Reduces LAG-3, TIM-3 and PD-1 expression on tumour-infiltrating CD8+ T cells in murine models.Unaltered regulatory T cell infiltration in murine tumour models.Increased granzyme B and no induction of immune checkpoints in MM patient samples.At high concentrations impairs TCR signaling and T cell proliferation. Here, PDCD1 is linked to Miyoshi myopathy.