A Humanized Animal Model Predicts Clonal Evolution and Therapeutic Vulnerabilities in Myeloproliferative Neoplasms

Evaluating targeted therapies in older patients with TP53-mutated AML

Mutation of thetumor suppressor gene, TP53 (tumor protein 53), occurs in up to 15% of all patients with acute myeloid leukemia (AML) and is enriched within specific clinical subsets, most notably in older adults, and including secondary AML cases arising from preceding myeloproliferative neoplasm (MPN), myelodysplastic syndrome (MDS), patients exposed to prior DNA-damaging, cytotoxic therapies. In all cases, these tumors have remained difficult to effectively treat with conventional therapeutic regimens. Newer approaches fortreatmentofTP53-mutated AML have shifted to interventions that maymodulateTP53 function, target downstream molecular vulnerabilities, target non-p53 dependent molecular pathways, and/or elicit immunogenic responses. This review will describe the basic biology of TP53, the clinical and biological patterns of TP53 within myeloid neoplasms with a focus on elderly AML patients and will summarize newer therapeutic strategies and current clinical trials.

Targeting exhausted cytotoxic T cells through CTLA-4 inhibition promotes elimination of neoplastic cells in human myelofibrosis xenografts

Myeloproliferative neoplasms represent a group of clonal hematopoietic disorders of which myelofibrosis (MF) is the most aggressive. In the context of myeloid neoplasms, there is a growing recognition of the dysregulation of immune response and T-cell function as significant contributors to disease progression and immune evasion. We investigated cytotoxic T-cell exhaustion in MF to restore immune response against malignant cells. Increased expression of inhibitory receptors like CTLA-4 was observed on cytotoxic T cells from MF patients together with a reduced secretion of IFNɣ and TNFɑ. CTLA-4 ligands CD80 and CD86 were increased on MF granulocytes and monocytes highlighting a possible role for myeloid cells in suppressing T-cell activation in MF patients. Unlike healthy donors, the activation of cytotoxic T cells from MF patients was attenuated in the presence of myeloid cells and restored when T cells were cultured alone or treated with anti-CTLA-4. Moreover, anti-CTLA-4 treatment promoted elimination of neoplastic monocytes and granulocytes in a co-culture system with cytotoxic T cells. To test CTLA-4 inhibition in vivo, patient-derived xenografts were generated by transplanting MF CD34+ cells and by infusing homologous T cells in NSGS mice. CTLA-4 blockade reduced human myeloid chimerism and led to T-cell expansion in spleen and bone marrow. Overall, these findings shed light on T-cell dysfunction in MF and suggest that CTLA-4 blockade can boost the cytotoxic T cell-mediated immune response against tumor cells.

Application of omics in the diagnosis, prognosis, and treatment of acute myeloid leukemia

Acute myeloid leukemia (AML) is the most frequent leukemia in adults with a high mortality rate. Current diagnostic criteria and selections of therapeutic strategies are generally based on gene mutations and cytogenetic abnormalities. Chemotherapy, targeted therapies, and hematopoietic stem cell transplantation (HSCT) are the major therapeutic strategies for AML. Two dilemmas in the clinical management of AML are related to its poor prognosis. One is the inaccurate risk stratification at diagnosis, leading to incorrect treatment selections. The other is the frequent resistance to chemotherapy and/or targeted therapies. Genomic features have been the focus of AML studies. However, the DNA-level aberrations do not always predict the expression levels of genes and proteins and the latter is more closely linked to disease phenotypes. With the development of high-throughput sequencing and mass spectrometry technologies, studying downstream effectors including RNA, proteins, and metabolites becomes possible. Transcriptomics can reveal gene expression and regulatory networks, proteomics can discover protein expression and signaling pathways intimately associated with the disease, and metabolomics can reflect precise changes in metabolites during disease progression. Moreover, omics profiling at the single-cell level enables studying cellular components and hierarchies of the AML microenvironment. The abundance of data from different omics layers enables the better risk stratification of AML by identifying prognosis-related biomarkers, and has the prospective application in identifying drug targets, therefore potentially discovering solutions to the two dilemmas. In this review, we summarize the existing AML studies using omics methods, both separately and combined, covering research fields of disease diagnosis, risk stratification, prognosis prediction, chemotherapy, as well as targeted therapy. Finally, we discuss the directions and challenges in the application of multi-omics in precision medicine of AML. Our review may inspire both omics researchers and clinical physicians to study AML from a different angle.

