T cells expressing CD123-specific chimeric antigen receptors exhibit specific cytolytic effector functions and antitumor effects against human acute myeloid leukemia. Blood. 2013;122:3138-3148. [PMID: 24030378 DOI: 10.1182/blood-2012-12-474056]

CAR-T cell therapy in AML: recent progress and future perspectives

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.

Overexpressing Bcl-2 enhances murine chimeric antigen receptor T cell therapy against solid tumor

Chimeric antigen receptor T (CART) cell therapy has demonstrated promising potential in the treatment of hematologic malignancies. However, its application to solid tumors is limited due to the restrictive nature of the tumor microenvironment, resulting in functional failure and poor persistence of CART cells. Overexpression of Bcl-2 in human CART cells (hCART) has been found to significantly enhance their anti-apoptotic effects both in vitro and in vivo. Nevertheless, the evaluation of hCART cells in preclinical studies has predominantly relied on immunodeficient mice xenograft tumor models, making it challenging to assess the impact of hCART cells on normal tissues and the immune system. We established a murine CART (mCART) that overexpresses Bcl-2 and targets the epidermal growth factor receptor variant III (EGFRvIII), named EGFRvIII·mCART-Bcl2. It demonstrated superior proliferation, cytotoxicity, and anti-apoptotic capabilities in vitro. In an immunocompetent mouse model of abdominal metastasis of colorectal cancer, EGFRvIII·mCART-Bcl2 exhibited improved survival of CART in the abdomen, increased tumor clearance, and significantly prolonged overall mouse survival. In summary, our study provides evidence that the introduction of Bcl-2 into mCART cells can enhance their therapeutic efficacy against solid tumors while ensuring safety.

CD37 is a safe chimeric antigen receptor target to treat acute myeloid leukemia

Acute myeloid leukemia (AML) is characterized by the accumulation of immature myeloid cells in the bone marrow and the peripheral blood. Nearly half of the AML patients relapse after standard induction therapy, and new forms of therapy are urgently needed. Chimeric antigen receptor (CAR) T therapy has so far not been successful in AML due to lack of efficacy and safety. Indeed, the most attractive antigen targets are stem cell markers such as CD33 or CD123. We demonstrate that CD37, a mature B cell marker, is expressed in AML samples, and its presence correlates with the European LeukemiaNet (ELN) 2017 risk stratification. We repurpose the anti-lymphoma CD37CAR for the treatment of AML and show that CD37CAR T cells specifically kill AML cells, secrete proinflammatory cytokines, and control cancer progression in vivo. Importantly, CD37CAR T cells display no toxicity toward hematopoietic stem cells. Thus, CD37 is a promising and safe CAR T cell AML target.

Chimeric antigen receptor T-cell therapy in childhood acute myeloid leukemia: how far are we from a clinical application?

Recurrent and/or refractory (R/R) pediatric acute myeloid leukemia (AML) remains a recalcitrant disease with poor outcomes. Cell therapy with genetically modified immune effector cells holds the promise to improve outcomes for R/R AML since it relies on cytotoxic mechanisms that are distinct from chemotherapeutic agents. While T cells expressing chimeric antigen receptors (CAR T cells) showed significant anti-AML activity in preclinical models, early phase clinical studies have demonstrated limited activity, irrespective of the targeted AML antigen. Lack of efficacy is most likely multifactorial, including: (i) a limited array of AML-specific targets and target antigen heterogeneity; (ii) the aggressive nature of R/R AML and heavy pretreatment of patients; (iii) T-cell product manufacturing, and (iv) limited expansion and persistence of the CAR T cells, which is in part driven by the immunosuppressive AML microenvironment. Here we review the results of early phase clinical studies with AML-specific CAR T cells, and avenues investigators are exploring to improve their effector function.

Recent progress in chimeric antigen receptor therapy for acute myeloid leukemia

Although CAR-T cell therapy has been particularly successful as a treatment for B cell malignancies, effectively treating acute myeloid leukemia with CAR remains a greater challenge. Multiple preclinical studies and clinical trials are underway, including on AML-related surface markers that CAR-T cells can target, such as CD123, CD33, NKG2D, CLL1, CD7, FLT3, Lewis Y and CD70, all of which provide opportunities for developing CAR-T therapies with improved specificity and efficacy. We also explored specific strategies for CAR-T cell treatment of AML, including immune checkpoints, suicide genes, dual targeting, genomic tools and the potential for universal CAR. In addition, CAR-T cell therapy for AML still has certain risks and challenges, including cytokine release syndrome (CRS) and haematotoxicity. Despite these challenges, as a new targeting method for AML treatment, CAR-T cell therapy still has great prospects. Ongoing research aims to further optimize this treatment mode.

Targeting PRAME for acute myeloid leukemia therapy

Despite significant progress in targeted therapy for acute myeloid leukemia (AML), clinical outcomes are disappointing for elderly patients, patients with less fit disease characteristics, and patients with adverse disease risk characteristics. Over the past 10 years, adaptive T-cell immunotherapy has been recognized as a strategy for treating various malignant tumors. However, it has faced significant challenges in AML, primarily because myeloid blasts do not contain unique surface antigens. The preferentially expressed antigen in melanoma (PRAME), a cancer-testis antigen, is abnormally expressed in AML and does not exist in normal hematopoietic cells. Accumulating evidence has demonstrated that PRAME is a useful target for treating AML. This paper reviews the structure and function of PRAME, its effects on normal cells and AML blasts, its implications in prognosis and follow-up, and its use in antigen-specific immunotherapy for AML.

Peptide-scFv antigen recognition domains effectively confer CAR T cell multiantigen specificity

The emergence of immune escape is a significant roadblock to developing effective chimeric antigen receptor (CAR) T cell therapies against hematological malignancies, including acute myeloid leukemia (AML). Here, we demonstrate feasibility of targeting two antigens simultaneously by combining a GRP78-specific peptide antigen recognition domain with a CD123-specific scFv to generate a peptide-scFv bispecific antigen recognition domain (78.123). To achieve this, we test linkers with varying length and flexibility and perform immunophenotypic and functional characterization. We demonstrate that bispecific CAR T cells successfully recognize and kill tumor cells that express GRP78, CD123, or both antigens and have improved antitumor activity compared to their monospecific counterparts when both antigens are expressed. Protein structure prediction suggests that linker length and compactness influence the functionality of the generated bispecific CARs. Thus, we present a bispecific CAR design strategy to prevent immune escape in AML that can be extended to other peptide-scFv combinations.

Mesenchymal stromal cells in myeloid malignancies: Immunotherapeutic opportunities

Myeloid malignancies are clonal disorders of the progenitor cells or hematopoietic stem cells, including acute myeloid leukemia, myelodysplastic syndromes, myeloproliferative malignancies, and chronic myelomonocytic leukemia. Myeloid neoplastic cells affect the proliferation and differentiation of other hematopoietic lineages in the bone marrow and peripheral blood, leading to severe and life-threatening complications. Mesenchymal stromal cells (MSCs) residing in the bone marrow exert immunosuppressive functions by suppressing innate and adaptive immune systems, thus creating a supportive and tolerant microenvironment for myeloid malignancy progression. This review summarizes the significant features of MSCs in myeloid malignancies, including their role in regulating cell growth, cell death, and antineoplastic resistance, in addition to their immunosuppressive contributions. Understanding the implications of MSCs in myeloid malignancies could pave the path for potential use in immunotherapy.

