Phenotypic characterization of innate lymphoid cells in myelodysplastic syndromes: towards the comprehension of their role in disease etiology and prognosis

Myelodysplastic syndromes (MDSs) are a heterogeneous group of myeloid neoplasms that primarily affect elderly people and, in the context of population aging, MDS incidence is set to increase substantially. MDSs are characterized by ineffective hematopoiesis, cytogenetic changes, molecular abnormalities and often include a dysregulation and dysfunction of the immune system with the acquisition of an immunosuppressive signature. In addition, MDS patients have a variable risk of progression to acute myeloid leukemia (AML) and frontline pharmacological therapies (i.e. hypomethylating agents, HMA) are not curative. Nowadays, patient risk stratification, based mainly on aspecific clinical/hematological parameters, omitting molecular and immune status, ineffectively predicts patients’ prognosis and response to therapies. Several lines of evidence highlighted the important role of innate lymphoid cells (ILCs) in generating a suppressive and tolerant environment that, in turn, facilitates tumor progression and aggressiveness. Given these premises, we aim at disclosing the impact of ILCs in MDS pathogenesis by inducing a de-regulation of other immune cells and creating a tolerant microenvironment that, in turn, increases genomic instability and facilitates disease progression. To this end, we investigated through extensive flow cytometry the phenotype and the function of ILCs in MDS patients stratified in low-risk (LR, n=44) and high-risk (HR, n=23) of progression towards AML based on blast counts. Our data demonstrated that while the frequency of helper ILCs is not affected by MDS severity, their distribution changes among the different patient groups. Indeed, ILC1-like CD56pos and ILC3/p frequencies decrease with the worsening of the disease, while the ILC1 CD56neg frequency increases. Our data also demonstrated that the frequency of the cytotoxic subset of ILC, namely natural killer (NK) cells, is reduced in HR patients, regardless HMA therapy. Focusing on the phenotype of these cells, we observed a higher frequency of more immature NK cells counterbalanced by the reduction of the more mature and cytotoxic NK cell subset in HR patients pre-HMA. In addition, HR patients post-HMA show the expansion of a peculiar NK cell subset characterized by the expression of maturity markers NKG2C and CD57. Noteworthy, in HR patients we observed that the decrease of total NK cells is balanced by the expansion of cells that do not express any marker of terminally differentiation. Among these cells, as expected, we found a higher frequency of NK cell precursors in HR pre-HMA patients. Taken together these results suggest a possible block in the differentiation of NK cells and a preferentially differentiation towards ILC1 CD56neg in HR patients, which could be partially restored by HMA treatment