Chimeric antigen receptor T-cell (CAR-T) therapy, which has demonstrated notable efficacy against B-cell malignancies and is approved by the US Food and Drug Administration for clinical use in this context, represents a significant milestone in cancer immunotherapy. However, the efficacy of CAR-T therapy for the treatment of acute myeloid leukemia (AML) is poor. The challenges associated with the application of CAR-T therapy for the clinical treatment of AML include, but are not limited to, nonspecific distribution of AML therapeutic targets, difficulties in the production of CAR-T cells, AML blast cell heterogeneity, the immunosuppressive microenvironment in AML, and treatment-related adverse events. In this review, we summarize the recent findings regarding various therapeutic targets for AML (CD33, CD123, CLL1, CD7, etc.) and the results of the latest clinical studies on these targets. Thereafter, we also discuss the challenges related to CAR-T therapy for AML and some promising strategies for overcoming these challenges, including novel approaches such as gene editing and advances in CAR design.
Recent advances in CAR-T therapy for acute myeloid leukemia Acute myeloid leukemia (AML) remains a clinical challenge despite the advent of chimeric receptor T-cell (CAR-T) therapy, as there are obstacles hindering the application of CAR-T cells in AML. In this review, we discuss the results of current relevant clinical trials, existing treatment strategies for AML and recent advances in preclinical research to provide insight for overcoming the inefficacy of CAR-T therapy for AML.

OBJECTIVE: To investigate the expression of CD123 in children with acute lymphoblastic leukemia (ALL) and its effect on the clinical characteristics and prognosis of children with B-lineage acute lymphoblastic leukemia (B-ALL).
METHODS: A retrospective analysis was conducted on the clinical data of 251 children with ALL who were admitted to the Department of Hematology and Oncology, Children\'s Hospital of Kunming Medical University, from December 2019 to June 2022. According to the expression of CD123 at initial diagnosis, the children were divided into CD123+ group and CD123- group, and the two groups were compared in terms of clinical characteristics and treatment outcome. The factors influencing the prognosis were analyzed.
RESULTS: Among the 251 children with ALL, there were 146 children (58.2%) in the CD123+ group. The B-ALL group had a significantly higher positive expression rate of CD123 than the acute T lymphocyte leukemia group (P<0.05). Compared with the CD123- group, the CD123+ group had significantly lower peripheral blood leukocyte count and percentage of juvenile cells and a significantly higher proportion of children with high hyperdiploid karyotype or an age of 1-10 years, with a relatively low proportion of children with E2A-PBX1 fusion gene (P<0.05). The multivariate Cox proportional-hazards regression model analysis showed that compared with the >10 years group, the 1-10 years group had a significantly higher overall survival rate (P<0.05), and compared with the high risk group, the moderate risk group had a significantly higher event-free survival rate in children with B-ALL (P<0.05).
CONCLUSIONS: CD123 is widely expressed in children with B-ALL, and positive expression of CD123 might be an indicator for good prognosis in children with B-ALL, which is of great significance for evaluating the efficacy of remission induction therapy and survival prognosis of children with B-ALL.
目的: 研究儿童急性淋巴细胞白血病（acute lymphoblastic leukemia, ALL）中CD123的表达情况及其对急性B淋巴细胞白血病（B-ALL）患儿临床特征及预后的影响。方法: 回顾性分析2019年12月—2022年6月昆明医科大学附属儿童医院血液肿瘤科收治的251例ALL患儿的临床资料。根据初诊CD123表达情况，分为CD123+组与CD123-组，比较两组的临床特征及疗效，并分析影响预后的因素。结果: 251例ALL患儿中，CD123+ 146例（58.2%），B-ALL患儿CD123阳性表达率高于急性T淋巴细胞白血病患儿（P<0.05）。相较于CD123-组，CD123+组初诊时外周血白细胞计数、幼稚细胞百分比更低，更易合并超二倍体染色体核型，1~10岁患儿比例更高，不易合并E2A-PBX1融合基因（P<0.05）。多因素Cox比例风险回归模型分析结果显示，相较于>10岁组，1~10岁组B-ALL患儿总生存率更高（P<0.05）；相较于高危组，中危组B-ALL患儿无事件生存率更高（P<0.05）。结论: CD123在B-ALL患儿中广泛表达，CD123阳性表达可能为儿童B-ALL预后良好的指标，对评估B-ALL患儿诱导缓解治疗及生存预后具有重要意义。.

