Graft-versus-leukaemia immunity is retained following treatment with post-transplant cyclophosphamide alone or combined with tocilizumab in humanised mice

Chloe Sligar; Ellie Reilly; Peter Cuthbertson; Kara L Vine; Katrina M Bird; Amal Elhage; Stephen I Alexander; Ronald Sluyter; Debbie Watson

doi:10.1002/cti2.1497

Graft-versus-leukaemia immunity is retained following treatment with post-transplant cyclophosphamide alone or combined with tocilizumab in humanised mice

Clin Transl Immunology. 2024 Mar 15;13(3):e1497. doi: 10.1002/cti2.1497. eCollection 2024.

Authors

Chloe Sligar^{1

2}, Ellie Reilly^{1

2}, Peter Cuthbertson^{1

2}, Kara L Vine^{1

2}, Katrina M Bird^{1

2}, Amal Elhage^{1

2}, Stephen I Alexander³, Ronald Sluyter^{1

2}, Debbie Watson^{1

2}

Affiliations

¹ Molecular Horizons and School of Chemistry and Molecular Bioscience University of Wollongong Wollongong NSW Australia.
² Illawarra Health and Medical Research Institute Wollongong NSW Australia.
³ The Children's Hospital at Westmead Westmead NSW Australia.

Abstract

Objectives: Donor haematopoietic stem cell transplantation treats leukaemia by inducing graft-versus-leukaemia (GVL) immunity. However, this benefit is often mitigated by graft-versus-host disease (GVHD), which is reduced by post-transplant cyclophosphamide (PTCy) alone or combined with tocilizumab (TOC) in humanised mice. This study established a preclinical humanised mouse model of GVL and investigated whether PTCy alone or combined with TOC impacts GVL immunity.

Methods: NOD-scid-IL2Rγ^null mice were injected with 2 × 10⁷ human peripheral blood mononuclear cells (hPBMCs) on day 0 and with 1 × 10⁶ THP-1 acute myeloid leukaemia cells on day 14. In subsequent experiments, mice were also injected with PTCy (33 mg kg^-1) or Dulbecco's phosphate buffered saline (PBS) on days 3 and 4, alone or combined with TOC or control antibody (25 mg kg^-1) twice weekly for 28 days. Clinical signs of disease were monitored until day 42.

Results: Mice with hPBMCs from three different donors and THP-1 cells showed similar survival, clinical score and weight loss. hCD33⁺ leukaemia cells were minimal in mice reconstituted with hPBMCs from two donors but present in mice with hPBMCs from a third donor, suggesting donor-specific GVL responses. hPBMC-injected mice treated with PTCy alone or combined with TOC (PTCy + TOC) demonstrated prolonged survival compared to control mice. PTCy alone and PTCy + TOC-treated mice with hPBMCs showed minimal hepatic hCD33⁺ leukaemia cells, indicating sustained GVL immunity. Further, the combination of PTCy + TOC reduced histological damage in the lung and liver.

Conclusion: Collectively, this research demonstrates that PTCy alone or combined with TOC impairs GVHD without compromising GVL immunity.

Keywords: graft‐versus‐leukaemia; humanised mice; post‐transplant cyclophosphamide; tocilizumab; xenogeneic graft‐versus‐host disease.