Siglec-6 is a novel target for CAR T-cell therapy in acute myeloid leukemia.

Acute myeloid leukemia (AML) is an attractive entity for the development of chimeric antigen receptor (CAR) T-cell immunotherapy because AML blasts are susceptible to T-cell-mediated elimination. Here, we introduce sialic acid-binding immunoglobulin-like lectin 6 (Siglec-6) as a novel target for CAR T cells in AML. We designed a Siglec-6-specific CAR with a targeting domain derived from the human monoclonal antibody JML-1. We found that Siglec-6 is commonly expressed on AML cell lines and primary AML blasts, including the subpopulation of AML stem cells. Treatment with Siglec-6 CAR T cells confers specific antileukemia reactivity that correlates with Siglec-6 expression in preclinical models, including induction of complete remission in a xenograft AML model in immunodeficient mice (NSG/U937). In addition, we confirmed Siglec-6 expression on transformed B cells in chronic lymphocytic leukemia (CLL), and specific anti-CLL reactivity of Siglec-6 CAR T cells in vitro. Of particular interest, we found that Siglec-6 is not detectable on normal hematopoietic stem and progenitor cells (HSPCs) and that treatment with Siglec-6 CAR T cells does not affect their viability and lineage differentiation in colony-formation assays. These data suggest that Siglec-6 CAR T-cell therapy may be used to effectively treat AML without the need for subsequent allogeneic hematopoietic stem cell transplantation. In mature normal hematopoietic cells, we detected Siglec-6 in a proportion of memory (and naïve) B cells and basophilic granulocytes, suggesting the potential for limited on-target/off-tumor reactivity. The lack of expression of Siglec-6 on normal HSPCs is a key to differentiating it from other Siglec family members (eg, Siglec-3 [CD33]) and other CAR target antigens (eg, CD123) that are under investigation in AML, and it warrants the clinical investigation of Siglec-6 CAR T-cell therapy.

Jetani H ，Navarro-Bailón A ，Maucher M ，Frenz S ，Verbruggen C ，Yeguas A ，Vidriales MB ，González M ，Rial Saborido J ，Kraus S ，Mestermann K ，Thomas S ，Bonig H ，Luu M ，Monjezi R ，Mougiakakos D ，Sauer M ，Einsele H ，Hudecek M ... -  《-》

Development of A Chimeric Antigen Receptor Targeting C-Type Lectin-Like Molecule-1 for Human Acute Myeloid Leukemia.

Laborda E ，Mazagova M ，Shao S ，Wang X ，Quirino H ，Woods AK ，Hampton EN ，Rodgers DT ，Kim CH ，Schultz PG ，Young TS ... -  《INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES》

Siglec-6 is a target for chimeric antigen receptor T-cell treatment of chronic lymphocytic leukemia.

The only current curative treatment for chronic lymphocytic leukemia (CLL) is allogenic hematopoietic stem cell transplantation. Chimeric antigen receptor treatment targeting CD19 for CLL achieved some complete responses, suggesting the need for alternative or combinational therapies to achieve a more robust response. In this work, we evaluated CAR-T cells specific for Siglec-6, an antigen expressed in CLL, as a novel CAR-T cell treatment for CLL. We found that detection of SIGLEC6 mRNA and Siglec-6 protein is highly restricted to placenta and immune cells in other tissues and it is not expressed in hematopoietic stem cells. We generated CAR-T cells specific for Siglec-6 based on the sequence of the fully human anti-Siglec-6 antibody (JML1), which was identified in a CLL patient that was cured after allo-hematopoietic stem cell transplantation (alloHSCT), and observed that it specifically targeted CLL cells in vitro and in a xenograft mouse model. Interestingly, a short hinge region increased the activity of CAR-T cells to target cells expressing higher Siglec-6 levels but similarly targeted CLL cells expressing lower Siglec-6 levels in vitro and in vivo. Our results identify a novel CAR-T cell therapy for CLL and establish Siglec-6 as a possible target for immunotherapy.

Kovalovsky D ，Yoon JH ，Cyr MG ，Simon S ，Voynova E ，Rader C ，Wiestner A ，Alejo J ，Pittaluga S ，Gress RE ... -  《-》

CAR-T cells targeting CLL-1 as an approach to treat acute myeloid leukemia.

Wang J ，Chen S ，Xiao W ，Li W ，Wang L ，Yang S ，Wang W ，Xu L ，Liao S ，Liu W ，Wang Y ，Liu N ，Zhang J ，Xia X ，Kang T ，Chen G ，Cai X ，Yang H ，Zhang X ，Lu Y ，Zhou P ... -  《Journal of Hematology & Oncology》

Treatment of Acute Myeloid Leukemia with T Cells Expressing Chimeric Antigen Receptors Directed to C-type Lectin-like Molecule 1.

The successful immunotherapy of acute myeloid leukemia (AML) has been hampered because most potential antigenic targets are shared with normal hematopoietic stem cells (HSCs), increasing the risk of sustained and severe hematopoietic toxicity following treatment. C-type lectin-like molecule 1 (CLL-1) is a membrane glycoprotein expressed by >80% of AML but is absent on normal HSCs. Here we describe the development and evaluation of CLL-1-specific chimeric antigen receptor T cells (CLL-1.CAR-Ts) and we demonstrate their specific activity against CLL-1+ AML cell lines as well as primary AML patient samples in vitro. CLL-1.CAR-Ts selectively reduced leukemic colony formation in primary AML patient peripheral blood mononuclear cells compared to control T cells. In a human xenograft mouse model, CLL-1.CAR-Ts mediated anti-leukemic activity against disseminated AML and significantly extended survival. By contrast, the colony formation of normal progenitor cells remained intact following CLL-1.CAR-T treatment. Although CLL-1.CAR-Ts are cytotoxic to mature normal myeloid cells, the selective sparing of normal hematopoietic progenitor cells should allow full myeloid recovery once CLL-1.CAR-T activity terminates. To enable elective ablation of the CAR-T, we therefore introduced the inducible caspase-9 suicide gene system and we show that exposure to the activating drug rapidly induced a controlled decrease of unwanted CLL-1.CAR-T activity against mature normal myeloid cells.

Tashiro H ，Sauer T ，Shum T ，Parikh K ，Mamonkin M ，Omer B ，Rouce RH ，Lulla P ，Rooney CM ，Gottschalk S ，Brenner MK ... -  《-》