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The past two decades have witnessed significant strides in leukemia therapies through approval of therapeutic inhibitors targeting oncogene-driving dysregulated tyrosine kinase activities and key epigenetic and apoptosis regulators. Although these drugs have brought about complete remission in the majority of patients, many patients face relapse or have refractory disease. The main factor contributing to relapse is the presence of a small subpopulation of dormant drug-resistant leukemia cells that possess stem cell features (termed as leukemia stem cells or LSCs). Thus, overcoming drug resistance and targeting LSCs remain major challenges for curative treatment of human leukemia. Chronic myeloid leukemia (CML) is a good example, with rare, propagating LSCs and drug-resistant cells that cannot be eradicated by BCR-ABL-directed tyrosine kinase inhibitor (TKI) monotherapy and that are responsible for disease relapse/progression. Therefore, it is imperative to identify key players in regulating BCR-ABL1-dependent and independent drug-resistance mechanisms, and their key pathways, so that CML LSCs can be selectively targeted or sensitized to TKIs. Here, we describe several easily adaptable gene knockdown approaches in CD34+ CML stem/progenitor cells that can be used to investigate the biological properties of LSCs and molecular effects of genes of interest (GOI), which can be further explored as therapeutic modalities against LSCs in the context of human leukemia.

We report that SHIP(-/-) mice, compared to SHIP(+/+) mice, are Th2 skewed with elevated serum IgE and twice as many splenic CD4(+) Th2 cells that, when stimulated with anti-CD3, produce more IL-4 and less IFN-$\gamma$. Exploring the reason for this Th2 skewing, we found that freshly isolated SHIP(-/-) splenic and bone marrow basophils are present in elevated numbers and secrete far more IL-4 in response to IL-3 or to Fc$\epsilon$RI stimulation than do WT basophils. These SHIP(-/-) basophils markedly skew wild-type macrophage colony stimulating factor-derived macrophages toward an M2 phenotype, stimulate OT-II CD4(+) Th cells to differentiate into Th2 cells, and trigger SHIP(+/+) B cells to become IgE-producing cells. All these effects are completely abrogated with neutralizing anti-IL-4 Ab. Exploring the cell signaling pathways responsible for hyperproduction of IL-4 by SHIP(-/-) basophils, we found that IL-3-induced activation of the PI3K pathway is significantly enhanced and that PI3K inhibitors, especially a p110$\alpha$ inhibitor, dramatically suppresses IL-4 production from these cells. In vivo studies, in which basophils were depleted from mast cell-deficient SHIP(+/+) and SHIP(-/-) mice, confirmed the central role that basophils play in the Th2 skewing of naive SHIP-deficient mice. Taken together, these studies demonstrate that SHIP is a potent negative regulator of IL-4 production from basophils and thus may be a novel therapeutic target for Th1- and Th2-related diseases.