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Most vaccines against viral pathogens protect through the acquisition of immunological memory from long-lived plasma cells that produce antibodies and memory B cells that can rapidly respond upon an encounter with the pathogen or its variants. The COVID-19 pandemic and rapid deployment of effective vaccines have provided an unprecedented opportunity to study the immune response to a new yet rapidly evolving pathogen. Here we review the scientific literature and our efforts to understand antibody and B-cell responses to SARS-CoV-2 vaccines, the effect of SARS-CoV-2 infection on both primary and secondary immune responses, and how repeated exposures may impact outcomes.

Most studies of adaptive immunity to SARS-CoV-2 infection focus on peripheral blood, which may not fully reflect immune responses at the site of infection. Using samples from 110 children undergoing tonsillectomy and adenoidectomy during the COVID-19 pandemic, we identified 24 samples with evidence of previous SARS-CoV-2 infection, including neutralizing antibodies in serum and SARS-CoV-2-specific germinal center and memory B cells in the tonsils and adenoids. Single-cell B cell receptor (BCR) sequencing indicated virus-specific BCRs were class-switched and somatically hypermutated, with overlapping clones in the two tissues. Expanded T cell clonotypes were found in tonsils, adenoids and blood post-COVID-19, some with CDR3 sequences identical to previously reported SARS-CoV-2-reactive T cell receptors (TCRs). Pharyngeal tissues from COVID-19-convalescent children showed persistent expansion of germinal center and antiviral lymphocyte populations associated with interferon (IFN)-γ-type responses, particularly in the adenoids, and viral RNA in both tissues. Our results provide evidence for persistent tissue-specific immunity to SARS-CoV-2 in the upper respiratory tract of children after infection.

Responses to vaccination and to diseases vary widely across individuals, which may be partly due to baseline immune variations. Identifying such baseline predictors of immune responses and their biological basis is of broad interest, given their potential importance for cancer immunotherapy, disease outcomes, vaccination and infection responses. Here we uncover baseline blood transcriptional signatures predictive of antibody responses to both influenza and yellow fever vaccinations in healthy subjects. These same signatures evaluated at clinical quiescence are correlated with disease activity in patients with systemic lupus erythematosus with plasmablast-associated flares. CITE-seq profiling of 82 surface proteins and transcriptomes of 53,201 single cells from healthy high and low influenza vaccination responders revealed that our signatures reflect the extent of activation in a plasmacytoid dendritic cell–type I IFN–T/B lymphocyte network. Our findings raise the prospect that modulating such immune baseline states may improve vaccine responsiveness and mitigate undesirable autoimmune disease activity. Simultaneous single-cell protein and transcriptome analysis identifies a baseline immune circuit associated with antibody responses to vaccination in healthy individuals and the severity of disease flares in patients with a subtype of systemic lupus erythematosus.

Messenger RNA (mRNA) vaccines against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are highly effective at inducing protective immunity. However, weak antibody responses are seen in some individuals, and cellular correlates of immunity remain poorly defined, especially for B cells. Here we used unbiased approaches to longitudinally dissect primary antibody, plasmablast, and memory B cell (MBC) responses to the two-dose mRNA-1273 vaccine in SARS-CoV-2-naive adults. Coordinated immunoglobulin A (IgA) and IgG antibody responses were preceded by bursts of spike-specific plasmablasts after both doses but earlier and more intensely after dose 2. While antibody and B cell cellular responses were generally robust, they also varied within the cohort and decreased over time after a dose-2 peak. Both antigen-nonspecific postvaccination plasmablast frequency after dose 1 and their spike-specific counterparts early after dose 2 correlated with subsequent antibody levels. This correlation between early plasmablasts and antibodies remained for titers measured at 6 months after vaccination. Several distinct antigen-specific MBC populations emerged postvaccination with varying kinetics, including two MBC populations that correlated with 2- and 6-month antibody titers. Both were IgG-expressing MBCs: one less mature, appearing as a correlate after the first dose, while the other MBC correlate showed a more mature and resting phenotype, emerging as a correlate later after dose 2. This latter MBC was also a major contributor to the sustained spike-specific MBC response observed at month 6. Thus, these plasmablasts and MBCs that emerged after both the first and second doses with distinct kinetics are potential determinants of the magnitude and durability of antibodies in response to mRNA-based vaccination.

Atypical B cells represent an IFN-γ–driven B cell lineage that may be similarly expanded in malaria, HIV, and autoimmunity., Chronic infectious diseases have a substantial impact on the human B cell compartment including a notable expansion of B cells here termed atypical B cells (ABCs). Using unbiased single-cell RNA sequencing (scRNA-seq), we uncovered and characterized heterogeneities in naïve B cell, classical memory B cells, and ABC subsets. We showed remarkably similar transcriptional profiles for ABC clusters in malaria, HIV, and autoimmune diseases and demonstrated that interferon-γ drove the expansion of ABCs in malaria. These observations suggest that ABCs represent a separate B cell lineage with a common inducer that further diversifies and acquires disease-specific characteristics and functions. In malaria, we identified ABC subsets based on isotype expression that differed in expansion in African children and in B cell receptor repertoire characteristics. Of particular interest, IgD+IgMlo and IgD−IgG+ ABCs acquired a high antigen affinity threshold for activation, suggesting that ABCs may limit autoimmune responses to low-affinity self-antigens in chronic malaria.

