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Antibody Targeting to a Class I MHC-Peptide Epitope Promotes Tumor Cell Death

Vaughan P. Wittman^*,, David Woodburn, Tiffany Nguyen, Francisca A. Neethling, Stephen Wright and Jon A. Weidanz^1,*,

^* Department of Pharmaceutical Sciences, School of Pharmacy, Texas Tech University Health Sciences Center, Amarillo, TX 79106; Receptor Logic, Ltd., Amarillo, TX 79106; and Department of Internal Medicine, School of Medicine, Texas Tech University Health Sciences Center, Amarillo, TX 79106

Therapeutic mAbs that target tumor-associated Ags on the surface of malignant cells have proven to be an effective and specific option for the treatment of certain cancers. However, many of these protein markers of carcinogenesis are not expressed on the cells’ surface. Instead these tumor-associated Ags are processed into peptides that are presented at the cell surface, in the context of MHC class I molecules, where they become targets for T cells. To tap this vast source of tumor Ags, we generated a murine IgG2a mAb, 3.2G1, endowed with TCR-like binding specificity for peptide-HLA-A*0201 (HLA-A2) complex and designated this class of Ab as TCR mimics (TCRm). The 3.2G1 TCRm recognizes the GVL peptide (GVLPALPQV) from human chorionic gonadotropin presented by the peptide-HLA-A*0201 complex. When used in immunofluorescent staining reactions using GVL peptide-loaded T2 cells, the 3.2G1 TCRm specifically stained the cells in a peptide and Ab concentration-dependent manner. Staining intensity correlated with the extent of cell lysis by complement-dependent cytotoxicity (CDC), and a peptide concentration-dependent threshold level existed for the CDC reaction. Staining of human tumor lines demonstrated that 3.2G1 TCRm was able to recognize endogenously processed peptide and that the breast cancer cell line MDA-MB-231 highly expressed the target epitope. The 3.2G1 TCRm-mediated CDC and Ab-dependent cellular cytotoxicity of a human breast carcinoma line in vitro and inhibited in vivo tumor implantation and growth in nude mice. These results provide validation for the development of novel TCRm therapeutic reagents that specifically target and kill tumors via recognition and binding to MHC-peptide epitopes.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ Address correspondence and reprint requests to Dr. Jon A. Weidanz, Department of Pharmaceutical Sciences, School of Pharmacy, Texas Tech University Health Sciences Center, 1300 Coulter Drive, Amarillo, TX 79106. E-mail address: jon.weidanz{at}ttuhsc.edu

² Abbreviations used in this paper: MHC-I, MHC class I; CDC, complement-dependent cytotoxicity; ADCC, Ab-dependent cellular cytoxicity; TCRm, TCR mimic; hCG, human chorionic gonadotropin -chain; ₂m, ₂-microglobulin; SB, stain buffer; LDH, lactate dehydrogenase; MFI, mean fluorescence intensity; NHL, non-Hodgkin’s lymphoma.