Delayed donor lymphocyte infusion (DLI) already plays a key role in supporting the graft-versus-tumor effect after allogeneic hematopoietic stem cell transplantation (HSCT) although the potency of DLI differs for each disease entitiy. The graft-versus-leukemia (GvL)-effect observed after DLI is based on the CTL-mediated immunity which is reactive against minor histocompatibility antigens (mHAg). To date, the role of leukemia-associated antigens (LAAs) in GvL is not clear.
We therefore analysed peripheral blood of a 57-year old woman with AML with NPM1 mutation (NPM1mut) who developed molecular relapse without detection of myeloid blasts in the peripheral blood and bone marrow at d+171 after allo-HSCT and received preemptive DLI at d+ 260. In parallel to the molecular relapse, chimerism continuously decreased to 60 % in the polymorphonuclear and 75 % in the mononuclear cell fraction. Blood samples were taken before and after DLI and investigated for specific T-cell responses against several LAAs for which cytotoxic T-cell responses were already described. In addition, the immune status of the patient was determined by measuring the counts of CD8+ and CD4+ T-cells as well as B-cells in the peripheral blood at several time points. To test specific CD8+ T-cell responses, ELISpot analysis for interferon gamma and granzyme B were perfomed. Two epitopes derived from the NPM1mut peptide (NPM1-P3 and –P9) and PRAME (P300 and P435) were tested as well as one epitope obtained from Survivin, RHAMM, Proteinase 3 and WT-1.
CD8+ T-cell responses against NPM1-P3, -P9, P300, Proteinase 3, Survivin and WT-1 were detected in blood samples after preemptive DLI but not in samples before DLI. In parallel, former detectable NPM1mut transcripts were no longer traceable – the patient achieved molecular complete remission - and former mixed chimerism became complete after DLI.
Here, we could demonstrate for the first time polyspecific cytotoxic CD8+ T-cell responses against several known LAAs in a patient with AML with NPM1mut after preemptive DLI in molecular relapse. Interestingly, the immune responses against LAAs were associated with MRD negativity. Whether specific cytotoxic T-cell responses against epitopes derived from the NPM1mut peptide or the polyspecificity of the cytotoxic T-cells against several LAAs are decisive in the elimination of the myeloid blasts with NPM1mut remains to be determined in a larger cohort of patients. All in all it is of interest to perform preemptive DLI in patients with molecular relapse systematically. In addition, boostering of T-cells against specific LAAs could possibly be an approach to enhance GvL-effect with reducing GvHD-effect at the same time, but the most suitable LAA or combination of LAAs for each disease entitiy still has to be investigated.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.