β2- Adrenergic Signaling Regulates Graft Versus Host Disease after Allogenic Transplantation While Preserving Graft Versus Leukemia Effect
Authors: Mohammadpour Hemn , Sarow Joseph L. , Chen George L. , MacDonald Cameron R. , Sharma Umesh , Herr Megan M. , Hahn Theresa E. , Repasky Elizabeth A. , McCarthy Philip L. 
Published: November 2019

β2 adrenergic receptor signaling is a key regulator of various immune cells, including T cells; however, its role in T cell function in the context of graft versus host disease (GvHD) is poorly understood. We previously showed that housing mice at thermoneutral temperature (TT; 30°C), which reduces systemic adrenergic stress, increased the incidence and severity of GvHD after allogeneic hematopoietic cell transplant (allo-HCT) compared to mice housed at standard temperature (ST; 22°C) which exerts a mild but chronic adrenergic stress (Leigh et al J Immunol 2015). The increased incidence and severity of GvHD in TT mice can be reversed by the administration of a β2-adrenergic receptor (β2-AR) agonist, suggesting an important role of epinephrine and norepinephrine in allo-HCT outcome (Leigh et al., J. Immunol 2015; Mohammadpour et al J Immunol 2018). We investigated the mechanisms and downstream events of β2-AR signaling in donor T cells after allo-HCT by using β2-AR knockout (β2-AR-/-) mice and commercially available β2-AR agonists. The main goal here was to explore whether signaling through β2-AR in donor T cells could control GvHD incidence and severity without minimizing the graft-versus leukemia (GvL) effect.
We utilized both a major MHC-mismatch C57B6 (H-2kb) into BALB/c (H-2kd) model and a MHC-matched, multiple minor histocompatibility antigen (miHA) mismatched B6 (H-2kb) into C3H/SW (H-2kb) model. Recipient BALB/c and C3H/SW WT mice were lethally irradiated with 850 and 1100 cGy respectively and injected by tail vein with T cell depleted bone marrow (TCD-BM) alone (3 ×106) or TCD-BM and splenic T cells derived from allogeneic WT or β2-AR-/- B6 donors (0.7 × 106 T cells in B6 → BALB/c and 1.5 × 106 in B6 → C3H/SW). We found that donor T cells express β2-AR after allo-HCT and that β2-AR expression on WT T cells plays an important role in controlling GvHD, as evidenced by less severe weight loss, and increased survival compared to mice receiving β2-AR-/- donor T cells (Figure 1A). Histopathologic examination showed that β2-AR-/- T cells induced more damage in the small and large intestine. To explore further the mechanism(s) by which β2-AR signaling controls the severity of GvHD, we used NanoString analysis and discovered that β2-AR-/- T cells have the Th1 phenotype with an increase in Tbx21, Ifng, Irf8 and Emoes genes, while WT CD4+ T cells had higher levels of Th2 and Treg associated genes, including Foxp3, Ptgs5, Tgfb2, Il10, Il21 and Il22. We also observed a significant increase in the inflammatory cytokines IFN-γ and IL-17 in β2-AR-/- CD4+ T cells from the spleen and liver on days 7 and 14 after allo-HCT as compared to WT T cells (Figure 1B), while the expression of IL-10 was significantly higher in WT T cells compared to β2-AR-/- T cells (P< 0.01).
We next sought to determine whether GvL may be affected by use of long acting β2-AR agonist (Bambuterol) to control GvHD. Bambuterol was administered daily at a dose of 1mg/kg from day 0. We observed that Bambuterol controlled the severity and mortality of GvHD after allo-HCT in both major and minor mismatch mouse models, as evidenced by reduced weight loss and an improved clinical score and survival rate in mice receiving Bambuterol compared to vehicle (P<0.001). We showed that treatment increased the expression of IL-10 and decreased the expression of IFN-γ and IL-17 in CD4+ T cells. Interestingly, we found that β2-AR agonist treatment significantly increased the generation of myeloid derived suppressor cells (MDSCs) from WT BM without any effect on β2-AR-/- BM both in vitro and in vivo, suggesting an important role of β2-AR signaling in the generation of MDSCs. To investigate the effect of Bambuterol on GvL, the A20 lymphoma cell line was injected 4 hours before allo-HCT. Using two different doses of T cells (0.5 × 106 and 0.2 × 106) in B6 → BALB/c model, we found that Bambuterol preserved GvL by inducing CD44+ CD62L- NKG2D+ effector cells and CD44+ CD62L+ central memory cells. Since β2-AR agonists can affect cardiac function, we measured heart rate (HR) and blood pressure (BP) using a tail-cuff. There was no difference in BP and HR at day 21 and 28 after allo-HCT between mice receiving Bambuterol compared to mice receiving vehicle.
In conclusion, these data reveal how β-AR signaling can influence donor T cell differentiation and function in murine GvHD models without decreasing GvL effect pointing to the feasibility of manipulation of β2-AR signaling to ameliorate clinical GvHD.

Disclosures
No relevant conflicts of interest to declare.