** Shares of drug developer Artiva ARTV.O surge 102.5% to $5.57 premarket
** Co on Thursday said U.S. FDA granted fast track designation to its cell therapy AlloNK for treating refractory rheumatoid arthritis
** U.S. FDA's "fast track" tag aims to speed development and review of drugs for serious conditions with unmet medical need
** Refractory rheumatoid arthritis is a chronic joint disease
** Over 20 patients tested with AlloNK plus antibody therapy across autoimmune trials, including RA and lupus- ARTV
** Lupus is a chronic autoimmune disease where the body's immune system mistakenly attacks its own tissues and organs
** Co says safety data to highlight tolerability and ease-of-use
** Up to last close, stock down ~73%
(Reporting by Sahil Pandey in Bengaluru)
((Sahil.pandey@thomsonreuters.com))