In vivo ablation of NF-κB cascade effectors alleviates disease burden in myeloproliferative neoplasms

ABSTRACT

Hyperactivation of the NF-κB cascade propagates oncogenic signaling and proinflammation, which together augments disease burden in myeloproliferative neoplasms (MPNs). Here, we systematically ablate NF-κB signaling effectors to identify core dependencies using a series of primary samples and syngeneic and patient-derived xenograft (PDX) mouse models. Conditional knockout of Rela attenuated Jak2V617F- and MPLW515L-driven onset of polycythemia vera and myelofibrosis disease hallmarks, respectively. In PDXs, RELA knockout diminished leukemic engraftment and bone marrow fibrosis while extending survival. Knockout of upstream effector Myd88 also alleviated disease burden; conversely, perturbation of negative regulator miR-146a microRNA induced earlier lethality and exacerbated disease. Perturbation of NF-κB effectors further skewed the abundance and distribution of hematopoietic multipotent progenitors. Finally, pharmacological targeting of interleukin-1 receptor-associated kinase 4 (IRAK4) with inhibitor CA-4948 suppressed disease burden and inflammatory cytokines specifically in MPN without inducing toxicity in nondiseased models. These findings highlight vulnerabilities in MPN that are exploitable with emerging therapeutic approaches.

Establishment of a humanized mouse model using steady-state peripheral blood-derived hematopoietic stem and progenitor cells facilitates screening of cancer-targeted T-cell repertoires

Background

Cancer-targeted T-cell receptor T (TCR-T) cells hold promise in treating cancers such as hematological malignancies and breast cancers. However, approaches to obtain cancer-reactive TCR-T cells have been unsuccessful.

Methods

Here, we developed a novel strategy to screen for cancer-targeted TCR-T cells using a special humanized mouse model with person-specific immune fingerprints. Rare steady-state circulating hematopoietic stem and progenitor cells were expanded via three-dimensional culture of steady-state peripheral blood mononuclear cells, and then the expanded cells were applied to establish humanized mice. The human immune system was evaluated according to the kinetics of dendritic cells, monocytes, T-cell subsets, and cytokines. To fully stimulate the immune response and to obtain B-cell precursor NAML-6- and triple-negative breast cancer MDA-MB-231-targeted TCR-T cells, we used the inactivated cells above to treat humanized mice twice a day every 7 days. Then, human T cells were processed for TCR β-chain (TRB) sequencing analysis. After the repertoires had been constructed, features such as the fraction, diversity, and immune signature were investigated.

Results

The results demonstrated an increase in diversity and clonality of T cells after treatment. The preferential usage and features of TRBV, TRBJ, and the V-J combination were also changed. The stress also induced highly clonal expansion. Tumor burden and survival analysis demonstrated that stress induction could significantly inhibit the growth of subsequently transfused live tumor cells and prolong the survival of the humanized mice.

Conclusions

We constructed a personalized humanized mouse model to screen cancer-targeted TCR-T pools. Our platform provides an effective source of cancer-targeted TCR-T cells and allows for the design of patient-specific engineered T cells. It therefore has the potential to greatly benefit cancer treatment.

Generation of complex bone marrow organoids from human induced pluripotent stem cells

The human bone marrow (BM) niche sustains hematopoiesis throughout life. We present a method for generating complex BM-like organoids (BMOs) from human induced pluripotent stem cells (iPSCs). BMOs consist of key cell types that self-organize into spatially defined three-dimensional structures mimicking cellular, structural and molecular characteristics of the hematopoietic microenvironment. Functional properties of BMOs include the presence of an in vivo-like vascular network, the presence of multipotent mesenchymal stem/progenitor cells, the support of neutrophil differentiation and responsiveness to inflammatory stimuli. Single-cell RNA sequencing revealed a heterocellular composition including the presence of a hematopoietic stem/progenitor (HSPC) cluster expressing genes of fetal HSCs. BMO-derived HSPCs also exhibited lymphoid potential and a subset demonstrated transient engraftment potential upon xenotransplantation in mice. We show that the BMOs could enable the modeling of hematopoietic developmental aspects and inborn errors of hematopoiesis, as shown for human VPS45 deficiency. Thus, iPSC-derived BMOs serve as a physiologically relevant in vitro model of the human BM microenvironment to study hematopoietic development and BM diseases.

