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Adoptive immunotherapy for AML with CD123-engager T cells
© Bonifant et al. 2015
Published: 4 November 2015
T cell immunotherapy is one promising approach to improve outcomes for patients with AML; however, infused T cells do not redirect resident T cells to tumors. To overcome this, we have genetically modified T cells to produce a secretable, bispecific T cell engager (ENG-T cells). Consistent synthesis of engagers by T cells should be superior to the direct infusion of the recombinant bispecific antibody, because bispecific proteins typically have short half-lives and do not accumulate at tumor sites. The goal of this project was to generate and characterize T cells expressing CD123-specific engagers and evaluate the feasibility of using transgenic expression of CD20 in combination with rituximab as a suicide gene.
CD123-ENG T cells were generated by transducing T cells with a retroviral vector encoding a CD123-specific T cell engager consisting of a scFv recognizing CD123 linked to a scFv recognizing CD3. The vector also contained mOrange or CD20 as a second transgene. Effector function of CD123-ENG T cells was evaluated in vitro and in a xenograft model. Toxicity of CD123-ENG T cells and the functionality of the suicide gene were evaluated in vitro and in vivo.
Mean transduction efficiency was 76% (49-95%), and CD123-ENG and CD20.CD123-ENG T cells recognized CD123+ cells (MV-4-11, MOLM-1, KG1a, K562-CD123) as judged by cytokine production and cytolytic activity. CD123-negative cells (K562) were not recognized by CD123-ENG T cells. Likewise, control ENG-T cells were not activated by CD123+ cells. Antigen-dependent recognition was confirmed with cytotoxicity assays. Since CD123 is expressed on normal hematopoietic progenitor cells (HPCs), we evaluated the ability of CD123-ENG T cells to recognize normal HPCs in colony formation assays. Only at high CD123-ENG to HPC ratios did we observe a decline in colony numbers. In contrast, toxicity to primary leukemia samples was apparent even at low CD123-ENG T cell:leukemia cell ratios, indicating that CD123+ AML cells can be targeted while preserving normal HPCs. In vivo, CD123-ENG T cells and CD20.CD123-ENG T cells had potent anti-tumor activity in the KG1a/NSG xenograft model resulting in a significant survival advantage of treated animals in comparison to mice that received Control-ENG T cells (p=0.002). Lastly, CD20.CD123-ENG T cells were efficiently eliminated by rituximab in the presence of complement in contrast to CD123-ENG T cells.
We have generated CD123-ENG T cells that can direct bystander T cells to CD123+ AML in an antigen-specific manner. These CD123-ENG T cells have powerful anti-AML activity in vivo and when further engineered to also express CD20, are eliminated by rituximab. These cells may present a promising addition to currently available AML therapies.
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.