How activated B cells build biosynthetic pathways and organelle structures necessary for subsequent robust antibody secretion is still unclear. The dominant model holds that nascent plasma cells ...adapt to increased antibody synthesis by activating the unfolded protein response (UPR) under the control of the transcription factor Xbp1. Here, by analyzing gene expression in activated B cells with or without plasma cell-inductive signals, we find that follicular B cells up-regulate a wide array of UPR-affiliated genes before initiating antibody secretion; furthermore, initial transcription of these loci requires the mTORC1 kinase adaptor, Raptor, but not Xbp1. Transcriptomic analyses of resting marginal zone B cells, which generate plasma cells with exceptionally rapid kinetics, reinforce these results by revealing the basal expression of UPR-affiliated mRNA networks without detectable Xbp1 activity. We thus conclude that B cells utilize mTORC1 to prepare for subsequent plasma cell function, before the onset of antibody synthesis.
The CD19 antigen, expressed on most B-cell acute lymphoblastic leukemias (B-ALL), can be targeted with chimeric antigen receptor-armed T cells (CART-19), but relapses with epitope loss occur in 10% ...to 20% of pediatric responders. We detected hemizygous deletions spanning the CD19 locus and de novo frameshift and missense mutations in exon 2 of CD19 in some relapse samples. However, we also discovered alternatively spliced CD19 mRNA species, including one lacking exon 2. Pull-down/siRNA experiments identified SRSF3 as a splicing factor involved in exon 2 retention, and its levels were lower in relapsed B-ALL. Using genome editing, we demonstrated that exon 2 skipping bypasses exon 2 mutations in B-ALL cells and allows expression of the N-terminally truncated CD19 variant, which fails to trigger killing by CART-19 but partly rescues defects associated with CD19 loss. Thus, this mechanism of resistance is based on a combination of deleterious mutations and ensuing selection for alternatively spliced RNA isoforms.
CART-19 yield 70% response rates in patients with B-ALL, but also produce escape variants. We discovered that the underlying mechanism is the selection for preexisting alternatively spliced CD19 isoforms with the compromised CART-19 epitope. This mechanism suggests a possibility of targeting alternative CD19 ectodomains, which could improve survival of patients with B-cell neoplasms.
Little is known about the role of mTOR signaling in plasma cell differentiation and function. Furthermore, for reasons not understood, mTOR inhibition reverses antibody-associated disease in a murine ...model of systemic lupus erythematosus. Here, we have demonstrated that induced B lineage-specific deletion of the gene encoding RAPTOR, an essential signaling adaptor for rapamycin-sensitive mTOR complex 1 (mTORC1), abrogated the generation of antibody-secreting plasma cells in mice. Acute treatment with rapamycin recapitulated the effects of RAPTOR deficiency, and both strategies led to the ablation of newly formed plasma cells in the spleen and bone marrow while also obliterating preexisting germinal centers. Surprisingly, although perturbing mTOR activity caused a profound decline in serum antibodies that were specific for exogenous antigen or DNA, frequencies of long-lived bone marrow plasma cells were unaffected. Instead, mTORC1 inhibition led to decreased expression of immunoglobulin-binding protein (BiP) and other factors needed for robust protein synthesis. Consequently, blockade of antibody synthesis was rapidly reversed after termination of rapamycin treatment. We conclude that mTOR signaling plays critical but diverse roles in early and late phases of antibody responses and plasma cell differentiation.