Altered erythropoiesis via JAK2 and ASXL1 mutations in myeloproliferative neoplasms

Myeloproliferative neoplasms (MPNs) are driven by hyperactivation of JAK-STAT signaling but can demonstrate skewed hematopoiesis upon acquisition of additional somatic mutations. Here, using primary MPN samples and engineered embryonic stem cells, we demonstrate that mutations in JAK2 induced a significant increase in erythroid colony formation, whereas mutations in additional sex combs-like 1 (ASXL1) led to an erythroid colony defect. RNA-sequencing revealed upregulation of protein arginine methyltransferase 6 (PRMT6) induced by mutant ASXL1. Furthermore, genetic perturbation of PRMT6 exacerbated the MPN disease burden, including leukemic engraftment and splenomegaly, in patient-derived xenograft models, highlighting a novel tumor-suppressive function of PRMT6. However, augmented erythroid potential and bone marrow human CD71+ cells following PRMT6 knockdown were reserved only for primary MPN samples harboring ASXL1 mutations. Last, treatment of CD34+ hematopoietic/stem progenitor cells with the PRMT6 inhibitor EPZ020411 induced expression of genes involved in heme metabolism, hemoglobin, and erythropoiesis. These findings highlight interactions between JAK2 and ASXL1 mutations and a unique erythroid regulatory network in the context of mutant ASXL1.

Humanized mouse models: A valuable platform for preclinical evaluation of human cancer

Animal models are routinely employed to assess the treatments for human cancer. However, due to significant differences in genetic backgrounds, traditional animal models are unable to meet bioresearch needs. To overcome this restriction, researchers have generated and optimized immunodeficient mice, and then engrafted human genes, cells, tissues, or organs in mice so that the responses in the model mice could provide a more reliable reference for treatments. As a bridge connecting clinical application and basic research, humanized mice are increasingly used in the preclinical evaluation of cancer treatments, particularly after gene interleukin 2 receptor gamma mutant mice were generated. Human cancer models established in humanized mice support exploration of the mechanism of cancer occurrence and provide an efficient platform for drug screening. However, it is undeniable that the further application of humanized mice still faces multiple challenges. This review summarizes the construction approaches for humanized mice and their existing limitations. We also report the latest applications of humanized mice in preclinical evaluation for the treatment of cancer and point out directions for future optimization of these models.

Patient-derived tumor models: a suitable tool for preclinical studies on esophageal cancer

Esophageal cancer (EC) is the tenth most common cancer worldwide and has high morbidity and mortality. Its main subtypes include esophageal squamous cell carcinoma and esophageal adenocarcinoma, which are usually diagnosed during their advanced stages. The biological defects and inability of preclinical models to summarize completely the etiology of multiple factors, the complexity of the tumor microenvironment, and the genetic heterogeneity of tumors severely limit the clinical treatment of EC. Patient-derived models of EC not only retain the tissue structure, cell morphology, and differentiation characteristics of the original tumor, they also retain tumor heterogeneity. Therefore, compared with other preclinical models, they can better predict the efficacy of candidate drugs, explore novel biomarkers, combine with clinical trials, and effectively improve patient prognosis. This review discusses the methods and animals used to establish patient-derived models and genetically engineered mouse models, especially patient-derived xenograft models. It also discusses their advantages, applications, and limitations as preclinical experimental research tools to provide an important reference for the precise personalized treatment of EC and improve the prognosis of patients.