A blastic plasmacytoid dendritic cell neoplasm-like immunophenotype is negatively associated with CEBPA bZIP mutation and predicts unfavorable prognosis in acute myeloid leukemia

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare and aggressive myeloid malignancy which characteristically expresses an atypical phenotype including CD123+, CD56+, and CD4+. We are aimed to investigate the clinical and prognostic characteristics of AML patients exhibiting BPDCN-like immunophenotype and provide additional insights for risk stratification of AML. A total of 241 newly diagnosed AML patients were enrolled in this retrospective study and categorized into BPDCN-like positive (n = 125)/negative (n = 116) groups, determined by the present with CD123+ along with either CD56+ or CD4+, or both. Subsequently, an analysis was conducted to examine the general clinical characteristics, genetic profiles, and prognosis of the two respective groups. Patients with BPDCN-like immunophenotype manifested higher frequencies of acute myelomonocytic leukemia and acute monoblastic leukemia. Surprisingly, the presence of the BPDCN-like immunophenotype exhibited an inverse relationship with CEBPA bZIP mutation. Notably, patients with BPDCN-like phenotype had both worse OS and EFS compared to those without BPDCN-like phenotype. In the CN-AML subgroups, the BPDCN-like phenotype was associated with worse EFS. Similarly, a statistically significant disparity was observed in both OS and EFS within the favorable-risk subgroup, while only OS was significant within the adverse-risk subgrouMoreover, patients possessing favorable-risk genetics without BPDCN-like phenotype had the longest survival, whereas those who had both adverse-risk genetics and BPDCN-like phenotype exhibited the worst survival. Our study indicated that BPDCN-like phenotype negatively associated with CEBPA bZIP mutation and revealed a significantly poor prognosis in AML. Moreover, the 2022 ELN classification, in combination with the BPDCN-like phenotype, may better distinguish between different risk groups.

Breakthrough in Blastic Plasmacytoid Dendritic Cell Neoplasm Cancer Therapy Owing to Precision Targeting of CD123

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare and aggressive hematologic cancer originating from the malignant transformation of plasmacytoid dendritic cell precursors. This malignancy progresses rapidly, with frequent relapses and a poor overall survival rate, underscoring the urgent need for effective treatments. However, diagnosing and treating BPDCN have historically been challenging due to its rarity and the lack of standardized approaches. The recognition of BPDCN as a distinct disease entity is recent, and standardized treatment protocols are yet to be established. Traditionally, conventional chemotherapy and stem cell transplantation have been the primary methods for treating BPDCN patients. Advances in immunophenotyping and molecular profiling have identified potential therapeutic targets, leading to a shift toward CD123-targeted immunotherapies in both clinical and research settings. Ongoing developments with SL-401, IMGN632, CD123 chimeric antigen receptor (CAR) T-cells, and bispecific antibodies (BsAb) show promising advancements. However, the therapeutic effectiveness of CD123-targeting treatments needs improvement through innovative approaches and combinations of treatments with other anti-leukemic drugs. The exploration of combinations such as CD123-targeted immunotherapies with azacitidine and venetoclax is suggested to enhance antineoplastic responses and improve survival rates in BPDCN patients. In conclusion, this multifaceted approach offers hope for more effective and tailored therapeutic interventions against this challenging hematologic malignancy.

Chimeric antigen receptor T cells for acute myeloid leukemia

The use of T cells expressing chimeric antigen receptors (CARs) that can target and eliminate cancer cells has revolutionized the treatment of B-cell malignancies. In contrast, CAR T cells have not yet become a routine treatment for myeloid malignancies such as acute myeloid leukemia (AML) or myeloproliferative neoplasms (MPNs). For these disease entities, allogeneic hematopoietic cell transplantation (allo-HCT) relying on polyclonal allo-reactive T cells is still the major cellular immunotherapy used in clinical routine. Here, we discuss major hurdles of CAR T-cell therapy for myeloid malignancies and novel approaches to enhance their efficacy and reduce toxicity. Heterogeneity of the malignant myeloid clone, CAR T-cell induced toxicity against normal hematopoietic cells, lack of long-term CAR T-cell persistence, and loss or downregulation of targetable antigens on myeloid cells are obstacles for successful CAR T cells therapy against AML and MPNs. Strategies to overcome these hurdles include pharmacological interventions, for example, demethylating therapy to increase target antigen expression, multi-targeted CAR T cells, and gene-therapy based approaches that delete the CAR target antigen in the hematopoietic cells of the recipient to protect them from CAR-induced myelotoxicity. Most of these approaches are still in preclinical testing but may reach the clinic in the coming years. In summary, we report on barriers to CAR T-cell use against AML and novel therapeutic strategies to overcome these challenges, with the goal of clinical treatment of myeloid malignancies with CAR T cells.

Plasmacytoid dendritic cell expansion in myeloid neoplasms: A novel distinct subset of myeloid neoplasm?

Plasmacytoid dendritic cells (pDCs) are a specific dendritic cell type stemming from the myeloid lineage. Clinically and pathologically, neoplasms associated with pDCs are classified as blastic plasmacytoid dendritic cell neoplasm (BPDCN), mature plasmacytoid dendritic myeloid neoplasm (MPDMN) and pDC expansion in myeloid neoplasms (MNs). BPDCN was considered a rare and aggressive neoplasm in the 2016 World Health Organization (WHO) classification. MPDMN, known as mature pDC-derived neoplasm, is closely related to MNs and was first recognized in the latest 2022 WHO classification, proposing a new concept that acute myeloid leukemia cases could show clonally expanded pDCs (pDC-AML). With the advances in detection techniques, an increasing number of pDC expansion in MNs have been reported, but whether the pathogenesis is similar to that of MPDMN remains unclear. This review focuses on patient characteristics, diagnosis and treatment of pDC expansion in MNs to gain further insight into this novel and unique provisional subtype.

Chimeric Antigen Receptor T Cells in Acute Myeloid Leukemia

Up to 30% of patients with acute myeloid leukemia (AML) who undergo chimeric antigen receptor (CAR) T-cell therapy have evidence of response, although trials are highly heterogeneous. These responses are rarely deep or durable. CD123, CD33, and CLL-1 have emerged as the most common targets for CAR T cells in AML. CAR T cells against myeloid antigens cause myeloablation as well as cytokine release syndrome, although neurotoxicity is rarely seen. Future efforts should focus on AML-specific antigen discovery or engineering, and on further enhancing the activity of CAR T cells.

Advancing CART therapy for acute myeloid leukemia: recent breakthroughs and strategies for future development

Chimeric antigen receptor (CAR) T therapies are being developed for acute myeloid leukemia (AML) on the basis of the results obtained for other haematological malignancies and the need of new treatments for relapsed and refractory AML. The biggest challenge of CART therapy for AML is to identify a specific target antigen, since antigens expressed in AML cells are usually shared with healthy haematopoietic stem cells (HSC). The concomitant expression of the target antigen on both tumour and HSC may lead to on-target/off-tumour toxicity. In this review, we guide researchers to design, develop, and translate to the clinic CART therapies for the treatment of AML. Specifically, we describe what issues have to be considered to design these therapies; what in vitro and in vivo assays can be used to prove their efficacy and safety; and what expertise and facilities are needed to treat and manage patients at the hospital.

