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Chimeric antigen receptor (CAR) T-cell therapy has had limited success in early-phase clinical studies for solid tumors. Lack of efficacy is most likely multifactorial, including a limited array of targetable antigens. We reasoned that targeting the cancer-specific extra domain B (EDB) splice variant of fibronectin might overcome this limitation because it is abundantly secreted by cancer cells and adheres to their cell surface. In vitro, EDB-CAR T cells recognized and killed EDB-positive tumor cells. In vivo, 1 × 106 EDB-CAR T cells had potent antitumor activity in both subcutaneous and systemic tumor xenograft models, resulting in a significant survival advantage in comparison with control mice. EDB-CAR T cells also targeted the tumor vasculature, as judged by IHC and imaging, and their antivascular activity was dependent on the secretion of EDB by tumor cells. Thus, targeting tumor-specific splice variants such as EDB with CAR T cells is feasible and has the potential to improve the efficacy of CAR T-cell therapy.

Cytokine storm syndromes (CSS) are severe hyperinflammatory conditions characterized by excessive immune system activation leading to organ damage and death. Hemophagocytic lymphohistiocytosis (HLH), a disease often associated with inherited defects in cell-mediated cytotoxicity, serves as a prototypical CSS for which the 5-year survival is only 60%. Frontline therapy for HLH consists of the glucocorticoid dexamethasone (DEX) and the chemotherapeutic agent etoposide. Many patients, however, are refractory to this treatment or relapse after an initial response. Notably, many cytokines that are elevated in HLH activate the JAK/STAT pathway, and the JAK1/2 inhibitor ruxolitinib (RUX) has shown efficacy in murine HLH models and humans with refractory disease. We recently reported that cytokine-induced JAK/STAT signaling mediates DEX resistance in T cell acute lymphoblastic leukemia (T-ALL) cells, and that this could be effectively reversed by RUX. On the basis of these findings, we hypothesized that cytokine-mediated JAK/STAT signaling might similarly contribute to DEX resistance in HLH, and that RUX treatment would overcome this phenomenon. Using ex vivo assays, a murine model of HLH, and primary patient samples, we demonstrate that the hypercytokinemia of HLH reduces the apoptotic potential of CD8 T cells leading to relative DEX resistance. Upon exposure to RUX, this apoptotic potential is restored, thereby sensitizing CD8 T cells to DEX-induced apoptosis in vitro and significantly reducing tissue immunopathology and HLH disease manifestations in vivo. Our findings provide rationale for combining DEX and RUX to enhance the lymphotoxic effects of DEX and thus improve the outcomes for patients with HLH and related CSS.

Respiratory syncytial virus (RSV)-induced immunopathogenesis and disease severity in neonatal mice and human infants have been related to elevated pulmonary IL-33. Thus, targeting IL-33 has been suggested as a potential therapy for respiratory viral infections. Yet, the regulatory mechanisms on IL-33 during early life remain unclear. Here, using a neonatal mouse model of RSV, we demonstrate that IL-1β positively regulates but is not required for RSV-induced expression of pulmonary IL-33 in neonatal mice early after the initial infection. Exogenous IL-1β upregulates RSV-induced IL-33 expression by promoting the proliferation of IL-33(+) lung epithelial stem/progenitor cells. These cells are exclusively detected in RSV-infected neonatal rather than adult mice, partially explaining the IL-1β–independent IL-33 expression in RSV-infected adult mice. Furthermore, IL-1β aggravates IL-33–mediated T-helper cell type 2–biased immunopathogenesis upon reinfection. Collectively, our study demonstrates that IL-1β exacerbates IL-33–mediated RSV immunopathogenesis by promoting the proliferation of IL-33(+) epithelial stem/progenitor cells in early life.

Spatial transcriptomics technologies have recently emerged as a powerful tool for measuring spatially resolved gene expression directly in tissues sections, revealing cell types and their dysfunction in unprecedented detail. However, spatial transcriptomics technologies are limited in their ability to separate transcriptionally similar cell types and can suffer further difficulties identifying cell types in slide regions where transcript capture is low. Here, we describe a conceptually novel methodology that can computationally integrate spatial transcriptomics data with cell-type-informative paired tissue images, obtained from, for example, the reverse side of the same tissue section, to improve inferences of tissue cell type composition in spatial transcriptomics data. The underlying statistical approach is generalizable to any spatial transcriptomics protocol where informative paired tissue images can be obtained. We demonstrate a use case leveraging cell-type-specific immunofluorescence markers obtained on mouse brain tissue sections and a use case for leveraging the output of AI annotated H&E tissue images, which we used to markedly improve the identification of clinically relevant immune cell infiltration in breast cancer tissue. Thus, combining spatial transcriptomics data with paired tissue images has the potential to improve the identification of cell types and hence to improve the applications of spatial transcriptomics that rely on accurate cell type identification.

