Inclusion Criteria:  Patient aged 18 or above Underwent allogeneic HSCT in QMH in the two-year recruitment period  Exclusion Criteria:  Underwent autologous HSCT Patient unable to attend follow-up visits  Family Control Subjects The research team will invite an accompanying family member to be the family control. Microbiome and tear samples will be collected for comparison. The sample collection schedule is the same as the corresponding post-HSCT case.