RecruitingEarly Phase 1Biological interventionAn Exploratory Clinical Study of CD19 CAR NK Cells for the Treatment of Refractory Antisynthetase Antibody Syndrome and Rheumatoid ArthritisA single-center, open-label dose-escalation design to evaluate the safety and efficacy of 3 infusions of anti CD19 CAR NK cells (KN5501), as well as the expansion and persistence of KN5501 in patients with refractory antisynthetase antibody syndrome (ASyS) and rheumatoid arthritis (RA); To evaluate the ability of KN5501 to clear CD19-positive B cells in patients to determine the feasibility of KN5501 for the treatment of refractory ASyS and or RA.