CD28 is a homodimeric receptor of the Ig superfamily that stimulates cell surface receptors, expressed on nearly all T cells in rodents, and predominantly on CD4 cells, providing the necessary costimulatory signals for T cell activation and survival. Inducing costimulatory signals within T cells, CD28 recognizes homologous antigens/major histocompatibility complexes through its T cell receptor (TCR). The costimulation mediated by CD28 is an indispensable signal required for activating naive and effector T cells. Blocking CD28-dependent T cell activation has been used to regulate harmful immune responses in transplantation rejection and autoimmune experimental models.Studies have shown that antibodies targeting the CD28/CD80 and CD86 interactions have shown promising applications in clinical trials for treating various cancers.Current methods for measuring the potential biological activity of CD28-targeted biopharmaceuticals rely on measuring human T cells and their functional products, such as cell proliferation, cell surface marker expression, and interferon-gamma (IFNγ) and interleukin-2 (IL-2) production. Due to the reliance on donor primary cells, complex experimental protocols, and inconsistent testing reagents, these assays are labor-intensive and variable. Therefore, these assay methods are challenging to establish in a quality-controlled drug development environment.CD28 Reporter Jurkat Cell Line, a luciferase reporter cell line based on the PKCθ signaling pathway, is designed for the optimal activation of T cells through the engagement of the T cell receptor (TCR)/CD3 complex and the costimulatory receptor CD28. Activating costimulation with CD28 initiates signal transduction in T cells, leading to the phosphorylation of tyrosine residues in CD28, activating PI3K, recruiting PLC and ZAP70. Through the PKCθ signaling pathway, downstream reporter genes are activated, thereby activating the expression of luciferase. Blocking CD28 with antibodies will inhibit costimulatory signals, leading to suppression of the TCR signal and preventing the activation of luciferase protein expression.