A functional genomics approach uncovers previously undescribed cell type–dependent responses that can be linked to the immunoregulatory actions of glucocorticoids in humans., Glucocorticoids remain the most widely used immunosuppressive and anti-inflammatory drugs, yet substantial gaps exist in our understanding of glucocorticoid-mediated immunoregulation. To address this, we generated a pathway-level map of the transcriptional effects of glucocorticoids on nine primary human cell types. This analysis revealed that the response to glucocorticoids is highly cell type dependent, in terms of the individual genes and pathways affected, as well as the magnitude and direction of transcriptional regulation. Based on these data and given their importance in autoimmunity, we conducted functional studies with B cells. We found that glucocorticoids impair upstream B cell receptor and Toll-like receptor 7 signaling, reduce transcriptional output from the three immunoglobulin loci, and promote significant up-regulation of the genes encoding the immunomodulatory cytokine IL-10 and the terminal-differentiation factor BLIMP-1. These findings provide new mechanistic understanding of glucocorticoid action and emphasize the multifactorial, cell-specific effects of these drugs, with potential implications for designing more selective immunoregulatory therapies., Graphical Abstract

Nearly all chronic human infections are associated with alterations in the memory B cell (MBC) compartment, including a large expansion of CD19(hi)T-bet(hi) MBC in the peripheral blood of HIV-infected individuals with chronic viremia. Despite their prevalence, it is unclear how these B cells arise and whether they contribute to the inefficiency of antibody-mediated immunity in chronic infectious diseases. We addressed these questions by characterizing T-bet-expressing B cells in lymph nodes (LN) and identifying a strong T-bet signature among HIV-specific MBC associated with poor immunologic outcome. Confocal microscopy and quantitative imaging revealed that T-bet(hi) B cells in LN of HIV-infected chronically viremic individuals distinctly accumulated outside germinal centers (GC), which are critical for optimal antibody responses. In single-cell analyses, LN T-bet(hi) B cells of HIV-infected individuals were almost exclusively found among CD19(hi) MBC and expressed reduced GC-homing receptors. Furthermore, HIV-specific B cells of infected individuals were enriched among LN CD19(hi)T-bet(hi) MBC and displayed a distinct transcriptome, with features similar to CD19(hi)T-bet(hi) MBC in blood and LN GC B cells (GCBC). LN CD19(hi)T-bet(hi) MBC were also related to GCBC by B cell receptor (BCR)–based phylogenetic linkage but had lower BCR mutation frequencies and reduced HIV-neutralizing capacity, consistent with diminished participation in GC-mediated affinity selection. Thus, in the setting of chronic immune activation associated with HIV viremia, failure of HIV-specific B cells to enter or remain in GC may help explain the rarity of high-affinity protective antibodies.

Background Changes in adaptive immune cells after chemotherapy in adult acute myeloid leukemia (AML) may have implications for the success of immunotherapy. This study was designed to determine the functional capacity of the immune system in adult patients with AML who have completed chemotherapy and are potential candidates for immunotherapy. Methods We used the response to seasonal influenza vaccination as a surrogate for the robustness of the immune system in 10 AML patients in a complete remission post-chemotherapy and performed genetic, phenotypic, and functional characterization of adaptive immune cell subsets. Results Only 2 patients generated protective titers in response to vaccination, and a majority of patients had abnormal frequencies of transitional and memory B-cells. B-cell receptor sequencing showed a B-cell repertoire with little evidence of somatic hypermutation in most patients. Conversely, frequencies of T-cell populations were similar to those seen in healthy controls, and cytotoxic T-cells demonstrated antigen-specific activity after vaccination. Effector T-cells had increased PD-1 expression in AML patients least removed from chemotherapy. Conclusion Our results suggest that while some aspects of cellular immunity recover quickly, humoral immunity is incompletely reconstituted in the year following intensive cytotoxic chemotherapy for AML. The observed B-cell abnormalities may explain the poor response to vaccination often seen in AML patients after chemotherapy. Furthermore, the uncoupled recovery of B-cell and T-cell immunity and increased PD-1 expression shortly after chemotherapy might have implications for the success of several modalities of immunotherapy. Electronic supplementary material The online version of this article (doi:10.1186/s12967-017-1252-2) contains supplementary material, which is available to authorized users.

Purpose of review Numerous B-cell abnormalities in HIV-1 infection have been described over the past three decades yet have remained poorly defined mechanistically. We review recent studies that describe mechanisms of B-cell dysregulation in chronic HIV-1 infection associated with IgG3 and T-bet. Recent findings HIV-1 infection causes hypergammaglobulinemia and dysregulation of B-cell populations, including the expansion during chronic viremia of functionally impaired tissue-like memory (TLM) B cells. TLM B cells and B cells in other conditions of chronic activation and inflammation with similar phenotypes are characterized by increased expression of the transcription factor T-bet and preferential immunoglobulin class-switching to IgG3. However, defects in B-cell function during chronic HIV-1 viremia are also associated with the binding of soluble IgG3 to IgM-expressing B cells, with the highest intensities observed on TLM B cells. The consequence of IgG3 binding to TLM B cells is increased clustering of the IgM B-cell receptor and decreased response to stimulation. Summary The identification of T-bet and IgG3 as the regulators of B-cell function in chronic HIV-1 viremia could provide new targets for therapeutic intervention aimed at reversing the damaging effects of HIV-1-associated chronic immune activation.