Ligand-based targeting of c-kit using engineered γδ T cells as a strategy for treating acute myeloid leukemia

The application of immunotherapies such as chimeric antigen receptor (CAR) T therapy or bi-specific T cell engager (BiTE) therapy to manage myeloid malignancies has proven more challenging than for B-cell malignancies. This is attributed to a shortage of leukemia-specific cell-surface antigens that distinguish healthy from malignant myeloid populations, and the inability to manage myeloid depletion unlike B-cell aplasia. Therefore, the development of targeted therapeutics for myeloid malignancies, such as acute myeloid leukemia (AML), requires new approaches. Herein, we developed a ligand-based CAR and secreted bi-specific T cell engager (sBite) to target c-kit using its cognate ligand, stem cell factor (SCF). c-kit is highly expressed on AML blasts and correlates with resistance to chemotherapy and poor prognosis, making it an ideal candidate for which to develop targeted therapeutics. We utilize γδ T cells as a cytotoxic alternative to αβ T cells and a transient transfection system as both a safety precaution and switch to remove alloreactive modified cells that may hinder successful transplant. Additionally, the use of γδ T cells permits its use as an allogeneic, off-the-shelf therapeutic. To this end, we show mSCF CAR- and hSCF sBite-modified γδ T cells are proficient in killing c-kit+ AML cell lines and sca-1+ murine bone marrow cells in vitro. In vivo, hSCF sBite-modified γδ T cells moderately extend survival of NSG mice engrafted with disseminated AML, but therapeutic efficacy is limited by lack of γδ T-cell homing to murine bone marrow. Together, these data demonstrate preclinical efficacy and support further investigation of SCF-based γδ T-cell therapeutics for the treatment of myeloid malignancies.

CAR-T cell therapy for hematological malignancies: History, status and promise

For many years, the methods of cancer treatment are usually surgery, chemotherapy and radiation therapy. Although these methods help to improve the condition, most tumors still have a poor prognosis. In recent years, immunotherapy has great potential in tumor treatment. Chimeric antigen receptor T-cell immunotherapy (CAR-T) uses the patient's own T cells to express chimeric antigen receptors. Chimeric antigen receptor (CAR) recognizes tumor-associated antigens and kills tumor cells. CAR-T has achieved good results in the treatment of hematological tumors. In 2017, the FDA approved the first CAR-T for the treatment of B-cell acute lymphoblastic leukemia (ALL). In October of the same year, the FDA approved CAR-T to treat B-cell lymphoma. In order to improve and enhance the therapeutic effect, CAR-T has become a research focus in recent years. The structure of CAR, the targets of CAR-T treatment, adverse reactions and improvement measures during the treatment process are summarized. This review is an attempt to highlight recent and possibly forgotten findings of advances in chimeric antigen receptor T cell for treatment of hematological tumors.

Targeted cellular therapy for treatment of relapsed or refractory leukemia

While the mainstay of treatment for high-risk or relapsed, refractory leukemia has historically revolved around allogeneic hematopoietic stem cell transplant (allo-HSCT), targeted immunotherapies have emerged as a promising therapeutic option, especially given the poor prognosis of patients who relapse after allo-HSCT. Novel cellular immunotherapies that harness the cytotoxic abilities of the immune system in a targeted manner (often called "adoptive" cell therapy), have changed the way we treat r/r hematologic malignancies and continue to change the treatment landscape given the rapid evolution of these powerful, yet sophisticated precision therapies that often offer a less toxic alternative to conventional salvage therapies. Importantly, adoptive cell therapy can be allo-HSCT-enabling or a therapeutic option for patients in whom transplantation has failed or is contraindicated. A solid understanding of the core concepts of adoptive cell therapy is necessary for stem cell transplant physicians, nurses and ancillary staff given its proximity to the transplant field as well as its inherent complexities that require specific expertise in compliant manufacturing, clinical application, and risk mitigation. Here we will review use of targeted cellular therapy for the treatment of r/r leukemia, focusing on chimeric antigen receptor T-cells (CAR T-cells) given the remarkable sustained clinical responses leading to commercial approval for several hematologic indications including leukemia, with brief discussion of other promising investigational cellular immunotherapies and special considerations for sustainability and scalability.

CAR-T cells dual-target CD123 and NKG2DLs to eradicate AML cells and selectively target immunosuppressive cells

Chimeric antigen receptor (CAR)-T cells have not made significant progress in the treatment of acute myeloid leukemia (AML) in earlyclinical studies. This lack of progress could be attributed in part to the immunosuppressive microenvironment of AML, such as monocyte-like myeloid-derived suppressor cells (M-MDSCs) and alternatively activated macrophages (M2 cells), which can inhibit the antitumor activity of CAR-T cells. Furthermore, AML cells are usually heterogeneous, and single-target CAR-T cells may not be able to eliminate all AML cells, leading to disease relapse. CD123 and NKG2D ligands (NKG2DLs) are commonly used targets for CAR-T therapy of AML, and M-MDSCs and M2 cells express both antigens. We developed dual-targeted CAR-T (123NL CAR-T) cells targeting CD123 and NKG2DL by various structural optimization screens. Our study reveals that 123NL CAR-T cells eradicate AML cells and selectively target immunosuppressive cells. A highly compact marker/suicide gene, RQR8, which binds targeting epitopes of CD34 and CD20 antigens, was also incorporated in front of the CAR structure. The binding of Rituximab to RQR8 leads to the elimination of 123NL CAR-T cells and cessation of their cytotoxicity. In conclusion, we successfully developed dual effects of 123NL CAR-T cells against tumor cells and immunosuppressive cells, which can avoid target escape and resist the effects of immunosuppressive microenvironment.

Valproic acid increases CAR T cell cytotoxicity against acute myeloid leukemia

The treatment of B cell malignancies has dramatically changed with the introduction of immunotherapy, especially chimeric antigen receptor T (CAR-T) cell therapy. However, only limited efficacy is observed in acute myeloid leukaemia (AML). In the study, We detected CD123 and CLL-1 expression on leukaemia cells from Relapsed/Refractory AML (R/R AML) patients. Then, we constructed anti-CD123 CAR and CLL-1 CAR with different co-stimulation domains (CD28 or 4-1BB) and detected their anti-AML effects. To increase the efficacy of CAR-T cell therapy, we tested different strategies, including application of combined checkpoint inhibitors and histone deacetylase inhibitors (HDACi) in vivo and in vitro We found CD123 and CLL-1 were highly expressed on AML cells. The proportions of T cell subsets and NK cells involved in anti-tumour or anti-inflammation processes in AML patients significantly decreased when compared with healthy donors. Both CD123 CAR and CLL-1 CAR displayed specific anti-AML effects in vitro To improve the lysis effects of CAR-T cells, we combined CAR-T cell therapy with different agents. PD-1/PD-L1 antibodies only slightly improved the potency of CAR-T cell therapy (CD123 CAR-T 60.92% ± 2.9087% vs. 65.43% ± 2.1893%, 60.92% ± 2.9087% vs. 67.43% ± 3.4973%; 37.37% ± 3.908% vs. 41.89% ± 5.1568%, 37.37% ± 3.908% vs. 42.84% ± 4.2635%). However, one HDACi (valproic acid [VPA]) significantly improved CAR-T cell potency against AML cells (CLL-1 CAR-T 34.97% ± 0.3051% vs. 88.167% ± 1.5327%, p < 0.0001; CD123 CAR-T 26.87% ± 2.7010% vs. 82.56% ± 3.086%, p < 0.0001 in MV411; CLL-1 CAR-T 78.77% ± 1.2061% vs. 93.743% ± 1.2333%, p < 0.0001; CD123 CAR-T 64.10% ± 1.5130% vs. 94.427% ± 0.142%, p = 0.0001 in THP-1). Combination therapy prolonged the overall survival of mice when compared with single CD123 CAR-T cell therapy (median survival: 180 days vs. unfollowed). A possible mechanism is that activated CD8+T cells upregulate natural-killer group 2 member D (NKG2D), and VPA upregulates NKG2D ligand expression in AML cells, contributing to NKG2D-mediated cytotoxicity of CAR-T cells against tumour cells. In conclusion, CD123 and CLL-1 are promising targets for AML CAR-T cell therapy. A combination of VPA pre-treatment and CAR-T against AML exhibits synergic effects.

