Daclizumab enhances aGVHD prophylaxis by modulating T-cell polarization while preserving the graft-versus-lymphoma effect

Abstract Introduction: Acute graft-versus-host disease (aGvHD) remains a major complication of allogeneic hematopoietic stem cell transplantation (allo-HSCT). Our prior clinical data showed that adding Daclizumab, an anti-CD25 monoclonal antibody, to standard prophylaxis (Mycophenolate mofetil/Tacrolimus/Methotrexate) significantly reduced grade 3–4 aGvHD incidence in thalassemia patients undergoing alternative donor HSCT. However, the underlying mechanisms remain unclear. Methods: We established a murine aGvHD model with three groups: aGvHD control, standard prophylaxis [mycophenolate mofetil (MMF) / Tacrolimus (Tac)/Methotrexate (MTX)], and Daclizumab+standard prophylaxis. Clinical scoring, survival, and histopathology of target organs (skin, liver, lung, colon) were assessed. Immune profiling was performed using flow cytometry of peripheral blood and splenocytes, evaluating T-cell subsets, activation (CD69+, CD25+), and regulatory T cells (Tregs). Serum cytokines and splenic mRNA levels were quantified. To evaluate graft-versus-lymphoma (GVL) activity, luciferase-tagged A20 lymphoma cells were infused at transplantation, and tumor burden was tracked via bioluminescence imaging. Four experimental groups were established: a bone marrow (BM) group (receiving BM cells+A20-luc), a BM+SP group (receiving BM cells+splenocyte+A20-luc), a standard prophylaxis group (receiving BM cells+splenocyte+A20-luc+MMF/Tac/MTX), and a Daclizumab group (receiving BM cells+splenocyte+A20-luc+Daclizumab+MMF/Tac/ MTX). Results: Daclizumab significantly reduced clinical and histological aGvHD scores and improved survival. Total T-cell (CD3+, CD4+, CD8+) reconstitution was comparable across groups, but NK cell frequency increased in the Daclizumab group. T-cell activation markers (CD3+CD69+, CD3+CD25+) were similar across groups. However, Daclizumab markedly reduced Th1, Th17, Tc1, and Tc17 cells, while increasing Th2 cells. Treg levels were elevated in both prophylaxis groups vs. control. CD8+ T cells in the Daclizumab group expressed lower levels of perforin and granzyme B. Pro-inflammatory cytokines (IFN-γ, IL-2, IL-17) were suppressed, while IL-4 was upregulated. In the GVL model, all splenocyte-transplanted groups controlled tumor progression. The Daclizumab group achieved superior GvHD control and survival without compromising GVL activity. Conclusion: Daclizumab enhances aGvHD prophylaxis by modulating T-cell polarization—favoring Th2/Treg balance and reducing cytotoxicity—while preserving graft-versus-lymphoma effects. These findings support anti-CD25 antibodies as a promising strategy to optimize immune tolerance and anti-tumor efficacy post-transplantation.