The outcome for metastatic pediatric osteosarcoma (OS) remains poor. Thus, there is an urgent need to develop novel therapies, and immunotherapy with CAR T cells has the potential to meet this challenge. However, there is a lack of preclinical models that mimic salient features of human disease including reliable development of metastatic disease post orthotopic OS cell injection. To overcome this roadblock, and also enable real-time imaging of metastatic disease, we took advantage of LM7 OS cells expressing firefly luciferase (LM7.ffLuc). LM7.ffLuc were implanted in a collagen mesh into the tibia of mice, and mice reliably developed orthotopic tumors and lung metastases as judged by bioluminescence imaging and histopathological analysis. Intratibial implantation also enabled surgical removal by lower leg amputation and monitoring for metastases development post-surgery. We then used this model to evaluate the antitumor activity of CAR T cells targeting B7-H3, an antigen that is expressed in a broad range of solid tumors including OS. B7-H3-CAR T cells had potent antitumor activity in a dose-dependent manner and inhibited the development of pulmonary metastases resulting in a significant survival advantage. In contrast T cells expressing an inactive B7-H3-CAR had no antitumor activity. Using unmodified LM7 cells also enabled us to demonstrate that B7-H3-CAR T cells traffic to orthotopic tumor sites. Hence, we have developed an orthotopic, spontaneously metastasizing OS model. This model may improve our ability not only to predict the safety and efficacy of current and next generation CAR T cell therapies but also other treatment modalities for metastatic OS.

The NOD.Cg- Prkdcscid Il2rgtm1Wjl/SzJ strain (NOD scid gamma, NSG) is a severely immunodeficient inbred laboratory mouse used for preclinical studies because it is amenable to engraftment with human cells. Combining scid and Il2rgnull mutations results in severe immunodeficiency by impairing the maturation, survival, and functionality of interleukin 2–dependent immune cells, including T, B, and natural killer lymphocytes. While NSG mice are reportedly resistant to developing spontaneous lymphomas/leukemias, there are reports of hematopoietic cancers developing. In this study, we characterized the immunophenotype of spontaneous lymphoma/leukemia in 12 NSG mice (20 to 38 weeks old). The mice had a combination of grossly enlarged thymus, spleen, or lymph nodes and variable histologic involvement of the bone marrow and other tissues. All 12 lymphomas were diffusely CD3, TDT, and CD4 positive, and 11 of 12 were also positive for CD8, which together was consistent with precursor T-cell lymphoblastic lymphoma/leukemia (pre-T-LBL). A subset of NSG tissues from all mice and neoplastic lymphocytes from 8 of 12 cases had strong immunoreactivity for retroviral p30 core protein, suggesting an association with a viral infection. These data highlight that NSG mice may develop T-cell lymphoma at low frequency, necessitating the recognition of this spontaneously arising disease when interpreting studies.

Systemic lupus erythematosus (SLE) is a complex autoimmune disease with genetic and environmental contributions. Hallmarks of the disease are the appearance of immune complexes (IC) containing autoreactive Abs and TLR-activating nucleic acids, whose deposition in kidney glomeruli is suspected to promote tissue injury and glomerulonephritis (GN). Here, using a mouse model based on the human SLE susceptibility locus TNFAIP3-interacting protein 1 (TNIP1, also known as ABIN1), we investigated the pathogenesis of GN. We found that GN was driven by TLRs but, remarkably, proceeded independently of ICs. Rather, disease in 3 different mouse models and patients with SLE was characterized by glomerular accumulation of patrolling monocytes (PMos), a cell type with an emerging key function in vascular inflammation. Consistent with such function in GN, monocyte-specific deletion of ABIN1 promoted kidney disease, whereas selective elimination of PMos provided protection. In contrast to GN, PMo elimination did not protect from reduced survival or disease symptoms such as IC generation and splenomegaly, suggesting that GN and other inflammatory processes are governed by distinct pathogenic mechanisms. These data identify TLR-activated PMos as the principal component of an intravascular process that contributes to glomerular inflammation and kidney injury.

