Effects of Cladribine on Immune Cell Subsets and Autoantibody Responses in Generalized Myasthenia Gravis Peripheral Blood Mononuclear Cells in Vitro
Yin Wu1, Elina Järvinen2, Dominic Jack3, Tobias Derfuss4, Kevin O'Connor5, Chia Chi Sun1
1EMD Serono, Billerica, MA, USA, 2Merck OY, Espoo, Finland (an affiliate of Merck KGaA, Darmstadt, Germany), 3Merck Serono Ltd., Feltham, UK (an affiliate of Merck KGaA, Darmstadt, Germany), 4Department of Biomedicine, University of Basel, Basel, Switzerland, 5Departments of Neurology and Immunobiology, Yale School of Medicine, New Haven, CN, USA
Objective:
To investigate the functional effects of cladribine on immune cells from generalized myasthenia gravis (gMG) peripheral blood mononuclear cells (PBMCs).
Background:
gMG is a B cell-driven, T cell-dependent, autoimmune disease characterized by autoantibody production. Cladribine incorporates into B and T lymphocytes, leading to their selective and temporal depletion. Cladribine tablets are approved for relapsing forms of multiple sclerosis, while cladribine capsules are under evaluation for gMG in a Phase 3 clinical trial (MyClad; NCT06463587).
Design/Methods:
Whole blood was collected from people with gMG. Isolated PBMCs were treated with cladribine in vitro and stimulated to activate B and T cell proliferation or induce plasma cell differentiation. Flow cytometry was used to assess cladribine half-maximal inhibitory concentrations (IC50) on cell depletion, cell proliferation, and plasma cell differentiation. Total IgG and anti-AChR IgG levels were analyzed using enzyme-linked immunosorbent assays.
Results:
Cladribine demonstrated concentration-dependent depletion of naïve and proliferating B and T cell subsets, memory-B cells and plasmablasts in gMG PBMCs (n=10). IC50 for total B cells = 0.03–0.06µM; T cells = 0.07–0.12µM; CD20+ T cells = 0.9µM [n=10]). In a plasma cell differentiation assay, cladribine reduced gMG plasma cells/plasmablasts (IC50=0.06µM; n=2), reduced production of IgG (IC50=0.3µM; n=12), and inhibited anti-AChR IgG production at 0.06 and 0.6µM; n=2.
Conclusions:
Cladribine, at concentrations intended to mimic the plasma exposure of people with gMG treated with oral cladribine, depletes B and T cell subsets, inhibits plasma cell differentiation, and reduces IgG and anti-AChR IgG production in gMG PBMCs in vitro. These data suggest that cladribine targets drivers of autoimmunity in gMG, supporting the upstream mechanism of cladribine in reducing autoantibody production in gMG.
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