Juvenile myelomonocytic leukemia (JMML) is a rare and aggressive stem cell disease of early childhood. RAS activation constitutes the core component of oncogenic signaling. In addition, leukemic blasts in one-fourth of JMML patients present with monosomy 7, and more than half of patients show elevated age-adjusted fetal hemoglobin (HbF) levels. Hematopoietic stem cell transplantation is the current standard of care and results in an event-free survival rate of 50% to 60%, indicating that novel molecular-driven therapeutic options are urgently needed. Using gene expression profiling in a series of 82 patient samples, we aimed at understanding the molecular biology behind JMML and identified a previously unrecognized molecular subgroup characterized by high LIN28B expression. LIN28B overexpression was significantly correlated with higher HbF levels, whereas patients with monosomy 7 seldom showed enhanced LIN28B expression. This finding gives a biological explanation of why patients with monosomy 7 are rarely diagnosed with high age-adjusted HbF levels. In addition, this new fetal-like JMML subgroup presented with reduced levels of most members of the let-7 microRNA family and showed characteristic overexpression of genes involved in fetal hematopoiesis and stem cell self-renewal. Lastly, high LIN28B expression was associated with poor clinical outcome in our JMML patient series but was not independent from other prognostic factors such as age and age-adjusted HbF levels. In conclusion, we identified elevated LIN28B expression as a hallmark of a novel fetal-like subgroup in JMML.

Recently our group and others have identified DDX41 mutations both as germ line and acquired somatic mutations in families with multiple cases of late onset myelodysplastic syndrome (MDS) and/or acute myeloid leukemia (AML), suggesting that DDX41 acts as a tumor suppressor. To determine whether novel DDX41 mutations could be identified in families with additional types of hematologic malignancies, our group screened two cohorts of families with a diverse range of hematologic malignancy subtypes. Among 289 families, we identified nine (3%) with DDX41 mutations. As previously observed, MDS and AML were the most common malignancies, often of the erythroblastic subtype, and 1 family displayed early-onset follicular lymphoma. Five novel mutations were identified, including missense mutations within important functional domains and start-loss and splicing mutations predicted to result in truncated proteins. We also show that most asymptomatic mutation carriers have normal blood counts until malignancy develops. This study expands both the mutation and phenotypic spectra observed in families with germ line DDX41 mutations. With an increasing number of both inherited and acquired mutations in this gene being identified, further study of how DDX41 disruption leads to hematologic malignancies is critical.

Patients with relapsed acute myeloid leukemia (AML) have limited therapeutic options. Vesicular stomatitis virus (VSV)-interferon β (IFNβ)-sodium iodide symporter (NIS) is an oncolytic VSV encoding IFNβ and the NIS reporter. Syngeneic AML C1498 tumors responded to IV therapy with VSV-murine IFNβ (mIFNβ)-NIS in a dose-dependent manner. Imaging for NIS expression showed robust virus infection within the tumors. Virus infection did not increase programmed death ligand 1 (PD-L1) on tumor cells. Combining VSV-mIFNβ-NIS with anti-PD-L1 antibody (Ab) therapy enhanced antitumor activity compared with treatment with virus alone or Ab alone; this enhancement was not significant at higher VSV-mIFNβ-NIS doses. Systemic VSV therapy reduced systemic C1498-green fluorescent protein (GFP) tumor burden in the blood, bone marrow, spleen, and liver of mice with AML. Combination VSV-mIFNβ-NIS and anti-PD-L1 Ab therapy significantly enhanced the survival of these mice with no evidence of toxicity, compared with isotype control, anti-PD-L1, or virus alone. There was an increase in tumor-infiltrating CD4 and CD8 cells. Single-agent VSV-mIFNβ-NIS virotherapy induced both VSV-specific and GFP-specific CD8 T cells as determined by IFN-γ enzyme-linked immunospot, pentamer, and intracellular IFN-γ staining assays. Both of these responses were further enhanced by addition of anti-PD-L1 Ab. Depletion of CD8 or natural killer cells, but not CD4 cells, resulted in loss of antitumor activity in the VSV/anti-PD-L1 group. Clinical samples from chronic myelomonocytic leukemia and acute myelomonocytic leukemia appear to be especially susceptible to VSV. Overall, our studies show that oncolytic virotherapy combined with immune checkpoint blockade is a promising approach to AML therapy.