OBJECTIVES/GOALS: Numerous diseases, including AL amyloidosis, are due to expression of aberrant antibodies. Significant effort has gone into plasma cell toxic therapies with varying degrees of ...success, but no therapies preventing antibody synthesis have been developed. The goal of this study is to assess BiP targeting to prevent antibody secretion in plasma cells. METHODS/STUDY POPULATION: Using 4 multiple myeloma cell lines (KMS11, RPMI8226, ANBL-6, U266), we knocked down BiP expression with RnaseH dependent siRNA or subA toxin, a bacterial toxin that specifically cleaves BiP, and measured changes in unfolded protein and intracellular light chains by flow cytometry during drug induced ER stress created by the intracellular calcium depleting agent thapsigargin. BiP is the master regulator of the unfolded protein response (UPR), an ER stress pathway important for protein folding. BiP is also an ER resident protein folding chaperone important for proper antibody folding. We hypothesized that BiP downregulation will lead to decreased folded antibody in the cell, increased unfolded antibody and constitutive activation of the UPR. RESULTS/ANTICIPATED RESULTS: 1 to 4 hours after treatment with thapsigargin plus siRNA against BiP, levels of BiP are significantly decreased. The levels of intracellular light chains decrease, and the level of unfolded protein within the cells increases dramatically. Interestingly, in alignment with the UPR literature, 24 hours post treatment, these levels have normalized again in surviving cells. SubA treatment increased BiP expression by 4 hours, contrary to our hypothesis, and minimally increased unfolded proteins and minimally decreased intracellular light chains. We expect that further functional testing of antibody secretion by ELIspot assays will show decreased secretion of antibody with BiP siRNA treatment. Combination therapies with other UPR stressing agents may act synergistically to affect antibody production. DISCUSSION/SIGNIFICANCE: BiP knockdown reduces antibodies and boosts unfolded proteins. SubA toxin ineffectiveness likely stems from increased BiP due to feedback loops. Combining anti-BiP treatments with UPR stressing drugs like bortezomib may halt antibody synthesis and induce cell death. These findings support BiP as a viable drug target for antibody-related diseases.
Bulk analysis of renal allograft biopsies (rBx) identified RNA transcripts associated with acute cellular rejection (ACR); however, these lacked cellular context critical to mechanistic understanding ...of how rejection occurs despite immunosuppression (IS). We performed combined single cell RNA transcriptomic and TCRα/β sequencing on rBx from patients with ACR under differing IS: tacrolimus, iscalimab, and belatacept. We found distinct CD8+ T cell phenotypes (e.g., effector, memory, exhausted) depending upon IS type, particularly within clonally expanded cells (CD8EXP). Gene expression of CD8EXP identified therapeutic targets that were influenced by IS type. TCR analysis revealed a highly restricted number of CD8EXP, independent of HLA mismatch or IS type. Subcloning of TCRα/β cDNAs from CD8EXP into Jurkat76 cells (TCR-/-) conferred alloreactivity by mixed lymphocyte reaction. Analysis of sequential rBx samples revealed persistence of CD8EXP that decreased, but were not eliminated, after successful anti-rejection therapy. In contrast, CD8EXP were maintained in treatment-refractory rejection. Finally, most rBx-derived CD8EXP were also observed in matching urine samples, providing precedent for using urine-derived CD8EXP as a surrogate for those found in the rejecting allograft. Overall, our data define the clonal CD8+ T cell response to ACR, paving the next steps to improve detection, assessment, and treatment of rejection.
Pancreatic ductal adenocarcinoma (PDAC) is a leading cause of cancer-related deaths worldwide, with an exceedingly low 5-year survival rate. PDAC tumors are characterized by an extensive desmoplastic ...stromal response and hypovascularity, suggesting that tumor hypoxia could regulate PDAC initiation and/or progression. Using a well-defined, autochthonous Kras(G12D)-driven murine model, as well as human tumors, we demonstrate that hypoxia and stabilization of hypoxia-inducible factor 1α (HIF1α), a principal mediator of hypoxic adaptation, emerge early during preinvasive stages of PDAC. Surprisingly, pancreas-specific Hif1a deletion drastically accelerated Kras(G12D)-driven pancreatic neoplasia and was accompanied by significant increases in intrapancreatic B lymphocytes, featuring prominent influx of a rare "B1b" B-cell subtype. Finally, treatment of HIF1α-deficient mice with B cell-depleting αCD20 monoclonal antibodies inhibited progression of pancreatic intraepithelial neoplasia (PanIN). Our data reveal a previously unrecognized role for B cells in promoting pancreatic tumorigenesis and implicate HIF1α as a critical regulator of PDAC development.
We show here that pancreas-specific Hif1a deletion promotes PDAC initiation, coincident with increased intrapancreatic accumulation of B cells, and that B-cell depletion suppresses pancreatic tumorigenesis. We therefore demonstrate a protective role for HIF1α in pancreatic cancer initiation and uncover a previously unrecognized function of B cells.
