Polycomb proteins are classical regulators of stem cell self-renewal and cell lineage commitment and are frequently deregulated in cancer. Here, we find that the non-canonical PRC1.1 complex, as identified by mass-spectrometry-based proteomics, is critically important for human leukemic stem cells. Downmodulation of PRC1.1 complex members, like the DNA-binding subunit KDM2B, strongly reduces cell proliferation in vitro and delays or even abrogates leukemogenesis in vivo in humanized xenograft models. PRC1.1 components are significantly overexpressed in primary AML CD34(+) cells. Besides a set of genes that is targeted by PRC1 and PRC2, ChIP-seq studies show that PRC1.1 also binds a distinct set of genes that are devoid of H3K27me3, suggesting a gene-regulatory role independent of PRC2. This set encompasses genes involved in metabolism, which have transcriptionally active chromatin profiles. These data indicate that PRC1.1 controls specific genes involved in unique cell biological processes required for leukemic cell viability.

Mice xenotransplanted with human cells and/or expressing human gene products (also known as “humanized mice”) recapitulate the human evolutionary specialization and diversity of genotypic and phenotypic traits. These models can provide a relevant in vivo context for understanding of human‐specific physiology and pathologies. Humanized mice have advanced toward mainstream preclinical models and are now at the forefront of biomedical research. Here, we considered innovations and challenges regarding the reconstitution of human immunity and human tissues, modeling of human infections and cancer, and the use of humanized mice for testing drugs or regenerative therapy products. As the number of publications exploring different facets of humanized mouse models has steadily increased in past years, it is becoming evident that standardized reporting is needed in the field. Therefore, an international community‐driven resource called “Minimal Information for Standardization of Humanized Mice” (MISHUM) has been created for the purpose of enhancing rigor and reproducibility of studies in the field. Within MISHUM, we propose comprehensive guidelines for reporting critical information generated using humanized mice.

It is increasingly becoming clear that cancers are a symbiosis of diverse cell types and tumor clones. Combined single-cell RNA sequencing, flow cytometry, and immunohistochemistry studies of the innate immune compartment in the bone marrow of patients with acute myeloid leukemia (AML) reveal a shift toward a tumor-supportive M2-polarized macrophage landscape with an altered transcriptional program, with enhanced fatty acid oxidation and NAD ⁺ generation. Functionally, these AML-associated macrophages display decreased phagocytic activity and intra–bone marrow coinjection of M2 macrophages together with leukemic blasts strongly enhances in vivo transformation potential. A 2-day in vitro exposure to M2 macrophages results in the accumulation of CALR ^low leukemic blast cells, which are now protected against phagocytosis. Moreover, M2-exposed “trained” leukemic blasts display increased mitochondrial metabolism, in part mediated via mitochondrial transfer. Our study provides insight into the mechanisms by which the immune landscape contributes to aggressive leukemia development and provides alternatives for targeting strategies aimed at the tumor microenvironment.

Interactions between hematopoietic stem cells and their niche are mediated by proteins within the plasma membrane (PM) and changes in these interactions might alter hematopoietic stem cell fate and ultimately result in acute myeloid leukemia (AML). Here, using nano-LC/MS/MS, we set out to analyze the PM profile of two leukemia patient samples. We identified 867 and 610 unique CD34⁺ PM (-associated) proteins in these AML samples respectively, including previously described proteins such as CD47, CD44, CD135, CD96, and ITGA5, but also novel ones like CD82, CD97, CD99, PTH2R, ESAM, MET, and ITGA6. Further validation by flow cytometry and functional studies indicated that long-term self-renewing leukemic stem cells reside within the CD34⁺/ITGA6⁺ fraction, at least in a subset of AML cases. Furthermore, we combined proteomics with transcriptomics approaches using a large panel of AML CD34⁺ (n = 60) and normal bone marrow CD34⁺ (n = 40) samples. Thus, we identified eight subgroups of AML patients based on their specific PM expression profile. GSEA analysis revealed that these eight subgroups are enriched for specific cellular processes.

Here we have explored whether inhibition of autophagy can be used as a treatment strategy for acute myeloid leukemia (AML). Steady-state autophagy was measured in leukemic cell lines and primary human CD34⁺ AML cells with a large variability in basal autophagy between AMLs observed. The autophagy flux was higher in AMLs classified as poor risk, which are frequently associated with TP53 mutations (TP53^mut), compared with favorable- and intermediate-risk AMLs. In addition, the higher flux was associated with a higher expression level of several autophagy genes, but was not affected by alterations in p53 expression by knocking down p53 or overexpression of wild-type p53 or p53^R273H. AML CD34⁺ cells were more sensitive to the autophagy inhibitor hydroxychloroquine (HCQ) than normal bone marrow CD34⁺ cells. Similar, inhibition of autophagy by knockdown of ATG5 or ATG7 triggered apoptosis, which coincided with increased expression of p53. In contrast to wild-type p53 AML (TP53^wt), HCQ treatment did not trigger a BAX and PUMA-dependent apoptotic response in AMLs harboring TP53^mut. To further characterize autophagy in the leukemic stem cell-enriched cell fraction AML CD34⁺ cells were separated into ROS^low and ROS^high subfractions. The immature AML CD34⁺-enriched ROS^low cells maintained higher basal autophagy and showed reduced survival upon HCQ treatment compared with ROS^high cells. Finally, knockdown of ATG5 inhibits in vivo maintenance of AML CD34⁺ cells in NSG mice. These results indicate that targeting autophagy might provide new therapeutic options for treatment of AML since it affects the immature AML subfraction.