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Potential of CAR T-cell therapy in acute myeloid leukemia

Jul 2, 2019

The success of anti-CD19 CAR T-cell therapy in relapsed pediatric B-lineage acute lymphoblastic leukemia (B-ALL) has so far not been translated into treatment for acute myeloid leukemia (AML). This might be due to a lack of unique antigens on the surface of AML cells that would allow selective targeting of these cells while sparing healthy hematopoietic stem/progenitor cells (HSPC). However, recent years have seen a lot of research activity in the field as researchers are aiming to find a way to introduce chimeric antigen receptor (CAR) T-cell therapy into the treatment of AML.

Katherine Cumminsand Saar Gillfrom the University of Pennsylvania, US, wrote an article on CAR T-cell therapy for AML, which appeared in the June issue of Haematologica. 1The article discusses CAR T-cell therapies in clinical development, novel target antigens, other immunotherapy options, and potential issues associated with these therapies.

CAR T-cell based clinical trials

A lot of effort is currently being put into assessing the efficacy and safety of CAR T-cells developed against a range of antigens in different subsets of patients with AML. The 13 clinical trials currently underway are summarised in table 1.

Table 1.Chimeric antigen receptor (CAR) T-cell therapies in clinical development.

*, antigen not stated; AML, acute myeloid leukemia; ALL, Acute lymphoblastic leukaemia; allo-HSCT, allogeneic hematopoietic stem cell transplantation; BPDCN, blastic plasmacytoid dendritic cell neoplasm; CLL1, C-type lectin molecule-1; DC, dendritic cells; MDS, myelodysplastic syndrome

CAR T-cells antigen

Trial number

Disease subtype
(age of patients, years)



R/R AML (>18)


R/R AML or relapsed BPDCN (>12)


R/R or adverse AML (18-65)


Relapsed AML after allo-HSCT (>18)


R/R AML (14–75)


R/R AML (2–75)


R/R AML or ALL (Child, adult, older adult)


R/R AML (3–80)


R/R AML (<6 months)

Anti-CD123 + CLL1 compound


R/R AML (< 70)



R/R AML (1–18; 18–80)


R/R AML (<6 months)

Anti-CD33 + CLL1 compound


R/R AML or other hematologic malignancy (child/ adult/ older adult)



R/R AML (<6 months)



R/R AML (<6 months)



R/R AML (<6 months)



R/R AML (<6 months)



R/R AML (<6 months)

CARTs* + Eps8/ WT1 peptide specific DC


R/R AML/ ALL or MDS (18–80)

Abundantly present on AML blasts, CD33 and CD123, are one of the promising targets for CAR T-cell therapy. In particular, CD123 has been identified as a marker of leukemia-initiating cells 2also expressed by other hematologic malignancies. 3However, both antigens are also present on normal HSPC, raising safety questions regarding potential myeloablation. 4Therefore, patients on these therapies will most likely require a rescue allogeneic stem cell transplant (allo-HSCT) donor. Additional toxicity is associated with CD123 expression on endothelial vessels 5that has resulted in a fatal cytokine release syndrome (CRS) and capillary leak syndrome (CLS). 6One approach to minimize those risks of vascular toxicity is the use of CAR-T cells with a limited capacity to expand in vivo 7.

Novel approaches

Other strategies to use adaptive immune responses in AML include targeting natural killer group 2D (NKG2D) ligands, using dual-specific CART, conducting bone marrow transplant with gene-edited allograft followed by CAR T-cells as well as trying other immunotherapy options.

NKG2D-CAR T-cells

NKG2D ligands, evaluated as antigens for CAR T-cells, are predominantly expressed on cancer cells. 8However, cellular stress, including CART induced CRS can upregulate their expression also in normal cells 9. Initial results of phase I clinical trial of autologous NKG2D-CAR T-cells in seven patients with AML showed no objective clinical responses and a limited life-span of the CART population without dose-limiting toxicities. 10Encouragingly, in the follow-up study using higher doses one of the two patients achieved an objective clinical response. 11Additionally, a combination of anti-NKG2D-CAR T-cells with azacytidine, which enhances the expression of NKG2D ligands on AML blasts, is in development to assess whether this could improve efficacy. 12

Dual specificity CARs and new target antigens

Researchers are also employing CAR T-cells expressing a dual-specific CAR directed against two different co-expressed target antigens, to enhance the killing of malignant cells. So far, ADGRE2, CCR1, CD70 and LILRB2, CLL1 have been identified as potentially useful targets in the dual CART approach. 13,14Moreover, there is a potential for the CLL1 to be used as a stand-alone antigen.