Immunocompromised mouse strains expressing human transgenes are being increasingly used in biomedical research. The genetic modifications in these mice cause various cellular responses, resulting in histologic features unique to each strain. The NSG-SGM3 mouse strain is similar to the commonly used NSG (NOD scid gamma) strain but expresses human transgenes encoding stem cell factor (also known as KIT ligand), granulocyte-macrophage colony-stimulating factor, and interleukin 3. This report describes 3 histopathologic features seen in these mice when they are unmanipulated or after transplantation with human CD34+ hematopoietic stem cells (HSCs), virally transduced hCD34+ HSCs, or a leukemia patient-derived xenograft. The first feature is mast cell hyperplasia: unmanipulated, naïve mice develop periductular pancreatic aggregates of murine mast cells, whereas mice given the aforementioned human cells develop a proliferative infiltrative interstitial pancreatic mast cell hyperplasia but with human mast cells. The second feature is the predisposition of NSG-SGM3 mice given these human cells to develop eosinophil hyperplasia. The third feature, secondary hemophagocytic lymphohistiocytosis/macrophage activation syndrome (HLH/MAS)–like disease, is the most pronounced in both its clinical and histopathologic presentations. As part of this disease, a small number of mice also have histiocytic infiltration of the brain and spinal cord with subsequent neurologic or vestibular signs. The presence of any of these features can confound accurate histopathologic interpretation; therefore, it is important to recognize them as strain characteristics and to differentiate them from what may be experimentally induced in the model being studied.

Prader-Willi syndrome (PWS) is a developmental disorder caused by loss of maternally imprinted genes on 15q11-q13, including melanoma antigen gene family member L2 (MAGEL2). The clinical phenotypes of PWS suggest impaired hypothalamic neuroendocrine function; however, the exact cellular defects are unknown. Here, we report deficits in secretory granule (SG) abundance and bioactive neuropeptide production upon loss of MAGEL2 in humans and mice. Unbiased proteomic analysis of Magel2pΔ/m+ mice revealed a reduction in components of SG in the hypothalamus that was confirmed in 2 PWS patient–derived neuronal cell models. Mechanistically, we show that proper endosomal trafficking by the MAGEL2-regulated WASH complex is required to prevent aberrant lysosomal degradation of SG proteins and reduction of mature SG abundance. Importantly, loss of MAGEL2 in mice, NGN2-induced neurons, and human patients led to reduced neuropeptide production. Thus, MAGEL2 plays an important role in hypothalamic neuroendocrine function, and cellular defects in this pathway may contribute to PWS disease etiology. Moreover, these findings suggest unanticipated approaches for therapeutic intervention., Prader-Willi Syndrome arises in part through loss of MAGEL2-regulated secretory granule biogenesis and neuropeptide production in the hypothalamus.

Arteriolar endothelial cell-expressed (EC-expressed) α-globin binds endothelial NOS (eNOS) and degrades its enzymatic product, NO, via dioxygenation, thereby lessening the vasodilatory effects of NO on nearby vascular smooth muscle. Although this reaction potentially affects vascular physiology, the mechanisms that regulate α-globin expression and dioxygenase activity in ECs are unknown. Without β-globin, α-globin is unstable and cytotoxic, particularly in its oxidized form, which is generated by dioxygenation and recycled via endogenous reductases. We show that the molecular chaperone α-hemoglobin-stabilizing protein (AHSP) promotes arteriolar α-globin expression in vivo and facilitates its reduction by eNOS. In Ahsp-/- mice, EC α-globin was decreased by 70%. Ahsp-/- and Hba1-/- mice exhibited similar evidence of increased vascular NO signaling, including arteriolar dilation, blunted α1-adrenergic vasoconstriction, and reduced blood pressure. Purified α-globin bound eNOS or AHSP, but not both together. In ECs in culture, eNOS or AHSP enhanced α-globin expression posttranscriptionally. However, only AHSP prevented oxidized α-globin precipitation in solution. Finally, eNOS reduced AHSP-bound α-globin approximately 6-fold faster than did the major erythrocyte hemoglobin reductases (cytochrome B5 reductase plus cytochrome B5). Our data support a model whereby redox-sensitive shuttling of EC α-globin between AHSP and eNOS regulates EC NO degradation and vascular tone.

