For patients with adult T-cell leukaemia, asymptomatic carriers of HTLV-1 have been widely considered acceptable as donors in allogeneic stem-cell transplantation.1 The immune system is thought to have an important role in leukaemia occurrence in HTLV-1-seropositive carriers.2 The only reported case of donor-derived adult T-cell leukaemia was in 2006, in an immunosuppressed recipient of a peripheral-blood stem-cell transplant.3 No cases of donorderived adult T-cell leukaemia have been reported in immunocompetent patients. The prognosis tends to be better for these patients than for those with CNS involvement subsequent to systemic adult T-cell leukaemia.4 Only two cases of isolated CNS involvement have been reported so far.4,5 The function of CD4-positive cells was not fully analysed, so there is a possibility of some functional deficit in immune reconstitution.