Vertebral Bone Marrow Transplant from a Deceased Lung Transplant Donor: Durable Hematopoiesis and Immune Tolerance

Background: Primary immunodeficiency patients are ineligible for lung transplant (LTX) due to futility and bone marrow transplant (BMT) for lung failure. We hypothesized that using marrow extracted from the vertebral bodies (VB) of a deceased lung donor with partial HLA-match would be able to establish persistent hematopoiesis and generate immunity and tolerance. Methods: A teenager with severe combined immunodeficiency in lung failure due to recurrent pneumonias underwent LTX in 2016 from a 1/8 HLA allele-matched unrelated donor followed by reduced intensity conditioning and infusion of T cell/B cell-depleted cryopreserved VB marrow 4 months later. Results: Immune competence and donor-derived thymopoiesis were evident by six months post-BMT, while immunosuppression was withdrawn at 16-month post-BMT. Donor T cell (>95%) and myeloid chimerism (7-10%) have persisted for over nine years. At two years post-BMT, circulating donor-derived T cells were hyporesponsive to host dendritic cells in vitro. T-cell receptor clonotyping revealed the disappearance of host-reactive clones identifiable in the marrow graft, while circulating donor T cells exhibited downmodulation of signaling pathways for cytotoxicity/rejection, paired with upregulated immunomodulatory pathways, suggesting active suppression. In parallel, circulating predominantly host monocytes upregulated signaling pathways compared to their donor-derived counterparts, indicating active interactions between post-thymic donor T cells and host monocytes. Conclusion: In summary, durable hematopoietic engraftment and protective immunity were demonstrable for the first time in a patient receiving deceased donor vertebral bone marrow graft. Moreover, tolerance exceeding 8-years without immunosuppression was attainable.