Lag3 and PD-1 pathways regulate NFAT-dependent TCR signalling programmes during early CD4+T cell activation

Summary Lag3 and PD-1 are immune checkpoints that regulate T cell responses and are current immunotherapy targets. Yet how they function to control early CD4 + T cell activation remains unclear. Here, we show that the PD-1 and Lag3 pathways exhibit layered control of the early CD4 + T cell activation process, with the effects of Lag3 more pronounced in the presence of PD-1 pathway co-blockade (CB). RNA-sequencing revealed that CB drove an early NFAT-dependent transcriptional profile, including promotion of ICOS hi T follicular helper (Tfh) cell differentiation. NFAT pathway inhibition abolished CB-induced upregulation of NFAT-dependent co-receptors ICOS and OX40, whilst unaffecting the NFAT-independent gene Nr4a1 . Mechanistically, Lag3 and PD-1 pathways functioned additively to regulate the duration of T cell receptor (TCR) signals during CD4 + T cell re-activation. Our data therefore reveal that PD-1 and Lag3 pathways converge to additively regulate TCR signal duration and NFAT-dependent transcriptional activity during early CD4 + T cell re-activation. Highlights PD-1 and Lag3 pathways exhibit layered control of early CD4 + T cell activation Their co-blockade enhances NFAT-dependent TCR transcriptional programmes Inhibition of NFAT signalling reverses the functional effects of PD-1 and Lag3 co-blockade Mechanistically, PD-1 and Lag3 function to additively regulate TCR signal duration during re-activation of CD4 + T cells