Type II HMG-CoA Reductase Inhibitors (Statins) Provide Acute-Graft-Versus-Host Disease Protection by Th-2 Cytokine Induction While Sparing Graft-Versus-Leukemia Activity.

Recent studies have shown the beneficial impact of 3-hydroxy-3-methyl-CoA (HMG-CoA) reductase inhibitors (statins) on autoimmunity and allograft rejection. To investigate whether statins are capable of protecting from acute graft vs host disease (aGVHD) we utilized an established murine model (FVB/N->Balb/c) across major MHC barriers. Type II statins were potent inducers of a T-helper cell (Th)-2 cytokine profile in the adoptively transferred T cells upon exposure in vitro or in vivo. Expansion of alloreactive luciferase transgenic T cells as measured by total body light emission was significantly reduced by donor pre-treatment (10mg/kg bodyweight) or in vitro T cell treatment (10nM) with atorvastatin (AT vs PBS; p=0.0008) and fluvastatin (FLU vs PBS; p=0.0007). The beneficial effect of statin treatment translated into significantly reduced aGvHD lethality in statin as compared to PBS treated animals. Th-2 biased donor T cells could be tracked until day 15 after BMT by intracellular cytokine staining and FACS analysis. Host treatment prior to transplantation induced down-regulation of the costimulatory molecules CD40, CD80 and CD86 and MHC class II on recipient APCs and enhanced the protective statin effect when donor and recipient were treated (survival AT vs PBS, p=0.0012). Induction of the Th-2 cytokine profile was still permissive for in vivo graft vs leukemia effects by cytolytic effector function of CD8⁺ T cells against A20 B-cell lymphoma cells as assessed by bioluminescence imaging, FACS, histology and survival. In vitro CD8⁺ T cells derived from AT treated animals displayed equal cytolytic activity against Yac1 T-cell lymphoma cells as compared to T cells derived from PBS treated animals. Mechanistically we identified a role for the STAT-6 pathway in statin induced Th-2 induction as aGvHD protection was partially reversed with STAT-6^−/− donors. The in vivo statin effect could be antagonized by L-mevalonate indicating the relevance of the mevalonate pathway for statin mediated aGvHD protection. Since L-mevalonate produced by the HMG-CoA reductase is the precursor of non steroidal isoprenoid compounds, such as farnesyl pyrophosphate and geranylgeranyl pyrophosphate, the statin impact on prenylation status of critical signaling proteins in alloreactive T cells was determined by Western blot. In vitro AT treatment reduced the levels of RAP-1, RhoB and Ras prenylation in allo-antigen exposed T cells and abrogated expression of T-bet which is critical for Th1 induction.

We conclude that type II statins have significant protective impact on aGvHD lethality by Th-2 cytokine induction and inhibition of an uncontrolled Th-1 response, which is of great clinical relevance given the widespread use and well defined toxicity profile of these agents.