** Drug developer Jasper Therapeutics' JSPR.O shares fall 70.7% to $1.98 premarket

** Company says its experimental drug, briquilimab, achieved a complete response at week 12 in an early-stage study to treat a skin condition called chronic spontaneous urticaria (CSU)

** But the results were affected by an issue with one specific drug product lot

** CSU causes red, itchy bumps on the skin that come and go without a clear reason

** Company says it halted the drug's asthma trial due to the same drug product lot issue

** In the 10 patients with CSU who received the problematic drug product lot, reduction in mean tryptase levels, a marker of mast cell activity, was lower than expected and there was no noticeable improvement, company says

** Jasper is investigating the issue and expects results in the coming weeks

** As of last close, stock down 68.33% YTD

(Reporting by Siddhi Mahatole)

((siddhi.mahatole@thomsonreuters.com))