Levels of Specific Peptide-HLA Class I Complex Predicts Tumor Cell Susceptibility to CTL Killing

Abstract

Recognition of tumor-associated Ags (TAAs) on tumor cells by CTLs and the subsequent tumor cell death are assumed to be dependent on TAA protein expression and to correlate directly with the level of peptide displayed in the binding site of the HLA class I molecule. In this study we evaluated whether the levels of Her-2/neu protein expression on human tumor cell lines directly correlate with HLA-A*0201/Her2/neu peptide presentation and CTL recognition. We developed a TCR mimic (TCRm) mAb designated 1B8 that specifically recognizes the HLA-A2.1/Her2/neu peptide (369–377) (Her2(369)-A2) complex. TCRm mAb staining intensity varied for the five human tumor cell lines analyzed, suggesting quantitative differences in levels of the Her2(369)-A2 complex on these cells. Analysis of tumor cell lines pretreated with IFN-γ and TNF-α for Her2/neu protein and HLA-A2 molecule expression did not reveal a direct correlation between the levels of Her2/neu Ag, HLA-A2 molecule, and Her2(369)-A2 complex expression. However, compared with untreated cells, cytokine-treated cell lines showed an increase in Her2(369)-A2 epitope density that directly correlated with enhanced tumor cell death (p = 0.05). Although a trend was observed between tumor cell lysis and the level of the Her2(369)-A2 complex for untreated cells, the association was not significant. These findings suggest that tumor cell susceptibility to CTL-mediated lysis may be predicted based on the level of specific peptide-MHC class I expression rather than on the total level of TAA expression. Further, these studies demonstrate the potential of the TCRm mAb for validation of endogenous HLA-peptide epitopes on tumor cells.

A Single TCRα-Chain with Dominant Peptide Recognition in the Allorestricted HER2/neu-Specific T Cell Repertoire

“…Second, the discriminative HER2 369 epitope density between tumor cells and nontransformed cells might be marginal for HER2 369 . In fact, HER2 369 peptide has been previously shown to be presented only at low levels on tumor cells (49). Moreover, overexpression of HER2 seems to result in proteasomal dysfunction and therefore reduced peptide presentation on tumor cells overexpressing this protein (50).…”

The HLA A*0201–restricted hTERT540–548 peptide is not detected on tumor cells by a CTL clone or a high-affinity T-cell receptor

“…Monoclonal antibodies, raised against peptide-MHC combinations, have also been used to study peptide presentation, mainly by flow cytometry. However, in some cases, antibodies give fluorescence shifts that indicate extremely large numbers of epitopes per cell, conflicting with estimates obtained with other quantitative techniques such as mass spectrometry (38). In other cases, shifts are more consistent with levels of antigen detected by other methods (39,40).…”

Manipulation of MHC-I/TCR Interaction for Immune Therapy

“…T cells are capable of detecting as few as 3~10 pMHC-I molecules on a target cell and have ability to specifically recognize low level of viral or tumor pMHC-I, even in the presence of orders of magnitude less than self-pMHC-I molecules (48). Tumor cell susceptibility to CTL-mediated lysis may base on the level of specific pMHC-I expression rather than on the total level of tumor associated antigen (TAA) expression (49).…”

“…The peptides supplied to MHC-I increase with enhanced MHC-I expression (73,74). Comparing with their control cells, cytokine-treated cell lines showed an increase in Her2 (369)-A2 epitope density (49). Macrophage colonystimulating factor (GM-CSF) has also been reported to increase greatly the expression of MHC-1 (H-2K d ) on tumor cells (75), so has TNF-α (76).…”