Faculty Bibliography

Abstract: T cell lymphomas comprise a distinct class of non-Hodgkin's lymphomas, which include mature T and natural killer (NK) cell neoplasms. While each malignancy within this group is characterized by unique clinicopathologic features, dysregulation in the Janus tyrosine family of kinases/Signal transducer and activator of transcription (JAK/STAT) signaling pathway, specifically aberrant STAT3 activation, is a common feature among these lymphomas. The mechanisms driving dysregulation vary among T cell lymphoma subtypes and include activating mutations in upstream kinases or STAT3 itself, formation of oncogenic kinases which drive STAT3 activation, loss of negative regulators of STAT3, and the induction of a pro-tumorigenic inflammatory microenvironment. Constitutive STAT3 activation has been associated with the expression of targets able to increase pro-survival signals and provide malignant fitness. Patients with dysregulated STAT3 signaling tend to have inferior clinical outcomes, which underscores the importance of STAT3 signaling in malignant progression. Targeting of STAT3 has shown promising results in pre-clinical studies in T cell lymphoma lines, ex-vivo primary malignant patient cells, and in mouse models of disease. However, targeting this pleotropic pathway in patients has proven difficult. Here we review the recent contributions to our understanding of the role of STAT3 in T cell lymphomagenesis, mechanisms driving STAT3 activation in T cell lymphomas, and current efforts at targeting STAT3 signaling in T cell malignancies.

B-1a cells are long-lived, self-renewing innate-like B cells that predominantly inhabit the peritoneal and pleural cavities. In contrast to conventional B-2 cells, B-1a cells have a receptor repertoire that is biased towards bacterial and self-antigens, promoting a rapid response to infection and clearing of apoptotic cells. Although B-1a cells are known to primarily originate from fetal tissues, the mechanisms by which they arise has been a topic of debate for many years. Here we show that in the fetal liver versus bone marrow environment, reduced IL-7R/STAT5 levels promote immunoglobulin kappa gene recombination at the early pro-B cell stage. As a result, differentiating B cells can directly generate a mature B cell receptor (BCR) and bypass the requirement for a pre-BCR and pairing with surrogate light chain. This 'alternate pathway' of development enables the production of B cells with self-reactive, skewed specificity receptors that are peculiar to the B-1a compartment. Together our findings connect seemingly opposing lineage and selection models of B-1a cell development and explain how these cells acquire their unique properties.

Pathogenic Th17 cells play important roles in many autoimmune and inflammatory diseases. Their function depends on T cell receptor (TCR) signaling and cytokines that activate signal transducer and activator of transcription 3 (STAT3). TCR engagement activates stromal interaction molecule 1 (STIM1) and calcium (Ca²⁺) influx through Ca²⁺-release-activated Ca²⁺ (CRAC) channels. Here, we show that abolishing STIM1 and Ca²⁺ influx in T cells expressing a hyperactive form of STAT3 (STAT3C) attenuates pathogenic Th17 cell function and inflammation associated with STAT3C expression. Deletion of STIM1 in pathogenic Th17 cells reduces the expression of genes required for mitochondrial function and oxidative phosphorylation (OXPHOS) but enhances reactive oxygen species (ROS) production. STIM1 deletion or inhibition of OXPHOS is associated with a non-pathogenic Th17 gene expression signature and impaired pathogenic Th17 cell function. Our findings establish Ca²⁺ influx as a critical regulator of mitochondrial function and oxidative stress in pathogenic Th17 cell-mediated multiorgan inflammation.

Multimodal single-cell assays provide high-resolution snapshots of complex cell populations, but are mostly limited to transcriptome plus an additional modality. Here, we describe expanded CRISPR-compatible cellular indexing of transcriptomes and epitopes by sequencing (ECCITE-seq) for the high-throughput characterization of at least five modalities of information from each single cell. We demonstrate application of ECCITE-seq to multimodal CRISPR screens with robust direct single-guide RNA capture and to clonotype-aware multimodal phenotyping of cancer samples.

