Summary Donor lymphocyte infusion (DLI) is an effective method to establish full donor chimerism or to prevent and treat relapse after allogeneic haematopoietic cell transplantation (allo‐HCT). Usually, DLIs are collected from naïve donors as steady‐state lymphocytes. When donor lymphocytes are collected during stem cell apheresis, donors are pre‐treated with granulocyte colony‐stimulating factor (G‐CSF). However, the impact of G‐CSF stimulation and the resulting composition of DLIs on beneficial anti‐leukaemic responses and survival remain elusive. Therefore, we performed a retrospective analysis to evaluate the role of G‐CSF‐DLIs: 44 patients received either steady‐state DLIs or G‐CSF‐DLIs to prevent and treat relapse or establish full donor chimerism after allo‐HCT. The G‐CSF‐DLI patient cohort showed an improved conversion to full donor chimerism and a lower cumulative incidence of relapse or disease progression without a significantly increased cumulative incidence of graft‐versus‐host disease (GVHD). CD34+ cells, monocytic myeloid‐derived suppressor cells and monocytes as well as donor age and the subsequent occurrence of chronic GVHD were identified as risk factors that significantly improve overall survival after DLI administration. In conclusion, our data suggest that administration of G‐CSF‐DLIs results in graft‐versus‐leukaemia effects without exacerbating GVHD, therefore, improving survival after DLIs.

Allogeneic hematopoietic cell transplantation (allo-HCT) is a curative treatment option for hematologic malignancies but relapse remains the most common cause of death. Infusion of donor lymphocytes (DLIs) can induce remission and prolong survival by exerting graft-vs.-leukemia (GVL) effects. However, sufficient tumor control cannot be established in all patients and occurrence of graft-vs.-host disease (GVHD) prevents further dose escalation. Previous data indicate that invariant natural killer T (iNKT) cells promote anti-tumor immunity without exacerbating GVHD. In the present study we investigated lysis of leukemic blasts through iNKT cells from donor-derived lymphocytes for leukemia control and found that iNKT cells constitute about 0.12% of cryopreserved donor T cells. Therefore, we established a 2-week cell culture protocol allowing for a robust expansion of iNKT cells from cryopreserved DLIs (DLI-iNKTs) that can be used for further preclinical and clinical applications. Such DLI-iNKTs efficiently lysed leukemia cell lines and primary patient AML blasts ex vivo in a dose- and CD1d-dependent manner. Furthermore, expression of CD1d on target cells was required to release proinflammatory cytokines and proapoptotic effector molecules. Our results suggest that iNKT cells from donor-derived lymphocytes are involved in anti-tumor immunity after allo-HCT and therefore may reduce the risk of relapse and improve progression-free and overall survival.