Differential Localization and Invasion of Tumor Cells in Mouse Models of Human and Murine Leukemias

Targeting Tumor Antigen 5T4 Using CAR T Cells for the Treatment of Acute Myeloid Leukemia

Chimeric antigen receptor (CAR) T cells represent a novel targeted approach to overcome deficits in the ability of the host immune system to detect and subsequently eradicate tumors. The identification of antigens expressed specifically on the surface of tumor cells is a critical first step for a targeted therapy that selectively targets cancer cells without affecting normal tissues. 5T4 is a tumor-associated antigen expressed on the cell surface of most solid tumors. However, very little is known about its expression in hematologic malignancies. In this study, we assess the expression of 5T4 in different types of leukemias, specifically acute myeloid leukemia (AML), and normal hematopoietic stem cells (HSC). We also provide an in vitro assessment of safety and efficacy of 5T4-targeting CAR T cells against HSCs and AML tumor cell lines. 5T4 expression was seen in about 50% of AML cases; AML with mutated nucleophosmin 1, AML-myelodysplasia-related, and AML not otherwise specified showed the highest percentage of 5T4+ cases. 5T4 CAR T cells efficiently and specifically killed AML tumor cell lines, including leukemic stem cells. Coculture of 5T4 CAR T cells with HSCs from healthy donors showed no impact on subsequent colony formation, thus confirming the safety profile of 5T4. A proof-of-concept study using a murine model for AML demonstrated that CAR T cells recognize 5T4 expressed on cells and can kill tumor cells both in vitro and in vivo. These results highlight 5T4 as a promising target for immune intervention in AML and that CAR T cells can be considered a powerful personalized therapeutic approach to treat AML.

Comparison of alemtuzumab, anti-thymocyte globulin, and post-transplant cyclophosphamide for graft-versus-host disease and graft-versus-leukemia in murine models

Graft-versus-host disease is a major complication after allogeneic hematopoietic stem cell transplantation for hematological malignancies. Immunosuppressive drugs, such as anti-thymocyte globulin, alemtuzumab, and post-transplant cyclophosphamide, have been used to prevent graft-versus-host disease in HLA-mismatched haploidentical hematopoietic stem cell transplantation. Here, we investigated whether these drugs could ameliorate graft-versus-host disease without diminishing the graft-versus-leukemia effect by using a xenogeneic transplanted graft-versus-host disease/graft-versus-leukemia model. Anti-thymocyte globulin treatment diminished graft-versus-host disease symptoms, completely depleted the infiltration of inflammatory cells in the liver and intestine, and led to prolonged survival. By contrast, improvement after post-transplant cyclophosphamide treatment remained minimal. Alemtuzumab treatment modestly prolonged survival despite an apparent decrease of Tregs. In the graft-versus-leukemia model, 1.5 to 2.0 mg/kg of anti-thymocyte globulin and 0.6 to 0.9 mg/kg of alemtuzumab reduced graft-versus-host disease with minimal loss of graft-versus-leukemia effect. Mice treated with 400 mg/kg of post-transplant cyclophosphamide did not develop graft-versus-host disease or leukemia, but it was difficult to evaluate the graft-versus-leukemia effect due to the sensitivity of A20 cells to cyclophosphamide. Although the current settings provide narrow optimal therapeutic windows, further studies are warranted to maximize the benefits of each immunosuppressant.