However, Chen et al. could demonstrate that percentages of CD3+PD-1+ and CD4+PD-1+ cells were significantly lower in AS patients with higher modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS) and reasoned that lack of PD-1 might facilitate radiographic progression [54]. Here, PDCD1 is linked to ankylosing spondylitis.