A therapeutic T cell receptor mimic antibody targets tumor-associated PRAME peptide/HLA-I antigens
Aaron Y. Chang, … , Cheng Liu, David A. Scheinberg
Aaron Y. Chang, … , Cheng Liu, David A. Scheinberg
Published June 19, 2017
Citation Information: J Clin Invest. 2017;127(7):2705-2718. https://doi.org/10.1172/JCI92335.
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Research Article Immunology Therapeutics

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

Abstract

Preferentially expressed antigen in melanoma (PRAME) is a cancer-testis antigen that is expressed in many cancers and leukemias. In healthy tissue, PRAME expression is limited to the testes and ovaries, making it a highly attractive cancer target. PRAME is an intracellular protein that cannot currently be drugged. After proteasomal processing, the PRAME300–309 peptide ALYVDSLFFL (ALY) is presented in the context of human leukocyte antigen HLA-A*02:01 molecules for recognition by the T cell receptor (TCR) of cytotoxic T cells. Here, we have described Pr20, a TCR mimic (TCRm) human IgG1 antibody that recognizes the cell-surface ALY peptide/HLA-A2 complex. Pr20 is an immunological tool and potential therapeutic agent. Pr20 bound to PRAME+HLA-A2+ cancers. An afucosylated Fc form (Pr20M) directed antibody-dependent cellular cytotoxicity against PRAME+HLA-A2+ leukemia cells and was therapeutically effective against mouse xenograft models of human leukemia. In some tumors, Pr20 binding markedly increased upon IFN-γ treatment, mediated by induction of the immunoproteasome catalytic subunit β5i. The immunoproteasome reduced internal destructive cleavages within the ALY epitope compared with the constitutive proteasome. The data provide rationale for developing TCRm antibodies as therapeutic agents for cancer, offer mechanistic insight on proteasomal regulation of tumor-associated peptide/HLA antigen complexes, and yield possible therapeutic solutions to target antigens with ultra-low surface presentation.

Authors

Aaron Y. Chang, Tao Dao, Ron S. Gejman, Casey A. Jarvis, Andrew Scott, Leonid Dubrovsky, Melissa D. Mathias, Tatyana Korontsvit, Victoriya Zakhaleva, Michael Curcio, Ronald C. Hendrickson, Cheng Liu, David A. Scheinberg

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Figure 5

Immunoproteasome catalytic subunit β5i is important for IFN-γ–mediated Pr20 binding in melanomas and other solid tumors.

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Immunoproteasome catalytic subunit β5i is important for IFN-γ–mediated P...
β1i, β2i, and β5i were knocked out in the SK-Mel5 melanoma line using a CRISPR approach. A CRISPR construct against GFP was used as a vector control. (A, left panel) Cells were treated with 10 ng/ml IFN-γ for 72 hours, and Western blot analysis was used to demonstrate successful knockouts. Blots were derived from replicate samples run on parallel gels with the GAPDH loading control shown from the β2i blot. (B) Flow cytometry was used to determine Pr20 binding and surface HLA-A2 on the indicated knockouts (sgRNA against β1i, β2i, and β5i) untreated or treated with IFN-γ for 72 hours. (B, top panels). Data are normalized to MFI of untreated GFP sgRNA CRISPR control. (B, lower panels) β5i CRISPR knockout experiments were performed in the same manner on the UACC257 melanoma line. Successful knockout was determined by Western blot (A, right panel), and Pr20 binding and surface HLA-A2 were determined by flow cytometry (B, lower panels). (C) SK-Mel5 and UACC257 cells were left untreated or treated with 10 ng/ml IFN-γ for 72 hours in the presence or absence of 200 nM of the β5i inhibitor ONX-0914. Flow cytometry was used to determine MFI relative to untreated cells. All data are representative of 3 experiments with 3 technical replicates per experiment and mean ± SEM plotted. Statistical significance was determined by unpaired t test compared with control. *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001.