Progress in building clinically relevant patient-derived tumor xenograft models for cancer research

Patient-derived tumor xenograft (PDX) models, a method involving the surgical extraction of tumor tissues from cancer patients and subsequent transplantation into immunodeficient mice, have emerged as a pivotal approach in translational research, particularly in advancing precision medicine. As the first stage of PDX development, the patient-derived orthotopic xenograft (PDOX) models implant tumor tissue in mice in the corresponding anatomical locations of the patient. The PDOX models have several advantages, including high fidelity to the original tumor, heightened drug sensitivity, and an elevated rate of successful transplantation. However, the PDOX models present significant challenges, requiring advanced surgical techniques and resource-intensive imaging technologies, which limit its application. And then, the humanized mouse models, as well as the zebrafish models, were developed. Humanized mouse models contain a human immune environment resembling the tumor and immune system interplay. The humanized mouse models are a hot topic in PDX model research. Regarding zebrafish patient-derived tumor xenografts (zPDX) and patient-derived organoids (PDO) as promising models for studying cancer and drug discovery, zPDX models are used to transplant tumors into zebrafish as novel personalized medical animal models with the advantage of reducing patient waiting time. PDO models provide a cost-effective approach for drug testing that replicates the in vivo environment and preserves important tumor-related information for patients. The present review highlights the functional characteristics of each new phase of PDX and provides insights into the challenges and prospective developments in this rapidly evolving field.

Updates on accelerated and blast phase myeloproliferative neoplasms: Are we making progress?

Management approaches for accelerated and blast phase myeloproliferative neoplasms remain challenging for clinicians and patients alike. Despite many therapeutic advances, outcomes for those patients who are not allogeneic haematopoietic cell transplant eligible remain, in general, very poor. Estimated survival rates for such blast phase patients is frequently reported as less than 6 months. No specific immunological, genomic or clinicopathological signature currently exists that accurately predicts the risk and timing of transformation, which frequently induces a high degree of anxiety among patients and clinicians alike. Within this review article, we provide an up-to-date summary of current understanding of the underlying pathogenesis of accelerated and blast phase disease and discuss current therapeutic approaches and realistic outcomes. Finally, we discuss how the horizon may look with the introduction of more novel agents into the clinical arena.

Single-cell multi-omics identifies chronic inflammation as a driver of TP53-mutant leukemic evolution

Understanding the genetic and nongenetic determinants of tumor protein 53 (TP53)-mutation-driven clonal evolution and subsequent transformation is a crucial step toward the design of rational therapeutic strategies. Here we carry out allelic resolution single-cell multi-omic analysis of hematopoietic stem/progenitor cells (HSPCs) from patients with a myeloproliferative neoplasm who transform to TP53-mutant secondary acute myeloid leukemia (sAML). All patients showed dominant TP53 'multihit' HSPC clones at transformation, with a leukemia stem cell transcriptional signature strongly predictive of adverse outcomes in independent cohorts, across both TP53-mutant and wild-type (WT) AML. Through analysis of serial samples, antecedent TP53-heterozygous clones and in vivo perturbations, we demonstrate a hitherto unrecognized effect of chronic inflammation, which suppressed TP53 WT HSPCs while enhancing the fitness advantage of TP53-mutant cells and promoted genetic evolution. Our findings will facilitate the development of risk-stratification, early detection and treatment strategies for TP53-mutant leukemia, and are of broad relevance to other cancer types.

Next generation organoid engineering to replace animals in cancer drug testing

Cancer therapies have several clinical challenges associated with them, namely treatment toxicity, treatment resistance and relapse. Due to factors ranging from patient profiles to the tumour microenvironment (TME), there are several hurdles to overcome in developing effective treatments that have low toxicity that can mitigate emergence of resistance and occurrence of relapse. De novo cancer development has the highest drug attrition rates with only 1 in 10,000 preclinical candidates reaching the market. To alleviate this high attrition rate, more mimetic and sustainable preclinical models that can capture the disease biology as in the patient, are required. Organoids and next generation 3D tissue engineering is an emerging area that aims to address this problem. Advancement of three-dimensional (3D) in vitro cultures into complex organoid models incorporating multiple cell types alongside acellular aspects of tissue microenvironments can provide a system for therapeutic testing. Development of microfluidic technologies have furthermore increased the biomimetic nature of these models. Additionally, 3D bio-printing facilitates generation of tractable ex vivo models in a controlled, scalable and reproducible manner. In this review we highlight some of the traditional preclinical models used in cancer drug testing and debate how next generation organoids are being used to replace not only animal models, but also some of the more elementary in vitro approaches, such as cell lines. Examples of applications of the various models will be appraised alongside the future challenges that still need to be overcome.