Despite the overwhelming benefits of antiretroviral therapy (ART) in curtailing viral load in HIV-infected individuals, ART does not fully restore cellular and humoral immunity. HIV-infected individuals under ART show reduced responses to vaccination and infections and are unable to mount an effective antiviral immune response upon ART cessation. Many factors contribute to these defects, including persistent inflammation, especially in lymphoid tissues, where T follicular helper (Tfh) cells instruct and help B cells launch an effective humoral immune response. In this study we investigated the phenotype and function of circulating memory Tfh cells as a surrogate of Tfh cells in lymph nodes and found significant impairment of this cell population in chronically HIV-infected individuals, leading to reduced B cell responses. We further show that these aberrant memory Tfh cells exhibit an IL-2–responsive gene signature and are more polarized toward a Th1 phenotype. Treatment of functional memory Tfh cells with IL-2 was able to recapitulate the detrimental reprogramming. Importantly, this defect was reversible, as interfering with the IL-2 signaling pathway helped reverse the abnormal differentiation and improved Ab responses. Thus, reversible reprogramming of memory Tfh cells in HIV-infected individuals could be used to enhance Ab responses. Altered microenvironmental conditions in lymphoid tissues leading to altered Tfh cell differentiation could provide one explanation for the poor responsiveness of HIV-infected individuals to new Ags. This explanation has important implications for the development of therapeutic interventions to enhance HIV- and vaccine-mediated Ab responses in patients under ART.

Immunoglobulin G3 (IgG3) has an uncertain role in the response to infection with and vaccination against human immunodeficiency virus (HIV). Here we describe a regulatory role for IgG3 in dampening the immune system–activating effects of chronic HIV viremia on B cells. Secreted IgG3 was bound to IgM-expressing B cells in vivo in HIV-infected chronically viremic individuals but not in early-viremic or aviremic individuals. Tissue-like memory (TLM) B cells, a population expanded by persistent HIV viremia, bound large amounts of IgG3. IgG3 induced clustering of B cell antigen receptors (BCRs) on the IgM+ B cells, which was mediated by direct interactions between soluble IgG3 and membrane IgM of the BCR (IgM-BCR). The inhibitory IgG receptor CD32b (FcγRIIb), complement component C1q and inflammatory biomarker CRP contributed to the binding of secreted IgG3 onto IgM-expressing B cells of HIV-infected individuals. Notably, IgG3-bound TLM B cells were refractory to IgM-BCR stimulation, thus demonstrating that IgG3 can regulate B cells during chronic activation of the immune system. Circulating IgG3 increases in chronic HIV infection. Moir and colleagues describe a negative regulatory role of secreted IgG3 in response to chronic HIV infection through its action on nonconventional CD27– memory B cells.

Lentivector mediated gene transfer into hematopoietic stem/progenitor cells and T cells has resulted in long-term stable integration of transgenes and significant clinical benefits in many diseases. We previously reported (De Ravin et al Sci Transl Med. 2016) early outcome data for 5 patients with X-linked severe combined immunodeficiency (X-SCID) enrolled in a first-in-human lentivector gene therapy clinical trial (NCT03315078) as salvage therapy for older children and young adults who had received prior haplo-identical hematopoietic stem cell transplantation (HSCT) as infants without chemotherapy-based conditioning. Lymphocyte-depleted haplo-identical stem cell transplant in X-SCID infants without conditioning generally results in only a T-cell engraftment that may also decline over time which, combined with B- and NK-cell dysfunction, may result in the progression of multi-system clinical problems (bronchiectasis, infections, gastrointestinal malabsorption, failure to grow, immune dysregulation). By 2016 three additional patients were treated and the cohort of 8 patients have now been followed for 3 to 7 years (Cohort A), where we observed gradual clinical benefit in the clearance of chronic norovirus and associated improved abdominal complaints, malabsorption, and growth and IgG production. Four patients were able to cease immunoglobulin replacement therapy. Despite these encouraging results, the relatively inefficient transduction of hematopoietic stem/progenitor cells (HSPCs) required large quantities of vector, and resulted in relatively low vector copy number in myeloid cells in some patients, with delayed immune cell recovery and persistent clinical disease especially in the last patient treated, P8. To address this, we developed a refined enhanced transduction (ET) procedure consisting of a single overnight transduction after 48hours pre-stimulation in cytokines (Stem cell factor, Thrombopoietin, Flt3-ligand; 100ng/mL) and incorporated transduction enhancers LentiBoost 1:100 and dimethyl prostaglandin 2 (dmPGE2; 1mM) and recently treat 6 patients, including re-treatment of P8 (Cohort B). Here we compared the early outcomes from Cohort B patients who received autologous CD34+ HSPCs processed with the enhanced transduction (ET) procedure. These patients (aged 12 to 36 yo) had significant problems with donor T cell infiltration of liver, bone marrow and kidneys, and near absent B and NK cells. Cryopreserved G-CSF/plerixafor mobilized peripheral blood CD34+ HSPCs (5x106/kg to 28x106/kg) were transduced by the ET process at 5% vector concentration, compared to previous method without transduction enhancers of two daily transductions at 20-30% final vector concentration, representing a 10-12 fold reduction in vector used. Colony forming unit assays showed 78%-92% versus 17%-58% vector-positive clones in Cohort B compared with Cohort A, with VCN of 1.5-12 copies (Cohort B), compared with 0.06 to 0.5 copies in Cohort A. At one month following infusion of gene corrected cell product, we isolated peripheral blood CD14+ myeloid cells as indication of early marrow output from engrafted HSPCs, and observed VCN of 1 to 4 copies (P9-12 and re-treat P8), a ≥10x increase from Cohort A (0.04 to 0.23) at same early time point after infusion (Fig 1). In addition to earlier clinical improvement (abdominal complaints, appetite, growth), there was also an early appearance of B and NK cells (Fig. 2) at much higher levels in Cohort B than previously observed even at years after treatment in Cohort A. In conclusion, we observed significantly improved measures of early clinical outcomes from lentivector gene therapy of older children and young adults with X-SCID using enhanced transduction procedure with addition of LentiBoost and dmPGE2, that achieves much greater transduction efficiencies with >10 fold less vector, and results in faster immune reconstitution and more significant clinical benefit by 3 months. The patients are monitored closely for potential risks from higher VCNs that may be balanced by reduced selection pressure due to the greater numbers of gene corrected clones. Figure Disclosures Puck: NIAID: Research Funding; Pfeizer: Other: spouse serves on Rare Disease Advisory Board; Invitae: Other: spouse employment. Cowan:bluebird bio: Consultancy; Homology Medicine: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; UpToDate: Honoraria; California Institute Of Regenerative Medicine: Research Funding; NIH NIAD: Research Funding; Rocket Pharma: Consultancy; Leadiant: Consultancy. Mamcarz:ASSISI Foundation of Memphis: Research Funding; MBIO: Other: St. Jude Children's Research Hospital has an existing exclusive license and ongoing partnership with Mustang Bio for the further clinical development and commercialization of this XSCID gene therapy; California Institute of Regenerative Medicine: Research Funding; NHLBI: Research Funding; UpToDate: Honoraria; American Lebanese Syrian Associated Charities: Research Funding. Gottschalk:Patents and patent applications in the fields of T-cell & Gene therapy for cancer: Patents & Royalties; California Institute for Regenerative Medicine: Research Funding; NHLBI: Research Funding; America Lebanese Syrian Associated Charities: Research Funding; TESSA Therapeutics: Other: Research Collaboration; ViraCyte: Consultancy; MBIO: Other: St. Jude Children's Research Hospital has an existing exclusive license and ongoing partnership with Mustang Bio for the further clinical development and commercialization of this XSCID gene therapy; Sanofi: Honoraria; Tidal: Membership on an entity's Board of Directors or advisory committees; Merck: Consultancy; EMD Serono: Honoraria; ASSISI fundation of Memphis: Research Funding; Inmatics: Membership on an entity's Board of Directors or advisory committees. Meagher:MBIO: Other: St. Jude Children's Research Hospital has an existing exclusive license and ongoing partnership with Mustang Bio for the further clinical development and commercialization of this XSCID gene therapy.

