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Treg sensitivity to FasL and relative IL-2 deprivation drive Idiopathic Aplastic Anemia immune dysfunction: Mechanism of Treg depletion in AA

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Shok Ping Lim, Benedetta Costantini, Syed A Mian, Pilar Perez Abellan, Shreyans A Gandhi, Marc Martinez-Llordella, Juan Jose Lozano, Rita Antunes Dos Reis, Giovanni A M Povoleri, Thanos P Mourikis, Ander Abarrategi, Linda Ariza-McNaughton, Susanne Heck, Jonathan Michael Irish, Giovanna Lombardi, Judith Marsh, Dominique Bonnet, Shahram Kordasti, Ghulam J Mufti

Original languageEnglish
Pages (from-to)885-897
Number of pages13
Issue number7
Early online date15 Apr 2020
Accepted/In press7 Apr 2020
E-pub ahead of print15 Apr 2020
Published13 Aug 2020


King's Authors


Idiopathic aplastic anemia (AA) has 2 key characteristics: an autoimmune response against hematopoietic stem/progenitor cells and regulatory T-cells (Tregs) deficiency. We have previously demonstrated reduction in a specific subpopulation of Treg in AA, which predicts response to immunosuppression. The aims of the present study were to define mechanisms of Treg subpopulation imbalance and identify potential for therapeutic intervention. We have identified 2 mechanisms that lead to skewed Treg composition in AA: first, FasL-mediated apoptosis on ligand interaction; and, second, relative interleukin-2 (IL-2) deprivation. We have shown that IL-2 augmentation can overcome these mechanisms. Interestingly, when high concentrations of IL-2 were used for in vitro Treg expansion cultures, AA Tregs were able to expand. The expanded populations expressed a high level of p-BCL-2, which makes them resistant to apoptosis. Using a xenograft mouse model, the function and stability of expanded AA Tregs were tested. We have shown that these Tregs were able to suppress the macroscopic clinical features and tissue manifestations of T-cell-mediated graft-versus-host disease. These Tregs maintained their suppressive properties as well as their phenotype in a highly inflammatory environment. Our findings provide an insight into the mechanisms of Treg reduction in AA. We have identified novel targets with potential for therapeutic interventions. Supplementation of ex vivo expansion cultures of Tregs with high concentrations of IL-2 or delivery of IL-2 directly to patients could improve clinical outcomes in addition to standard immunosuppressive therapy.

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