CCAAT enhancer binding protein-α (C/EBPα) inhibits proliferation in multiple cell types; therefore, we evaluated whether C/EBPα-deficient hematopoietic progenitor cells (HPCs) have an increased proliferative potential in vitro and in vivo. In this study we demonstrate that C/EBPα-/- fetal liver (FL) progenitors are hyperproliferative, show decreased differentiation potential, and show increased self-renewal capacity in response to hematopoietic growth factors (HGFs). There are fewer committed bipotential progenitors in C/EBPα-/- FL, whereas multipotential progenitors are unaffected. HGF-dependent progenitor cell lines can be derived by directly culturing C/EBPα-/- FL cells in vitro Hyperproliferative spleen colonies and myelodysplastic syndrome (MDS) are observed in mice reconstituted with C/EBPα-/- FL cells, indicating progenitor hyperproliferation in vitro and in vivo. C/EBPα-/- FL lacked macrophage progenitors in vitro and had impaired ability to generate macrophages in vivo. These findings show that C/EBPα deficiency results in hyperproliferation of HPCs and a block in the ability of multipotential progenitors to differentiate into bipotential granulocyte/macrophage progenitors and their progeny. (Blood. 2004; 104:1639-1647)

C/EBPα is an essential transcription factor required for myeloid differentiation. While C/EBPα can act as a cell fate switch to promote granulocyte differentiation in bipotential granulocyte-macrophage progenitors (GMPs), its role in regulating cell fate decisions in more primitive progenitors is not known. We found increased numbers of erythroid progenitors and erythroid cells in C/EBPα^–/– fetal liver (FL). Also, enforced expression of C/EBPα in hematopoietic stem cells resulted in a loss of erythroid progenitors and an increase in myeloid cells by inhibition of erythroid development and inducing myeloid differentiation. Conditional expression of C/EBPα in murine erythroleukemia (MEL) cells induced myeloid-specific genes, while inhibiting erythroid-specific gene expression including erythropoietin receptor (EpoR), which suggests a novel mechanism to determine hematopoietic cell fate. Thus, C/EBPα functions in hematopoietic cell fate decisions by the dual actions of inhibiting erythroid and inducing myeloid gene expression in multipotential progenitors.

Disease progression is a substantial challenge in patients with non-Hodgkin lymphoma (NHL) undergoing chimeric antigen receptor T cell (CAR-T) therapy. Here we present InflaMix (INFLAmmation MIXture Model), an unsupervised quantitative model integrating 14 pre-CAR-T infusion laboratory and cytokine measures capturing inflammation and end-organ function. Developed using a cohort of 149 patients with NHL, InflaMix revealed an inflammatory signature associated with a high risk of CAR-T treatment failure, including increased hazard of death or relapse (hazard ratio, 2.98; 95% confidence interval, 1.60–4.91; P < 0.001). Three independent cohorts comprising 688 patients with NHL from diverse treatment centers were used to validate our approach. InflaMix consistently and reproducibly identified patients with a higher likelihood of disease relapse and mortality, and it provided supplementary predictive value beyond established prognostic markers, including tumor burden. Moreover, InflaMix exhibited robust performance in cases with missing data, maintaining accuracy when considering only six readily available laboratory measures. These findings show that InflaMix is a valuable tool for point-of-care clinical decision-making in patients with NHL undergoing CAR-T therapy.

Birt-Hogg-Dubé (BHD) syndrome is an autosomal dominant disorder characterized by cutaneous fibrofolliculomas, pulmonary cysts, and kidney malignancies. Affected individuals carry germ line mutations in folliculin (FLCN), a tumor suppressor gene that becomes biallelically inactivated in kidney tumors by second-hit mutations. Similar to other factors implicated in kidney cancer, FLCN has been shown to modulate activation of mammalian target of rapamycin (mTOR). However, its precise in vivo function is largely unknown because germ line deletion of Flcn results in early embryonic lethality in animal models. Here, we describe mice deficient in the newly characterized folliculin-interacting protein 1 (Fnip1). In contrast to Flcn, Fnip1−/− mice develop normally, are not susceptible to kidney neoplasia, but display a striking pro-B cell block that is entirely independent of mTOR activity. We show that this developmental arrest results from rapid caspase-induced pre-B cell death, and that a Bcl2 transgene reconstitutes mature B-cell populations, respectively. We also demonstrate that conditional deletion of Flcn recapitulates the pro-B cell arrest of Fnip1−/− mice. Our studies thus demonstrate that the FLCN-FNIP complex deregulated in BHD syndrome is absolutely required for B-cell differentiation, and that it functions through both mTOR-dependent and independent pathways.