Optimized depletion of chimeric antigen receptor T cells in murine xenograft models of human acute myeloid leukemia

Abstract

We and others previously reported potent antileukemia efficacy of CD123-redirected chimeric antigen receptor (CAR) T cells in preclinical human acute myeloid leukemia (AML) models at the cost of severe hematologic toxicity. This observation raises concern for potential myeloablation in patients with AML treated with CD123-redirected CAR T cells and mandates novel approaches for toxicity mitigation. We hypothesized that CAR T-cell depletion with optimal timing after AML eradication would preserve leukemia remission and allow subsequent hematopoietic stem cell transplantation. To test this hypothesis, we compared 3 CAR T-cell termination strategies: (1) transiently active anti-CD123 messenger RNA-electroporated CART (RNA-CART123); (2) T-cell ablation with alemtuzumab after treatment with lentivirally transduced anti-CD123-4-1BB-CD3ζ T cells (CART123); and (3) T-cell ablation with rituximab after treatment with CD20-coexpressing CART123 (CART123-CD20). All approaches led to rapid leukemia elimination in murine xenograft models of human AML. Subsequent antibody-mediated depletion of CART123 or CART123-CD20 did not impair leukemia remission. Time-course studies demonstrated that durable leukemia remission required CAR T-cell persistence for 4 weeks prior to ablation. Upon CAR T-cell termination, we further demonstrated successful hematopoietic engraftment with a normal human donor to model allogeneic stem cell rescue. Results from these studies will facilitate development of T-cell depletion strategies to augment the feasibility of CAR T-cell therapy for patients with AML.

Overcoming the Immunosuppressive Tumor Microenvironment of Hodgkin Lymphoma Using Chimeric Antigen Receptor T Cells

“…(70–72). If the predicted CART123 myelotoxicity is confirmed in ongoing trials, we propose that CART123 could be depleted once remission is obtained (using clinically available anti-T cell antibodies) (73) prior to a subsequent stem cell transplant. Since SCT is already a standard strategy for r/r HL and metabolic remission prior to SCT is an important prognostic factor, it may be possible to use adoptive cellular therapy with potent CART123 to achieve a complete remission prior to salvage SCT.…”

CAR-Expressing Natural Killer Cells for Cancer Retargeting

“…Other than CD33, which is expressed on malignant cells and healthy haematopoietic stem cells [46], CD123 expression is increased in malignant haematological cells but rather low on haematopoietic stem cells [47]. Despite the favourable expression profile of CD123, T cells expressing CD123-guided CARs were shown to induce severe haematological off-target toxicities in AML mouse models [48, 49]. For further studies, strategies to either eradicate CAR-modified T cells from the periphery or to transiently express CARs are urgently needed.…”

Targeting T cell malignancies using CAR-based immunotherapy: challenges and potential solutions

“…Their data supports that infusion of the anti-CD20 antibody, rituximab, an approved antibody for in vivo therapeutic applications, results in efficient, specific elimination of CD20-positive T lymphocytes through ADCC [205,206,218]. Studies have also demonstrated that rituximab can eliminate CD20positive cells in vivo through inducing complementdependent cytotoxicity, a rapid and efficient mode of cell death [219]. CD20 co-expression with a CD123-CAR demonstrated strong and rapid anti-leukemia activity in a human AML mouse model.…”