LTA and progressive multifocal leukoencephalopathy: Despite using BKV-specific T cells to treat PML caused by JCV, significant cross-reactivity occurs due to the substantial protein similarity between the VP1 (78%) and LT (83%) proteins of these viruses.17 In our cohort, we observed that the administration of BKV-specific T cells also led to the detection of JCV-specific T cells in the blood of responders after 6 weeks of treatment.