Despite several small-molecule drugs that have revolutionized the current treatment strategy for acute myeloid leukemia (AML), hematopoietic stem cell transplantation remains the only curative treatment in most cases to date. Chimeric antigen receptor (CAR)-T cell therapy is one of the most promising next-generation cancer therapies for hematological malignancies and is clinically available for treatment of AML. However, developing AML-targeted CAR-T therapy is challenging because of the heterogeneity of target antigen expression across leukemic cells and patients, the difficulty in excluding on-/off-target tumor effects, and the immunosuppressive tumor microenvironment. To date, various targets, including CD33, NKG2D, CD123, CLL-1, and CD7, have been actively studied for CAR-T cells. Although no CAR-T cell products are close to practical use, several clinical trials have shown promising results, particularly for CAR-T cells targeting CLL-1 or CD123. Meanwhile, research exploring the ideal target for AML-targeted CAR-T therapy continues. Furthermore, as collecting autologous lymphocytes from patients with AML is difficult, development of off-the-shelf CAR-T products is being actively pursued. This review discusses the challenges in AML-targeted CAR-T cell therapy development from the perspectives of target antigen characteristics and AML-specific on-target/off-tumor toxicity. Moreover, it discusses the clinical development and prospects of AML-targeting CAR-T cells.

Interleukin (IL)-3 has long been known for its hematopoietic properties. However, recent evidence has expanded our understanding of IL-3 function by identifying IL-3 as a critical orchestrator of inflammation in a wide array of diseases. Depending on the type of disease, the course of inflammation, the cell or the tissue involved, IL-3 promotes either pathologic inflammation or its resolution. Here, we describe the cell-specific functions of IL-3 and summarize its role in diseases. We discuss the current treatments targeting IL-3 or its receptor, and highlight the potential and the limitations of targeting IL-3 in clinics.

Objective: To construct a novel dual-specific antibody targeting human CD123 (CD123 DuAb) and study its effects in acute myeloid leukemia (AML) . Methods: Based on the variable region of the CD123 monoclonal antibody independently developed at our institution, the CD123 DuAb expression plasmid was constructed by molecular cloning and transfected into ExpiCHO-S cells to prepare the antibody protein. Through a series of in vitro experiments, its activation and proliferation effect on T cells, as well as the effect of promoting T-cell killing of AML cells, were verified. Results: ① A novel CD123 DuAb plasmid targeting CD123 was successfully constructed and expressed in the Expi-CHO eukaryotic system. ②The CD123 DuAb could bind both CD3 on T cells and CD123 on CD123(+) tumor cells. ③When T cells were co-cultured with MV4-11 cells with addition of the CD123 DuAb at a concentration of 1 nmol/L, the positive expression rates of CD69 and CD25 on T cells were 68.0% and 44.3%, respectively, which were significantly higher than those of the control group (P<0.05). ④Co-culture with CD123 DuAb at 1 nmol/L promoted T-cell proliferation, and the absolute T-cell count increased from 5×10(5)/ml to 3.2×10(6)/ml on day 9, and CFSE fluorescence intensity decreased significantly. ⑤ With the increase in CD123 DuAb concentration in the culture system, T-cell exhaustion and apoptosis increased. When the CD123 DuAb was added at a concentration of 1 nmol/L to the culture system, the proportion of CD8(+) PD-1(+) LAG-3(+) T cells was 10.90%, and the proportion of propidium iodide (PI) (-) Annexin Ⅴ(+) T cells and PI(+) Annexin Ⅴ(+) T cells was 18.27% and 11.43%, respectively, which were significantly higher than those in the control group (P<0.05). ⑥ The CD123 DuAb significantly activated T cells, and the activation intensity was positively correlated with its concentration. The expression rate of CD107a on T cells reached 16.05% with 1 nmol/L CD123 DuAb, which was significantly higher than that of the control group (P<0.05). ⑦The CD123 DuAb promoted cytokine secretion by T cells at a concentration of 1 nmol/L, and the concentration of IFN-γ and TNF-α in the supernatant of the co-culture system reached 193.8 pg/ml and 169.8 pg/ml, respectively, which was significantly higher than that of the control group (P<0.05). ⑧When CD123 DuAb was added at a concentration of 1 nmol/L to the co-culture system of T cells and CD123(+) tumor cells, the killing intensity of T cells significantly increased, and the residual rates of CD123(+) MV4-11 cells, CD123(+) Molm13 cells, and CD123(+) THP-1 cells were 7.4%, 6.7%, and 14.6% on day 3, respectively, which were significantly lower than those in the control group (P<0.05) . Conclusion: In this study, a novel CD123 DuAb was constructed and expressed. In vitro experiments verified that the DuAb binds to CD123(+) tumor cells and T cells simultaneously, promotes T-cell activation and proliferation, and facilitates their anti-leukemia effect, which provides a basis for further clinical research.
目的： 构建一种新的靶向CD123抗原的双特异性抗体（CD123 DuAb），研究CD123DuAb在急性髓系白血病（AML）治疗中的作用。 方法： 以自主研发的CD123单克隆抗体可变区为基础，利用分子克隆技术，构建CD123 DuAb表达质粒，转染ExpiCHO-S细胞，表达该双功能抗体。通过功能实验，验证CD123 DuAb在T细胞活化及增殖中的作用，及其促进T细胞对AML细胞的杀伤作用。 结果： ①构建了CD123 DuAb表达质粒，并通过Expi-CHO真核系统表达。②CD123 DuAb可以分别与T细胞上的CD3位点及CD123阳性肿瘤细胞上的CD123位点结合。③将1 nmol/L CD123 DuAb加入T细胞与MV4-11细胞共培养体系中，T细胞中CD69阳性表达率为68.0%，CD25阳性表达率为44.3%，均显著高于对照组（P值均<0.05）。④在CD123 DuAb浓度为1 nmol/L的条件下培养T细胞，可促进T细胞增殖，其绝对计数第1天为5×10(5)/ml，第9天扩增至3.2×10(6)/ml，且CFSE荧光强度显著降低。⑤CD123 DuAb能够显著激活T细胞，且激活强度与其浓度呈正相关，浓度为1 nmol/L时，T细胞CD107a表达率可达16.05%，较对照组显著升高（P<0.05）。⑥随培养体系中CD123 DuAb浓度的升高，T细胞耗竭和凋亡也随之增加，浓度为1 nmol/L时，T细胞CD8(+)PD-1(+)LAG-3(+)比例为10.90%，PI(-)Annexin Ⅴ(+)比例为18.27%，PI(+)Annexin Ⅴ(+)比例为11.43%，均较对照组显著升高（P<0.05）。⑦CD123 DuAb能够促进T细胞分泌细胞因子，浓度为1 nmol/L时，共培养体系上清中的IFN-γ和TNF-α的浓度可分别达到193.8 pg/ml和169.8 pg/ml，较对照组显著升高（P<0.05）。⑧将CD123 DuAb以1 nmol/L的浓度加入T细胞与CD123阳性肿瘤细胞共培养体系中，能显著增强T细胞对肿瘤细胞的杀伤作用，共培养3 d，CD123(+)MV4-11细胞、CD123(+)Molm13细胞和CD123(+)THP-1细胞的残留率分别为7.4%、6.7%和14.6%，较对照组显著降低（P<0.05）。 结论： 本研究构建及表达了一种靶向CD123的双特异性抗体，并通过体外实验验证其可以同时结合CD123阳性肿瘤细胞和T细胞，促进T细胞的活化和增殖，增强其抗白血病作用，为进一步临床研究提供了基础。.

