ELTROMBOPAG INHIBITS THE PROLIFERATION OF CD8 T CELLS THROUGH AN IRON CHELATION MANNER

Michelle Tan,
Imperial College London, Immunology and Inflammation, London, United Kingdom

Background
  • Immune thrombocytopenia (ITP) involves dysregulated T cell activity, with specific CD8+ T cell subsets implicated in platelet destruction.
  • While thrombopoietin receptor agonists (TPO-RAs) like romiplostim, eltrombopag, and avatrombopag have replaced immunosuppressants as first-line therapy due to their potent megakaryopoiesis stimulation, their broader immunomodulatory effects remain partially unclear.
  • Eltrombopag, in addition to stimulating thrombopoietin receptor and increasing platelet production, is also an iron chelator and has been shown to reduce rapidly proliferating cells. Our previous work identified a subpopulation of platelet specific CD8+ T cells contributing to ITP pathogenesis.
  • We now investigate the potential of eltrombopag to modulate these CD8+ T cells, focusing on its effect on their proliferation and activity.
Methods
  • Peripheral blood mononuclear cells (PBMCs) of eight ITP patients who received eltrombopag were stained for CD3, CD8, CD45RA and CD62L, and analysed using flow cytometry for the characterisation of CD8+ T cells over time.
  • In addition, PBMCs of healthy donors were stimulated ex vivo with anti-CD3/CD28 in the presence of increasing doses of eltrombopag, romiplostim, deferoxamine (control for iron chelation), or human recombinant TPO (control for TPO-R).
  • Cell proliferation and cycle were measured using Cell Trace Violet and propidium iodide (PI), respectively using flow cytometry
Results
  • In patients with ITP who started eltrombopag treatment, there was a significant reduction in the percentage of a subset of CD8+ T cells, terminally differentiated effector memory (TEMRA; CD45RA+CD62L-) cells (p < 0.05).
  • This shift correlated with an increase in platelet count (p < 0.001). In CD8+ T cells stimulated with CD3/CD28 ex vivo, in the presence of eltrombopag, we observed a dose-dependent reduction in CD8+ T cell proliferation (p < 0.01), inducing cell cycle arrest into G1 phase (p < 0.05).
  • Notably, deferoxamine mimicked these effects (p < 0.0001), while romiplostim and recombinant TPO did not, suggesting an iron chelation-mediated mechanism.
  • Further, rescuing arrested CD8+ T cells with ferric ammonium citrate confirmed the role of iron in this process.
Conclusions
  • These findings suggest that eltrombopag’s effectiveness may go beyond megakaryopoiesis stimulation.
  • We proposed that eltrombopag may have a dual mechanism of action: inhibiting the proliferation of CD8+ TEMRA cells and inducing G1 cell cycle arrest.
  • This iron chelation-dependent effect suggests a novel immunomodulatory role for eltrombopag. This dual action could explain its efficacy in patients who lose response to other TPO-RAs, offering a potential avenue for future therapeutic strategies in ITP