In lymphopenic environments, secondary lymphoid organs regulate the size of B and T-cell compartments by supporting homeostatic proliferation of mature lymphocytes. The molecular mechanisms ...underlying these responses and their functional consequences remain incompletely understood. To evaluate homeostasis of the mature B-cell pool during lymphopenia, we turned to an adoptive transfer model of purified follicular B-cells into Rag2-/- mouse recipients. Highly purified follicular B-cells transdifferentiated into marginal zone-like B-cells when transferred into Rag2-/- lymphopenic hosts, but not into wild-type hosts. In lymphopenic spleens, transferred B-cells gradually lost their follicular phenotype and acquired characteristics of marginal zone B-cells, as judged by cell surface phenotype, expression of integrins and chemokine receptors, positioning close to the marginal sinus, and an ability to rapidly generate functional plasma cells. Initiation of follicular to marginal zone B-cell transdifferentiation preceded proliferation. Furthermore, the transdifferentiation process was dependent on Notch2 receptors in B-cells and expression of Delta-like1 Notch ligands by splenic Ccl19-Cre+ fibroblastic stromal cells. Gene expression analysis showed rapid induction of Notch-regulated transcripts followed by upregulated Myc expression and acquisition of broad transcriptional features of marginal zone B-cells. Thus, naïve mature B-cells are endowed with plastic transdifferentiation potential in response to increased stromal Notch ligand availability during lymphopenia.
Plasma cells (PCs) are the major source of pathogenic allo‐ and autoantibodies and have historically demonstrated resistance to therapeutic targeting. However, significant recent clinical progress ...has been made with the use of second‐generation proteasome inhibitors (PIs). PIs provide efficient elimination of plasmablast‐mediated humoral responses; however, long‐lived bone marrow (BM) resident PCs (LLPCs) demonstrate therapeutic resistance, particularly to first‐generation PIs. In addition, durability of antibody (Ab) reduction still requires improvement. More recent clinical trials have focused on conditions mediated by LLPCs and have included mechanistic studies of LLPCs from PI‐treated patients. A recent clinical trial of carfilzomib (a second‐generation irreversible PI) demonstrated improved efficacy in eliminating BM PCs and reducing anti‐HLA Abs in chronically HLA‐sensitized patients; however, Ab rebound was observed over several weeks to months following PI therapy. Importantly, recent murine studies have provided substantial insights into PC biology, thereby further enhancing our understanding of PC populations. It is now clear that BMPC populations, where LLPCs are thought to primarily reside, are heterogeneous and have distinct gene expression, metabolic, and survival signatures that enable identification and characterization of PC subsets. This review highlights recent advances in PC biology and clinical trials in transplant populations.
Recent application of powerful new investigative tools are beginning to reveal previously unrecognized aspects of the biology of plasma cells, thereby identifying promising new approaches for enhancing current targeting strategies.
Current models hold that serum Ab titers are maintained chiefly by long-lived bone marrow (BM) plasma cells (PCs). In this study, we characterize the role of subpopulations of BM PCs in long-term ...humoral responses to T cell-dependent Ag. Surprisingly, our results indicate that 40-50% of BM PCs are recently formed cells, defined, in part, by rapid steady-state turnover kinetics and secretion of low-affinity IgM Abs. Further, for months after immunization with a hapten-protein conjugate, newly formed Ag-induced, IgM-secreting BM PCs were detected in parallel with longer-lived IgG-secreting cells, suggesting ongoing and parallel input to the BM PC pool from two distinct pools of activated B cells. Consistent with this interpretation, IgM and IgG Abs secreted by cells within distinct PC subsets exhibited distinct L chain usage. We conclude that long-term Ab responses are maintained by a dynamic BM PC pool composed of both recently formed and long-lived PCs drawn from clonally disparate precursors.
Editorial: The nose knows Cancro, Michael P.; Allman, David M.
Journal of leukocyte biology,
September 2017, 2017-09-00, 2017-09-01, 20170901, Letnik:
102, Številka:
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Discussion on how nasal epithelial cells govern the quality of local humoral immunity.
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