Toll-like receptor 2 intracellular signaling domain (TLR2-ICD)

The Toll-like receptor 2 (TLR2) intracellular signaling domain is a specialized costimulatory component utilized in the engineering of advanced Chimeric Antigen Receptor (CAR) T cell therapies. In its native biological context, TLR2 is a transmembrane pattern recognition receptor that identifies pathogen-associated molecular patterns, such as microbial lipopeptides, to trigger innate immune responses (PubMed: 10426990). When repurposed as a CAR endodomain, the TLR2 intracellular signaling complex—specifically its TIR domain—provides a potent alternative to traditional costimulatory domains like CD28 or 4-1BB. This complex functions by recruiting MyD88 and MAL adapter proteins, which subsequently activate the NF-κB and MAPK signaling pathways to drive T cell proliferation and effector function. Research has demonstrated that incorporating this TLR2 complex into CAR T cells can significantly improve their metabolic fitness and long-term persistence, particularly in the challenging immunosuppressive environments of solid tumors (Lai et al., 2020). Consequently, it is being investigated as a therapeutic strategy to overcome the limitations of current CAR T cell products in treating a broader range of malignancies. While primarily a synthetic application in cell therapy, the signaling complex remains a critical focal point for enhancing the durability of anti-tumor immune responses.

Other names

TLR2 costimulatory domainTLR2-TIR domainTLR2 signaling complexTLR2-MyD88 signaling axisToll-like receptor 2-mediated costimulation

The TLR2 intracellular signaling complex, when integrated into a chimeric antigen receptor (CAR), functions as a costimulatory endodomain. Upon antigen recognition by the CAR's extracellular domain, the TLR2 Toll/Interleukin-1 receptor (TIR) domain recruits adapter proteins, primarily MyD88 (Myeloid differentiation primary response 88) and MAL (MyD88-adapter-like). This recruitment initiates a signaling cascade involving IRAK kinases, leading to the activation of the NF-κB and MAPK (p38, JNK) pathways. These pathways promote the transcription of genes associated with T cell survival, proinflammatory cytokine production (e.g., IFN-γ, IL-2), and metabolic reprogramming, which collectively enhance the persistence and cytotoxic activity of the CAR T cells within the tumor microenvironment (Lai et al., 2020, Nature Communications; UniProt P33535).