NK Cell Reconstitution in Paediatric Leukemic Patients after T-Cell-Depleted HLA-Haploidentical Haematopoietic Stem Cell Transplantation Followed by the Reinfusion of iCasp9-Modified Donor T Cells

GAS6/TAM signaling pathway controls MICA expression in multiple myeloma cells

NKG2D ligands play a relevant role in Natural Killer (NK) cell -mediated immune surveillance of multiple myeloma (MM). Different levels of regulation control the expression of these molecules at cell surface. A number of oncogenic proteins and miRNAs act as negative regulators of NKG2D ligand transcription and translation, but the molecular mechanisms sustaining their basal expression in MM cells remain poorly understood. Here, we evaluated the role of the growth arrest specific 6 (GAS6)/TAM signaling pathway in the regulation of NKG2D ligand expression and MM recognition by NK cells. Our data showed that GAS6 as well as MERTK and AXL depletion in MM cells results in MICA downregulation and inhibition of NKG2D-mediated NK cell degranulation. Noteworthy, GAS6 derived from bone marrow stromal cells (BMSCs) also increases MICA expression at both protein and mRNA level in human MM cell lines and in primary malignant plasma cells. NF-kB activation is required for these regulatory mechanisms since deletion of a site responsive for this transcription factor compromises the induction of mica promoter by BMSCs. Accordingly, knockdown of GAS6 reduces the capability of BMSCs to activate NF-kB pathway as well as to enhance MICA expression in MM cells. Taken together, these results shed light on molecular mechanism underlying NKG2D ligand regulation and identify GAS6 protein as a novel autocrine and paracrine regulator of basal expression of MICA in human MM cells.

Optimization of Donor Lymphocyte Infusion for AML Relapse After Allo-HCT in the Era of New Drugs and Cell Engineering

Donor lymphocyte infusion (DLI) is a key strategy for the treatment of AML relapse after allogeneic hematopoietic cell transplantation (allo-HCT) and has been used for either prophylactic, pre-emptive, or therapeutic purposes. However, the prognosis of these patients remains dismal even after DLI infusion (2-year overall survival, ~25%), and the efficacy is achieved at the cost of toxicities such as graft-versus-host (GVH) disease. Attempts to optimize DLI efficacy and safety, such as dose/timing modification and the use of cytoreduction, before DLI have been performed previously. Recently, a great number of novel targeted and immunomodulatory agents have emerged. Some of them, such as hypomethylating agents, FLT3 and Bcl-2 inhibitors, have been used in combination with DLI, aiming to enhance the graft-versus-leukemia effect. Moreover, manipulation of the DLI graft through cell selection (e.g., donor NK cells) or cell engineering (donor CAR-T cells) has shown potentially superior anti-tumor effects but less GVH effect than conventional DLI in clinical trials. This review summarizes the recent advances on the use of DLI for the prophylaxis/treatment of AML relapse and discusses future strategies which may further improve the treatment efficacy.

Phenotypic and Functional Characterization of NK Cells in αβT-Cell and B-Cell Depleted Haplo-HSCT to Cure Pediatric Patients with Acute Leukemia

NK cells can exert remarkable graft-versus-leukemia (GvL) effect in HLA-haploidentical hematopoietic stem cell transplantation (haplo-HSCT). Here, we dissected the NK-cell repertoire of 80 pediatric acute leukemia patients previously reported to have an excellent clinical outcome after αβT/B-depleted haplo-HSCT. This graft manipulation strategy allows the co-infusion of mature immune cells, mainly NK and γδT cells, and hematopoietic stem cells (HSCs). To promote NK-cell based antileukemia activity, 36/80 patients were transplanted with an NK alloreactive donor, defined according to the KIR/KIR-Ligand mismatch in the graft-versus-host direction. The analysis of the reconstituted NK-cell repertoire in these patients showed relatively high proportions of mature and functional KIR⁺NKG2A^-CD57⁺ NK cells, including the alloreactive NK cell subset, one month after HSCT. Thus, the NK cells adoptively transfused with the graft persist as a mature source of effector cells while new NK cells differentiate from the donor HSCs. Notably, the alloreactive NK cell subset was endowed with the highest anti-leukemia activity and its size in the reconstituted repertoire could be influenced by human cytomegalovirus (HCMV) reactivation. While the phenotypic pattern of donor NK cells did not impact on post-transplant HCMV reactivation, in the recipients, HCMV infection/reactivation fostered a more differentiated NK-cell phenotype. In this cohort, no significant correlation between differentiated NK cells and relapse-free survival was observed.