Comprehensive profiling of clinical JAK inhibitors in myeloproliferative neoplasms

Small molecule inhibitors targeting JAK2 provide symptomatic benefits for myeloproliferative neoplasm (MPN) patients and are among first-line therapeutic agents. However, despite all having potent capacity to suppress JAK-STAT signaling, they demonstrate distinct clinical profiles suggesting contributory effects in targeting other ancillary pathways. Here, we performed comprehensive profiling on four JAK2 inhibitors either FDA-approved (ruxolitinib, fedratinib, and pacritinib) or undergoing phase 3 studies (momelotinib) to better outline mechanistic and therapeutic efficacy. Across JAK2-mutant in vitro models, all four inhibitors demonstrated similar anti-proliferative phenotypes, whereas pacritinib yielded greatest potency on suppressing colony formation in primary samples, while momelotinib exhibited unique erythroid colony formation sparing. All inhibitors reduced leukemic engraftment, disease burden, and extended survival across patient-derived xenograft (PDX) models, with strongest effects elicited by pacritinib. Through RNA-sequencing and gene set enrichment analyses, differential suppressive degrees of JAK-STAT and inflammatory response signatures were revealed, which we validated with signaling and cytokine suspension mass cytometry across primary samples. Lastly, we assessed the capacity of JAK2 inhibitors to modulate iron regulation, uncovering potent suppression of hepcidin and SMAD signaling by pacritinib. These comparative findings provide insight into the differential and beneficial effects of ancillary targeting beyond JAK2 and may help guide the use of specific inhibitors in personalized therapy.

Phenotypic characterization of disease-initiating stem cells in JAK2- or CALR-mutated myeloproliferative neoplasms

Myeloproliferative neoplasms (MPN) are characterized by uncontrolled expansion of myeloid cells, disease-related mutations in certain driver-genes including JAK2, CALR, and MPL, and a substantial risk to progress to secondary acute myeloid leukemia (sAML). Although behaving as stem cell neoplasms, little is known about disease-initiating stem cells in MPN. We established the phenotype of putative CD34+ /CD38- stem cells and CD34+ /CD38+ progenitor cells in MPN. A total of 111 patients with MPN suffering from polycythemia vera, essential thrombocythemia, or primary myelofibrosis (PMF) were examined. In almost all patients tested, CD34+ /CD38- stem cells expressed CD33, CD44, CD47, CD52, CD97, CD99, CD105, CD117, CD123, CD133, CD184, CD243, and CD274 (PD-L1). In patients with PMF, MPN stem cells often expressed CD25 and sometimes also CD26 in an aberrant manner. MPN stem cells did not exhibit substantial amounts of CD90, CD273 (PD-L2), CD279 (PD-1), CD366 (TIM-3), CD371 (CLL-1), or IL-1RAP. The phenotype of CD34+ /CD38- stem cells did not change profoundly during progression to sAML. The disease-initiating capacity of putative MPN stem cells was confirmed in NSGS mice. Whereas CD34+ /CD38- MPN cells engrafted in NSGS mice, no substantial engraftment was produced by CD34+ /CD38+ or CD34- cells. The JAK2-targeting drug fedratinib and the BRD4 degrader dBET6 induced apoptosis and suppressed proliferation in MPN stem cells. Together, MPN stem cells display a unique phenotype, including cytokine receptors, immune checkpoint molecules, and other clinically relevant target antigens. Phenotypic characterization of neoplastic stem cells in MPN and sAML should facilitate their enrichment and the development of stem cell-eradicating (curative) therapies.

Human gene-engineered calreticulin mutant stem cells recapitulate MPN hallmarks and identify targetable vulnerabilities

Calreticulin (CALR) mutations present the main oncogenic drivers in JAK2 wildtype (WT) myeloproliferative neoplasms (MPN), including essential thrombocythemia and myelofibrosis, where mutant (MUT) CALR is increasingly recognized as a suitable mutation-specific drug target. However, our current understanding of its mechanism-of-action is derived from mouse models or immortalized cell lines, where cross-species differences, ectopic over-expression and lack of disease penetrance are hampering translational research. Here, we describe the first human gene-engineered model of CALR MUT MPN using a CRISPR/Cas9 and adeno-associated viral vector-mediated knock-in strategy in primary human hematopoietic stem and progenitor cells (HSPCs) to establish a reproducible and trackable phenotype in vitro and in xenografted mice. Our humanized model recapitulates many disease hallmarks: thrombopoietin-independent megakaryopoiesis, myeloid-lineage skewing, splenomegaly, bone marrow fibrosis, and expansion of megakaryocyte-primed CD41⁺ progenitors. Strikingly, introduction of CALR mutations enforced early reprogramming of human HSPCs and the induction of an endoplasmic reticulum stress response. The observed compensatory upregulation of chaperones revealed novel mutation-specific vulnerabilities with preferential sensitivity of CALR mutant cells to inhibition of the BiP chaperone and the proteasome. Overall, our humanized model improves purely murine models and provides a readily usable basis for testing of novel therapeutic strategies in a human setting.

