Eltrombopag-associated remodeling of the MAIT, MR1+ and γδ T cells in pediatric immune thrombocytopenia.

Pediatric immune thrombocytopenia (ITP) is an autoimmune cytopenia characterized by immune-mediated platelet destruction and impaired thrombopoiesis. Mucosa-associated invariant T (MAIT) cells are innate-like T cells activated by MR1-presented microbial metabolites and inflammatory cytokines, but their role in pediatric ITP and their relationship to eltrombopag therapy remain unclear. We analyzed peripheral blood mononuclear cells from healthy controls (n = 20), untreated pediatric ITP patients (n = 60), and eltrombopag-treated patients (n = 16). MAIT cells were quantified using MR1-5-OP-RU tetramers and surrogate gating (CD3+Vα7.2+CD161+). MAIT subsets, memory phenotype, chemokine receptor expression (CXCR3, CXCR5, CCR6), HLA-DR, intracellular cytokines (IFN-γ, TNF-α, IL-17 A, IL-22), and MR1+CD3- cells were analyzed by flow cytometry. Tetramer-defined MAIT cells were reduced in absolute number in pediatric ITP, including eltrombopag-treated patients, most prominently within the CD8+ subset, whereas their frequency among CD3+ T cells did not differ between untreated and eltrombopag-treated groups. In contrast, CD3+Vα7.2+CD161+ cells increased in untreated ITP and were lower in eltrombopag-treated patients. Untreated ITP patients exhibited reduced frequencies of IFN-γ- and TNF-α-producing MAIT cells, accompanied by increased IL-17-producing cells and TNF-α signal intensity. Conventional αβ T cells were reduced, whereas γδ T cells were increased; eltrombopag-treated patients exhibited γδ T-cell frequencies and cytokine-positive fractions closer to those of healthy controls. MR1+CD3- cells were expanded and displayed reduced HLA-DR expression in untreated ITP, whereas eltrombopag-treated patients showed lower MR1+CD3- frequencies and HLA-DR levels closer to healthy controls. These findings demonstrate coordinated alterations of the MAIT/MR1 axis and unconventional T-cell compartments in pediatric ITP and identify immunophenotypic differences associated with eltrombopag treatment.