HLA-DR modulation and PD-1/PD-L2 checkpoint signaling identify a mechanistic potency axis for mesenchymal stromal cell immunosuppression
Abstract
Introduction: Mesenchymal stromal cells exhibit potent immunomodulatory properties and are under active investigation for the treatment of immune-mediated disorders. However, their clinical translation is hindered by the lack of standardized potency assays.
Methods: Here, we established a reproducible mixed lymphocyte reaction platform by systematically optimizing peripheral blood mononuclear cell donor composition, culture conditions, and co-culture ratios to define a robust activation window.
Using this optimized mixed lymphocyte reaction-based potency assay, we compared bone marrow and adipose-derived mesenchymal stromal cells across independent donor batches.
Results: Both sources of mesenchymal stromal cells effectively suppressed T-cell proliferation, with the adipose-derived source demonstrating greater inhibitory activity under the experimental conditions, while a conserved lower threshold of suppression was observed across both sources. Mesenchymal stromal cells reduced early (CD25+) and late (CD25+ HLA-DR+) T-cell activation, with downregulation of CD25 and HLA-DR emerging as sensitive correlates of functional potency. Notably, bone marrow-derived mesenchymal stromal cells exerted stronger suppression of late-stage HLA-DR+ activation and preferentially inhibited CD8+ T-cell expansion, demonstrating source-dependent immunomodulatory functions. Mechanistically, this suppression was associated with modulation of the PD-1 pathway, characterized by decreased soluble PD-1, increased soluble PD-L1, and induction of soluble PD-L2 by mesenchymal stromal cells. PD-L2 levels inversely correlated with T-cell proliferation in the mixed lymphocyte reaction, supporting a PD-1/PD-L2 regulatory axis linked to mesenchymal stromal cell potency.
Conclusion: These findings support a standardized and mechanistically informed mixed lymphocyte reaction-based potency assay framework integrating functional suppression, HLA-DR modulation, and PD-1/PD-L2 pathway signaling as complementary indicators of mesenchymal stromal cell activity.
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BibTeX
@article{zarif2026hladr,
title = {{HLA-DR modulation and PD-1/PD-L2 checkpoint signaling identify a mechanistic potency axis for mesenchymal stromal cell immunosuppression}},
author = {Mahin Nikougoftar Zarif and Katia Lefsihane and Neda Khanlarkhani and Lina Sorvik and Jan Fredrik Talts and Katarina Le Blanc and Nadir Kadri},
journal = {Stem Cells Translational Medicine},
year = {2026},
month = nov,
doi = {10.1093/stcltm/szag090},
url = {https://doi.org/10.1093/stcltm/szag090},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - HLA-DR modulation and PD-1/PD-L2 checkpoint signaling identify a mechanistic potency axis for mesenchymal stromal cell immunosuppression
AU - Mahin Nikougoftar Zarif
AU - Katia Lefsihane
AU - Neda Khanlarkhani
AU - Lina Sorvik
AU - Jan Fredrik Talts
AU - Katarina Le Blanc
AU - Nadir Kadri
PY - 2026
DA - 2026/11/05
JO - Stem Cells Translational Medicine
DO - 10.1093/stcltm/szag090
UR - https://doi.org/10.1093/stcltm/szag090
AB - Introduction: Mesenchymal stromal cells exhibit potent immunomodulatory properties and are under active investigation for the treatment of immune-mediated disorders. However, their clinical translation is hindered by the lack of standardized potency assays. Methods: Here, we established a reproducible mixed lymphocyte reaction platform by systematically optimizing peripheral blood mononuclear cell donor composition, culture conditions, and co-culture ratios to define a robust activation window. Using this optimized mixed lymphocyte reaction-based potency assay, we compared bone marrow and adipose-derived mesenchymal stromal cells across independent donor batches. Results: Both sources of mesenchymal stromal cells effectively suppressed T-cell proliferation, with the adipose-derived source demonstrating greater inhibitory activity under the experimental conditions, while a conserved lower threshold of suppression was observed across both sources. Mesenchymal stromal cells reduced early (CD25+) and late (CD25+ HLA-DR+) T-cell activation, with downregulation of CD25 and HLA-DR emerging as sensitive correlates of functional potency. Notably, bone marrow-derived mesenchymal stromal cells exerted stronger suppression of late-stage HLA-DR+ activation and preferentially inhibited CD8+ T-cell expansion, demonstrating source-dependent immunomodulatory functions. Mechanistically, this suppression was associated with modulation of the PD-1 pathway, characterized by decreased soluble PD-1, increased soluble PD-L1, and induction of soluble PD-L2 by mesenchymal stromal cells. PD-L2 levels inversely correlated with T-cell proliferation in the mixed lymphocyte reaction, supporting a PD-1/PD-L2 regulatory axis linked to mesenchymal stromal cell potency. Conclusion: These findings support a standardized and mechanistically informed mixed lymphocyte reaction-based potency assay framework integrating functional suppression, HLA-DR modulation, and PD-1/PD-L2 pathway signaling as complementary indicators of mesenchymal stromal cell activity.
SN - 2157-6564
SN - 2157-6580
ER -