TLR7/8 ligands R848 and imiquimod induce differentiation of bone marrow cells from patients with myelodysplastic syndrome towards mature neutrophils

Myelodysplastic syndromes (MDS) and acute myeloid leukaemia (AML) arise as a consequence of acquisition and progressive accumulation of genetic and epigenetic modifications by haematopoietic stem and progenitor cells (HSPC) which result in an impaired cell differentiation and the clonal expansion of myeloid progenitors leading to blast-cell accumulation in bone marrow (BM) and myelodysplasia. TLRs are expressed on HSPC and play a role in modulating haematopoiesis by instructing commitment to the myeloid lineage, and therefore may have potential therapeutic application. We have determined the in vitro effect of R848 (TLR7/TLR8 agonist) and Imiquimod (TLR7 agonist), on differentiation, apoptosis and cell viability in primary cultures of bone marrow samples from MDS (n = 6) and AML patients (n = 13). Differentiation was determined by a combined approach of conventional flow cytometry and t-SNE (t-distributed stochastic neighbour embedding) analysis based on the expression of cell markers (CD34, CD11b, CD13, CD117 and CD45). Cell viability and apoptosis were determined according to standard procedures. Statistical analyses were performed according to the two-tailed Student's t test for dual comparison (treated versus control samples). All major cell populations of the differentiation path from blasts towards neutrophils were found. Treatment with R848 or with Imiquimod did not induce significant changes in cell differentiation in AML samples. However, both R848 and, to a lesser extent, Imiquimod were able to induce differentiation of bone marrow cells from MDS patients from myelocytes to mature neutrophils in five out of six samples. Results also showed absence of toxic effects of both ligands on cells from MDS patients, as both apoptosis and cell viability were not altered by treatments. As for the differentiation assays, the effect of both ligands on apoptosis and cell viability in primary cultures from AML patients was not significant. Treatment with TLR7/8 ligands can revert the blockade of myeloid differentiation in most MDS samples and increase the amount of neutrophils, and therefore could represent a potential alternative treatment for MDS patients.