Bone marrow transplant with a gene-edited allograft followed by CAR T-cells

In order to increase the persistence and to protect normal hematopoiesis, an antigen can be edited out from the allo-HSPCs before transplantation. In one study, the CD33 was knocked-out from HSPC and their progeny using CRISPR/Cas9. 15Although this novel approach minimizes hematopoietic toxicity, it also reduces the in vivopersistence of CAR T-cells. However, the feasibility and clinical implications of this approach are not yet clear, and there are some concerns about the severity of CRS response due to the role of CD33 in immunomodulation. 16

Other immunotherapies for AML

Lack of antigen specificity in AML has led to exploring immunotherapy options beyond CAR T-cell therapy. These include engineered T cell receptor (TCR) cells against tumor-associated antigens (TAA) and neoantigens. TCRs have potentially increased anti-tumor specificity compared to CAR T-cells as they recognize intracellular antigens presented on MHC of malignant cells. The TCR chains are cloned from patients or normal donors with an immune response to the TAA and may be further affinity-enhanced to amplify reactivity to the target. The use of Wilms’ tumor 1 (WT1), as a TAA, has demonstrated safety and some efficacy as a single TCR therapy 17,18and is assessed in combination with IL-2 (02550535).

Despite encouraging results in solid tumors using PD1/PD-L1 immuno-checkpoint inhibitor, their use in patients with AML has been disappointing so far. 19Also, an attempt to use vaccination against leukemia-specific peptides has  failed to show a clinical impact 20(NCT00433745). In contrast, the expansion of T-cells targeting ex vivogenerated autologous dendritic cells and AML fusion cells has resulted in promising results. This approach has been assessed as consolidation therapy after allo-HSCT, alone and in combination with decitabine (NCT03679650). In a recently reported clinical trial in a small group of patients after standard chemotherapy and a median follow-up of 57 months, it resulted in remission in 71% of patients and a good safety profile. 21

Potential issues with CAR T-cell therapies

As some patients with AML achieved long-term remission after donor lymphocyte infusions and allo-HSCT, CAR T-cell therapy was anticipated to have a similar positive effect on disease control. Unfortunately, various mechanisms of immuno-evasion have been described, including loss of HLA, 22downregulation of antigen expression, upregulation of proteins protecting from apoptosis, and alterations in the composition of T-cell populations such as an expansion of regulatory T-cells and exhaustion of T-cells. 23It is therefore likely that AML will also generate resistance to CART. However, even if the satisfactory efficacy is achieved, the therapy must also have an acceptable toxicity, which will be assessed against other new targeted therapies such as those against BCL2, FLT3, and IDH1/2. Moreover, the manufacturing of T-cells possesses its own challenges due to the cost, complexity, and length of the process, with one of the studies reporting the median time of 45 days from enrolment to infusion. 24


In the future, CAR T-cell therapy for AML might be a possible way to cure patients. It is unlikely the therapy will benefit all patients and might be considered unsuitable for older and more fragile patients. But hopefully, in the next few years, we will be able to identify subgroups of AML patients that would be most likely to respond to the therapy. The authors are hoping that the combination of established allo-HSCT and the CAR-T cells will improve the outcome of the R/R patients with AML, and the CART field will continue to develop into safe, feasible and effective therapies.

Once the ongoing trials start reporting their findings, we should have a better understanding of the role of CAR T-cell therapies can play in the treatment of AML patients, and how they compare to the recent developments in the therapeutic area.

