** Shares of Artiva Biotherapeutics ARTV.O rises 25% to $14.02 premarket

** The biotech firm says its therapy AlloNK targets rheumatoid arthritis, a disease where the immune system attacks joints; 71% saw meaningful improvement at 6 months

** No patients relapsed or needed extra immune drugs; therapy was well tolerated with no serious side effects - ARTV

** Adds that U.S. FDA backs single late-stage trial comparing AlloNK + rituximab vs rituximab alone in ~150 patients; to start in the second half of 2026

** Also shows benefit in Sjögren's (dry eyes/mouth) and systemic sclerosis (skin thickening)

** Says therapy works by reducing B cells that drive autoimmune disease

** As of last close, stock up more than two fold YTD