TCR Signal Strength and Duration In Primary Mouse CD8+ T Cell Activation and Differentiation: A Standardized In Vitro Approach

T cell receptor (TCR) signal intensity and duration are critical determinants of CD8⁺ T cell activation, proliferation, and functional differentiation. However, standardized in vitro models that systematically compare how varying TCR signal inputs shape T cell fate remain limited. This study presents a reproducible method for activating primary mouse T cells in vitro using plate-bound anti-CD3 and soluble anti-CD28, supplemented with interleukin-2 (IL-2), and examines how modulating anti-CD3 concentration (signal strength) and stimulation time (signal duration) influences activation outcomes of T cells. We detail a protocol for isolating naive T cells from C57BL/6 mice, followed by stimulation across a range of anti-CD3 concentrations (0.1-10 µg/mL) and durations (6-48 h). We conducted flow cytometric analysis to assess early TCR-induced signaling via intracellular phosphorylated S6 ribosomal protein (p-S6) as a readout of mechanistic target of rapamycin complex 1 (mTORC1) activity, and then evaluated downstream events including surface activation markers (CD69, CD25, ICOS, PD-1), cellular proliferation via violet proliferation-tracking dye (CTV) dilution, and effector molecule expression (Granzyme B, TNF-α) as indicators of functional differentiation. The method provides a clear, stepwise visual guide for executing reproducible T cell stimulations, enabling researchers to dissect how specific TCR signal parameters direct T cell fate decisions. This approach not only supports mechanistic studies of T cell activation and differentiation but also offers a platform for optimizing T cell conditioning for adoptive immunotherapy and in vitro priming assays. By integrating video demonstration with detailed protocol narration, this protocol will enhance methodological transparency and reproducibility in T cell immunology research.