Human Bone Marrow Organoids for Disease Modeling, Discovery, and Validation of Therapeutic Targets in Hematologic Malignancies

A lack of models that recapitulate the complexity of human bone marrow has hampered mechanistic studies of normal and malignant hematopoiesis and the validation of novel therapies. Here, we describe a step-wise, directed-differentiation protocol in which organoids are generated from induced pluripotent stem cells committed to mesenchymal, endothelial, and hematopoietic lineages. These 3D structures capture key features of human bone marrow-stroma, lumen-forming sinusoids, and myeloid cells including proplatelet-forming megakaryocytes. The organoids supported the engraftment and survival of cells from patients with blood malignancies, including cancer types notoriously difficult to maintain ex vivo. Fibrosis of the organoid occurred following TGFβ stimulation and engraftment with myelofibrosis but not healthy donor-derived cells, validating this platform as a powerful tool for studies of malignant cells and their interactions within a human bone marrow-like milieu. This enabling technology is likely to accelerate the discovery and prioritization of novel targets for bone marrow disorders and blood cancers.

SIGNIFICANCE

We present a human bone marrow organoid that supports the growth of primary cells from patients with myeloid and lymphoid blood cancers. This model allows for mechanistic studies of blood cancers in the context of their microenvironment and provides a much-needed ex vivo tool for the prioritization of new therapeutics. See related commentary by Derecka and Crispino, p. 263. This article is highlighted in the In This Issue feature, p. 247.

DUSP6 mediates resistance to JAK2 inhibition and drives leukemic progression

Myeloproliferative neoplasms (MPNs) exhibit a propensity for transformation to secondary acute myeloid leukemia (sAML), for which the underlying mechanisms remain poorly understood, resulting in limited treatment options and dismal clinical outcomes. Here, we performed single-cell RNA sequencing on serial MPN and sAML patient stem and progenitor cells, identifying aberrantly increased expression of DUSP6 underlying disease transformation. Pharmacologic dual-specificity phosphatase (DUSP)6 targeting led to inhibition of S6 and Janus kinase (JAK)-signal transducer and activator of transcription (STAT) signaling while also reducing inflammatory cytokine production. DUSP6 perturbation further inhibited ribosomal S6 kinase (RSK)1, which we identified as a second indispensable candidate associated with poor clinical outcome. Ectopic expression of DUSP6 mediated JAK2-inhibitor resistance and exacerbated disease severity in patient-derived xenograft (PDX) models. Contrastingly, DUSP6 inhibition potently suppressed disease development across Jak2V617F and MPLW515L MPN mouse models and sAML PDXs without inducing toxicity in healthy controls. These findings underscore DUSP6 in driving disease transformation and highlight the DUSP6-RSK1 axis as a vulnerable, druggable pathway in myeloid malignancies.