Expert Opinion

  1. Cummins KD. & Gill S. Chimeric antigen receptor T-cell therapy for acute myeloid leukemia: how close to reality? Haematologica. 2019 Jun 20; 104(7):1302-1308. DOI:10.3324/haematol.2018.208751
  2. Vergez F. et al., High levels of CD34+CD38low/-CD123+ blasts are predictive of an adverse outcome in acute myeloid leukemia: a Groupe Ouest-Est des Leucemies Aigues et Maladies du Sang (GOELAMS) study. Haematologica. 2011;96(12):1792-1798. DOI:10.3324/haematol.2011.047894
  3. Munoz L. et al.,Interleukin-3 receptor alpha chain (CD123) is widely expressed in hematologic malignancies. Haematologica. 2001;86(12):1261-1269
  4. Ehninger A. et al.,Distribution and levels of cell surface expression of CD33 and CD123 in acute myeloid leukemia. Blood Cancer J.2014; 4:e218. DOI: 10.1038/bcj.2014.39
  5. Arcangeli S. et al.,Balance of Anti-CD123 Chimeric Antigen Receptor (CAR) Binding Affinity and Density for the Treatment of Acute Myeloid Leukemia. MOL Ther. 2017; 25(8):1933-1945. DOI:10.1016/j.ymthe.2017.04.017
  6. Cellectis. Cellectis Reports Clinical Hold of UCART123 Studies http://www.cellectis.comAvailable from:[Accessed 8 February 2019]
  7. Cummins KD. et al.,Treating Relapsed / Refractory (RR) AML with Biodegradable AntiCD123 CAR Modified T Cells. Blood. 2017;130(Suppl1):1359
  8. Spear P. et al.,NKG2D ligands as therapeutic targets. Cancer Immun. 2013;13:8
  9. Champsaur M.& Lanier LL. Effect of NKG2D ligand expression on host immune responses. Immunol Rev. 2010;235(1):267-285. DOI:10.1111/j.0105-2896.2010.00893.x
  10. Baumeister SH. et al.,Phase I Trial of Autologous CAR T Cells Targeting NKG2D Ligands in Patients with AML/MDS and Multiple Myeloma. Cancer Immunol Res. 2019;7(1):100-112. DOI:10.1158/2326-6066.CIR-18-0307
  11. Sallman DA. et al.,Abstract CT129: The THINK clinical trial: Preliminary evidence of clinical activity of NKG2D chimeric antigen receptor T cell therapy (CYAD-01) in acute myeloid leukemia. Cancer Res. 2018;78(13 Supplement):CT129. DOI: 10.1158/1538-7445.AM2018-CT129
  12. Baragano Raneros A. et al.,Methylation of NKG2D ligands contributes to immune system evasion in acute myeloid leukemia. Genes Immun. 2015;16(1):71-82. DOI:10.1038/gene.2014.58
  13. Liu F. et al.,First-in-Human CLL1-CD33 Compound CAR T Cell Therapy Induces Complete Remission in Patients with Refractory Acute Myeloid Leukemia: Update on Phase 1 Clinical Trial. Blood. 2018;132(Suppl 1):901
  14. Perna F. et al.,Integrating Proteomics and Transcriptomics for Systematic Combinatorial Chimeric Antigen Receptor Therapy of AML. Cancer Cell.2017;32(4):506-519.e5. DOI:10.1016/j.ccell.2017.09.004
  15. Kim MY. et al.,Genetic Inactivation of CD33 in Hematopoietic Stem Cells to Enable CAR T Cell Immunotherapy for Acute Myeloid Leukemia. Cell. 2018;173(6):1439-1453.e19. DOI:10.1016/j.cell.2018.05.013
  16. Laszlo GS. et al.,The past and future of CD33 as therapeutic target in acute myeloid leukemia. Blood Rev.2014;28(4):143-153. DOI:10.1016/j.blre.2014.04.001
  17. Chapuis AG. et al.,Transferred WT1-reactive CD8+ T cells can mediate antileukemic activity and persist in post-transplant patients. Sci Transl Med. 2013;5(174):174ra27. DOI:10.1126/scitranslmed.3004916
  18. Tawara I. et al.,Safety and persistence of WT1-specific Tcell receptor gene−transduced lymphocytes in patients with AML and MDS. Blood.2017;130(18):1985. DOI:10.1182/blood-2017-06-791202
  19. Brodská B. et al.,PDL1 Is Frequently Expressed in Acute Myeloid Leukemia Patients with Leukocytosis. Blood. 2016;128(22):522
  20. Uttenthal B. et al.,Wilms' Tumour 1 (WT1) peptide vaccination in patients with acute myeloid leukaemia induces short-lived WT1-specific immune responses. Br J Haematol. 2014;164(3):366-375. DOI:10.1111/bjh.12637
  21. Rosenblatt J. et al.,Individualized vaccination of AML patients in remission is associated with induction of antileukemia immunity and prolonged remissions. Sci Transl Med. 2016;8(368):368ra171. DOI:10.1126/scitranslmed.aag1298
  22. Teague RM. & Kline J. Immune evasion in acute myeloid leukemia: current concepts and future directions. J Immunother Cancer. 2013;1(13). DOI:10.1186/2051-1426-1-13
  23. Austin R. et al.,  Harnessing the immune system in acute myeloid leukaemia. Crit Rev Oncol Hematol. 2016;103:62-77. DOI:10.1016/j.critrevonc.2016.04.020
  24. Maude SL. et al., Tisagenlecleucel in Children and Young Adults with B-Cell Lymphoblastic Leukemia. N Engl J Med. 2018;378(5):439-448. DOI: 10.1056/NEJMoa1709866