Journal Article; Research Support, N.I.H., Intramural; Research Support, Non-U.S. Gov't;Erratium en J Clin Invest. 2016 Feb 1;126(2):795. doi: 10.1172/JCI86020: https://www.jci.org/articles/view/86020 Autosomal recessive mutations in proteasome subunit β 8 (PSMB8), which encodes the inducible proteasome subunit β5i, cause the immune-dysregulatory disease chronic atypical neutrophilic dermatosis with lipodystrophy and elevated temperature (CANDLE), which is classified as a proteasome-associated autoinflammatory syndrome (PRAAS). Here, we identified 8 mutations in 4 proteasome genes, PSMA3 (encodes α7), PSMB4 (encodes β7), PSMB9 (encodes β1i), and proteasome maturation protein (POMP), that have not been previously associated with disease and 1 mutation in PSMB8 that has not been previously reported. One patient was compound heterozygous for PSMB4 mutations, 6 patients from 4 families were heterozygous for a missense mutation in 1 inducible proteasome subunit and a mutation in a constitutive proteasome subunit, and 1 patient was heterozygous for a POMP mutation, thus establishing a digenic and autosomal dominant inheritance pattern of PRAAS. Function evaluation revealed that these mutations variably affect transcription, protein expression, protein folding, proteasome assembly, and, ultimately, proteasome activity. Moreover, defects in proteasome formation and function were recapitulated by siRNA-mediated knockdown of the respective subunits in primary fibroblasts from healthy individuals. Patient-isolated hematopoietic and nonhematopoietic cells exhibited a strong IFN gene-expression signature, irrespective of genotype. Additionally, chemical proteasome inhibition or progressive depletion of proteasome subunit gene transcription with siRNA induced transcription of type I IFN genes in healthy control cells. Our results provide further insight into CANDLE genetics and link global proteasome dysfunction to increased type I IFN production. Yes

Humoral immunity is critical for viral control, but the identity and mechanisms regulating human antiviral B cells are unclear. Here, we characterized human B cells expressing T-bet and analyzed their dynamics during viral infections. T-bet+ B cells demonstrated an activated phenotype, a distinct transcriptional profile, and were enriched for expression of the antiviral immunoglobulin isotypes IgG1 and IgG3. T-bet+ B cells expanded following yellow fever virus and vaccinia virus vaccinations and also during early acute HIV infection. Viremic HIV-infected individuals maintained a large T-bet+ B cell population during chronic infection that was associated with increased serum and cell-associated IgG1 and IgG3 expression. The HIV gp140-specific B cell response was dominated by T-bet-expressing memory B cells, and we observed a concomitant biasing of gp140-specific serum immunoglobulin to the IgG1 isotype. These findings suggest that T-bet induction promotes antiviral immunoglobulin isotype switching and development of a distinct T-bet+ B cell subset that is maintained by viremia and coordinates the HIV Env-specific humoral response.

