Abstract 874: Adoptive transfer of cytotoxic lymphocytes generated by engineered human dendritic cells for AML treatment
Authors: Zhao Chenchen , Jia Bei , Jiang Yixing , Shike Hiroko , Claxton David F. , Ehmann W Christopher , Schell Todd D. , Cheng Hua , Liu Bei , Zheng Hong 
Published: September 2020

Introduction: Acute myeloid leukemia (AML) is a devastating blood cancer. The clinical benefit of allogeneic stem cell transplantation (alloSCT) greatly relies on the graft-versus-leukemia (GVL) effect mediated by donor T cells, but it may also cause graft-versus-host disease (GVHD). One strategy to improve GVL without promoting GVHD is to adoptive transfer of cytotoxic T cells (CTLs) against leukemia-associated antigen (LAA). Generating potent CTLs is challenging. Stimulating naïve T cells with monocyte-derived dendritic cells loaded with LAA is commonly used, but it is severely limited due to low efficacy. We have developed a novel DC methodology and established immortalized human primary blood DC lines (ihv-DCs) by transducing human peripheral blood mononuclear cells (PBMCs) with a viral protein Tax. The constitutively activated ihv-DCs expand efficiently in vitro and can potently prime naïve T cells. They can be genetically modified to deliver given tumor antigens and stimulate antigen-specific CTLs in high efficiency. Here, we generate CTLs by stimulating donor PBMCs with ihv-DCs that carry HLA-A2 restrict human telomerase reverse transcriptase (hTERT), a known LAA. We investigate, in vitro and in vivo, the CTL killing efficacy.

Methods: ihv-DCs that carry HLA-A2 restrict hTERT was engineered as previously described (Wu et al., PNAS 2018). HLA-A2 restrict hTERT-specific CTLs were generated by co-culturing ihv-DCs in the presence of IL-2 with donor PBMCs. In vitro cytotoxicity was performed by culturing CTLs with target cells that labeled with cell-track dye at different E:T ratio. Cell lysis was tested by flow-cytometry-based cell apoptosis analysis. In vivo cytotoxicity was examined by adoptive transfer CTLs into xenograft AML model. Flow cytometry was used to detect the leukemia burden.

Results: Although variable, THP-1 cell line and blasts from all HLA-A2+ AML patients (11/11) in our study express significant intracellular hTERT. CTLs were successfully established by co-culturing ihv-DCs carrying hTERT with PBMCs from HLA-A2+ healthy donors. We observed an increasing proportion of effector memory T cells over time. We observed significant cytotoxic activities of purified CD8 T cells to U2OS that engineered to express hTERT, THP-1 cells, and primary leukemia blasts from AML patients in vitro. The cytotoxicity is predominantly hTERT specific as the killing to the primary U2OS cell line (negative for hTERT) is minimal. In addition, the cytotoxic effect was significantly diminished upon adding blockade antibody against HLA-A2, indicating the killing is through an HLA-A2 restrict manner. To study whether the CTLs can eradicate AML in vivo, we adoptively transferred CTLs into a xenograft AML model generated by engrafting primary AML into NSG mice (n=5), 5 × 106 cells were injected every 5 days for 4 times. Mice injected with PBS were set as control. On day 20, we found significant reduction of leukemia burden in blood and bone marrow from mice treated with CTLs. Importantly, no GVHD was observed. Persistent CTLs were detected in all organs (blood, bone marrow, liver, spleen, and lungs).

Conclusion: Using a novel ihv-DC delivering LAA, we established CTLs that are highly efficient in killing primary leukemia blasts derived from AML patients both in vitro and in vivo. Our study provides a proof of principle for applying the novel DC methodology to AML treatment.

Citation Format: Chenchen Zhao, Bei Jia, Yixing Jiang, Hiroko Shike, David F. Claxton, W Christopher Ehmann, Todd D. Schell, Hua Cheng, Bei Liu, Hong Zheng. Adoptive transfer of cytotoxic lymphocytes generated by engineered human dendritic cells for AML treatment [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 874.