKI in 50 mL DMSO per mouse. All TKIs and ESKM treatments were administered IP at these schedules: ESKM 100 mg twice weekly 23 and TKIs daily. Male NSG mice, aged 6 to 8 weeks, were purchased from Jackson Labs.…”

“…20 We have developed an antibody, ESKM, directed against the 9-amino acid peptide RMFPNAPYL (RMF), expressed in the context of HLA-A*02:01. [21][22][23] ESKM is a T-cell receptor mimic (TCRm) monoclonal human IgG1 in which the Fc portion has been modified by alternative glycosylation that results in stronger binding to effector cell-activating Fcg receptors and increased antibodydependent cell cytotoxicity (ADCC). 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.…”

Tapping the treasure of intracellular oncotargets with immunotherapy

“…They showed that intracellular tumor antigens can be captured by mAbs and engaged in an efficient induction of CD8 T-cell responses, suggesting the possible use of mAbs for passive cancer immunotherapy. Furthermore, in 2013, another research group has also reported that targeting the intracellular Wilms tumor 1 (WT1) oncoprotein with human antibodies reveals therapeutic effects in mice [20]. WT1 oncoprotein is an intracellular oncogenic transcription factor overexpressed in a wide range of leukemias and solid tumors.…”