Adoptive Transfer Of Ex Vivo “Educated” CD4+CD25+FoxP3+ Regulatory T Cells Effectively Treats Acute Graft Versus Host Disease Preserving Graft Versus Tumor Effect

Donor derived regulatory T cells (Tregs) effectively prevent graft versus host disease (GVHD) in mouse models and in early phase clinical trials. Interleukin 2 (IL-2) therapy in patients with chronic GVHD (cGVHD) can increase Treg number and the Treg/CD4+ T cell ratio resulting in organ damage reduction and symptom relief. Less is known regarding Treg-based treatment for acute GVHD (aGVHD). In this study we evaluated the role of donor Treg cellular therapy for aGVHD treatment in well established murine models.

T cell depleted bone marrow (TCD BM) from C57BL/6 mice was transplanted into lethally irradiated (8 Gy) BALB/C recipients together with 7.5x10⁵ to 1x10⁶/animal donor derived luc+ Tcons. Naturally occurring CD4+CD25+FoxP3+ donor type Tregs (nTregs) were purified from C57BL/6 donor mice. 2.5x10⁵/mouse nTregs were injected at day 6 or 7 after transplant in mice that showed clear clinical signs of aGVHD and Tcon proliferation assessed by bioluminescence imaging (BLI). Survival analysis showed a favorable trend for nTreg treated mice, but the impact of this treatment was modest and not statistically significant (p 0.08).

aGVHD is a disease characterized by the activation and rapid proliferation of alloreactive donor conventional T cells (Tcons) directed against host antigens, so one of the major obstacles of this approach is to overcome the large number and effector function of activated Tcons. Several studies have utilized ex vivo expansion of Tregs to increase their number with the goal of maintaining suppressive function. We developed a different strategy with the intent to “educate” Tregs to specifically suppress the reactive Tcon population. We incubated 2.5x10⁵ donor derived Tregs with irradiated (3000 cGy) blood of aGVHD affected mice for 20 hours without further stimulation and injected the entire pool of these cells, termed educated Treg (eTregs), at day 7 or 8 after transplant and Tcon injection. Interestingly eTregs significantly improved aGVHD affected mouse survival (p = 0.0025 vs Tcons alone). BLI showed no difference between the groups (p = 0.85) because the treatment intervened after Tcon proliferation and activation was initiated. To evaluate eTreg impact on graft versus tumor (GVT) effects, we transplanted BALB/C mice with C57BL/6 TCD BM and 1x10⁴/mouse luc+ A20 tumor cells along with 1x10⁶/mouse donor Tcons and 2.5x10⁵ eTregs. Mice that received TCD BM and A20 tumor cells alone died from progressive tumor growth, while mice that received Tcons died from GVHD without tumor engraftment. Further animals that received both Tcon and eTreg treatment did not have tumor engraftment demonstrating that eTregs do not impact Tcon mediated GVT effects.

Further studies are ongoing to characterize the eTreg population as compared to nTreg, with respect to expression of activation markers and in functional assays. Our observations indicate that Tregs can be ex vivo educated to suppress in vivo reactive and proliferating Tcons. Moreover our data demonstrate that eTreg adoptive transfer is clinically feasible and promising. These findings may be relevant for the development of clinical grade Treg based cellular therapy for the treatment of conditions caused by immune dysregulation such as aGVHD and autoimmune diseases and for transplant tolerance induction.