Inflammasomes promote interleukin (IL)-1β secretion and pyroptosis. Kanneganti et al. now show that the pyroptosis effector gasdermin D (GSDMD) is required for systemic IL-1β secretion and autoinflammatory pathology in a mouse model of Familial Mediterranean Fever (FMF), suggesting GSDMD inhibitors as potential antiinflammatory treatments., Pyroptosis is an inflammasome-induced lytic cell death mode, the physiological role of which in chronic inflammatory diseases is unknown. Familial Mediterranean Fever (FMF) is the most common monogenic autoinflammatory disease worldwide, affecting an estimated 150,000 patients. The disease is caused by missense mutations in Mefv that activate the Pyrin inflammasome, but the pathophysiologic mechanisms driving autoinflammation in FMF are incompletely understood. Here, we show that Clostridium difficile infection of FMF knock-in macrophages that express a chimeric FMF-associated MefvV726A Pyrin elicited pyroptosis and gasdermin D (GSDMD)–mediated interleukin (IL)-1β secretion. Importantly, in vivo GSDMD deletion abolished spontaneous autoinflammatory disease. GSDMD-deficient FMF knock-in mice were fully protected from the runted growth, anemia, systemic inflammatory cytokine production, neutrophilia, and tissue damage that characterize this autoinflammatory disease model. Overall, this work identifies pyroptosis as a critical mechanism of IL-1β–dependent autoinflammation in FMF and highlights GSDMD inhibition as a potential antiinflammatory strategy in inflammasome-driven diseases.

Summary Alternative polyadenylation (APA) contributes to transcriptome complexity by generating mRNA isoforms with varying 3′ UTR lengths. APA leading to 3′ UTR shortening (3′ US) is a common feature of most cancer cells; however, the molecular mechanisms are not understood. Here, we describe a widespread mechanism promoting 3′ US in cancer through ubiquitination of the mRNA 3′ end processing complex protein, PCF11, by the cancer-specific MAGE-A11–HUWE1 ubiquitin ligase. MAGE-A11 is normally expressed only in the male germline but is frequently re-activated in cancers. MAGE-A11 is necessary for cancer cell viability and is sufficient to drive tumorigenesis. Screening for targets of MAGE-A11 revealed that it ubiquitinates PCF11, resulting in loss of CFIm25 from the mRNA 3′ end processing complex. This leads to APA of many transcripts affecting core oncogenic and tumor suppressors, including cyclin D2 and PTEN. These findings provide insights into the molecular mechanisms driving APA in cancer and suggest therapeutic strategies.

In β-thalassemia, accumulated free α-globin forms intracellular precipitates that impair erythroid cell maturation and viability. Protein quality control systems mitigate β-thalassemia pathophysiology by degrading toxic free α-globin, although the associated mechanisms are poorly understood. We show that loss of the autophagy-activating Unc-51–like kinase 1 (Ulk1) gene in β-thalassemic mice reduces autophagic clearance of α-globin in red blood cell precursors and exacerbates disease phenotypes, whereas inactivation of the canonical autophagy-related 5 (Atg5) gene has relatively minor effects. Systemic treatment with the mTORC1 inhibitor rapamycin reduces α-globin precipitates and lessens pathologies in β-thalassemic mice via an ULK1-dependent pathway. Similarly, rapamycin reduces free α-globin accumulation in erythroblasts derived from CD34(+) cells of β-thalassemic individuals. Our findings define a drug-regulatable pathway for ameliorating β-thalassemia.

High throughput omics approaches provide an unprecedented opportunity for dissecting molecular mechanisms in cancer biology. Here we present deep profiling of whole proteome, phosphoproteome and transcriptome in two high-grade glioma (HGG) mouse models driven by mutated RTK oncogenes, PDGFRA and NTRK1, analyzing 13,860 proteins and 30,431 phosphosites by mass spectrometry. Systems biology approaches identify numerous master regulators, including 41 kinases and 23 transcription factors. Pathway activity computation and mouse survival indicate the NTRK1 mutation induces a higher activation of AKT downstream targets including MYC and JUN, drives a positive feedback loop to up-regulate multiple other RTKs, and confers higher oncogenic potency than the PDGFRA mutation. A mini-gRNA library CRISPR-Cas9 validation screening shows 56% of tested master regulators are important for the viability of NTRK-driven HGG cells, including TFs (Myc and Jun) and metabolic kinases (AMPKa1 and AMPKa2), confirming the validity of the multiomics integrative approaches, and providing novel tumor vulnerabilities., Multi-omic profiling is a powerful approach to dissecting molecular mechanisms in disease. Here the authors generate whole proteome, phosphoproteome and transcriptome profiles from two mouse models of high-grade glioma driven by different oncogenes, and validate identified master regulators with a CRISPR screen.

