Functional Characterization of Potential New Agents for Cancer Immunotherapy

Abstract

PD-1/PD-L1 checkpoint blockade has demonstrated promise in a variety of malignancies. The blockade of T cell inhibitory molecules PD-1 and PD-L1 can rejuvenate T cells and improve tumor cell killing. However, the overall response rate of PD-1/PD-L1 immunotherapy is only about 20-30%. One promising method to improve cancer immunotherapy is combinatory immunotherapies that target new receptors/ligands regulating T cell activity, so the functional characterization of these new receptors/ligands is urgent. Due to the functional importance of the B7 superfamily in T cell activation, I studied T cell regulating functions of two poorly characterized B7 superfamily members, IgC domain-truncated CD86 and butyrophilin-like 2 (BTNL2). To study their function in a natural cell-cell interaction scenario, the murine IgC domain-truncated CD86 or murine BTNL2 was cloned and transfected into Chinese Hamster Ovary Cells that already expressed MHC Class II IAd. After co-culturing the transfectants, OVA peptide 323-339 and transgenic T cells from DO11.10 mice, I tested T cell proliferation and cytokine expression. The data suggested cell-membrane bound BTNL2 will moderately stimulate T cells and increase IFN-γ secretion significantly. Similarly, stimulatory results were also demonstrated with mBTNL2 hIgG1 fusion protein and recombinant mBTNL2 protein. The stimulatory effect of BTNL2 on T cell activation suggested that BTNL2 could be targeted as a T cell activity modulator or be a potential checkpoint ligand to be lentiviral delivered to dendritic cells as a therapy. My study indicated additional B7 proteins may be another potential target for combinatory cancer immunotherapy with PD-1/PD-L1 blockade.