** Cell therapy developer Atara's ATRA.O shares rise 5.1% to $14.69, its highest in more than eight months

** Co to lay off 29% of staff, retaining about 15 employees

** ATRA expects to complete cuts by Jan 2026

** Co expects ~$1.3 mln in layoff costs related to severance and other benefits

** Company says more charges may arise depending on events tied to layoffs

** Including session's move, stock up ~10% YTD

(Reporting by Sahil Pandey in Bengaluru)

((Sahil.Pandey@thomsonreuters.com;))