TCR mimic monoclonal antibody targets a specific peptide/HLA class I complex and significantly impedes tumor growth in vivo using breast cancer models.

Our laboratory has developed a process for generating mAbs with selectivity to unique peptides in the context of MHC molecules. Recently, we reported that RL4B, an mAb that we have called a TCR mimic (TCRm) because it recognizes peptide in the context of MHC, has cytotoxic activity in vitro and prevented growth of tumor cells in a prophylactic setting. When presented in the context of HLA-A2, RL4B TCRm recognizes the peptide GVLPALPQV derived from human chorionic gonadotropin (hCG)-beta. In this study, we show that RL4B TCRm has strong binding affinity for the GVLPALPQV peptide/HLA-A2 epitope and fine binding specificity for cells that express endogenous hCGbeta Ag and HLA-A2. In addition, suppression of tumor growth with RL4B TCRm was observed in orthotopic models for breast cancer. Using two aggressive human tumor cell lines, MDA-MB-231 and MCF-7, we provide evidence that RL4B TCRm significantly retards tumor growth, supporting a possible role for TCRm agents in therapeutic settings. Moreover, tumors in mice responded to RL4B TCRm therapy in a dose-dependent manner, eliminating tumors at the highest dose. RL4B TCRm strongly detects the hCGbeta peptide/HLA-A2 epitope in human primary breast tumor tissue, but does not react or reacts weakly with normal breast tissue from the same patient. These results further illustrate the selective nature of TCRm Abs and the clinical relevance of the GVLPALPQV peptide/HLA-A2 epitope expression in tumor cells, because they provide the first evidence that Abs that mimic the TCR can be used to markedly reduce and suppress tumor growth.

Direct discovery and validation of a peptide/MHC epitope expressed in primary human breast cancer cells using a TCRm monoclonal antibody with profound antitumor properties.

The identification and validation of new cancer-specific T cell epitopes continues to be a major area of research interest. Nevertheless, challenges remain to develop strategies that can easily discover and validate epitopes expressed in primary cancer cells. Regarded as targets for T cells, peptides presented in the context of the major histocompatibility complex (MHC) are recognized by monoclonal antibodies (mAbs). These mAbs are of special importance as they lend themselves to the detection of epitopes expressed in primary tumor cells. Here, we use an approach that has been successfully utilized in two different infectious disease applications (WNV and influenza). A direct peptide-epitope discovery strategy involving mass spectrometric analysis led to the identification of peptide YLLPAIVHI in the context of MHC A*02 allele (YLL/A2) from human breast carcinoma cell lines. We then generated and characterized an anti-YLL/A2 mAb designated as RL6A TCRm. Subsequently, the TCRm mAb was used to directly validate YLL/A2 epitope expression in human breast cancer tissue, but not in normal control breast tissue. Moreover, mice implanted with human breast cancer cells grew tumors, yet when treated with RL6A TCRm showed a marked reduction in tumor size. These data demonstrate for the first time a coordinated direct discovery and validation strategy that identified a peptide/MHC complex on primary tumor cells for antibody targeting and provide a novel approach to cancer immunotherapy.