Abstract

Simple SummaryChimeric antigen receptor (CAR) therapy has increased treatment options for many patients who have failed standard chemotherapy. So far, CAR therapy has been used more frequently in B-cell mediated cancers due to unique challenges posed by patients with acute myeloid leukemia (AML) and concern for life-threatening side effects. This review discusses both challenges to creating effective and safe CARs for use in AML, as well as recent advances in CAR development both in pre-clinical and human studies. Overall, continued improvement in AML CAR therapy would be of great benefit to a disease that still has a high morbidity and mortality. The advent of chimeric antigen receptor (CAR) T-cell therapy has led to dramatic remission rates in multiple relapsed/refractory hematologic malignancies. While CAR T-cell therapy has been particularly successful as a treatment for B-cell malignancies, effectively treating acute myeloid leukemia (AML) with CARs has posed a larger challenge. AML not only creates an immunosuppressive tumor microenvironment that dampens CAR T-cell responses, but it also lacks many unique tumor-associated antigens, making leukemic-specific targeting difficult. One advantage of CAR T-cell therapy compared to alternative treatment options is the ability to provide prolonged antigen-specific immune effector and surveillance functions. Since many AML CAR targets under investigation including CD33, CD117, and CD123 are also expressed on hematopoietic stem cells, CAR T-cell therapy can lead to severe and potentially lethal myeloablation. Novel strategies to combat these issues include creation of bispecific CARs, CAR T-cell “safety switches”, TCR-like CARs, NK CARs, and universal CARs, but all vary in their ability to provide a sustained remission, and consolidation with an allogeneic hematopoietic cell transplantation (allo-HCT) will be necessary in most cases This review highlights the delicate balance between effectively eliminating AML blasts and leukemic stem cells, while preserving the ability for bone marrow to regenerate. The impact of CAR therapy on treatment landscape of AML and changing scope of allo-HCT is discussed. Continued advances in AML CAR therapy would be of great benefit to a disease that still has high morbidity and mortality.

Highlights

  • Since the FDA approved tisagenlecleucel (KymriahTM ) for pediatric and young adult patients with relapsed/refractory (r/r) B-cell acute lymphoblastic leukemia (ALL) in August 2017, there are four additional chimeric antigen receptor (CAR)-T cell therapies approved for clinical use

  • leukemic stem cells (LSCs) making cussed in thisofreview article, but some of the promising are on discussed below.it a popular antigen for CAR T-cell therapy [90]

  • Harnessing the immune system for tumor surveillance and to seek out chemo-resistant leukemic stem cells remains the goal of such therapy

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Summary

Introduction

The emergence of chimeric antigen receptor (CAR) T-cell therapy has revolutionized how we think about cancer therapeutics and harnessing the immune system to fight cancer. Since the FDA approved tisagenlecleucel (KymriahTM ) for pediatric and young adult patients with relapsed/refractory (r/r) B-cell acute lymphoblastic leukemia (ALL) in August 2017, there are four additional CAR-T cell therapies approved for clinical use. Except for idecabtagene vicleucel (AbecmaTM ), which targets B cell maturation antigen (BCMA) for use in r/r multiple myeloma [1], the remaining FDA-approved CAR-T cell therapies all target CD19 and are approved for treatment of various malignancies of. Despite the increasing availability of CAR T-cell therapy, the success far has largely been in treating B-cell and plasma cell driven hematologic malignancies. CAR T-cells for acute myeloid leukemia (AML) has posed some unique challenges limiting their widespread availability. We discuss barriers to development of AML CARs, potential strategies to circumvent these barriers, and therapeutic targets currently under investigation for AML CARs

Overview of CARs
Barriers to Development of AML CARs
Lack of AML-Specific Antigens
Antigen Escape
AML-Induced Immunosuppressive Microenvironment
Issues with Quality of Autologous Cells
Experimental Targets under Investigation for AML CARs
CAR targets in AML
Experimental
CD44v6
4.15. Siglec-6
Target Population for AML CARs
Bridging Treatment for AML CAR
Combining Targeted Inhibitors with CAR Products
Integrating AML CARs with Allogenic SCTs
Findings
Conclusions
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