Rapamycin-treated human endothelial cells preferentially activate allogeneic regulatory T cells

Abstract

Human graft endothelial cells (ECs) can act as antigen-presenting cells to initiate allograft rejection by host memory T cells. Rapamycin, an mTOR inhibitor used clinically to suppress T cell responses, also acts on DCs, rendering them tolerogenic. Here, we report the effects of rapamycin on EC alloimmunogenicity. Compared with mock-treated cells, rapamycin-pretreated human ECs (rapa-ECs) stimulated less proliferation and cytokine secretion from allogeneic CD4 + memory cells, an effect mimicked by shRNA knockdown of mTOR or raptor in ECs. The effects of rapamycin persisted for several days and were linked to upregulation of the inhibitory molecules PD-L1 and PD-L2 on rapa-ECs. Additionally, rapa-ECs produced lower levels of the inflammatory cytokine IL-6. CD4 + memory cells activated by allogeneic rapa-ECs became hyporesponsive to restimulation in an alloantigen-specific manner and contained higher percentages of suppressive CD4 + CD25 hi CD127 lo FoxP3 + cells that did not produce effector cytokines. In a human-mouse chimeric model of allograft rejection, rapamycin pretreatment of human arterial allografts increased graft EC expression of PD-L1 and PD-L2 and reduced subsequent infiltration of allogeneic effector T cells into the artery intima and intimal expansion. Preoperative conditioning of allograft ECs with rapamycin could potentially reduce immune-mediated rejection.

Enhancement of the immunoregulatory potency of mesenchymal stromal cells by treatment with immunosuppressive drugs

“…A rapid partition of ISDs into cells would appear to explain our observations of increased suppression by brief pretreatments of MSCs, fibroblasts, APCs and HUVECs and may explain at least part of the increased suppression reported for rapamycintreated endothelia and Tregs [30,36].…”

“…The same number of untreated cells had no apparent effect, and, even a dose of 2 Â 10 6 , similar to that used in other studies [37,38], showed only a trend toward greater survival. Whereas rapamycin alone has been used for prevention of solid-organ transplant rejection and aGVHD in mice transplant models [30,31], doses of 3 Â 50 mg were insufficient in our experiments, as was a single dose of 50 ng that we calculate to be the approximate amount of drug introduced by the pretreated MSC (data not shown). Therefore, whereas the suppressive effects of MSCs and rapamycin were seen to be additive in vitro, synergism is indicated by the in vivo model.…”

Overnutrition, mTOR signaling, and cardiovascular diseases

“…IL-2, as well as other growth-promoting cytokines, activates mTOR. In this scenario, rapamycin functions to inhibit lymphocyte proliferation, costimulator molecule expression, and cytokine production (82). mTOR inhibition also promotes the generation of CD4 ϩ FoxP3 ϩ regulatory T (Treg) cells both in vitro and in vivo (45).…”

Evolving Perspectives of mTOR Complexes in Immunity and Transplantation

“…Furthermore, alloAbs, that portend poor long-term graft outcome in kidney transplantation, are thought to contribute to this pathogenic process by mediating HLA-I molecule ligation on EC surfaces. Wang et al (82) have shown recently that RAPA-pretreated human vascular EC can dampen Tmem proliferation and cytokine production (IL-2 and IFNg), while upregulating their co-inhibitory molecule expression (PDL-1 and PDL-2) in vitro. Furthermore, they enrich for Treg among CD25 þ activated T cells.…”