Preemptive Donor Lymphocyte Infusion Induces Polyspecific T-Cell Responses in a Patient with AML with NPM1 Mutation

Abstract 4311

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 (NPM1^mut) 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 NPM1^mut 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 NPM1^mut 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 NPM1^mut 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 NPM1^mut peptide or the polyspecificity of the cytotoxic T-cells against several LAAs are decisive in the elimination of the myeloid blasts with NPM1^mut 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.