CD141 Expressing Monocytes Show an Inflammatory Profile and Are Associated with Low-Risk Features in Myelodysplastic Syndromes

Introduction

Immune responses play an important role in the pathogenesis and progression of myelodysplastic syndromes (MDS). It has been shown that a consistent immunological signature in MDS comprises an increase in Th17 cells in low risk MDS and an expansion of T regulatory cells (Tregs) in high risk subtypes. Additionally, the presence of high Treg numbers in lower risk stages is an independent prognostic value and is associated with poor survival. The high pro-inflammatory response in low risk MDS is also linked to autoimmune features in these patients. Identification of immune cells that could potentially contribute to the inflammatory environment are of interest to prevent disease progression and, on the other hand, restore excessive immune responses by therapeutic interaction. The exact role of monocytes in this early immune disturbance is yet to be understood. Our preliminary findings showed that MDS-derived monocytes have elevated expression levels of the dendritic cell marker BDCA3/CD141 compared to healthy monocytes. The aim of this study was therefore to investigate the phenotypic and functional characteristics of CD141+ versus CD141- monocytes in MDS patients and compare them with healthy monocytes.

Patients and methods

Monocytes were gated as CD14^hiCD11c^hiHLA-DR⁺. The percentage of CD141+ monocytes was determined in 143 MDS bone marrow (BM) and 22 normal bone marrow (NBM) samples, and in the peripheral blood (PB) of 33 MDS patients and 28 normal PB (NPB) samples. Furthermore, CD141 expression was assessed in different disease stages and correlated to several disease characteristics such as the presence of ring sideroblasts (RS), blast percentage and cytogenetic risk group. Additionally, sorted CD141- and CD141+ monocytes of two MDS patients were tested for their functional capacities, including their ability to skew T cells and to up-regulate the co-stimulatory molecules CD80 and CD86 upon stimulation. The production of different cytokines was measured in culture supernatants by using Cytometric Bead Array (CBA).

Results

The percentage of CD141+ monocytes was highly increased in MDS BM compared to NBM (36% vs 12%, p<0.0001), and, also in MDS PB compared to NPB (24% vs 11%, p=0.012). Additionally, the presence of CD141+ monocytes in PB and BM was positively correlated between the two compartments (r= 0.82, p<0.0001). The increased percentage of BM-derived CD141+ monocytes was more evident in low risk groups (RA, RARS and RCMD) than in high risk groups ([RAEB-I/II], 39% vs 22%, p<0.001), and hence, was associated with low blast counts (<5% vs ≥5% blasts: 40% vs 22%, p=0.004). The presence of RS was also correlated with elevated rates of CD141+ monocytes (50% vs 28%, p=0.002). In addition, MDS patients that showed a very good-to-good cytogenetic risk profile had increased frequencies of CD141+ monocytes compared to patients in poor and very poor risk groups (36% vs 22%, p=0.013). Phenotypic analyses showed elevated expression levels of HLA-DR on CD141+ monocytes compared to total monocytes (1.5 fold, p<0.001). Preliminary functional tests revealed no differences in up-regulation of CD80 and CD86 upon stimulation in CD141+ or CD141- MDS monocytes. However, there was a trend towards higher production of IL-1β, IL-6 and TNF and a reduction in FoxP3+ Treg skewing in cultures of CD141+ monocytes compared to CD141- monocytes.

Conclusion

In conclusion, CD141+ monocytes were found in much higher frequencies in the BM and PB of MDS patients compared to healthy control BM and PB. Their presence was associated with a low risk stage of the disease, low blast counts, the presence of RS and a very good-to-good cytogenetic risk profile. The first functional analyses point to a high pro-inflammatory state of CD141+ compared to CD141- monocytes. Therefore we hypothesize that these monocytes may contribute to an immune stimulatory environment in low risk MDS patients with potentially a favourable prognostic value.