While immune checkpoint inhibitors (ICI) have revolutionized the treatment of many cancers, including metastatic clear cell renal cell carcinoma (ccRCC), the development of agents that overcome resistance to anti-PD-1/PD-L1 based therapy represents a critical unmet need for ccRCC patients. We have shown that the B7 family member HERV-H LTR-associating 2 (HHLA2) is expressed in the majority of ccRCC and recently have discovered an inhibitory receptor (KIR3DL3) for HHLA2. Monoclonal antibodies that selectively block the HHLA2/KIRDL3 interaction, which we call the HHLA2 Inhibitory Pathway (HIP), could be an important means to enhance anti-tumor immune responses. In this proposal, we will study the expression of HHLA2 and it receptors in kidney cancer on tumor cells and immune cells and the relationship of HHLA2 and PD-L1 expression on tumors cells. Using clinically annotated specimens from clinical trials of patients with ccRCC on anti-PD-1 therapy, we will determine whether HHLA2 expression is associated with lack of response to PD-1 therapy. We will elucidate the regulatory pathways that are similar and different between HHLA2 and PD-L1 to better understand the expression of these immune checkpoints in kidney cancer and how their expression may change over the course of tumor progression and selection pressures. We will identify the optimal reagents for activating T cells and NK cells through the HHLA2:KIR3DL3 pathway in both in vitro and in vivo models. Our results will direct the selection of humanized blocking antibodies of HHLA2 Inhibitory Pathway that will move into primate toxicity and human Phase I clinical trials during year two of this grant.
In this proposal we show that expression of the B7 family member HERV-H LTR-associating 2 (HHLA2) is present in the majority of ccRCC and may serve to suppress T cell function and promote resistance to PD-1 blockade. We have developed antibodies that selectively block the binding of HHLA2 to a newly discovered inhibitory receptor (KIR3DL3) and enhance anti-tumor responses. Our goal is to identify therapeutic antibodies that block the HHLA2 Inhibitory Pathway and test the optimized agent in human ccRCC clinical trials.
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