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 4

Melanomas and other solid tumors do not readily bind Pr20, but treatment with IFN-γ induces immunoproteasome expression and dramatically increases Pr20 binding.

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Melanomas and other solid tumors do not readily bind Pr20, but treatment...
(A) HLA-A2+ melanomas and a colon adenocarcinoma that expressed PRAME by qPCR (Table 1) were either left untreated (blue) or treated with 10 ng/ml of IFN-γ for 72 hours (red) and stained with Pr20 compared with untreated cells stained with an isotype control Ab (gray). HLA-A2 staining was performed in parallel. Data represent 3 independent experiments. (B) Melanomas were pretreated with 10 ng/ml IFN-γ for 72 hours or left untreated before 51Cr-ADCC assay was used to determine specific lysis by Pr20M. Samples were assayed in 3 technical replicates, and data are representative of 3 experiments per cell line. (C) PRAME expression after 72 hours of IFN-γ treatment was also measured by qPCR and Western blot analysis. qPCR data were analyzed by unpaired t test and are representative of 3 experiments with 3 technical replicates per experiment where mean ± SEM are plotted. Western blot data are representative of 3 experiments. (D) The expression of each immunoproteasome subunit was also determined after IFN-γ treatment by Western blot analysis. Blots were derived from replicate samples run on parallel gels with the GAPDH loading control shown from the β2i blot. Data are representative of 3 experiments.