The transplantation of allogeneic haematopoietic stem cells (HSCs) can lead to serious complications after transplantation, such as graft-versus-host disease (GvHD), infections and relapse due to immunosuppression. Invariant NKT cells (iNKT cells) play a pivotal role in modulating the immune response and have been demonstrated to be instrumental in the pathogenesis of GvHD, cytomegalovirus (CMV) infection, and relapse. Their levels are associated with the development of these complications. This multicentre study aims to test the feasibility of standardising iNKT cell monitoring and to investigate the association between iNKT cell levels and post-transplant complications.

Allogeneic haematopoietic stem cell transplantation (HSCT) is a treatment for many serious haematological malignancies. Despite advances in pre- and post-transplant management, a significant proportion of patients still develop adverse effects such as graft-versus-host disease (GvHD), relapse or cytomegalovirus reactivation. These reactions can significantly reduce patients' quality of life and may even be fatal. Invariant NKT cells (hereafter referred to as iNKT cells) are a rare population of T lymphocytes that play an important role in regulating the immune response. Depending on the expression of CD4 and CD8 markers, they can be divided into several subpopulations. iNKT cells can simultaneously support both Th1 and Th2 immune responses while suppressing the inflammatory response. Therefore, they appear to be suitable for treating diseases involving deregulated immunity, such as GvHD, autoimmune diseases, and oncological diseases. The concentration of iNKT cells after HSCT is highly variable. According to the available data, iNKT cell kinetics correspond to the severity of GvHD, as well as the risk of relapse and the development of infectious complications. However, these data are usually obtained using locally set protocols and come from single-centre measurements, which reduces their validity and clinical utility as both a biomarker and background data for possible allogeneic applications of iNKT cells in patients with low levels. To eliminate bias caused by specific local data processing and provide a robust dataset, a multicentre study is necessary to yield a representative set of results, as this is the only way to definitively establish the impact of iNKT cell levels on post-transplant outcomes. Flow cytometric analysis enables the combined examination of specific markers on the surface of cells and inside them. Due to the increasing complexity and heterogeneity of protocols, antibody manufacturers often resort to standardised dried panels, which ensure high consistency of measured data.

This project will involve monitoring iNKT cells at defined time points following allogeneic transplantation. The project's outcomes will be to determine the feasibility of standardising iNKT monitoring using the DryTube flow cytometry assay, establish differences in iNKT levels in transplanted patients across different centres, and estimate the association between iNKT levels and post-transplant complications.

Inclusion Criteria:

• Diagnosis: AML (exlusion of secondary disease)
• Disease status at time of HSCT: complete remission
• Karnofsky performance status: ≥80%
• Source of HSC: PBSC

Exclusion Criteria:

• Prior transplant
• Uncontrolled Malignancy

Patients who have undergone allogeneic hematopoietic cell transplantation and have been diagnosed with acute myeloid leukemia.