Atara Biotherapeutics announces FDA clearance to initiate two Phase 3 clinical studies to evaluate tabelecleucel in patients with rituximab-refractory Epstein-Barr virus associated post-transplant lymphoproliferative disorder (EBV+PTLD). Atara Biotherapeutics, Inc., an off-the-shelf T-cell immunotherapy company developing novel treatments for patients with cancer, autoimmune, and viral diseases, today announced that it received clearance from the U.S. Food and…