Background: Systemic lupus erythematosus (SLE) is a complex and highly multifactorial autoimmune disease, resulting in an imbalance between proinflammatory and regulatory cells. Among regulatory cells, the involvement of Myeloid Derived Suppressor Cells (MDSCs) remains unclear.

Objectives: The main objective of the study was to assess the proportion of MDSC among peripheral blood mononuclear cells (PBMCs), as well as their correlation with SLEDAI-2K. Secondary objectives were to assess their immunosuppressive functions, as well as their metabolic and transcriptomic profiles.

Methods: Adult patients with SLE (ACR/EULAR 2019 and/or SLICC criteria) with a SLEDAI-2K > 1 were prospectively included, after having given written informed consent. Blood samples were collected at inclusion, as well as at 3 months and 6 months of follow-up, before any therapeutic modification. After isolation of PBMCs by Ficoll-density gradient centrifugation, MDSCs were quantified and characterized by multiparametric flow cytometry (27 parameters, BD® Symphony A3 cytometer). Their metabolic profile was also assessed by flow cytometry, by membrane staining (MDSCs identification and GLUT1 staining) followed by overnight intracellular staining after fixation and permeabilization (ACAC, PRDX2, HK1, CPT1A,ASS1, ATP5A, IDH2). MDSCs were isolated from Ficoll-purified PBMCs, by a three step magnetic sorting process, consisting into a first negative selection (HLA-DR depletion kit, Miltenyi Biotec®) followed by a second negative selection (CD3, CD19, CD45RA, HLA-DR staining with phycoerythrin (PE)-coupled antibodies, then with anti-PE microbeads, Miltenyi Biotec®) and finally a CD11b-positive selection (Miltenyi Biotec®). T cells from healthy donors were purified by negative selection using a pan T-cell depletion kit (Miltenyi Biotec), stained with carboxyfluorescein succinimidyl ester (CFSE) (Invitrogen), and activated in a 96-well culture plate coated anti-CD3 mAb and anti-CD28 mAb (Biotechne) for 6 to 8 hours before the addition of T cells. MDSCs were plated at 5 x 10 ⁴ /well (1:1 ratio). MDSCs’ transcriptomic signature was analysed using a publicly available single-cell RNA-seq dataset [1]. Flow-cytometry data were acquired using Diva® software, and analysed using FlowJo ^TM software (v10.10). Statistical analysis were performed using GraphPad® et R. This study was approved by local ethics committee, and registered on ClinicalTrials.com (NCT05424627).

Results: Twenty three patients (20 women, median age = 39 [26-45] years old) with active SLE (SLEDAI-2K > 1, median SLE = 10) were included. Patients presented mainly with cutaneous and articular involvement (12/23, 52% and 11/23, 48%, respectively). Six patient presented also active lupus nephritis (2 class III, 4 class IV), serositis (n=4), intra-alveolar hemorrhage (n=2), myocarditis (n=1) and pulmonary arterial hypertension (n=1). Total MDSCs were rare, representing approximatively 1% of PBMCs. A statistically non-significant increase of MDSC was noted in patients with SLE at inclusion, mainly regarding granulocytic and monocytic MDSCs (G-MDSC and M-MDSCs, respectively), while a significant decrease of early stage MDSC (E-MDSC) was observed. No correlation between total MDSC nor their subpopulations and SLEDAI or other biological activity markers (C3, C4, CH50, anti-DNA antibodies level) was noted. When co-cultured with activated T cells, sorted MDSCs exerted no immunosuppressive effect, beside in one patient during follow-up, after receiving cyclophosphamide, in a dose-dependent manner. The comparison of the metabolic profile of immunosuppressive MDSCs (obtained from peripheral stem cell graft or samples from patients with myelodysplastic syndrome after allogenic hematopoietic stem cell transplant) to non-immunosuppressive MDSCs show a reduced median fluorescence intensity (MFI) of HK1 (and, to a lesser extent, of GLUT1) in immunosuppressive MDSCs. In addition, the MFI of these two enzymes was increased in patients with SLE compared to healthy subjects. Finally, single cell RNA-seq analyses of mainly M-MDSC identified a distinct signature profile in SLE patients compared to healthy subjects. In particular, Il-10 mRNA was decreased in SLE patients.

Conclusion: MDSCs are rare in peripheral among PBMCs, both in SLE patients and healthy subjects, making them difficult to study. Theses latter seem to be dysregulated in SLE, regarding the increase of G- and M-MDSC and the decrease of E-MDSC, and do no exert any immunosuppressive activity in untreated SLE patients. They display a different transcriptomic signature, with a downregulation of Il-10, consistent with their lack of immunosuppressive activity. Finally, immunosuppressive capacities in other contexts seem to be associated with a decrease of enzymes involved in glycolysis (GLUT1 and HK1), which expression is increased in SLE patients. Mechanisms linking MDSCs immunosuppressive activity to the decrease of glycolytic enzymes remain to be determined, although methylglyoxal production, transfer to T cells and glycation of L-arginine might participate to such function [2].

REFERENCES: [1] Perez RK, Gordon MG, Subramaniam M, et al. Single-cell RNA-seq reveals cell type-specific molecular and genetic associations to lupus. Science . 2022;376:eabf1970. doi: 10.1126/science.abf1970.

[2] Baumann T, Dunkel A, Schmid C, et al. Regulatory myeloid cells paralyze T cells through cell-cell transfer of the metabolite methylglyoxal. Nat Immunol . 2020;21:555–66. doi: 10.1038/s41590-020-0666-9.

Acknowledgements: NIL.

Disclosure of Interests: None declared.

© The Authors 2025. This abstract is an open access article published in Annals of Rheumatic Diseases under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ). Neither EULAR nor the publisher make any representation as to the accuracy of the content. The authors are solely responsible for the content in their abstract including accuracy of the facts, statements, results, conclusion, citing resources etc.