Using mass cytometry (cytometry by time-of-flight [CyTOF]) on serial peripheral blood samples obtained from patients with AML/MDS after hematopoietic allogeneic stem cell transplantation and healthy controls, Gournay et al documented immune reconstitution during the first 12 months after transplant (left). They further showed that TIGIT⁺ and CD161⁺ CD4⁺ T cells were associated with subsequent disease recurrence through comparison of patients with AML who relapsed after transplant with patients who did not relapse (right). CLEC2D, C-type lectin domain family 2 member D; MHC, major histocompatibility complex; PVR, poliovirus receptor (CD155); TCR, T-cell receptor.