Bicistronic CAR-T cells targeting CD123 and CLL1 for AML to reduce the risk of antigen escape

PURPOSE

Acute myeloid leukemia (AML) is a highly heterogeneous neoplastic disease with a poor prognosis that relapses even after its treatment with chimeric antigen receptor (CAR)-T cells targeting a single antigen. CD123 and CLL1 are expressed in most AML blasts and leukemia stem cells, and their low expression in normal hematopoietic stem cells makes them ideal targets for CAR-T. In this study, we tested the hypothesis that a new bicistronic CAR targeting CD123 and CLL1 can enhance antigenic coverage and prevent antigen escape and subsequent recurrence of AML.

METHODS

CD123 and CLL1 expressions were evaluated on AML cell lines and blasts. Then, in addition to concentrating on CD123 and CLL1, we introduced the marker/suicide gene RQR8 with a bicistronic CAR. Xenograft models of disseminated AML and in vitro coculture models were used to assess the anti-leukemia efficacy of CAR-T cells. The hematopoietic toxicity of CAR-T cells was evaluated in vitro by colony cell formation assays. It was demonstrated in vitro that the combination of rituximab and NK cells caused RQR8-mediated clearance of 123CL CAR-T cells.

RESULTS

We have successfully established bicistronic 123CL CAR-T cells that can target CD123 and CLL1. 123CL CAR-T cells effectively cleared AML cell lines and blasts. They also demonstrated appreciable anti-AML activity in animal transplant models. Moreover, 123CL CAR-T cells can be eliminated in an emergency by a natural safety switch and don't target hematopoietic stem cells.

CONCLUSIONS

The bicistronic CAR-T cells targeting CD123 and CLL1 may be a useful and secure method for treating AML.

B7-H3 chimeric antigen receptor-modified T cell shows potential for targeted treatment of acute myeloid leukaemia

BACKGROUND AND AIMS

Chimeric antigen receptor (CAR)-T cell therapy is a novel type of immunotherapy. However, the use of CAR-T cells to treat acute myeloid leukaemia (AML) has limitations. B7-H3 is expressed in several malignancies, including some types of AML cells. However, its expression in normal tissues is low. Therefore, B7-H3 is ideal for targeted AML therapy.

MATERIALS AND METHODS

First, we constructed B7-H3 CAR that can target B7-H3, and then constructed B7-H3-CAR-T cells in vitro, which were co-incubated with six AML cell lines expressing different levels of B7-H3, respectively. The toxicity and cytokines were detected by flow cytometry. In vivo, AML model was established in B-NSG mice to study the toxicity of B7-H3-CAR T on AML cells.

RESULTS

In vitro functional tests showed that B7-H3-CAR-T cells were cytotoxic to B7-H3-positive AML tumor cells and had good scavenging effect on B7-H3-expressing AML cell lines, and the cytokine results were consistent. In vivo, B7-H3-CAR-T cells significantly inhibited tumor cell growth in a mouse model of AML, prolonging mouse survival compared with controls.

CONCLUSION

B7-H3-CAR-T cells may serve as a novel therapeutic method for the targeted treatment of AML.

Preclinical development and evaluation of nanobody-based CD70-specific CAR T cells for the treatment of acute myeloid leukemia

BACKGROUND

Acute myeloid leukemia (AML) treatment remains challenging. CD70 was reported as a promising AML-specific antigen. Preclinically, CAR T-cell with single-chain-variable fragment (scFv) or truncated CD27 targeting CD70 has been reported to treat AML. However, various disadvantages including spontaneous exhaustion, proteinase-mediated loss of functional receptors, and high immunogenicity, limited its further application to clinical settings. Alternatively, the single-variable domain on heavy chain (VHH), also known as nanobodies, with comparable binding ability and specificity, provides an optional solution.

METHOD

We generated CD70 knocked-out novel nanobody-based anti-CD70-CAR T-cells (nb70CAR-T) with two different VHHs for antigen detection. Next, we detected the CD70 expression on primary AML blasts by flow cytometry and associated the efficacy of nb70CAR-T with the target antigen density. Finally, epigenetic modulators were investigated to regulate the CD70 expression on AML cells to promote the functionality of nb70CAR-T.

RESULTS

Our nb70CAR-T exhibited expected tumoricidal functionality against CD70-expressed cell lines and primary AML blasts. However, CD70 expression in primary AML blasts was not consistently high and nb70CAR-T potently respond to an estimated 40.4% of AML patients when the CD70 expression level was over a threshold of 1.6 (MFI ratio). Epigenetic modulators, Decitabine and Chidamide can up-regulate CD70 expression on AML cells, enhancing the treatment efficacy of nb70CAR-T.

CONCLUSION

CD70 expression in AML blasts was not fully supportive of its role in AML targeted therapy as reported. The combinational use of Chidamide and Decitabine with nb70CAR-T could provide a new potential for the treatment of AML.

Diagnosis, treatment, and genetic characteristics of blastic plasmacytoid dendritic cell neoplasm: A review

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a highly aggressive and extremely rare hematologic disease with a poor prognosis, involving mainly the skin and bone marrow. The immunophenotype of these tumor cells is characterized by the expression of CD4, CD56, CD123, TCL-1, and CD303. To date, no consensus has been reached on the standard of care for BPDCN. Currently, clinical treatment is mainly based on high-dose chemotherapy combined with hematopoietic stem cell transplantation. However, this treatment method has limitations for elderly, frail, and relapsed/refractory patients. In recent years, breakthroughs in molecular biology and genetics have not only provided new ideas for the diagnosis of BPDCN but also helped develop targeted treatment strategies for this disease. The emergence of targeted drugs has filled the gap left by traditional therapies and shown great clinical promise. This article focuses on the latest advances in genetics and targeted therapies for BPDCN, especially the emerging therapies that may provide new ideas for the clinical treatment of BPDCN.

CD123 a Therapeutic Target for Acute Myeloid Leukemia and Blastic Plasmocytoid Dendritic Neoplasm

In spite of consistent progress at the level of basic research and of clinical treatment, acute myeloid leukemia (AML) still represents an unmet clinical need for adult and pediatric patients. To improve the outcomes of these patients, it is necessary to identify new therapeutic targets. IL3RA (CD123, alpha subunit of the interleukin 3 receptor) is a cell membrane protein overexpressed in several hematologic malignancies, including AML blastic plasmocytoid dendritic cell neoplasms (BPDCN). Given the higher expression of CD123 on leukemic cells compared to normal hematopoietic cells and its low/absent expression on normal hematopoietic stem cells, it appears as a suitable and attractive target for therapy. Various drugs targeting CD123 have been developed and evaluated at clinical level: interleukin-3 conjugated with diphtheria toxin; naked neutralizing anti-CD123 antibodies; drug-antibody conjugates; bispecific antibodies targeting both CD123 and CD3; and chimeric antigen receptor (CAR) T cells engineered to target CD123. Some of these agents have shown promising results at the clinical level, including tagraxofusp (CD123 conjugated with diphtheria toxin) for the treatment of BPDCN and IMGN632 (anti-CD123 drug-conjugate), and flotetuzumab (bispecific anti-CD123 and anti-CD3 monoclonal antibody) for the treatment of AML. However, the therapeutic efficacy of CD123-targeting treatments is still unsatisfactory and must be improved through new therapeutic strategies and combined treatments with other antileukemic drugs.

