Combined mTOR inhibition and post-transplant infusion of alloantigen-specific Treg promotes long-term graft survival in otherwise unmanipulated hosts (141.42)

Abstract

Abstract Protocols that achieve donor-specific tolerance of MHC-mismatched organ grafts remain an unmet clinical goal. We report a strategy that combines post-transplant administration of alloAg-specific Treg (AAsTreg) with inhibition of the mammalian target of rapamycin (Rapa) (mTOR) to promote long-term, donor-specific heart graft survival. AAsTreg selection was achieved by co-culture of CD4+CD25+ Treg with immature dendritic cells (DC) in the presence of conditioned media. This rendered cells that potently inhibited T cell proliferation in an Ag-specific manner. However, AAsTreg remained unable to control T cell activation when stimulated by mature DC, - a phenomenon dependent on IL-6 release. Exploiting the in vivo inhibitory effects of Rapa on inflammatory cytokine (IL-6) production, T cell proliferation and graft infiltration, AAsTreg were administered post-transplant (d7) in combination with short-term Rapa. AAsTreg exerted a pro-tolerogenic effect: >80% long-term graft survivors [LTS] (MST>150d). Polyclonal Treg exerted an inferior protective effect: 40% LTS (MST=45d). Moreover, the pro-tolerogenic effect was Ag-specific as AAsTreg selected against third party DC failed to prolong graft survival. Significantly, LTS exhibited alloreactive T cell anergy. Thus, combination of mTOR inhibition with AAsTreg is an effective, clinically-applicable approach to promote long-term graft survival.