T cell receptor activation pathway

T cell activation pathways refer to a complex network of intracellular signaling cascades initiated upon engagement of the T cell receptor (TCR) with antigen-major histocompatibility complex (MHC) on antigen-presenting cells, together with co-stimulatory and accessory molecules[1][2][4][8]. The primary signaling events involve phosphorylation of immunoreceptor tyrosine-based activation motifs (ITAMs) on the CD3 complex by kinases such as Lck and Fyn, followed by recruitment and activation of Zap-70, which then phosphorylates adaptor proteins like LAT and SLP-76, forming multi-component signalosomes[2][6][8]. Downstream pathways include activation of the Ras-MAPK/ERK pathway, the PLCγ1 pathway leading to calcium influx and NFAT activation, the PKCθ-IKK-NF-κB pathway, and mTOR signaling, among others[1][3][4]. These pathways integrate signals from co-stimulatory and co-inhibitory receptors (such as CD28, CTLA-4, PD-1, LFA-1, TIM family, TIGIT, and others) to determine T cell fate, including activation, proliferation, cytokine production, and differentiation[2][4][5]. Dysregulation of TCR activation pathways has roles in cancer progression, autoimmunity, chronic inflammation, immunodeficiencies, and response to infections[3][7]. Drugs targeting components of these pathways are used for immunosuppression, treatment of autoimmune conditions, and, via checkpoint inhibition, for cancer immunotherapy[3][5]. However, “T cell activation pathways” is not a specific molecule, protein, or classical druggable target, but rather a set of intracellular signaling processes. Therefore, it is not, strictly speaking, a canonical target in the sense of a receptor, enzyme, or transporter. Instead, the designated targets within these pathways include individual molecules like T cell receptor (TCR)/CD3 complex, CD28, Lck, Zap-70, calcineurin, CTLA-4, PD-1, integrins, etc. that can each be considered therapeutic targets individually[1][2][4][8].

Other names

T cell activation signaling pathwayTCR signaling pathwayT cell signaling pathwayTCR-mediated activation

Inhibition of calcineurin, Blockade of co-stimulatory signals, Inhibition of integrin-mediated interactions, Immune checkpoint inhibition