Chronic Myelomonocytic Leukemia (CMML) Cell Models for Research

Chronic Myelomonocytic Leukemia (CMML) is a rare but aggressive hematological malignancy classified as a myelodysplastic/myeloproliferative neoplasm (MDS/MPN) by the World Health Organization (WHO). The global incidence is estimated at 0.3-0.5 per 100,000 person-years, with a median age at diagnosis of 70-75 years (WHO 2022). Risk factors include advanced age, male sex, and prior exposure to chemotherapy or radiation. The 5-year overall survival is approximately 20-30% (NCI SEER data), with transformation to acute myeloid leukemia (AML) occurring in 15-30% of patients within 3-5 years. Prognosis is stratified by the CMML Prognostic Scoring System (CPSS), which considers blast percentage, white blood cell count, hemoglobin, and platelet counts.

CMML is an ideal model for studying the intersection of myelodysplasia and myeloproliferation. Its unique biology—chronic inflammation, aberrant splicing, and epigenetic dysregulation—offers insights into clonal hematopoiesis and leukemic transformation. Public datasets from TCGA and COSMIC provide comprehensive genomic profiles, yet many mechanistic questions remain unanswered, such as the cooperative effects of driver mutations and the role of the bone marrow microenvironment. Gene-edited cell models enable controlled dissection of these pathways, accelerating target validation and drug development.

CMML pathogenesis is driven by mutations in epigenetic regulators, splicing factors, and signaling genes. The key pathways include:

• • Epigenetic dysregulation: Mutations in TET2, ASXL1, and IDH1/2 lead to aberrant DNA methylation and histone modifications, promoting clonal expansion.
• • RNA splicing: Mutations in SRSF2, SF3B1, and ZRSR2 cause mis-splicing of genes involved in cell cycle and apoptosis.
• • RAS/MAPK signaling: Mutations in NRAS, KRAS, and CBL activate the MAPK pathway, enhancing proliferation.
• • JAK-STAT signaling: Mutations in JAK2 and MPL (less common) drive myeloproliferation.

These pathways often co-occur, leading to a complex mutational landscape.

Data from TCGA (LAML cohort) and COSMIC (CMML-specific studies).

The signaling networks deregulated in CMML include:

• • MAPK/ERK pathway: Constitutive activation via RAS mutations or CBL loss, leading to increased proliferation.
• • PI3K/AKT/mTOR: Upstream of RAS, often hyperactivated, promoting survival.
• • JAK-STAT: Mutations in JAK2 (V617F) or MPL lead to cytokine-independent signaling.
• • NF-κB: Chronic inflammation activates this pathway, contributing to myelomonocytic expansion.
• • Wnt/β-catenin: Aberrant activation in leukemic stem cells, promoting self-renewal.

Key nodes: NRAS, KRAS, BRAF, CBL, JAK2, STAT5, PI3K, AKT, MTOR.

Organoid models from CMML patient bone marrow are emerging, offering 3D culture systems that preserve the microenvironment and allow drug testing. However, they are less established than cell lines.

• • Patient-derived xenografts (PDX): Immunodeficient mice (NSG) engrafted with CMML patient cells, preserving the mutational landscape.
• • Genetically engineered mouse models (GEMM): Conditional knock-in of Tet2, Srsf2, or Asxl1 mutations, often combined with NRAS G12D, to recapitulate CMML-like disease.
• • Induced models: CRISPR-mediated gene editing in mouse hematopoietic stem cells followed by transplantation, allowing rapid modeling of specific mutations.

CRISPR-based gene editing enables the creation of isogenic cell lines with precise knockouts or knock-ins of CMML-relevant mutations. For example:

• • TET2 knockout: Loss-of-function in hematopoietic cell lines (e.g., THP-1) to study DNA methylation changes.
• • SRSF2 P95H knock-in: Mimics the hotspot mutation to investigate splicing defects.
• • NRAS G12D knock-in: Constitutive MAPK activation in isogenic backgrounds.

These models are commercially available from various sources, sequence-verified, and validated for functional studies. They provide a controlled system to dissect mutation-specific effects, screen drugs, and identify synthetic lethal interactions, accelerating translational research.

Knockout and knock-in lines are used to validate the role of genes in CMML pathogenesis. For example, TET2 knockout in THP-1 cells leads to increased self-renewal and altered differentiation, confirming its tumor suppressor role. Similarly, SRSF2 P95H knock-in in K562 cells induces splicing changes that affect apoptosis regulators, linking the mutation to disease phenotype.

Isogenic pairs (wild-type vs. mutant) are ideal for high-throughput screening. For instance, NRAS G12D knock-in cells show increased sensitivity to MEK inhibitors, while TET2 knockout cells are resistant to azacitidine, providing a platform to test combination therapies. Resistance can be modeled by prolonged drug exposure and subsequent genomic analysis.

CRISPR synthetic lethality screens using gene-edited cells identify vulnerabilities specific to CMML mutations. For example, TET2-deficient cells are sensitive to inhibitors of the DNA damage response, suggesting biomarkers for patient stratification. Such screens also uncover novel therapeutic targets.