DEPTOR, a recently described modulator of PI-3K/mTOR signaling, is expressed by CD4⁺ T cells, and functions to modulate CD4⁺ Teff cell differentiation. Upon CD4⁺ T cell activation, intrinsic DEPTOR is degraded, which in turn decreases its negative regulation of Teff responses. We also find that forced overexpression of DEPTOR in CD4⁺ cells stabilizes Foxp3 expression and increases Treg function in vitro.

Here, we used a doxycycline (dox)-inducible DEPTOR transgenic mouse (rtTA^+/+DEPTOR^+/+, iDEP) to evaluate its effect on alloimmune Teff/Treg responses. Fully MHC mismatched BALB/c (H-2^d) hearts were transplanted into C57BL/6 or iDEP recipients (both H-2^b). Administration of dox to iDEP recipients resulted in a marked overexpression of DEPTOR within CD4⁺ cells, and was associated with a significant (p<0.001) prolongation of graft survival (MST 35 days, n=5) vs. WT recipients (MST 7 days, n=14). iDEP recipients (day 6) had a lower frequency of CD4⁺ T_EM cells (CD44^highCD62L^low) and increased numbers of CD4⁺Foxp3⁺ Tregs vs. WT recipients. CD4⁺ T cells from iDEP transgenic mice were also adoptively transferred into BALB/c heart transplanted Rag2^-/-IL2Rγ^-/- mice (H-2^b) two days post-transplant. Treatment of iDEP recipients with dox again resulted in a significant prolongation of graft survival (MST 37 days, n=5 vs. 16 days in controls, n=6; p<0.01). These findings indicate that overexpression of DEPTOR in CD4⁺cells is immunosuppressive. We next administered anti-CD25 (PC-61, 250[micro]g on d-5, d-2 and d+2) to iDEP recipients which results in >70% depletion of CD4⁺Foxp3⁺ Tregs and evaluated graft survival. Surprisingly, the graft prolonging effect of forced DEPTOR overexpression was completely abrogated in these Treg-depleted recipients (MST 9 days, n=5). Finally, we treated recipients of fully MHC mismatched allografts (BALB/c into C57BL/6) with MLN4924 (60 mg/kg BID x 5 days) as a pharmacologic agent to inhibit DEPTOR degradation and found a similar prolongation of graft survival (MST 18 days, n=5 vs. 7 days in controls, n=3; p<0.01).

Collectively, these findings identify DEPTOR as a novel cell intrinsic immunomodulatory protein in CD4⁺ T cells that enhances T regulatory cell function following transplantation. These findings provide for the intriguing possibility that targeting DEPTOR degradation has promise as a future therapeutic.

CITATION INFORMATION: Wedel J, Bruneau S, Liu K, Kochupurakkal N, Laplante M, Briscoe D. Novel Function of CD4⁺ T Cell DEPTOR in Treg Homeostasis and Alloimmunity. Am J Transplant. 2016;16 (suppl 3).

« Back to 2016 American Transplant Congress