How I treat high-risk acute myeloid leukemia using preemptive adoptive cellular immunotherapy

Allogeneic hematopoietic stem cell transplantation (alloHSCT) is a potentially curative treatment for patients with high-risk acute leukemias, but unfortunately disease recurrence remains the major cause of death in these patients. Infusion of donor lymphocytes (DLI) has the potential to restore graft-versus-leukemia immunologic surveillance; however, efficacy varies across different hematologic entities. Although relapsed chronic myeloid leukemia, transplanted in chronic phase, has proven remarkably susceptible to DLI, response rates are more modest for relapsed acute myeloid leukemia and acute lymphoblastic leukemia. To prevent impending relapse, a number of groups have explored administering DLI preemptively on detection of measurable residual disease (MRD) or mixed chimerism. Evidence for the effectiveness of this strategy, although encouraging, comes from only a few, mostly single-center retrospective, nonrandomized studies. This article seeks to (1) discuss the available evidence supporting this approach while highlighting some of the inherent challenges of MRD-triggered treatment decisions post-transplant, (2) portray other forms of postremission cellular therapies, including the role of next-generation target-specific immunotherapies, and (3) provide a practical framework to support clinicians in their decision-making process when considering preemptive cellular therapy for this difficult-to-treat patient population.

Chimeric antigen receptor T-cell therapy for T-ALL and AML

Non-B-cell acute leukemia is a term that encompasses T-cell acute lymphoblastic leukemia (T-ALL) and acute myeloid leukemia (AML). Currently, the therapeutic effectiveness of existing treatments for refractory or relapsed (R/R) non-B-cell acute leukemia is limited. In such situations, chimeric antigen receptor (CAR)-T cell therapy may be a promising approach to treat non-B-cell acute leukemia, given its promising results in B-cell acute lymphoblastic leukemia (B-ALL). Nevertheless, fratricide, malignant contamination, T cell aplasia for T-ALL, and specific antigen selection and complex microenvironment for AML remain significant challenges in the implementation of CAR-T therapy for T-ALL and AML patients in the clinic. Therefore, designs of CAR-T cells targeting CD5 and CD7 for T-ALL and CD123, CD33, and CLL1 for AML show promising efficacy and safety profiles in clinical trials. In this review, we summarize the characteristics of non-B-cell acute leukemia, the development of CARs, the CAR targets, and their efficacy for treating non-B-cell acute leukemia.

Case report: CD38-directed CAR-T cell therapy: A novel immunotherapy targeting CD38- positive blasts overcomes TKI and chemotherapy resistance of myeloid chronic myeloid leukemia in blastic phase

Resistance to tyrosine kinase inhibitor (TKI) is a tough problem in the treatment of chronic myeloid leukemia in blastic phase (CML-BP), which was often associated with acquired mutations in the kinase domain and not eliminating the leukemic stem cells. The efficacy of TKI or combination with chemotherapy in CML-BP remains unsatisfactory. Chimeric antigen receptor T (CAR-T) cell immunotherapy may overcome TKI and chemotherapy resistance. However, lack of ideal targetable antigens is a major obstacle for treating patients with myeloid malignancies. CD38 is known to be expressed on most (acute myeloid leukemia) AML cells, and its lack of expression on hematopoietic stem cells renders it as a potential therapeutic target for myeloid CML-BP. We develop a CD38-directed CAR-T cell therapy for AML, and two patients with myeloid CML-BP were enrolled (NCT04351022). Two patients, harboring E255K and T315I mutation in the ABL kinase domain, respectively, were resistant to multiple TKIs (imatinib, dasatinib, nilotinib, and ponatinib) and intensive chemotherapy. The blasts in the bone marrow of two patients exhibited high expression of CD38. After tumor reduction chemotherapy and lymphodepletion chemotherapy, 1 × 10⁷ CAR-T-38 cells per kilogram of body weight were administered. They achieved minimal residual disease-negative and BCR::ABL1-negative complete remission and experienced grade II cytokine release syndrome manifesting as fever. Our data highlighted that CAR-T-38 cell therapy may overcome TKI and chemotherapy resistance in patients with myeloid CML-BP.

Conventional Therapeutics in BPDCN Patients-Do They Still Have a Place in the Era of Targeted Therapies?

No benchmark treatment exists for blastic plasmacytoid dendritic cell neoplasm (BPDCN). Since the malignancy is chemo-sensitive, chemotherapy followed by hematopoietic stem cell transplantation remains an effective treatment. However, relapses frequently occur with the development of resistance. New options arising with the development of therapies targeting signaling pathways and epigenetic dysregulation have shown promising results. In this review, we focus on conventional therapies used to treat BPDCN and the novel therapeutic approaches that guide us toward the future management of BPDCN.

Applying a Clinical Lens to Animal Models of CAR-T Cell Therapies

Chimeric antigen receptor (CAR)-T cells have emerged as a promising treatment modality for various hematologic and solid malignancies over the past decade. Animal models remain the cornerstone of pre-clinical evaluation of human CAR-T cell products and are generally required by regulatory agencies prior to clinical translation. However, pharmacokinetics and pharmacodynamics of adoptively transferred T cells are dependent on various recipient factors, posing challenges for accurately predicting human engineered T cell behavior in non-human animal models. For example, murine xenograft models did not forecast now well-established cytokine-driven systemic toxicities of CAR-T cells seen in humans, highlighting the limitations of animal models that do not perfectly recapitulate complex human immune systems. Understanding the concordance as well as discrepancies between existing pre-clinical animal data and human clinical experiences, along with established advantages and limitations of each model, will facilitate investigators’ ability to appropriately select and design animal models for optimal evaluation of future CAR-T cell products. We summarize the current state of animal models in this field, and the advantages and disadvantages of each approach depending on the pre-clinical questions being asked.

CAR T-Cell-Based gene therapy for cancers: new perspectives, challenges, and clinical developments

Chimeric antigen receptor (CAR)-T cell therapy is a progressive new pillar in immune cell therapy for cancer. It has yielded remarkable clinical responses in patients with B-cell leukemia or lymphoma. Unfortunately, many challenges remain to be addressed to overcome its ineffectiveness in the treatment of other hematological and solidtumor malignancies. The major hurdles of CAR T-cell therapy are the associated severe life-threatening toxicities such as cytokine release syndrome and limited anti-tumor efficacy. In this review, we briefly discuss cancer immunotherapy and the genetic engineering of T cells and, In detail, the current innovations in CAR T-cell strategies to improve efficacy in treating solid tumors and hematologic malignancies. Furthermore, we also discuss the current challenges in CAR T-cell therapy and new CAR T-cell-derived nanovesicle therapy. Finally, strategies to overcome the current clinical challenges associated with CAR T-cell therapy are included as well.

Preclinical In Vitro and In Vivo Models for Adoptive Cell Therapy of Cancer

ABSTRACT

Adoptive cellular therapies are making major strides in the treatment of cancer, both for hematologic and solid tumors. These cellular products include chimeric antigen receptor T cells and T-cell receptor-modified T cells, tumor-infiltrating lymphocytes, marrow-infiltrating T cells, natural killer cells as well as macrophage-based therapeutics. Advancement in genomics, computational biology, immunology, and cell therapy manufacturing has facilitated advancement of adoptive T cell therapies into the clinic, whereas clinical efficacy has driven Food and Drug Administration approvals. The growth of adoptive cellular therapy has, in turn, led to innovation in the preclinical models available, from ex vivo cell-based models to in vivo xenograft models of treatment. This review focuses on the development and application of in vitro models and in vivo models (cell line xenograft, humanized mice, and patient-derived xenograft models) that directly evaluate these human cellular products.

