Las células natural killer en la leucemia pediátrica: mecanismos de inmunovigilancia y su papel en la eficacia del tratamiento en un haplo-hsct

Abstract

Tesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Medicina, Departamento de Bioquímica. Fecha de Lectura: 29-05-2025Esta Tesis tiene embargado el acceso al texto completo hasta el 29-11-2026Pediatric acute leukemia is the most common cancer in children. Despite significant advances in survival rates, leukemia cells develop immune escape mechanisms that contribute to relapses or refractory disease. Hematopoietic stem cell transplantation (HSCT) remains the most effective curative option when combined with intensive chemotherapy, particularly for relapsed and high-risk patients. However, for those without a human leukocyte antigen (HLA)-matched donor, haploidentical HSCT (haplo-HSCT) serves as a viable alternative. HLA mismatch in haplo-HSCT increases the risk of graft-versus-host disease (GvHD). Nevertheless, alloreactive natural killer (NK) cells, arising from HLA/KIR (killer immunoglobulin-like receptor) disparity between the donor and recipient, mediate the graft-versus-leukemia (GvL) effect, reducing the risk of relapse and infections. Thus, optimizing therapies that mitigate GvHD while preserving the GvL effect could significantly improve clinical outcomes for pediatric patients. This doctoral research aimed to explore three main hypotheses: first, that an in-depth analysis of the interaction between bone marrow infiltrating NK (BiNK) cells and leukemia cells would reveal tumor escape mechanisms responsible for disease relapse. Second, that IL-15-stimulated NK (IL15-NK) cells could replicate the GvL effects mediated by alloreactive NK (allo-NK) cells in HLA-matched haplo-HSCT. Finally, that the NK cell-mediated GvL effect would remain unaffected by the use of ruxolitinib, a drug used to eliminate GvHD complications. The results revealed that the leukemic microenvironment inhibits the proper development and degranulation capacity of BiNK cells and NK cells. NK cells from peripheral blood (PB) regain their functionality during treatment. In contrast, BiNK cells fail to recover their functional capacity. Additionally, leukemic blasts at relapse were found to increase the expression of inhibitory ligands for BiNK cells, contributing to immune evasion. Furthermore, patients who received IL15-NK cell infusions exhibited similar clinical outcomes to those receiving allo-NK cell infusions, despite showing a more inflammatory environment during one year of follow-up. The NK cells infused after IL-15 activation demonstrated comparable immune reconstitution, immunophenotype, and functional capacity to allo-NK cells. Finally, experiments with TLR4/9 ligand-activated NK cells showed that ruxolitinib did not impair their cytotoxic capacity. Only at high concentrations, above the basal dose, did the drug alter the phenotypic profile and reduce the proliferative capacity of NK cells. In conclusion, this study elucidates the intricate interaction between BiNK cells and the leukemic microenvironment, providing key insights into tumor immune escape mechanisms and their role in disease relapse. It highlights the therapeutic potential of IL-15-stimulated NK cells in haplo-HSCT as a strategy to counteract NK cell hyporesponsiveness in pediatric patients with HLA/KIR compatibility. However, the inflammatory state observed in patients receiving IL-15-stimulated NK cell infusions could be managed with innovative pharmacological approaches, such as ruxolitinib, which effectively controls GVHD without compromising the NK cell-mediated IcL effect. Collectively, this thesis underscores the critical role of NK cells from the onset of acute leukemia to its eradication through transplantation, emphasizing their significance in improving clinical outcomes in pediatric leukemia patient