Research ArticleGraft-Versus-Host Disease

Combined OX40L and mTOR blockade controls effector T cell activation while preserving Treg reconstitution after transplant

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Science Translational Medicine  20 Sep 2017:
Vol. 9, Issue 408, eaan3085
DOI: 10.1126/scitranslmed.aan3085

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Tackling T cells in GVHD

Graft-versus-host disease (GVHD) after stem cell transplantation is mediated by effector T cells derived from donor stem cells, but GVHD can also be abrogated by donor-derived regulatory T cells. GVHD prophylaxis ideally should then allow regulatory T cell responses while inhibiting effector T cells. Tkachev et al. now provide very promising results in a nonhuman primate model, which suggest that such therapy is possible. They used mTOR inhibition in combination with OX40L blockade, which resulted in reduced damaging T cell reconstitution but preserved regulatory T cell activity. The combination therapy also led to a considerable survival benefit. These findings support testing of this therapy in patients.


A critical question facing the field of transplantation is how to control effector T cell (Teff) activation while preserving regulatory T cell (Treg) function. Standard calcineurin inhibitor–based strategies can partially control Teffs, but breakthrough activation still occurs, and these agents are antagonistic to Treg function. Conversely, mechanistic target of rapamycin (mTOR) inhibition with sirolimus is more Treg-compatible but is inadequate to fully control Teff activation. In contrast, blockade of OX40L signaling has the capacity to partially control Teff activation despite maintaining Treg function. We used the nonhuman primate graft-versus-host disease (GVHD) model to probe the efficacy of combinatorial immunomodulation with sirolimus and the OX40L-blocking antibody KY1005. Our results demonstrate significant biologic activity of KY1005 alone (prolonging median GVHD-free survival from 8 to 19.5 days), as well as marked, synergistic control of GVHD with KY1005 + sirolimus (median survival time, >100 days; P < 0.01 compared to all other regimens), which was associated with potent control of both TH/TC1 (T helper cell 1/cytotoxic T cell 1) and TH/TC17 activation. Combined administration also maintained Treg reconstitution [resulting in an enhanced Treg/Teff ratio (40% over baseline) in the KY1005/sirolimus cohort compared to a 2.9-fold decrease in the unprophylaxed GVHD cohort]. This unique immunologic signature resulted in transplant recipients that were able to control GVHD for the length of analysis and to down-regulate donor/recipient alloreactivity despite maintaining anti–third-party responses. These data indicate that combined OX40L blockade and sirolimus represents a promising strategy to induce immune balance after transplant and is an important candidate regimen for clinical translation.

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