** Shares of drug developer Atara Biotherapeutics ATRA.O fall 4.6% to $6.27 premarket

** Co says the US FDA has placed a clinical hold on trials testing its experimental cancer cell therapies

** The hold applies to studies of co's experimental cancer therapies, tabelecleucel, and ATA3219

** Co says the hold is related to the issues observed at a third-party manufacturing facility

** The FDA last week declined to approve its cancer therapy tabelecleucel to treat patients with a rare cancer that develops after organ or stem cell transplants, due to third-party manufacturing concerns

** "Atara and FDA have discussed and agreed upon the actions necessary to release the clinical holds"- ATRA

** Co says it has paused enrollment of new participants in the trials; adding that some participants "who have the potential to derive clinical benefit" can continue to receive treatment

** Up last close, stock had fallen 63.2% in the past 12 months

(Reporting by Sneha S K)

((Sneha.SK@thomsonreuters.com;))