Chest CT scans document an increase in the volume of active thymic tissue after TK⁺-cell add-backs. (A-D) Detail on the thymic region (indicated by white arrows) from chest CT scans performed for diagnostic purposes in 2 representative TK007 patients (panels A-B: UPN# 25, age 64; panels C-D: UPN#15, age 17). Note the increase in density in the thymic region in the scans performed after TK⁺-cell add-backs (for panel B, TI = 2 and for panel D, TI = 3, performed at 50 and 135 days from last TK⁺-cell add-back, respectively) compared with their counterparts before treatment (panels A and C, both TI = 1). (E) Summary of results obtained from the retrospective analysis of 61 chest CT scans from TK007 patients, each scored a TI value by 2 independent expert radiologists (y-axis). **P = .0039; ***P < .0001 in a paired-sample Student t test.