Autosomal dominant gain of function mutations in the gene encoding PI3K p110δ were recently associated with a novel combined immune deficiency characterized by recurrent sinopulmonary infections, CD4 lymphopenia, reduced class-switched memory B cells, lymphadenopathy, CMV and/or EBV viremia and EBV-related lymphoma. A subset of affected patients also had elevated serum IgM. Here we describe three patients in two families who were diagnosed with HIGM at a young age and were recently found to carry heterozygous mutations in PIK3CD. These patients had an abnormal circulating B cell distribution featuring a preponderance of early transitional (T1) B cells and plasmablasts. When stimulated in vitro, PIK3CD mutated B cells were able to secrete class-switched immunoglobulins. This finding implies that the patients' elevated serum IgM levels were unlikely a product of an intrinsic B cell functional inability to class switch. All three patients developed malignant lymphoproliferative syndromes that were not associated with EBV. Thus, we identified a novel subset of patients with PIK3CD mutations associated with HIGM, despite indications of preserved in vitro B cell class switch recombination, as well as susceptibility to non-EBV-associated malignancies.

Kaposi's sarcoma-associated herpesvirus (KSHV) is causatively linked to two B cell lymphoproliferative disorders, multicentric Castleman's disease and primary effusion lymphoma. Latently infected B cells are a major KSHV reservoir, and virus activation from tonsillar B cells can result in salivary shedding and virus transmission. Paradoxically, human B cells (primary and continuous) are notoriously refractory to infection, thus posing a major obstacle to the study of KSHV in this cell type. By performing a strategic search of human B cell lymphoma lines, we found that MC116 cells were efficiently infected by cell-free KSHV. Upon exposure to recombinant KSHV.219, enhanced green fluorescent protein reporter expression was detected in 17 to 20% of MC116 cells. Latent-phase transcription and protein synthesis were detected by reverse transcription-PCR and detection of latency-associated nuclear antigen expression, respectively, in cell lysates and individual cells. Selection based on the puromycin resistance gene in KSHV.219 yielded cultures with all cells infected. After repeated passaging of the selected KSHV-infected cells without puromycin, latent KSHV was maintained in a small fraction of cells. Infected MC116 cells could be induced into lytic phase with histone deacetylase inhibitors, as is known for latently infected non-B cell lines, and also selectively by the B cell-specific pathway involving B cell receptor cross-linking. Lytic-phase transition was documented by red fluorescent protein reporter expression, late structural glycoprotein (K8.1A, gH) detection, and infectious KSHV production. MC116 cells were CD27 − /CD10 + , characteristic of transitional B cells. These findings represent an important step in the establishment of an efficient continuous B cell line model to study the biologically relevant steps of KSHV infection. IMPORTANCE Kaposi's sarcoma-associated herpesvirus (KSHV) causes two serious pathologies of B cells, the antibody-producing cells of the immune system. B cells are a major reservoir for KSHV persistence in the body. Paradoxically, in the laboratory, B cells are extremely difficult to infect with KSHV; this problem greatly hinders scientific analysis of B cell infection. We describe our search for and successful identification of a stable human B cell line that can be efficiently infected by KSHV. Upon infection of these cells, the virus goes into a quiet latent phase, a characteristic feature of many herpesvirus infections. The virus can be triggered to enter an active lytic phase by treatments known to stimulate normal B cell functions. These findings suggest that the new B cell line will be a valuable model in which to study KSHV infection of this major target cell type.

Objective Immune restoration disease (IRD) can develop in HIV-infected patients following antiretroviral therapy (ART) initiation as unmasking or paradoxical worsening of opportunistic infections and, rarely, autoimmune phenomena. Although IRD usually occurs in the first months of ART during memory CD4 T-cell recovery, Graves' disease occurs as a distinctive late-onset IRD and its pathogenesis is unclear. Design Seven patients who developed Graves' disease following ART initiation from the primary HIV care clinic at the National Institutes of Health were retrospectively identified and each was matched with two HIV-infected controls based on age, sex, and baseline CD4 T-cell count. Laboratory evaluations on stored cryopreserved samples were performed. Methods Immunophenotyping of peripheral blood mononuclear cells (PBMCs), T-cell receptor excision circle (TREC) analysis in PBMCs, measurement of serum cytokines, and luciferase immunoprecipitation systems (LIPS) analysis for autoimmune antibodies were performed on stored samples for cases and controls at baseline and longitudinally following ART initiation. TSH/thyrotropin receptor (TSH-R) antibody testing was performed on serum from cases. Data were analyzed using nonparametric testing. Results In comparison with controls, the proportion of naive CD4 T cells increased significantly (P = 0.0027) in the Graves' disease-IRD patients. TREC/10 PBMCs also increased significantly following ART in Graves' disease-IRD patients compared with controls (P = 0.0071). Similarly, LIPS analysis demonstrated increases in nonthyroid-related autoantibody titers over time following ART in cases compared with controls. Conclusion Our data suggest that Graves' disease-IRD, in contrast to early-onset IRD, is associated with naive and primary thymic emigrant CD4 T-cell recovery and inappropriate autoantibody production.

