This is an open-label, single-dose, prospective, monocenter, Phase I interventional study (not first-in-human) to assess the safety, tolerability, and preliminary efficacy of autologous anti-CD19 CAR-T cells as an advanced therapy medicinal product in adult patients; with severe and refractory systemic autoimmune rheumatic diseases, including rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), Sjogren's disease (SjD), systemic sclerosis (SSc) and idiopathic inflammatory myositis (IIM).