Hemophagocytic lymphohistiocytosis (HLH) is an often-fatal disorder characterized by the overactivation of T cells and macrophages that excessively produce proinflammatory cytokines, including interferon-γ (IFN-γ). Previously, we reported that the JAK inhibitor ruxolitinib dampens T-cell activation and lessens inflammation in a model of HLH in which perforin-deficient (Prf1−/−) mice are infected with lymphocytic choriomeningitis virus (LCMV). Ruxolitinib inhibits signaling downstream of IFN-γ, as well as several other JAK-dependent cytokines. As a consequence, it remained unclear whether ruxolitinib was exerting its beneficial effects in HLH by inhibiting IFN-γ signaling or by targeting signaling initiated by other proinflammatory cytokines. To address this question, we compared the effects of ruxolitinib with those obtained using an IFN-γ–neutralizing antibody (αIFN-γ) in 2 murine HLH models. In both models, ruxolitinib and αIFN-γ reduced inflammation-associated anemia, indicating that ruxolitinib operates in an IFN-γ–dependent manner to reverse this HLH manifestation. In contrast, the number and activation status of T cells and neutrophils, as well as their infiltration into tissues, were significantly reduced following treatment with ruxolitinib, but they remained unchanged or were increased following treatment with αIFN-γ. Notably, despite discontinuation of ruxolitinib, LCMV-infected Prf1−/− mice exhibited enhanced survival compared with mice in which αIFN-γ was discontinued. This protective effect could be mimicked by transient treatment with αIFN-γ and a neutrophil-depleting antibody. Thus, ruxolitinib operates through IFN-γ–dependent and -independent mechanisms to dampen HLH by targeting the deleterious effects of T cells and neutrophils, with the latter representing an unappreciated and understudied cell type that contributes to HLH pathogenesis.

Mammals evolved testis-specific Mage-a genes to protect the male germline under starvation stress and are co-opted in cancer., Ensuring robust gamete production even in the face of environmental stress is of utmost importance for species survival, especially in mammals that have low reproductive rates. Here, we describe a family of genes called melanoma antigens (MAGEs) that evolved in eutherian mammals and are normally restricted to expression in the testis (http://MAGE.stjude.org) but are often aberrantly activated in cancer. Depletion of Mage-a genes disrupts spermatogonial stem cell maintenance and impairs repopulation efficiency in vivo. Exposure of Mage-a knockout mice to genotoxic stress or long-term starvation that mimics famine in nature causes defects in spermatogenesis, decreased testis weights, diminished sperm production, and reduced fertility. Last, human MAGE-As are activated in many cancers where they promote fuel switching and growth of cells. These results suggest that mammalian-specific MAGE genes have evolved to protect the male germline against environmental stress, ensure reproductive success under non-optimal conditions, and are hijacked by cancer cells.

The cell membrane glycolipid GD2 is expressed by multiple solid tumors, including 88% of osteosarcomas and 98% of neuroblastomas. However, osteosarcomas are highly heterogeneous with many tumors exhibiting GD2 expression on 99%, p

Background Intrinsic and acquired resistance to drug therapies remains a challenge for malignant melanoma patients. Intratumoral heterogeneities within the tumor microenvironment contribute additional complexity to the determinants of drug efficacy and acquired resistance. Methods We use 3D biomimetic platforms to understand dynamics in extracellular matrix (ECM) biogenesis following pharmaceutical intervention against mitogen-activated protein kinases (MAPK) signaling. We further determined temporal evolution of secreted ECM components by isogenic melanoma cell clones. Results We found that the cell clones differentially secrete and assemble a myriad of ECM molecules into dense fibrillar and globular networks. We show that cells can modulate their ECM biosynthesis in response to external insults. Fibronectin (FN) is one of the key architectural components, modulating the efficacy of a broad spectrum of drug therapies. Stable cell lines engineered to secrete minimal levels of FN showed a concomitant increase in secretion of Tenascin-C and became sensitive to BRAFV600E and ERK inhibition as clonally- derived 3D tumor aggregates. These cells failed to assemble exogenous FN despite maintaining the integrin machinery to facilitate cell- ECM cross-talk. We determined that only clones that increased FN production via p38 MAPK and β1 integrin survived drug treatment. Conclusions These data suggest that tumor cells engineer drug resistance by altering their ECM biosynthesis. Therefore, drug treatment may induce ECM biosynthesis, contributing to de novo resistance. Electronic supplementary material The online version of this article (doi:10.1186/s12885-016-2211-7) contains supplementary material, which is available to authorized users.