Terminal differentiation of B cells and hypergammaglobulinemia are hallmarks of B-cell hyperactivity in HIV disease. Plasmablasts are terminally differentiating B cells that circulate transiently in the blood following infection or vaccination; however, in HIV infection, they arise early and are maintained at abnormally high levels in viremic individuals. Here we show that only a small fraction of plasmablasts in the blood of viremic individuals is HIV specific. Assessment of plasmablast immunoglobulin isotype distribution revealed increased IgG + plasmablasts in early and most prominently during chronic HIV viremia, contrasting with a predominantly IgA + plasmablast profile in HIV-negative individuals or in aviremic HIV-infected individuals on treatment. Of note, IgG is the predominant immunoglobulin isotype of plasmablasts that arise transiently in the blood following parenteral immunization. Serum immunoglobulin levels were also elevated in HIV-infected viremic individuals, especially IgG, and correlated with levels of IgG + plasmablasts. Several soluble factors associated with immune activation were also increased in the sera of HIV-infected individuals, especially in viremic individuals, and correlated with serum immunoglobulin levels, particularly IgG. Thus, our data suggest that while plasmablasts in the blood may contribute to the HIV-specific immune response, the majority of these cells are not HIV specific and arise early, likely from indirect immune-activating effects of HIV replication, and reflect over time the effects of chronic antigenic stimulation. Such B-cell dysregulation may help explain why the antibody response is inadequate in HIV-infected individuals, even during early infection.

A primary immunodeficiency syndrome caused by loss-of-function mutations in the IL-21 receptor exhibits impaired B, T, and NK cell function., Primary immunodeficiencies (PIDs) represent exquisite models for studying mechanisms of human host defense. In this study, we report on two unrelated kindreds, with two patients each, who had cryptosporidial infections associated with chronic cholangitis and liver disease. Using exome and candidate gene sequencing, we identified two distinct homozygous loss-of-function mutations in the interleukin-21 receptor gene (IL21R; c.G602T, p.Arg201Leu and c.240_245delCTGCCA, p.C81_H82del). The IL-21RArg201Leu mutation causes aberrant trafficking of the IL-21R to the plasma membrane, abrogates IL-21 ligand binding, and leads to defective phosphorylation of signal transducer and activator of transcription 1 (STAT1), STAT3, and STAT5. We observed impaired IL-21–induced proliferation and immunoglobulin class-switching in B cells, cytokine production in T cells, and NK cell cytotoxicity. Our study indicates that human IL-21R deficiency causes an immunodeficiency and highlights the need for early diagnosis and allogeneic hematopoietic stem cell transplantation in affected children.

Targeted gene therapy has been hampered by the inability to correct mutations in stem cells that can reconstitute the immune system after transplant into patients. De Ravin et al . now report that CRISPR, a DNA editing technology, corrected blood stem cells from patients with an immunodeficiency disorder (chronic granulomatous disease) caused by mutations in NOX2. CRISPR-repaired human stem cells engrafted in mice after transplant and differentiated into leukocytes with a functional NOX2 protein for up to 5 months. The authors did not detect off-target treatment effects, suggesting that this gene repair strategy may benefit patients with chronic granulomatous disease or other blood disorders.

linked severe combined immunodeficiency (SCID-X1) is a profound deficiency of T, B, and natural killer (NK) cell immunity caused by mutations in IL2RG encoding the common chain (γc) of several interleukin receptors. Gamma-retroviral (γRV) gene therapy of SCID-X1 infants without conditioning restores T cell immunity without B or NK cell correction, but similar treatment fails in older SCID-X1 children. We used a lentiviral gene therapy approach to treat five SCID-X1 patients with persistent immune dysfunction despite haploidentical hematopoietic stem cell (HSC) transplant in infancy. Follow-up data from two older patients demonstrate that lentiviral vector γc transduced autologous HSC gene therapy after nonmyeloablative busulfan conditioning achieves selective expansion of gene-marked T, NK, and B cells, which is associated with sustained restoration of humoral responses to immunization and clinical improvement at 2 to 3 years after treatment. Similar gene marking levels have been achieved in three younger patients, albeit with only 6 to 9 months of follow-up. Lentiviral gene therapy with reduced-intensity conditioning appears safe and can restore humoral immune function to posthaploidentical transplant older patients with SCID-X1.

Despite the rare appearance of potent HIV-neutralizing mAbs in infected individuals requiring prolonged affinity maturation, little is known regarding this process in the majority of viremic individuals. HIV-infected individuals with chronic HIV viremia have elevated numbers of nonconventional tissue-like memory (TLM) B cells that predominate in blood over conventional resting memory (RM) B cells. Accordingly, we investigated affinity maturation in these 2 memory B cell populations. Analysis of IgG-expressing TLM B cells revealed a higher number of cell divisions compared with RM B cells; however, TLM B cells paradoxically displayed significantly lower frequencies of somatic hypermutation (SHM). To assess Ab reactivity in TLM and RM B cells, single-cell cloning was performed on HIV envelope CD4–binding site–sorted (CD4bs-sorted) B cells from 3 individuals with chronic HIV viremia. Several clonal families were present among the 127 cloned recombinant mAbs, with evidence of crosstalk between TLM and RM B cell populations that was largely restricted to non-VH4 families. Despite evidence of common origins, SHM frequencies were significantly decreased in TLM-derived mAbs compared with SHM frequencies in RM-derived mAbs. However, both cell populations had lower frequencies of SHMs than did broadly neutralizing CD4bs–specific mAbs. There was a significant correlation between SHM frequencies and the HIV-neutralizing capacities of the mAbs. Furthermore, HIV neutralization was significantly higher in the RM-derived mAbs compared with that seen in the TLM-derived mAbs, and both SHM frequencies and neutralizing capacity were lowest in TLM-derived mAbs with high polyreactivity. Thus, deficiencies in memory B cells that arise during chronic HIV viremia provide insight into the inadequacy of the Ab response in viremic individuals.

