mTORC1 Inhibition Protects Human Regulatory T Cells From Granzyme-B-Induced Apoptosis

Abstract

Regulatory T cells (Tregs) have shown great promise as a means of cellular therapy in a multitude of allo- and auto-immune diseases—due in part to their immunosuppressive potency. Nevertheless, the clinical efficacy of human Tregs in patients has been limited by their poor in vivo homeostasis. To avert apoptosis, Tregs require stable antigenic (CD3ζ/T-cell-receptor-mediated), co-stimulatory (CD28-driven), and cytokine (IL-2-dependent) signaling. Notably, this sequence of signals supports an activated Treg phenotype that includes a high expression of granzymes, particularly granzyme B (GrB). Previously, we have shown that aside from the functional effects of GrB in lysing target cells to modulate allo-immunity, GrB can leak out of the intracellular lysosomal granules of host Tregs, initiating pro-apoptotic pathways. Here, we assessed the role of inhibiting mechanistic target of rapamycin complex 1 (mTORC1), a recently favored drug target in the transplant field, in regulating human Treg apoptosis via GrB. Using ex vivo models of human Treg culture and a humanized mouse model of human skin allotransplantation, we found that by inhibiting mTORC1 using rapamycin, intracytoplasmic expression and functionality of GrB diminished in host Tregs; lowering human Treg apoptosis by in part decreasing the phosphorylation of S6K and c-Jun. These findings support the already clinically validated effects of mTORC1 inhibition in patients, most notably their stabilization of Treg bioactivity and in vivo homeostasis.

Prediction of Acute Cardiac Rejection Based on Gene Expression Profiles

“…Interestingly, a significant decrease in expression levels of this enzyme was noted after initiation of anti-rejection therapy [27][28][29]. Granzyme B plays a key role in inducing apoptosis in target cells during immune responses and mediating early allograft injury [45,46]. Several recent studies investigated the possibilities of its application for noninvasive diagnosis of transplant rejection [30,31].…”

Eras of designer Tregs: Harnessing synthetic biology for immune suppression

“…In contrast to previously described drugs, certain immunosuppressive drugs can also have a positive impact on Tregs. For example, the beneficial effects of rapamycin (sirolimus) on Tregs has been extensively explored 170,171 . Rapamycin can also synergize with TGF‐β1 and/or retinoic acid to promote Treg induction from Tconvs 172,173 .…”

“…For example, the beneficial effects of rapamycin (sirolimus) on Tregs has been extensively explored. 170,171 Rapamycin can also synergize with TGF-β1 and/or retinoic acid to promote Treg induction from Tconvs. 172,173 Accordingly, in a mouse model of heterotopic heart transplant, A2-CAR Tregs synergized with rapamycin to prolong allograft survival compared to either monotherapy.…”

Immunomodulatory nano-preparations for rheumatoid arthritis

“…There are now two categories of immunomodulators that are frequently employed to construct immunomodulatory nano-preparations. The first is the nuclear factor kappa-B (NF-κB) signaling pathway inhibitors (Koide et al., 2015 ; Herrington et al., 2016 ; Riemann et al., 2017 ; L. Zhang et al., 2019 ; Barnabei et al., 2021 ), and the second is the mammalian target of rapamycin (mTOR) inhibitors (Benjamin et al., 2011 ; Chapman & Chi, 2014 ; Hoshii et al., 2014 ; Eskandari et al., 2022 ).…”