JAK2 inhibitor persistence in MPN: uncovering a central role of ERK activation

The Philadelphia chromosome negative myeloproliferative neoplasms, including polycythemia vera, essential thrombocytosis, and myelofibrosis, are driven by hyper activation of the JAK2 tyrosine kinase, the result of mutations in three MPN driving genes: JAK2, MPL, and CALR. While the anti-inflammatory effects of JAK2 inhibitors can provide improved quality of life for many MPN patients, the upfront and persistent survival of disease-driving cells in MPN patients undergoing JAK2 inhibitor therapy thwarts potential for remission. Early studies indicated JAK2 inhibitor therapy induces heterodimeric complex formation of JAK2 with other JAK family members leading to sustained JAK2-dependent signaling. Recent work has described novel cell intrinsic details as well as cell extrinsic mechanisms that may contribute to why JAK2 inhibition may be ineffective at targeting MPN driving cells. Diverse experimental strategies aimed at uncovering mechanistic details that contribute to JAK2 inhibitor persistence have each highlighted the role of MEK/ERK activation. These approaches include, among others, phosphoproteomic analyses of JAK2 signaling as well as detailed assessment of JAK2 inhibition in mouse models of MPN. In this focused review, we highlight these and other studies that collectively suggest targeting MEK/ERK in combination with JAK2 inhibition has the potential to improve the efficacy of JAK2 inhibitors in MPN patients. As MPN patients patiently wait for improved therapies, such studies should further strengthen optimism that pre-clinical research is continuing to uncover mechanistic insights regarding the ineffectiveness of JAK2 inhibitors, which may lead to development of improved therapeutic strategies.

The Hematology of Tomorrow Is Here-Preclinical Models Are Not: Cell Therapy for Hematological Malignancies

Simple Summary

Cell therapy is revolutionizing the prospect of deadly hematological malignancies such as high-risk acute myeloid leukemia. Stem cell therapy of allogeneic source from compatible human leukocyte antigen donor has exceptional success promoting durable remissions, but the rate of relapse is currently still high and there is transplant-related mortality. This review presents the current knowledge on the clinical use of mesenchymal stromal cells to improve outcomes in hematopoietic stem cell transplants. As an alternative or adjuvant approach to prevent relapse, we summarize the status of the promising forms of cellular immunotherapy aimed at targeting not only the bulk but also the cells of origin of leukemia. Finally, we discuss the available in vivo models for disease modelling and treatment efficacy prediction in these contexts.

Abstract

The purpose of this review is to present the current knowledge on the clinical use of several forms of cell therapy in hematological malignancies and the preclinical models available for their study. In the context of allogeneic hematopoietic stem cell transplants, mesenchymal stromal cells are pursued to help stem cell engraftment and expansion, and control graft versus host disease. We further summarize the status of promising forms of cellular immunotherapy including CAR T cell and CAR NK cell therapy aimed at eradicating the cells of origin of leukemia, i.e., leukemia stem cells. Updates on other forms of cellular immunotherapy, such as NK cells, CIK cells and CAR CIK cells, show encouraging results in AML. The considerations in available in vivo models for disease modelling and treatment efficacy prediction are discussed, with a particular focus on their strengths and weaknesses for the study of healthy and diseased hematopoietic stem cell reconstitution, graft versus host disease and immunotherapy. Despite current limitations, cell therapy is a rapidly evolving field that holds the promise of improved cure rates, soon. As a result, we may be witnessing the birth of the hematology of tomorrow. To further support its development, improved preclinical models including humanized microenvironments in mice are urgently needed.

Culturing patient-derived malignant hematopoietic stem cells in engineered and fully humanized 3D niches

Human malignant hematopoietic stem and progenitor cells (HSPCs) reside in bone marrow (BM) niches, which remain challenging to explore due to limited in vivo accessibility and constraints with humanized animal models. Several in vitro systems have been established to culture patient-derived HSPCs in specific microenvironments, but they do not fully recapitulate the complex features of native bone marrow. Our group previously reported that human osteoblastic BM niches (O-N), engineered by culturing mesenchymal stromal cells within three-dimensional (3D) porous scaffolds under perfusion flow in a bioreactor system, are capable of maintaining, expanding, and functionally regulating healthy human cord blood-derived HSPCs. Here, we first demonstrate that this 3D O-N can sustain malignant CD34⁺ cells from acute myeloid leukemia (AML) and myeloproliferative neoplasm patients for up to 3 wk. Human malignant cells distributed in the bioreactor system mimicking the spatial distribution found in native BM tissue, where most HSPCs remain linked to the niches and mature cells are released to the circulation. Using human adipose tissue-derived stromal vascular fraction cells, we then generated a stromal-vascular niche and demonstrated that O-N and stromal-vascular niche differentially regulate leukemic UCSD-AML1 cell expansion, immunophenotype, and response to chemotherapy. The developed system offers a unique platform to investigate human leukemogenesis and response to drugs in customized environments, mimicking defined features of native hematopoietic niches and compatible with the establishment of personalized settings.