ePoster Presentation 49th Annual Scientific Meeting of the Australian and New Zealand Society for Immunology 2021

Combinational therapy with post-transplant cyclophosphamide and the P2X7 antagonist Brilliant Blue-G increases human CD39+ regulatory T cells and reduces GVHD in a humanised mouse model of graft-versus-host disease (#104)

Peter Cuthbertson 1 2 , Sam R Adhikary 1 2 , Debbie Watson 1 2 , Ronald Sluyter 1 2
  1. Illawarra Health and Medical Research Institute, Wollongong, NSW, Australia
  2. Molecular Horizons and School of Chemistry and Molecular Bioscience, University of Wollonong, Wollongong, NSW

Graft-versus-host disease (GVHD) is a severe and often lethal complication that arises following allogenic haematopoietic stem cell transplantation. We have previously shown that treatment with the clinically used therapy post-transplant cyclophosphamide (PTCy) delayed GVHD and extended survival in a humanised mouse model. This treatment also reduced human (donor) regulatory T cells (hTregs) and mice still developed GVHD. We have also previously shown that the P2X7 antagonist Brilliant Blue G (BBG) preserved hTregs and reduced clinical disease but did not increase survival in humanised mice. Therefore, we investigated whether a combinational therapy with PTCy and BBG would further prevent GVHD in our humanised mouse model. Immunodeficient NOD-scid Il2rγnull (NSG) mice were humanised by injecting 20 x 106 human peripheral blood mononuclear cells i.p. (day 0). Mice were injected daily (days 0-10) with BBG (50 mg/kg) or saline, and twice (days 3, 4) with cyclophosphamide (33 mg/kg) i.p. Mice were monitored for clinical GVHD for up to 70 days and tissues assessed at day 21 or ethical endpoint. Combinational therapy with PTCy+BBG allowed engraftment of hCD45+ leukocytes, the majority of which were hCD3+ T cells with small proportions of hCD19+ B cells and hCD56+ NK cells. Further, PTCy+BBG treatment partially increased splenic proportions of hTregs (P = 0.07) and significantly increased the proportion of hCD39+ Tregs (P < 0.01) at day 21. Humanised mice treated with PTCy+BBG had slightly decreased clinical scores at day 70 compared to PTCy alone. PTCy+BBG treatment significantly reduced histological GVHD grades in the liver (P < 0.05) and reduced serum concentrations of hIFNγ (P < 0.01) at endpoint compared to PTCy alone. This study shows that combinational therapy with PTCy+BBG provides additional benefits to either drug alone in preventing GVHD in humanised mice.