Human IFN-α2- and PD-L1-Modified T Cells (αp-T cells) Inhibit Graft-Versus-Host Disease but Retain Anti-Leukemia Activity

Current strategies to prevent and treat graft-versus-host disease (GVHD) after allogeneic hematopoietic stem cell transplantation (allo-HSCT) primarily utilize pan-immune suppressive agents. These pharmacological approaches cause nonspecific immune suppression, require long-term treatment and are restricted by drug toxicity. Cellular therapies such as regulatory T cells and mesenchymal stem cells target alloreactive T cells to prevent lethal GVHD in humans without systemic immunosuppression. However, they also have major challenges, including cell purification, ex vivo expansion to an adequate amount to meet the therapy need, and loss of immune suppressive effects. New cellular therapies are needed to address these challenges. Our previous studies and others have shown that adoptive transfer of murine plasmacytoid dendritic cells (pDCs) can suppress alloreactive T cell responses and GVHD. These pDCs produce high levels of IFN-α and PD-L1 that directly suppress alloreactive murine T cell responses; however, they are a rare population in peripheral blood and also require purification and ex vivo expansion to meet the therapy requirement. We therefore hypothesize that delivering immune suppressive molecules derived from human pDCs using alternative hematopoietic cells could lead to the development of a novel living cell therapy for inhibiting GVHD. We report here that IFN-α2a- and PD-L1-overexpressing human T cells (αp-T cells) acquire potent capacity to inhibit xenogeneic GVHD (x-GVHD) but preserve the ability to eliminate human xenograft leukemia in NOD/SCID/IL2Rg^−/− (NSG) mice. Our initial studies showed that a lower level of pDCs or PDL1⁺ pDCs in donor G-CSF-mobilized allografts correlated with a significantly higher risk of severe GVHD in patients undergoing allo-HSCT. Like their mouse counterparts, human pDCs expressed high levels of IFN-α and PD-L1, and dose-dependently suppressed expansion and survival of TCR-activated autologous CD4⁺ T cells in cultures. To assess whether human T cells transduced with IFN-α and PD-L1 may acquire immune suppressive functionality, we produced lentivirus encoding IFN-α2a and PD-L1 and transduced them into human T cells (both CD4 and CD8 T cells) to create αp-T cells. While 80% of NSG mice receiving vector control T cells died from x-GVHD, adoptive transfer of these αp-T cells (purity: 60~75%) significantly inhibited x-GVHD with all surviving over 70 days. Compared to vector control, αp-T cells showed 25-fold fewer total donor T cells and a 15-fold decrease in IFN-γ⁺ effector CD4⁺ T cells in peripheral blood at day 46 after transplantation, and had about 5-fold fewer donor CD4⁺ T cells in the bone marrow and spleen at the study's endpoint. The reduction of donor CD4⁺ T cells in αp-T cell-treated x-GVHD NSG mice was accompanied with increased cell death and elevation of PD-1⁺TIM3⁺ terminal exhaustion-like T cells. Furthermore, PD-L1-expressing αp-T cells persisted in these NSG mice throughout the observation period of 85 days. These data indicate that infused αp-T cells can reduce the survival and persistence capacity of x-GVHD-mediated effector T cells in NSG mice. In an immune-competent setting of allo-HSCT using a C57BL/6 mouse anti-Balb/c GVHD model, we verified that adoptive transfer of murine αp-T cells also significantly inhibited the production of lethal GVHD, with 50% of these recipients survived at 60 days after transplantation. Importantly, treatment by co-transfer of αp-T cells and vector control T cells eliminated human xenograft leukemia in NSG mice challenged by human Raji cells without causing x-GVHD. Notably, CD8⁺ T cells derived from αp-T cell-treated leukemia-bearing mice produced approximately 2-fold higher frequency of IFN-γ than those T cells from control group. Our findings identified for the first time that treatment with human αp-T cells may represent a new and clinically relevant cell therapy strategy to reduce GVHD while preserving potent graft-versus-leukemia effects, resulting in significantly improved overall survival of leukemia-bearing mice. Ongoing studies are exploring the effect of these αp-T cells on allogeneic CAR-T cell induction of GVHD and anti-tumor activity. If successful, αp-T cells may have additional applications to the utilization of allogeneic CAR T cells to eliminate tumors without causing GVHD in the context of allo-HSCT.