Programming of Donor T Cells Using Allogeneic Delta-like Ligand 4-Positive Dendritic Cells to Reduce Gvhd but Retain GVL Activity
Authors: Mochizuki Kazuhiro , Meng Lijun , Mochizuki Izumi , Tong Qing , He Shan , Liu Yongnian , Purushe Janaki , Sun Hongxing , Fung Henry , Zaidi Raza , Reshef Ran , Blazar Bruce R. , Yagita Hideo , Mineishi Shin , Zhang Yi 
Published: October 2019

Abstract
Host antigen-presenting cells (APCs) are critical for inducing a potent graft-versus-leukemia (GVL) response after allogeneic hematopoietic stem-cell transplantation (allo-HSCT). In this setting, host APCs activate donor T cells to become effector T cells that recognize and react to antigens in malignant cells. However, alloreactive T cells also mediate graft-versus-host disease (GVHD), which causes significant morbidity and mortality after allo-HSCT. Many studies suggest that if alloreactive T cells have reduced capacity to expand in local tissues, they will be unable to trigger severe GVHD. Thus, it is possible that host APC induction of qualitative changes in donor T cells can potentially modify their anti-host toxicities while retaining the GVL effect.
Here we report the establishment of a cellular programming approach that reduces the GVHD toxicity of donor T cells using host dendritic cells (DCs) that express high levels of Dll4 (named Dll4hi DCs). We have previously identified inflammatory Dll4hi DCs. They occurred in HSCT mice early during GVHD induction and had a greater ability than Dll4-negative DCs to induce IFN-γ and IL-17 in alloantigen-activated T cells. However, only approximately 0.03 X 105 Dll4hi DCs were recovered from one HSCT mouse. To provide adequate numbers of Dll4hi DCs for therapeutic translation, we developed a novel culture system capable of producing large number of Dll4hi DCs (about 100.0 X 105) from the bone marrow (BM) of one mouse using Flt3L and the TLR agonists lipopolysaccharide (LPS) and R848, which activate TLR4 and TLR7/8, respectively. Dll4hi DCs showed significantly different phenotype as compared to conventional DCs derived from GM-CSF-stimulated BM cells (named GM-DCs), as evidenced by expressing higher levels of Dll4, Ifnb, Il4, Il6 and Ido, and producing lower levels of iNOS and arginase I. When cultured with C57BL/6 (B6) mouse CD4+ T cells (H2b) at a T cell: DC ratio of 4:1 for 5 days, BALB/c mouse Dll4hi DCs (H2d) induced 3- to 5-fold more in frequency of alloreactive effector T cells producing high levels of IFN-γ and IL-17 compared to GM-DCs. Following transfer, allogeneic Dll4hi DC-induced CD4+ T cells were unable to mediate severe GVHD in BALB/c recipients, with all of them surviving 60 days after allo-HSCT. In contrast, both unstimulated B6 CD4+ T cells and allogeneic GM-DC-induced B6 CD4+ T cells caused lethal GVHD in all BALB/c recipients, indicating that GM-DCs could not be used for reducing the GVHD toxicity of donor CD4+ T cells. Mechanistic analysis showed that Dll4hi DC-induced CD4+ T cell recipients showed 2- to 6-fold less donor CD4+ T cells in the spleen, liver, and intestine 12 days after transplantation compared to unstimulated CD4+ T cell recipients. This reduction of Dll4hi DC-induced CD4+ T cells was associated with markedly increased apoptosis in recipient mice. IFN-γ production by Dll4hi DC-induced CD4+ T cells was essential for their anti-GVHD effects. Absence of T cell IFN-γ led to improved survival and expansion of Dll4hi DC-induced CD4+ T cells in transplant recipients and caused lethal GVHD. Finally, we demonstrated that Dll4hi DC-induced alloreactive T cells had acquired the ability to kill A20 leukemic cells in BALB/c recipients and control growth of P815 mastocytoma cells in the second model of BDF1 recipients, leading to significantly improved survival of mice receiving allo-HSCT. Furthermore, in the third mouse model of GVHD directed against minor histocompatibility antigens, B6 Dll4hi DC-induced C3H.SW CD8+ T cells produced high levels of IFN-γ, had reduced capacity to mediate GVHD in B6 recipients, but preserved GVL activity against C1498 myeloid leukemic cells.
In summary, our findings demonstrate that in vitro Dll4hi DC programming represents a novel and effective platform to reduce toxicities of donor T cells. This strategy has several potential advantages compared to current and developing methods for the modification of donor T cells to reduce GVHD, including a relatively short period of culture, no requirement for T cell subset selection and no need of viral transduction. Importantly, this method may lead to new strategies that can produce large amount of leukemic cell-reactive donor T cells with decrease capability of causing severe GVHD.

Disclosures
No relevant conflicts of interest to declare.