Characteristics of Pyroptosis-Related Subtypes and Novel Scoring Tool for the Prognosis and Chemotherapy Response in Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is usually associated with poor prognosis and low complete remission (CR) rate due to individual biological heterogeneity. Pyroptosis is a special form of inflammatory programmed cell death related to the progression, treatment response, and prognosis of multiple tumors. However, the potential connection of pyroptosis-related genes (PRGs) and AML still remains unclear. We described the genetic and transcriptional alterations of PRGs in 151 AML samples and presented a consensus clustering of these patients into two subtypes with distinct immunological and prognostic characteristics. Cluster A, associated with better prognosis, was characterized by relatively lower PRG expression, activated immune cells, higher immune scores in the tumor microenvironment (TME), and downregulation of immunotherapy checkpoints. Subsequently, a PRG score was constructed to predict overall survival (OS) of AML patients by using univariate and multivariate Cox regression analysis, and its immunological characteristics and predictive capability were further validated by 1,054 AML samples in external datasets. Besides an immune-activated status, low-PRG score cohorts exhibited higher chemotherapeutic drug sensitivity and significant positive correlation with the cancer stem cell (CSC) index. Combined with age, clinical French-American-British (FAB) subtypes, and PRG score, we successfully constructed a nomogram to effectively predict the 1-/3-/5-year survival rate of AML patients, and the predictive capability was further validated in multiple external datasets with a high area under the curve (AUC) value. The various transcriptomic analysis helps us screen significant pyroptosis-related signatures of AML and provide a new clinical application of PRG scores in predicting the prognosis and benefits of treatment for AML patients.

Non-cleavable hinge enhances avidity and expansion of CAR-T cells for acute myeloid leukemia

Chimeric antigen receptor (CAR) T cell therapy is effective in lymphoid malignancies, but there has been limited data in myeloid cancers. Here, we start with a CD27-based CAR to target CD70 ("native") in acute myeloid leukemia (AML), and we find modest efficacy in vivo, consistent with prior reports. We then use orthogonal approaches to increase binding on both the tumor and CAR-T cell sides of the immune synapse: a pharmacologic approach (azacitidine) to increase antigen density of CD70 in myeloid tumors, and an engineering approach to stabilize binding of the CAR to CD70. To accomplish the latter, we design a panel of hinge-modified regions to mitigate cleavage of the extracellular portion of CD27. Our CD8 hinge and transmembrane-modified CD70 CAR-T cells are less prone to cleavage, have enhanced binding avidity, and increased expansion, leading to more potent in vivo activity. This enhanced CD70-targeted CAR is a promising candidate for further clinical development.

CD123 and More: How to Target the Cell Surface of Blastic Plasmacytoid Dendritic Cell Neoplasm

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare and aggressive leukemia derived from plasmacytoid dendritic cells (pDCs). It is associated with a remarkably poor prognosis and unmet need for better therapies. Recently, the first-in-class CD123-targeting therapy, tagraxofusp, was approved for treatment of BPDCN. Other CD123-targeting strategies are in development, including bispecific antibodies and combination approaches with tagraxofusp and other novel agents. In other blood cancers, adoptive T-cell therapy using chimeric antigen receptor (CAR)-modified T cells represents a promising new avenue in immunotherapy, showing durable remissions in some relapsed hematologic malignancies. Here, we report on novel and innovative therapies in development to target surface molecules in BPDCN currently in clinical trials or in preclinical stages. We also discuss new cell surface targets that may have implications for future BPDCN treatment.

Allogeneic TCRαβ deficient CAR T-cells targeting CD123 in acute myeloid leukemia

Acute myeloid leukemia (AML) is a disease with high incidence of relapse that is originated and maintained from leukemia stem cells (LSCs). Hematopoietic stem cells can be distinguished from LSCs by an array of cell surface antigens such as CD123, thus a candidate to eliminate LSCs using a variety of approaches, including CAR T cells. Here, we evaluate the potential of allogeneic gene-edited CAR T cells targeting CD123 to eliminate LSCs (UCART123). UCART123 cells are TCRαβneg T cells generated from healthy donors using TALEN® gene-editing technology, decreasing the likelihood of graft vs host disease. As safety feature, cells express RQR8 to allow elimination with Rituximab. UCART123 effectively eliminates AML cells in vitro and in vivo with significant benefits in overall survival of AML-patient derived xenograft mice. Furthermore, UCART123 preferentially target AML over normal cells with modest toxicity to normal hematopoietic stem/progenitor cells. Together these results suggest that UCART123 represents an off-the shelf therapeutic approach for AML.

CD123, the interleukin-3 receptor alpha chain, is aberrantly expressed in acute myeloid leukemia blasts and leukemia stem cells. Here the authors report the design and characterize the anti-tumor activity of allogeneic CD123-targeted CAR-T cells as a therapeutic approach for acute myeloid leukemia.

Targeting CD123 in blastic plasmacytoid dendritic cell neoplasm using allogeneic anti-CD123 CAR T cells

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare hematologic malignancy with poor outcomes with conventional therapy. Nearly 100% of BPDCNs overexpress interleukin 3 receptor subunit alpha (CD123). Given that CD123 is differentially expressed on the surface of BPDCN cells, it has emerged as an attractive therapeutic target. UCART123 is an investigational product consisting of allogeneic T cells expressing an anti-CD123 chimeric antigen receptor (CAR), edited with TALEN^® nucleases. In this study, we examine the antitumor activity of UCART123 in preclinical models of BPDCN. We report that UCART123 have selective antitumor activity against CD123-positive primary BPDCN samples (while sparing normal hematopoietic progenitor cells) in the in vitro cytotoxicity and T cell degranulation assays; supported by the increased secretion of IFNγ by UCART123 cells when cultured in the presence of BPDCN cells. UCART123 eradicate BPDCN and result in long-term disease-free survival in a subset of primary patient-derived BPDCN xenograft mouse models. One potential challenge of CD123 targeting therapies is the loss of CD123 antigen through diverse genetic mechanisms, an event observed in one of three BPDCN PDX studied. In summary, these results provide a preclinical proof-of-principle that allogeneic UCART123 cells have potent anti-BPDCN activity.

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare and highly aggressive hematologic malignancy derived from the precursors of plasmacytoid dendritic cells. Here the authors characterize the anti-tumor activity of allogeneic anti-CD123 CAR-T cells in preclinical models of BPDCN.

CLEC12A plays an important role in immunomodulatory function and prognostic significance of patients with acute myeloid leukemia

The physiological function and prognostic significance of C-type lectin domain family 12 member A (CLEC12A) in acute myeloid leukemia (AML) patients are unclear. CLEC12A transcriptional expression in a variety of tumors from several public databases was collected and compared. We found that CLEC12A was highly expressed in AML cell lines and in tissues from AML patients and a higher CLEC12A expression in leukemia stem cells. CLEC12A low expression was associated with poor prognosis in the chemotherapy-only group and high CLEC12A expression may benefit from autologous or allogeneic hematopoietic stem cell transplantation (HSCT). CLEC12A expression was positively correlated with infiltrating levels of type 2 macrophages and monocytes and negatively associated with NK cells and regulatory T cells in AML. CLEC12A high was positively associated with immune checkpoint genes as well as macrophage associated genes. CLEC12A is an ideal chimeric antigen receptor T-cell (CAR-T) therapy target for AML and its expression level was closely linked to treatment response and patients' survival outcome. CLEC12A plays an important immunomodulatory role in AML.

