Table 3.

Preclinical and early-phase TCRT targets for AML

Targeta	Reported on-tumor expression	Reported off-tumor expression	Advantages	Disadvantages	Additional notes
CD33	AML bulk cells and LSCs84	myeloid progenitor cells, neutrophils, macrophages, T cells, dendritic cells, Kupffer cells, and hepatocytes84,86	expressed in most AML patients, on both bulk cells and LSCs84 CD33 expression is retained in relapsed disease341	high risk for OTOT toxicities due to expression on hematopoietic cells, including CD34+CD38+ progenitor cells84 severe hepatotoxicity and fatal cytopenias have been reported using CD33-ADCs86,87,88 risk for CAR-T cell fratricide due to low T cell expression84	gemtuzumab ozogamicin, a CD33-ADC, received accelerated approval in 2000, but was withdrawn in 2010 due to serious adverse events. Gemtuzumab ozogamicin was approved again in 2017 KO of CD33 (discussed later) in CD34+ HSPCs prior to SCT may provide a means of safely targeting this antigen267 limited efficacy for CD33-targeting TCRTs in clinical trials89,90,91,94,342,343
CD123	AML bulk cells and LSCs84	HPCs, monocytes, granulocytes, and endothelial cells106,344	expressed in most AML patients, on both bulk cells and LSCs84 pro-survival role in AML95 lower expression on HPCs than AML blasts may provide protection97,98,195	expression on myeloid progenitors, monocytes, granulocytes pose a risk for severe myelotoxicity.96 OTOT expression on endothelial cells may cause serious adverse events (capillary leak syndrome and severe CRS)106	limited efficacy and severe CRS for CD123-targeting TCEs.99,100,101 CAR-T cell efficacy may be greater102,103 but severe adverse events (two grade 4 capillary leak syndromes and a grade 5 CRS) pose a serious concern.104,105
CLL-1 (CLEC12A)	AML bulk cells and LSCs84,107	myeloid progenitor cells, monocytes and granulocytes 107,108	expressed in most AML patients, on both bulk cells and LSCs84,108 restricted to the myeloid-lineage, minimal expression on CD34+CD38− HSCs and lymphoid progenitor cells107,108	expression in myeloid-lineage cells pose a risk for severe myelotoxicity.107,108 CLEC12Aneg cells have been observed in some AML patients345	impressive efficacy for CLEC12A-CAR T cells in a phase I trial (70% ORR) but all patients developed severe pancytopenia and two died of severe infection due to chronic agranulocytosis112
FLT3	AML bulk cells and LSCs116 and B-ALL118	HSPCs346	expressed in most AML patients, on both bulk cells and LSCs116 activating mutations in AML are common and a marker of adverse prognosis347,348 low risk for OTOT toxicities: healthy tissue expression restricted to a subset of HSPCs116 pro-survival role in HSPCs suggests a reduced risk for antigen escape/loss346	expression on HSPCs could lead to profound myelosuppression346 cytoplasmic expression has been detected in the cerebellum346	FLT3 is overexpressed in KMT2Ar B-ALL. KMT2Ar B-ALL can lineage switch (ALL to AML) as a means of antigen escape to lymphoid-targeting therapies. FLT3 CAR T cells may provide therapeutic benefit in the lineage-switch setting118 clinical trials are ongoing with results pending
ILT3 (LILRB4)	monocytic AML121,340	monocytes121,340	expression in highly restricted to the monocyte lineage, with no expression on HSCs or on non-hematopoietic cells340 highly and homogenously expressed in monocytic AML, with variable partial expression in myelomonocytic AML121,340 expressed on immunosuppressive cells. Eliminating these cells may enhance anti-tumor efficacy121 immunoinhibitory and promotes AML migration and infiltration121	restricted to a subset of AML121,340 expressed on monocytic cells may result in monocytopenia121,340	a first-in-class myeloid checkpoint inhibitor ILT3-blocking antibody has been developed and a phase I study is underway (NCT04372433)
IL1RAP	AML bulk cells and LSCs126	monocytes and epithelial cells349	expressed on both bulk cells and LSCs126,350 pro-survival role in AML126,351 not expressed on HSPCs126	approximately one-third of patients do not express IL1RAP350,352 expression on monocytes and epithelial cells poses a risk for monocytopenia and endothelial cell damage (which can aggravate CRS)349	also a target of interest for CML353
CD70	AML bulk cells and LSCs125 DLBCL, FL, HL, WM, and MM 306	subset of activated B and T cells and dendritic cells 306	pro-leukemic role, which may reduce the risk for antigen escape/loss354 not expressed on HSPCs and only transiently expressed on a subset of hematopoietic cells125	variable expression in AML125	CD70 expression is upregulated by the hypomethylating agent azacitidine (already used clinically in AML), providing a rationale for combination therapy355
CD44v6	MM and AML (FLT3/DNMT3A mut)122	keratinocytes, skin, and oral mucosa. Circulating monocytes and T cells122,190	not expressed on HSCs122 pro-leukemic role, which may reduce the risk for antigen escape/loss122	variable expression in AML122 expression on monocytes poses a risk for modest monocytopenia122 transient expression on activated T cells may result in CAR-T cell fratricide190	a phase I/II trial (NCT04097301) for CD44v6 CAR T cells in AML or MM was terminated early due to lower-than-expected proportion of patients expressing CD44v6 (Clinicaltrials.gov, accessed 02.03.2024)
Folate receptor β	AML123	myeloid-lineage cells123	not detected on adult HSCs123	expression on monocytes poses a risk for monocytopenia123 variable expression in AML123	–
GRP78	AML124	none under normal conditions	only expressed at the cell surface during ER stress, so should be absent on healthy cells124	variable expression in AML and little to no expression LSCs124	also a target of interest for myeloma202

^aCML, chronic myeloid leukemia; HPCs, hematopoietic progenitor cells; HSCs, hematopoietic stem cells; LSCs, leukemic stem cells. Other abbreviations as in Tables 1 and 2.