Human immunodeficiency virus (HIV)-specific B-cell responses in infected individuals are maintained by active HIV replication. Suppression of viremia by antiretroviral therapy (ART) leads to quantitative and qualitative changes that remain unclear. Accordingly, B-cell responses were investigated in elite controllers (ECs), who maintain undetectable HIV levels without ART, and in individuals whose viremia was suppressed by ART. Despite a higher HIV burden in the ART group, compared with the EC group, frequencies of HIV-specific B cells were higher in the EC group, compared with those in the ART group. However, the initiation of ART in several ECs was associated with reduced frequencies of HIV-specific B cells, suggesting that responses are at least in part sustained by HIV replication. Furthermore, B-cell responses to tetanus toxin but not influenza hemagglutinin in the ART group were lower than those in the EC group. Thus, the superior HIV-specific humoral response in ECs versus ART-treated individuals is likely due to a more intact humoral immune response in ECs and/or distinct responses to residual HIV replication.

Germline mutations in CARD11 that result in constitutive NF-κB activation and selective B cell expansion underlie congenital B cell lymphocytosis., Nuclear factor-κB (NF-κB) controls genes involved in normal lymphocyte functions, but constitutive NF-κB activation is often associated with B cell malignancy. Using high-throughput whole transcriptome sequencing, we investigated a unique family with hereditary polyclonal B cell lymphocytosis. We found a novel germline heterozygous missense mutation (E127G) in affected patients in the gene encoding CARD11, a scaffolding protein required for antigen receptor (AgR)–induced NF-κB activation in both B and T lymphocytes. We subsequently identified a second germline mutation (G116S) in an unrelated, phenotypically similar patient, confirming mutations in CARD11 drive disease. Like somatic, gain-of-function CARD11 mutations described in B cell lymphoma, these germline CARD11 mutants spontaneously aggregate and drive constitutive NF-κB activation. However, these CARD11 mutants rendered patient T cells less responsive to AgR-induced activation. By reexamining this rare genetic disorder first reported four decades ago, our findings provide new insight into why activating CARD11 mutations may induce B cell expansion and preferentially predispose to B cell malignancy without dramatically perturbing T cell homeostasis.

Chronic lymphocytic leukemia (CLL) is characterized by immune dysregulation, often including hypogammaglobulinemia, which contributes to a high rate of infections and morbidity. Ibrutinib, a covalent inhibitor of Bruton tyrosine kinase (BTK), inhibits B-cell receptor signaling and is an effective, US Food and Drug Administration (FDA)-approved treatment of CLL. Inactivating germline mutations in BTK cause a severe B-cell defect and agammaglobulinemia. Therefore, we assessed the impact of ibrutinib on immunoglobulin levels, normal B cells, and infection rate in patients with CLL treated with single-agent ibrutinib on a phase 2 investigator-initiated trial. Consistent with previous reports, immunoglobulin G (IgG) levels remained stable during the first 6 months on treatment, but decreased thereafter. In contrast, there were a transient increase in IgM and a sustained increase in IgA (median increase 45% at 12 months, P < .0001). To distinguish the effects on clonal B cells from normal B cells, we measured serum free light chains (FLCs). In κ-clonal CLL cases, clonal (κ) FLCs were elevated at baseline and normalized by 6 months. Nonclonal (λ) FLCs, which were often depressed at baseline, increased, suggesting the recovery of normal B cells. Consistently, we observed normal B-cell precursors in the bone marrow and an increase in normal B-cell numbers in the peripheral blood. Patients with superior immune reconstitution, as defined by an increase in serum IgA of ≥50% from baseline to 12 months, had a significantly lower rate of infections (P = .03). These data indicate that ibrutinib allows for a clinically meaningful recovery of humoral immune function in patients with CLL. This trial was registered at www.clinicaltrials.gov as #NCT015007330.

The immunomodulatory receptor CD300a is expressed on human B cells. Naive B cells express very low levels of this receptor, whereas memory B cells and plasmablasts/cells express variable levels of CD300a. Germinal center B cells are negative for CD300a expression. Stimulation of naive B cells via B-cell receptor (BCR) and Toll-like receptor 9, along with T-cell help, failed to up-regulate CD300a cell surface expression despite the increased expression of the memory marker CD27 and the down-regulation of CD305. However, Toll-like receptor 9 stimulation alone significantly increased CD300a expression on memory B cells, whereas interleukin-4 and transforming growth factor-β1 act as negative regulators of CD300a expression on memory B cells. Coligation of BCR and CD300a inhibits Ca2+ mobilization and nuclear factor of activated T cell transcriptional activity evoked by BCR ligation alone. Suppression of CD300a expression in primary B cells with siRNA resulted in increased BCR-mediated proliferation, thereby confirming the inhibitory capacity of CD300a. Finally, we show that CD300a expression levels are significantly down-regulated in the circulating B cells of HIV-infected patients. Altogether, these data demonstrate a novel mechanism for suppressing the activity of B cells and suggest a potential role for CD300a in the B-cell dysfunction observed in HIV-induced immunodeficiency.

Characterization of lymphocytes including B cells during early versus chronic HIV infection is important for understanding the impact of chronic viremia on immune cell function. In this setting, we investigated B cells before and after reduction of HIV plasma viremia by antiretroviral therapy (ART). At baseline, peripheral blood B-cell counts were significantly lower in both early and chronic HIV-infected individuals compared with uninfected controls. Similar to CD4+ but not CD8+ T cells, B-cell numbers in both groups increased significantly after ART. At baseline, B cells of early HIV-infected individuals were composed of a higher percentage of plasmablasts and resting memory B cells compared with chronic HIV-infected individuals whose B cells were composed of a higher percentage of immature/transitional and exhausted B cells compared with their early infection counterparts. At 1 year after ART, the percentage of resting memory B cells remained higher in early compared with chronic HIV-infected individuals. This difference translated into a better functional profile in that memory B-cell responses to HIV and non-HIV antigens were superior in early- compared with chronic-treated HIV infected individuals. These findings provide new insights on B cells in HIV infection and how early initiation of ART may prevent irreversible immune system damage.

