A recent study performed in the USA used a single cell transcriptome and CD8 T cell receptor (TCR) sequencing of CD8 to suggest that cytotoxic CD8+ T cells targeting citrullinated antigens play a role in driving synovitis and joint tissue destruction in anti-citrullinated protein antibodies (ACPA)-positive rheumatoid arthritis [8]. Here, PRTN3 is linked to rheumatoid arthritis.