Design, Synthesis, and Targeted Delivery of an Immune Stimulant that Selectively Reactivates Exhausted CAR T Cells

Although chimeric antigen receptor (CAR) T cells have demonstrated significant promise in suppressing hematopoietic cancers, their applications in treating solid tumors have been limited by onset of CAR T cell exhaustion that accompanies continuous CAR T cell exposure to tumor antigen. To address this limitation, we have exploited the abilities of recently designed universal CARs to bind fluorescein and internalize a fluorescein-TLR7 agonist conjugate by CAR-mediated endocytosis. We demonstrate here that anti-fluorescein CAR-mediated uptake of a fluorescein-TLR7-3 conjugate can reactivate exhausted CAR T cells, leading to dramatic reduction in T cell exhaustion markers (PD-1⁺ Tim-3⁺ ) and shrinkage of otherwise resistant tumors without inducing systemic activation of the immune system. We conclude that CAR T cell exhaustion can be reversed by administration of a CAR-targeted TLR7 agonist, thereby enabling the CAR T cells to successfully treat solid tumors without incurring the systemic toxicity that commonly accompanies administration of nontargeted TLR7 agonists.

Emerging CAR T Cell Strategies for the Treatment of AML

Simple Summary

Chimeric antigen receptors (CARs) targeting CD19 have emerged as a new treatment for hematological malignancies. As a “living therapy”, CARs can precisely target and eliminate tumors while proliferating inside the patient’s body. Various preclinical and clinical studies are ongoing to identify potential CAR-T cell targets for acute myeloid leukemia (AML). We shed light on the continuing efforts of CAR development to overcome tumor escape, exhaustion, and toxicities. Furthermore, we summarize the recent progress of a range of putative targets exploring this unmet need to treat AML. Lastly, we discuss the advances in preclinical models that built the foundation for ongoing clinical trials.

Abstract

Engineered T cells expressing chimeric antigen receptors (CARs) on their cell surface can redirect antigen specificity. This ability makes CARs one of the most promising cancer therapeutic agents. CAR-T cells for treating patients with B cell hematological malignancies have shown impressive results. Clinical manifestation has yielded several trials, so far five CAR-T cell therapies have received US Food and Drug Administration (FDA) approval. However, emerging clinical data and recent findings have identified some immune-related toxicities due to CAR-T cell therapy. Given the outcome and utilization of the same proof of concept, further investigation in other hematological malignancies, such as leukemias, is warranted. This review discusses the previous findings from the pre-clinical and human experience with CAR-T cell therapy. Additionally, we describe recent developments of novel targets for adoptive immunotherapy. Here we present some of the early findings from the pre-clinical studies of CAR-T cell modification through advances in genetic engineering, gene editing, cellular programming, and formats of synthetic biology, along with the ongoing efforts to restore the function of exhausted CAR-T cells through epigenetic remodeling. We aim to shed light on the new targets focusing on acute myeloid leukemia (AML).

Single-Cell Analysis of Target Antigens of CAR-T Reveals a Potential Landscape of "On-Target, Off-Tumor Toxicity"

Cellular immunotherapy represented by CD19-directed chimeric antigen receptor T (CAR-T) cells has achieved great success in recent years. An increasing number of CAR-T therapies are being developed for cancer treatment, but the frequent and varied adverse events, such as “on-target, off-tumor toxicity”, limit CAR-T application. Here, we identify the target antigen expression patterns of CAR therapies in 18 tissues and organs (peripheral blood mononuclear cells, bone marrow, lymph nodes, spleen, heart, ascending aortic tissue, trachea, lung, skin, kidney, bladder, esophagus, stomach, small intestine, rectum, liver, common bile duct, and pancreas) from healthy human samples. The atlas determines target antigens expressed on some normal cell types, which facilitates elucidating the cause of “on-target, off-tumor toxicity” in special tissues and organs by targeting some antigens, but not others. Moreover, we describe the target antigen expression patterns of B-lineage-derived malignant cells, acute myeloid leukemia (AML), and solid tumors. Overall, the present study indicates the pathogenesis of “on-target, off-tumor toxicity” during CAR therapies and provides guidance on taking preventive measures during CAR treatment.

Straight to the Point-The Novel Strategies to Cure Pediatric AML

Although the outcome has improved over the past decades, due to improved supportive care, a better understanding of risk factors, and intensified chemotherapy, pediatric acute myeloid leukemia remains a life-threatening disease, and overall survival (OS) remains near 70%. According to French-American-British (FAB) classification, AML is divided into eight subtypes (M0–M7), and each is characterized by a different pathogenesis and response to treatment. However, the curability of AML is due to the intensification of standard chemotherapy, more precise risk classification, improvements in supportive care, and the use of minimal residual disease to monitor response to therapy. The treatment of childhood AML continues to be based primarily on intensive, conventional chemotherapy. Therefore, it is essential to identify new, more precise molecules that are targeted to the specific abnormalities of each leukemia subtype. Here, we review abnormalities that are potential therapeutic targets for the treatment of AML in the pediatric population.

[Development and functional verification of CAR-T cells targeting CLL-1]

Objective: To explore the development of a CAR-T cells targeting CLL-1 and verify its function. Methods: The expression levels of CLL-1 targets in cell lines and primary cells were detected by flow cytometry. A CLL-1 CAR vector was constructed, and the corresponding lentivirus was prepared. After infection and activation of T cells, CAR-T cells targeting CLL-1 were produced and their function was verified in vitro and in vivo. Results: CLL-1 was expressed in acute myeloid leukemia (AML) cell lines and primary AML cells. The transduction rate of the prepared CAR T cells was 77.82%. In AML cell lines and AML primary cells, CLL-1-targeting CAR-T cells significantly and specifically killed CLL-1-expressing cells. Compared to untransduced T cells, CAR-T cells killed target cells and secreted inflammatory cytokines, such as interleukin-6 and interferon-γ, at significantly higher levels (P<0.001) . In an in vivo human xenograft mouse model of AML, CLL-1 CAR-T cells also exhibited potent antileukemic activity and induced prolonged mouse survival compared with untransduced T cells [not reached vs 22 days (95%CI 19-24 days) , P=0.002]. Conclusion: CAR-T cells targeting CLL-1 have been successfully produced and have excellent functions.

CAR T cells redirected to cell surface GRP78 display robust anti-acute myeloid leukemia activity and do not target hematopoietic progenitor cells

Developing CAR T cells for acute myeloid leukemia (AML) has been hampered by a paucity of targets that are expressed on AML blasts and not on hematopoietic progenitor cells (HPCs). Here we demonstrate that GRP78 is expressed on the cell surface of primary AML blasts but not HPCs. To target GRP78, we generate T cell expressing a GRP78-specific peptide-based CAR, which show evidence of minimal fratricide post activation/transduction and antigen-dependent T cell differentiation. GRP78-CAR T cells recognize and kill GRP78-positive AML cells without toxicity to HPCs. In vivo, GRP78-CAR T cells have significant anti-AML activity. To prevent antigen-dependent T cell differentiation, we block CAR signaling and GRP78 cell surface expression post activation by using dasatinib during GRP78-CAR T cell manufacturing. This significantly improves their effector function in vitro and in vivo. Thus, targeting cell surface GRP78-positive AML with CAR T cells is feasible, and warrants further active exploration.

