Figure 10.

PD-L1:PD-1 engagement suppresses TCR55-induced ERK activation efficiently in human primary CD8⁺ T cells. (A) Workflow of engineering TCR55⁺ PD-1⁺ human primary PBMC-derived T cells for coculture time course experiments and the subsequent intracellular staining analysis. (B) FACS gating strategy for PD-1⁺ CD8⁺ T cells (top left). Population pERK response curves and AUC (mean ± s.d.; bottom left) for top 20% PD-1⁺ CD8⁺ T cells comparing PD-L1⁻ versus PD-L1⁺ SQL-loaded (100 μM) APC condition. Dashed line indicates pERK background activation level in the absence of SQL peptide ligand (Fig. S5 F). **P value between 0.001 and 0.01, one-tailed unpaired t test. Single-cell analysis with multivariable model predictions (right panels) for top 40% PD-1⁺ CD8⁺ T cells. Model-predicted pERK expression over a discrete range of PD-1 expression (top right), accounting for the true distribution of CD28 expression in the data at each PD-1 expression value. Data points indicate mean values from the data, and error bars indicate standard error around those means. Model-predicted pERK expression over a continuous range of PD-1 expression values (bottom right), assuming that CD28 expression is fixed at its overall mean. Solid lines indicate model predictions and shaded intervals represent the 95% credible intervals around those predictions. Results are representative of two independent experiments with human PBMC from the same donor.