Thymocyte selection associated high mobility group box 1 (Tox1), a transcription factor that is essential to establish the CD4+ lineage, is overexpressed in malignant cells from patients with CTCL. Knockdown of Tox1 leads to decreased malignant cell viability, while treatment with HDAC inhibitors results in normalization of Tox1expression. Another gene which is consistently overexpressed in patient samples is signal transducers and activators of transcription3 (Stat3), a transcription factor essential for the differentiation of Th17 and follicular helper T cells. Treating CTCL cell lines with a STAT3 inhibitor results in decreased cell number and increased apoptosis, highlighting the importance of this pathway for malignant cell survival. Importantly, the Koralov lab has developed a mouse model which constitutively expresses a hyperactive STAT3 allele, STAT3C, that recapitulates several key features of MF. To examine the contribution of TOX1overexpression to CTCL pathogenesis, we have introduced Tox1 cDNA downstream of a floxed stop cassette into the ubiquitously expressed Rosa26 locus of C57Bl/6J embryonic stem (ES) cells. We have screened the ES clones to validate the presence of the correctly targeted allele, and we have treated ES clones with TAT-Cre to delete the floxed stop cassette and drive subsequent expression of Tox1 cDNA. We have now generated R26Tox1^stopflmice using tetraploid complementation to generate 100% ES cell derived animals. These animals will be crossed to CD4Cre and CD4Cre STAT3C^stopflstrains, thus enabling us to study the contribution of Tox1 overexpression to T cell lymphomagenesis and allowing us to examine synergy between Tox1 overexpression and hyperactive STAT3 signaling in CTCL pathogenesis. We hope that these mice will pave the way to a better understanding of this enigmatic malignancy and allow us to develop a relevant small animal model of this disease.

The immunoglobulin heavy chain (Igh) locus features a dynamic chromatin landscape to promote class switch recombination (CSR), yet the mechanisms that regulate this landscape remain poorly understood. CHD4, a component of the chromatin remodeling NuRD complex, directly binds H3K9me3, an epigenetic mark present at the Igh locus during CSR. We find that CHD4 is essential for early B cell development but is dispensable for the homeostatic maintenance of mature, naive B cells. However, loss of CHD4 in mature B cells impairs CSR because of suboptimal targeting of AID to the Igh locus. Additionally, we find that CHD4 represses p53 expression to promote B cell proliferation. This work reveals distinct roles for CHD4 in B cell development and CSR and links the H3K9me3 epigenetic mark with AID recruitment to the Igh locus.

The pathogenesis of Staphylococcus aureus is thought to depend on the production of pore-forming leukocidins that kill leukocytes and lyse erythrocytes. Two leukocidins, Leukocidin ED (LukED) and γ-Hemolysin AB (HlgAB), are necessary and sufficient to kill mice upon infection and toxin challenge. We demonstrate that LukED and HlgAB cause vascular congestion and derangements in vascular fluid distribution that rapidly cause death in mice. The Duffy antigen receptor for chemokines (DARC) on endothelial cells, rather than leukocytes or erythrocytes, is the critical target for lethality. Consistent with this, LukED and HlgAB injure primary human endothelial cells in a DARC-dependent manner, and mice with DARC-deficient endothelial cells are resistant to toxin-mediated lethality. During bloodstream infection in mice, DARC targeting by S. aureus causes increased tissue damage, organ dysfunction, and host death. The potential for S. aureus leukocidins to manipulate vascular integrity highlights the importance of these virulence factors.

B cell development is a highly regulated process that requires stepwise rearrangement of immunoglobulin genes to generate a functional B cell receptor (BCR). The polycomb group protein BMI1 is required for B cell development, but its function in developing B cells remains poorly defined. We demonstrate that BMI1 functions in a cell-autonomous manner at two stages during early B cell development. First, loss of BMI1 results in a differentiation block at the pro-B cell to pre-B cell transition due to the inability of BMI1-deficient cells to transcribe newly rearranged Igh genes. Accordingly, introduction of a pre-rearranged Igh allele partially restored B cell development in Bmi1^-/- mice. In addition, BMI1 is required to prevent premature p53 signaling, and as a consequence, Bmi1^-/- large pre-B cells fail to properly proliferate. Altogether, our results clarify the role of BMI1 in early B cell development and uncover an unexpected function of BMI1 during VDJ recombination.