CD123 Expression Is Associated With High-Risk Disease Characteristics in Childhood Acute Myeloid Leukemia: A Report From the Children's Oncology Group

PURPOSE

Increased CD123 surface expression has been associated with high-risk disease characteristics in adult acute myeloid leukemia (AML), but has not been well-characterized in childhood AML. In this study, we defined CD123 expression and associated clinical characteristics in a uniformly treated cohort of pediatric patients with newly diagnosed AML enrolled on the Children's Oncology Group AAML1031 phase III trial (NCT01371981).

MATERIALS AND METHODS

AML blasts within diagnostic bone marrow specimens (n = 1,040) were prospectively analyzed for CD123 protein expression by multidimensional flow cytometry immunophenotyping at a central clinical laboratory. Patients were stratified as low-risk or high-risk on the basis of (1) leukemia-associated cytogenetic and molecular alterations and (2) end-of-induction measurable residual disease levels.

RESULTS

The study population was divided into CD123 expression-based quartiles (n = 260 each) for analysis. Those with highest CD123 expression (quartile 4 [Q4]) had higher prevalence of high-risk KMT2A rearrangements and FLT3-ITD mutations (P < .001 for both) and lower prevalence of low-risk t(8;21), inv(16), and CEBPA mutations (P < .001 for all). Patients in lower CD123 expression quartiles (Q1-3) had similar relapse risk, event-free survival, and overall survival. Conversely, Q4 patients had a significantly higher relapse risk (53% v 39%, P < .001), lower event-free survival (49% v 69%, P < .001), and lower overall survival (32% v 50%, P < .001) in comparison with Q1-3 patients. CD123 maintained independent significance for outcomes when all known contemporary high-risk cytogenetic and molecular markers were incorporated into multivariable Cox regression analysis.

CONCLUSION

CD123 is strongly associated with disease-relevant cytogenetic and molecular alterations in childhood AML. CD123 is a critical biomarker and promising immunotherapeutic target for children with relapsed or refractory AML, given its prevalent expression and enrichment in patients with high-risk genetic alterations and inferior clinical outcomes with conventional therapy.

An Update on Immune Based Therapies in Acute Myeloid Leukemia: 2021 and Beyond!

Despite advances in the treatment of acute myeloid leukemia (AML), relapse is still widely observed and represents the major cause of death among patients with AML. Treatment options in the relapse setting are limited, still relying predominantly on allogeneic hematopoietic stem cell transplantation (allo-HSCT) and cytotoxic chemotherapy, with poor outcomes. Novel targeted and venetoclax-based combinations are being investigated and have shown encouraging results. Immune checkpoint inhibitors in combination with low-intensity chemotherapy demonstrated encouraging response rates and survival among patients with relapsed and/or refractory (R/R) AML, especially in the pre- and post-allo-HSCT setting. Blocking the CD47/SIRPα pathway is another strategy that showed robust anti-leukemic activity, with a response rate of around 70% and an encouraging median overall survival in patients with newly diagnosed, higher-risk myelodysplastic syndrome and patients with AML with a TP53 mutation. One approach that was proven to be very effective in the relapsed setting of lymphoid malignancies is chimeric antigen receptor (CAR) T cells. It relies on the infusion of genetically engineered T cells capable of recognizing specific epitopes on the surface of leukemia cells. In AML, different CAR constructs with different target antigens have been evaluated and demonstrated safety and feasibility in the R/R setting. However, the difficulty of potently targeting leukemic blasts in AML while sparing normal cells represents a major limitation to their use, and strategies are being tested to overcome this obstacle. A different approach is based on endogenously redirecting the patient's system cells to target and destroy leukemic cells via bispecific T-cell engagers (BiTEs) or dual antigen receptor targeting (DARTs). Early results have demonstrated the safety and feasibility of these agents, and research is ongoing to develop BiTEs with longer half-life, allowing for less frequent administration schedules and developing them in earlier and lower disease burden settings.

The IL-3, IL-5, and GM-CSF common receptor beta chain mediates oncogenic activity of FLT3-ITD-positive AML

FLT3-ITD is the most predominant mutation in AML being expressed in about one-third of AML patients and is associated with a poor prognosis. Efforts to better understand FLT3-ITD downstream signaling to possibly improve therapy response are needed. We have previously described FLT3-ITD-dependent phosphorylation of CSF2RB, the common receptor beta chain of IL-3, IL-5, and GM-CSF, and therefore examined its significance for FLT3-ITD-dependent oncogenic signaling and transformation. We discovered that FLT3-ITD directly binds to CSF2RB in AML cell lines and blasts isolated from AML patients. A knockdown of CSF2RB in FLT3-ITD positive AML cell lines as well as in a xenograft model decreased STAT5 phosphorylation, attenuated cell proliferation, and sensitized to FLT3 inhibition. Bone marrow from CSF2RB-deficient mice transfected with FLT3-ITD displayed decreased colony formation capacity and delayed disease onset together with increased survival upon transplantation into lethally irradiated mice. FLT3-ITD-dependent CSF2RB phosphorylation required phosphorylation of the FLT3 juxtamembrane domain at tyrosines 589 or 591, whereas the ITD insertion site and sequence were of no relevance. Our results demonstrate that CSF2RB participates in FLT3-ITD-dependent oncogenic signaling and transformation in vitro and in vivo. Thus, CSF2RB constitutes a rational treatment target in FLT3-ITD-positive AML.

Highly aminated iron oxide nanoworms for simultaneous manufacturing and labeling of chimeric antigen receptor T cells

Cell based therapies including chimeric antigen receptor (CAR) T cells are promising for treating leukemias and solid cancers. At the same time, there is interest in enhancing the functionality of these cells via surface decoration with nanoparticles (backpacking). Magnetic nanoparticle cell labeling is of particular interest due to opportunities for magnetic separation, in vivo manipulation, drug delivery and magnetic resonance imaging (MRI). While modification of T cells with magnetic nanoparticles (MNPs) was explored before, we questioned whether MNPs are compatible with CAR-T cells when introduced during the manufacturing process. We chose highly aminated 120 nm crosslinked iron oxide nanoworms (CLIO NWs, ~36,000 amines per NW) that could efficiently label different adherent cell lines and we used CD123 CAR-T cells as the labeling model. The CD123 CAR-T cells were produced in the presence of CLIO NWs, CLIO NWs plus protamine sulfate (PS), or PS only. The transduction efficiency of lentiviral CD123 CAR with only NWs was ~23% lower than NW+PS and PS groups (~33% and 35%, respectively). The cell viability from these three transduction conditions was not reduced within CAR-T cell groups, though lower compared to non-transduced T cells (mock T). Use of CLIO NWs instead of, or together with cationic protamine sulfate for enhancement of lentiviral transduction resulted in comparable levels of CAR expression and viability but decreased the proportion of CD8+ cells and increased the proportion of CD4+ cells. CD123 CAR-T transduced in the presence of CLIO NWs, CLIO NWs plus PS, or PS only, showed similar level of cytotoxicity against leukemic cell lines. Furthermore, fluorescence microscopy imaging demonstrated that CD123 CAR-T cells labeled with CLIO NW formed rosettes with CD123+ leukemic cells as the non-labeled CAR-T cells, indicating that the CAR-T targeting to tumor cells has maintained after CLIO NW labeling. The in vivo trafficking of the NW labeled CAR-T cells showed the accumulation of CAR-T labeled with NWs primarily in the bone marrow and spleen. CAR-T cells can be magnetically labeled during their production while maintaining functionality using the positively charged iron oxide NWs, which enable the in vivo biodistribution and tracking of CAR-T cells.