The recurrence of prostate cancer metastases to bone after androgen deprivation therapy is a major clinical challenge. We identified FN14 (TNFRSF12A), a TNF receptor family member, as a factor that promotes prostate cancer bone metastasis. In experimental models, depletion of FN14 inhibited bone metastasis, and FN14 could be functionally reconstituted with IKKβ-dependent, NFκB signaling activation. In human prostate cancer, upregulated FN14 expression was observed in more than half of metastatic samples. In addition, FN14 expression was correlated inversely with androgen receptor (AR) signaling output in clinical samples. Consistent with this, AR binding to the FN14 enhancer decreased expression. We show here that FN14 may be a survival factor in low AR output prostate cancer cells. Our results define one upstream mechanism, via FN14 signaling, through which the NFκB pathway contributes to prostate cancer metastasis and suggest FN14 as a candidate therapeutic and imaging target for castrate-resistant prostate cancers. Cancer Res; 74(16); 4306–17. ©2014 AACR.

Genomic rearrangements commonly occur in many types of cancers and often initiate or alter the progression of disease. Here we describe an in vivo mouse model that recapitulates the most frequent rearrangement in prostate cancer, the fusion of the promoter region of TMPRSS2 with the coding region of the transcription factor, ERG. A recombinant bacterial artificial chromosome including an extended TMPRSS2 promoter driving genomic ERG was constructed and used for transgenesis in mice. TMPRSS2-ERG expression was evaluated in tissue sections and FACS-fractionated prostate cell populations. In addition to the anticipated expression in luminal cells, TMPRSS2-ERG was similarly expressed in the Sca-1(hi)/EpCAM(+) basal/progenitor fraction, where expanded numbers of clonogenic self-renewing progenitors were found, as assayed by in vitro sphere formation. These clonogenic cells increased intrinsic self renewal in subsequent generations. In addition, ERG dependent self-renewal and invasion in vitro was demonstrated in prostate cell lines derived from the model. Clinical studies have suggested that the TMPRSS2-ERG translocation occurs early in prostate cancer development. In the model described here, the presence of the TMPRSS2-ERG fusion alone was not transforming but synergized with heterozygous Pten deletion to promote PIN. Taken together, these data suggest that one function of TMPRSS2-ERG is the expansion of self-renewing cells, which may serve as targets for subsequent mutations. Primary prostate epithelial cells demonstrated increased post transcriptional turnover of ERG compared to the TMPRSS2-ERG positive VCaP cell line, originally isolated from a prostate cancer metastasis. Finally, we determined that TMPRSS2-ERG expression occurred in both castration-sensitive and resistant prostate epithelial subpopulations, suggesting the existence of androgen-independent mechanisms of TMPRSS2 expression in prostate epithelium.

SummaryPrimary prostate cancer almost always has a luminal phenotype. However, little is known about the stem/progenitor properties of transformed cells within tumors. Using the aggressive Pten/Tp53-null mouse model of prostate cancer, we show that two classes of luminal progenitors exist within a tumor. Not only did tumors contain previously described multipotent progenitors, but also a major population of committed luminal progenitors. Luminal cells, sorted directly from tumors or grown as organoids, initiated tumors of adenocarcinoma or multilineage histological phenotypes, which is consistent with luminal and multipotent differentiation potentials, respectively. Moreover, using organoids we show that the ability of luminal-committed progenitors to self-renew is a tumor-specific property, absent in benign luminal cells. Finally, a significant fraction of luminal progenitors survived in vivo castration. In all, these data reveal two luminal tumor populations with different stem/progenitor cell capacities, providing insight into prostate cancer cells that initiate tumors and can influence treatment response.