BACKGROUND: It is reported that CD123 + HLA-DR- cells in PBMC are basophils, and CD203c, CD63, and FcεRI molecules are activation markers of basophils. However, little is known of CD123 + HLA-DR-cells in blood granulocytes.
OBJECTIVE: To investigate the presence of CD123 + HLA-DR- cells in the blood granulocytes and peripheral PBMC of patients with allergic rhinitis (AR), as well as the impact of allergens on the cell membrane markers of basophils.
METHODS: Flow cytometry was used to detect the expression of the membrane molecules.
RESULTS: While CD123 + HLA-DR- PBMCs are representative of basophils, their presence did not significantly change in patients with AR. In contrast, both the percentage and number of CD123 + HLA-DR- granulocytes, which make up only up to 50% of basophils, were significantly increased in patients with seasonal (sAR) and perennial AR (pAR). CD63+, CD203c+, and FcεRIα+ cells within CD123 + HLA-DR- granulocytes also showed enhanced activity in patients with AR. Allergen extracts from house dust mite allergen extract (HDME) and Artemisia sieversiana wild extract further increased the number of CD123 + HLA-DR- cells in granulocytes of sAR and pAR patients, as well as in PBMCs of pAR patients.
CONCLUSIONS: The use of CD123 + HLA-DR- granulocytes and PBMC may not be sufficient for diagnosing AR. Allergens could potentially contribute to the development of AR by influencing the number of CD123 + HLA-DR- cells, as well as the expression of CD63, CD203c, and FcεRIαin these cells.

