Enhancing the Antitumor Immunity of T Cells by Engineering the Lipid-Regulatory Site of the TCR/CD3 Complex

Abstract

The engagement of the T cell receptor (TCR) by a specific peptide-MHC ligand initiates transmembrane signaling to induce T-cell activation, a key step in most adaptive immune responses. Previous studies have indicated that TCR signaling is tightly regulated by cholesterol and its sulfate metabolite, cholesterol sulfate (CS), on the membrane. Here, we report a novel mechanism by which CS modulates TCR signaling through a conformational change of CD3 subunits. We found that the negatively charged CS interacted with the positively charged cytoplasmic domain of CD3ε (CD3εCD) to enhance its binding to the cell membrane and induce a stable secondary structure. This secondary structure suppressed the release of CD3εCD from the membrane in the presence of Ca2+, which in turn inhibited TCR phosphorylation and signaling. When a point mutation (I/A) was introduced to the intracellular immunoreceptor tyrosine-based activation motifs (ITAMs; YxxI-x6–8-YxxL) of CD3ε subunit, it reduced the stability of the secondary structure and regained sensitivity to Ca2+, which abolished CS-mediated inhibition and enhanced the signaling of the TCR complex. Notably, the I/A mutation could be applied to both murine and human TCR-T cell therapy to improve the anti-tumor efficacy. Our study reveals insights into the regulatory mechanism of TCR signaling and provides a strategy to functionally engineer the TCR/CD3 complex for T cell-based cancer immunotherapy.

The role of PD-1 signaling in health and immune-related diseases

“…Recent years have seen a rapid expansion of our knowledge of immune regulation. T-cell activation is a key step in the initiation and modulation of the immune response ( 1 ). The activation of T cells relies mainly on a two-signal model.…”

“…The first signal confers specific recognition of cognate antigenic peptides presented by major histocompatibility complex (MHC) molecules, which triggers T cell receptor (TCR) signaling. The second signal comprises co-stimulatory and co-inhibitory signals, which modulate TCR signaling positively or negatively to direct T cell function ( 1 – 3 ). A group of inhibitory or stimulatory molecules expressed on immune cells, antigen-presenting cells (APCs), tumor cells, or other types of cells are regarded as immune checkpoints, including programmed cell death-1 (PD-1), cytotoxic T lymphocyte-associated antigen-4 (CTLA-4), cluster of differentiation 28 (CD28), cluster of differentiation 80 (CD80), galectin-9 (Gal-9), and T cell immunoglobulin and mucin domain 3 (TIM-3) ( 4 – 7 ).…”