Impact of Sorafenib Maintenance on Immune Reconstitution after Allogeneic Stem-Cell Transplantation in FLT3-ITD Acute Myeloid Leukemia
Authors: Morin Sarah , Pradier Amandine , Bernardi Chiara , Ducrot Aurelie , Wang Sisi , Melotti Astrid , Masouridi-Levrat Stavroula , Giannotti Federica , Mamez Anne-Claire , Chalandon Yves , Simonetta Federico 
Published: December 2024

Introduction: Sorafenib maintenance reduces the risk of relapse and improves survival in FLT3-ITD acute myeloid leukemia (AML) patients after allogeneic hematopoietic stem cell transplantation (allo-HSCT). The mechanisms underlying the beneficial effect of sorafenib in the context of allo-HSCT are largely unknown. In addition to FLT3 inhibition, one hypothesis is that sorafenib may increase the Graft-versus-Leukemia (GvL) effect. Preclinical evidence indicates that AML cells can support GvL by secreting of T and NK cells growth factors, namely IL-15 (doi.org/10.1038/nm.4484). However, the positive effect of sorafenib as maintenance in patients in remission of AML after allo-HSCT suggests that other immunological mechanisms can be involved. We hypothesized that sorafenib might induce quantitative and/or qualitative changes on lymphocytes subsets during immune-reconstitution after allo-HSCT.
Methods: We conducted a phenotypic characterization of T cells before (1 month after allo-HSCT) and after (6 months after allo-HSCT) starting sorafenib maintenance in 11 FLT3-ITD AML patients. Sorafenib maintenance was started at a median of two months after allo-HSCT. 13 non-FLT3-ITD AML patients who did not receive sorafenib and analyzed at the same time-points served as controls. RNA-sequencing analysis was performed on FACS-sorted T cells before and after sorafenib exposure in three patients.
Results: We did not observe any differences in the proportions of major CD4 and CD8 T cell subsets, namely naïve, central memory, effector memory and terminal effector memory T cells, induced by sorafenib maintenance. Interestingly, we observed a significant reduction of the expression of the exhaustion marker Programmed cell death protein 1 (PD-1) at the surface of CD8 but not CD4 T cells after starting sorafenib maintenance (median 23%, range 13%-33%) compared to before treatment (37%, 14%-92%; p=0.019). Importantly, PD-1 expression on CD8 T cells from sorafenib treated patients was significantly lower than on CD8 T cells from control patients analyzed at the same time-point (58%, 19%-96%; p=0.0007). Moreover, sorafenib exposure did not influence CD4 or CD8 T cell activation status based on CD38 and HLA-DR expression suggesting that differences in PD-1 expression were not a mere consequence of differences in T-cell activation status. Transcriptomic analysis of CD8 T cells before and after sorafenib treatment revealed the downregulation of the EZH2 and BCAT1 genes, whose inhibition has been recently reported to prevent CD8 T cell exhaustion.
Conclusions: Collectively, our results point to a qualitative impact of sorafenib on CD8 T cells during immune reconstitution. They suggest that sorafenib treatment might prevent or even reverse CD8 T cell exhaustion by down-regulating PD-1 expression, unraveling one of the potential mechanisms of action of sorafenib after allo-HSCT. A better understanding of the impact of sorafenib on the immune system in patients receiving maintenance therapy will help to optimize strategies to prevent AML relapse after allo-HSCT.