Recipient BCL2 inhibition and NK cell ablation form part of a reduced intensity conditioning regime that improves allo-bone marrow transplantation outcomes



Allogeneic hematopoietic stem cell transplantation (alloSCT) is used to treat over 15,000 patients with acute myeloid leukemia (AML) per year. Donor graft-versus-leukemia (GVL) effect can prevent AML relapse; however, alloSCT is limited by significant toxicity related to conditioning intensity, immunosuppression, opportunistic infections, and graft-versus-host disease (GVHD). Reducing the intensity of conditioning regimens prior to alloSCT has improved their tolerability, but does not alter the pattern of GVHD and has been associated with increased rates of graft rejection and relapse. Here, using a murine pre-clinical model, we describe a novel recipient conditioning approach combining reduced intensity conditioning with either genetic or pharmacological inhibition of NK cell numbers that permits efficient donor engraftment and promotes GVL without inducing GVHD. We show that NK cell-specific deletion of Bcl2 or Mcl1 in mice, or pharmacological inhibition of BCL2 impairs radio-resistant NK cell-mediated rejection of allogeneic engraftment and allows reduction of conditioning intensity below that associated with GVHD priming. The combination of reduced intensity conditioning and NK cell targeting in mice allowed successful donor T cell engraftment and protective immunity against AML while avoiding GVHD. These findings suggest that reduced conditioning in combination with targeted therapies against recipient NK cells may allow the delivery of effective alloSCT against AML while reducing the toxicities associated with more intensive conditioning including GVHD.

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This work is supported by program and project grants from the National Health and Medical Research Council (NHMRC) of Australia (1049407, 1066770, 1057852, 1027472 to N.D.H.), as well as an NHMRC Independent Research Institute Infrastructure Support scheme grant and a Victorian State Government Operational Infrastructure Scheme grant. J.E.D. is supported by a Rabinowicz & Amarant Family Cancer Research Fellowship from the Royal Melbourne Hospital Foundation. F.S.-F.G. was supported by a NHMRC Early Career Fellowship (1088703), a National Breast Cancer Foundation (NBCF) Fellowship (PF-15-008), and grant #1120725 awarded through the Priority-driven Collaborative Cancer Research Scheme and funded by Cure Cancer Australia with the assistance of Cancer Australia. N.D.H. is a recipient of a Melanoma Research Grant from the Harry J Lloyd Charitable Trust (USA), Melanoma Research Alliance (USA), a research grant from the Ian Potter Foundation (AUS) and a CLIP grant from Cancer Research Institute (USA). This work is also supported by fellowships from the NHMRC (10461276 to N.D.H.), the Menzies Foundation (to N.D.H.), and by an enabling grant from The Fight Cancer Foundation.

Authorship contributions

Y.J., J.E.D., J.R., M.J.L.-M., W.G., R.B.D., F.S.-F.G., D.S.R. and N.D.H. designed and/or performed experiments. E.M., D.G., D.H., A.M.L., B.T.K. and R.K. provided key reagents. Y.J., J.E.D., N.D.H. and D.S.R. supervised experimental design, and provided input into interpretation of results and writing of the paper.

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Correspondence to David S. Ritchie or Nicholas D. Huntington.

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J.R. and N.D.H. are co-founders and share-holders of oNKo-innate Pty Ltd. N.D.H. has a collaborative research agreement with Servier.

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