Early and Profound Exhausted Phenotype of Central Memory and Memory Stem T Cells in the Bone Marrow of AML Patients Characterizes and Predicts Relapse after Allo-HSCT

Abstract Background: Allogeneic Hematopoietic Stem Cell Transplantation (HSCT) is the only cure for high-risk acute myeloid leukemia (AML). Unfortunately, relapse remains the major cause of death after HSCT. We investigated if T-cell dysfunction is associated to post-transplant relapse. Patients and Methods: We longitudinally analysed T-cell dynamics in bone marrow (BM) and peripheral blood (PB) of 32 AML patients receiving HSCT from HLA-matched (20 pts) or HLA haploidentical (Haplo, 12 pts) donors. BM and PB samples were collected 60 days after HSCT and at relapse (median 237 days; 16 pts) or, when complete remission was maintained, at 1 year (CR; 16 pts). 10 healthy donors (HD) were used as controls. Samples were analysed by polychromatic flow cytometry for the expression of inhibitory receptors (IR) on CD4 and CD8 T-cell subsets defined by CD45RA, CD62L and CD95 expression. Results were also analysed with BH-SNE, an unbiased dimensionality reduction algorithm. To evaluate T-cell function and specificity, CD107a expression, cytokine profiles and killing of autologous blasts were quantified. Results: After Haplo-HSCT, PD-1, CTLA-4, 2B4 and Tim-3 were expressed in BM and PB T cells at higher percentage when compared to HD and independently from the clinical outcome. Conversely, after HLA-matched HSCT, patients who relapsed displayed a higher frequency of BM-infiltrating T cells expressing PD-1, CTLA-4 and Tim-3 than CR pts (p Consistent with the exhausted phenotype, BM CD8 T-cells at relapse displayed lower degranulation ability and IL-2 production compared to CR (p Interestingly, we observed that, at day 60 after HLA-matched HSCT, BM CD8 TSCM and TCM cells from patients who shall subsequently relapse already expressed PD-1, Tim-3 and LAG3 at higher percentage when compared to patients who shall maintain long-term CR (p Conclusions: After HSCT, the molecular signature of exhausted CD8 cells in relapsing patients includes PD-1, CTLA-4, 2B4 and Tim-3, expressed on early differentiated T cells. Exhausted BM-T cells are preferentially enriched in specificities directed against leukemic blasts. Taken together, these results highlight a wide, though reversible, immunological dysfunction mediated by AML relapsing blasts. Interestingly, the analysis on early time points suggests that the exhausted phenotype may be predictive of leukemia relapse. Download : Download high-res image (189KB) Download : Download full-size image Figure 1 . Disclosures Bondanza: TxCell SA: Research Funding; Menarini Biotech: Consultancy; Molmed Spa: Research Funding. Bonini: MolMed: Consultancy.