Using mTOR Inhibitor Nanoimmunotherapy to Induce Cardiac Allograft Tolerance in Non-Human Primates

Abstract

<h3>Purpose</h3> Though tolerance to kidney allografts has been consistently achieved using a mixed chimerism model, cardiac allografts remain resistant to tolerance induction. Lipoprotein-based nanobiologics loaded with a mammalian target of rapamycin inhibiting prodrug (mTOR inhibiting nanobiologics, mTORi-NBs) inhibit trained immunity and promote graft infiltrating M2-macrophages that provide a favorable local immunologic milieu for tolerance induction. In this study, we evaluate the ability of mTORi-NBs to induce tolerance in a cardiac allograft model in NHPs. <h3>Methods</h3> Six NHPs underwent simultaneous heterotopic heart and bone marrow transplantation for mixed chimerism induction. Group A (n=3) was conditioned with 3 Gy total body irradiation (TBI), 7 Gy thymic irradiation (TI), ATGAM, anti-CD40L monoclonal antibody on days 0, 2, 5,7, 9, and 12 post-bone marrow transplant (pBMTx), and cyclosporine until day 28 pBMTx. Group B recipients (n=3) underwent the same conditioning regimen with the addition of mTORi-NBs at a dose of 0.15 mg/kg on days 2, 5, 12, 19, and 26 pBMTx. Group B donors were also treated with a single dose of mTORi-NBs two days before transplant. <h3>Results</h3> In group A, all allografts had end stage rejection by day 175 pBMTx with a mean duration of lymphocyte chimerism of 74 days. The first recipient in group B developed durable full chimerism and mild graft versus host disease (GVHD) which resolved after a course of steroids and cyclosporine. After resolution of his GVHD, his graft continued beating strongly with no evidence of rejection through day 239 pBMTx. The second and third recipients received half dose (1.5 Gy) TBI and both allografts are contracting strongly at days 271 and 26 pBMTx, though the second recipient had some evidence of rejection at day 212 pBMTx. Currently, the mean duration of lymphocyte chimerism in Group B is 149 days. <h3>Conclusion</h3> Preliminary studies suggest that adding mTORi-NB nanoimmunotherapy to a mixed chimerism protocol prolongs both donor lymphocyte chimerism and heart graft survival in NHPs even when reducing pre-operative TBI.