While conventional chimeric antigen-receptor (CAR)-T therapies have shown remarkable clinical activity in some settings, they can induce severe toxicities and are rarely curative. To address these challenges, we developed a controllable cell therapy where synthetic D-domain-containing proteins (soluble protein antigen-receptor X-linker [SparX]) bind one or more tumor antigens and mark those cells for elimination by genetically modified T cells (antigen-receptor complex [ARC]-T). The chimeric antigen receptor was engineered with a D-domain that specifically binds to the SparX protein via a unique TAG, derived from human alpha-fetoprotein. The interaction is mediated through an epitope on the TAG that is occluded in the native alpha-fetoprotein molecule. In vitro and in vivo data demonstrate that the activation and cytolytic activity of ARC-T cells is dependent on the dose of SparX protein and only occurs when ARC-T cells are engaged with SparX proteins bound to antigen-positive cells. ARC-T cell specificity was also redirected in vivo by changing SparX proteins that recognized different tumor antigens to combat inherent or acquired tumor heterogeneity. The ARC-SparX platform is designed to expand patient and physician access to cell therapy by controlling potential toxicities through SparX dosing regimens and enhancing tumor elimination through sequential or simultaneous administration of SparX proteins engineered to bind different tumor antigens.

CD123 \"expression\" is common in hematological malignancies, including acute lymphoblastic leukemia (ALL). Flotetuzumab is a novel, investigational CD3/CD123 DART®. We conducted a phase 1 study evaluating safety and efficacy of flotetuzumab in relapsed/refractory ALL (Cohort A) and other advanced CD123-positive hematological malignancies (excluding myeloid malignancies) (cohort B). Thirteen patients (9 in Cohort A and 4 in Cohort B) were treated at dose level 1 (500 ng/kg/day) before early closure due to discontinuation of drug development by sponsor. Two dose limiting toxicities (Grade 4 thrombocytopenia and neutropenia) occurred in one patient in Cohort B. Cytokine release syndrome occurred in most patients (85%), all being grade ≤2. Responses only occurred in Cohort B, with a partial response in one patient with Hodgkin\'s lymphoma and morphological complete remission in the bone marrow in one patient with blastic plasmacytoid dendritic cell neoplasm. In conclusion, flotetuzumab had a manageable safety profile in advanced CD123-positive hematological malignancies.

Tagraxofusp is a first-in-class CD123-directed conjugate of an amended diphtheria toxin platform and recombinant interleukin 3. Binding and subsequent internalization of the drug result in cell death via disruption of intracellular protein synthesis. CD123 is a surface marker that is expressed in several hematological malignancies, especially blastic plasmacytoid dendritic cell neoplasm (BPDCN), where its expression is ubiquitous. A pivotal study of tagraxofusp in BPDCN resulted in its approval for the treatment of BPDCN, the first treatment approved for this indication. Since the introduction of tagraxofusp, research has focused on the management of adverse effects, combination therapy to improve outcomes in fit patients, and dosing and combination strategies to mitigate toxicities while preserving efficacy, especially among older patients. The successful targeting of CD123 in BPDCN has also encouraged research into a variety of other CD123-positive hematological neoplasms, including acute myeloid leukemia (AML), and informed the development of other novel agents targeting CD123. This review examines the clinical data leading to the development and approval of tagraxofusp in BPDCN, how it is being used in combination to improve outcomes in BPDCN and AML, and its developing role in other hematological malignancies.

Using multi-color flow cytometry analysis, we studied the immunophenotypical differences between leukemic cells from patients with AML/MDS and hematopoietic stem and progenitor cells (HSPCs) from patients in complete remission (CR) following their successful treatment. The panel of markers included CD34, CD38, CD45RA, CD123 as representatives for a hierarchical hematopoietic stem and progenitor cell (HSPC) classification as well as programmed death ligand 1 (PD-L1). Rather than restricting the evaluation on a 2- or 3-dimensional analysis, we applied a t-distributed stochastic neighbor embedding (t-SNE) approach to obtain deeper insight and segregation between leukemic cells and normal HPSCs. For that purpose, we created a t-SNE map, which resulted in the visualization of 27 cell clusters based on their similarity concerning the composition and intensity of antigen expression. Two of these clusters were \"leukemia-related\" containing a great proportion of CD34+/CD38- hematopoietic stem cells (HSCs) or CD34+ cells with a strong co-expression of CD45RA/CD123, respectively. CD34+ cells within the latter cluster were also highly positive for PD-L1 reflecting their immunosuppressive capacity. Beyond this proof of principle study, the inclusion of additional markers will be helpful to refine the differentiation between normal HSPCs and leukemic cells, particularly in the context of minimal disease detection and antigen-targeted therapeutic interventions. Furthermore, we suggest a protocol for the assignment of new cell ensembles in quantitative terms, via a numerical value, the Pearson coefficient, based on a similarity comparison of the t-SNE pattern with a reference.