Little is known about the transcriptional regulators that control the proliferation of multipotent bone marrow progenitors. Understanding the mechanisms that restrict proliferation is of significant interest since the loss of cell cycle integrity can be associated with hematopoietic exhaustion, bone marrow failure, or even oncogenic transformation. Herein, we show that multipotent LSKs (lineage−Scahighc-kit+) from E47-deficient mice exhibit a striking hyperproliferation associated with a loss of cell cycle quiescence and increased susceptibility to in vivo challenge with a mitotoxic drug. Total LSKs contain long-term self-renewing hematopoietic stem cells and downstream multipotential progenitors (MPPs) that possess very limited or no self-renewal ability. Within total LSKs, we found specific developmental and functional deficits in the MPP subset. E47 knockout mice have grossly normal numbers of self-renewing hematopoietic stem cells but a 50–70% reduction in nonrenewing MPPs and downstream lineage-restricted populations. The residual MPPs in E47 knockout mice fail to fully up-regulate flk2 or initiate V(D)J recombination, hallmarks of normal lymphoid lineage progression. Consistent with the loss of normal cell cycle restraints, we show that E47-deficient LSKs have a 50% decrease in p21, a cell cycle inhibitor and known regulator of LSK proliferation. Moreover, enforced expression studies identify p21 as an E47 target gene in primary bone marrow LSKs. Thus, E47 appears to regulate the developmental and functional integrity of early hematopoietic subsets in part through effects on p21-mediated cell cycle quiescence.

Several potent and broadly neutralizing Abs to HIV-1 have been isolated recently from peripheral blood B cells of infected individuals, based on prescreening of Ab activity in the serum. However, little is known regarding the cells that make the Abs that circulate in the blood. Accordingly, we investigated the most likely source, the bone marrow, of chronically HIV-1–infected individuals who were not receiving antiretroviral therapy. Increased frequencies of plasma cells, as well as B cell precursors, namely preB-I and preB-II, and decreased frequencies of mature B cells were observed in bone marrow aspirates of these individuals compared with HIV-negative counterparts. Increased frequencies of bone marrow plasma cells are consistent with known hallmarks of HIV-1 infection, namely hypergammaglobulinemia and increased frequencies of peripheral blood plasmablasts. Levels of HIV-1 envelope (Env)-binding and HIV-1–neutralizing Abs were measured in serum, and corresponding frequencies of Ab-secreting or Env-binding cells were measured in the blood (plasmablasts and memory B cells) and in the bone marrow (plasma cells). A strong correlation was observed between serum HIV-1–specific Abs and Env-specific bone marrow–derived plasma cells, but not circulating plasmablasts or memory B cells. These findings demonstrate that, despite HIV-1–induced phenotypic and functional B cell dysregulation in the peripheral blood and secondary lymphoid tissues, bone marrow plasma cells remain a primary source for circulating HIV-1–specific Abs in HIV-1–infected individuals.

Activating germline mutations in CARD11 have recently been linked to a rare genetic disorder associated with congenital B cell lymphocytosis. We describe a patient with a similar clinical phenotype who had a de novo germline G123D CARD11 mutation.Whole exome sequencing was performed on DNA from the patient and his biological parents. Laboratory studies examined characteristics of the patient's B and T lymphocytes. A CARD11 cDNA containing the mutation was transfected into a lymphocyte cell line to gain an understanding of its function. RNA sequencing was performed on samples from the patient and from patients with alternate germline CARD11 mutations and differential gene expression analysis was performed.The patient had a decade-long history of severe polyclonal B lymphocytosis in the 20,000-90,000 lymphocytes/mm(3) range, which was markedly exacerbated by EBV infection and splenectomy at different times. He had a heterozygous germline CARD11 mutation causing a G123D amino acid substitution, which was demonstrated to induce NF-κB activation in unstimulated lymphocytes. In contrast to previous patients with CARD11 mutations, this patient's B cells exhibited higher expression of several cell cycle progression genes, as well as enhanced proliferation and improved survival following B cell receptor stimulation.This is the third reported germline and first de novo CARD11 mutation shown to cause congenital B cell lymphocytosis. The mutation was associated with a dramatically greater lymphocytosis than in previously described cases, disproportionate to the level of constitutive NF-κB activation. However, comparative review of the patient's clinical history, combined with additional genomic and functional analyses, underscore other important variables that may affect pathophysiology or regulate mutant CARD11 function in B cell proliferation and disease. We now refer to these patients as having BENTA disease (B cell Expansion with NF-κB and T cell Anergy).

Background We previously reported abnormalities in circulating B cells in patients with chronic granulomatous disease (CGD) and those with HIV infection. Gastrointestinal complications are common to both diseases and likely involve perturbation of immune cells, including plasma cells (PCs). IgA is the most abundant immunoglobulin in the human body, with roles in protection and maintenance of intestinal homeostasis. IgA is produced primarily by PCs residing in mucosal tissues that are also thought to circulate in the blood. Objective We sought to characterize and compare PCs in patients with infectious (HIV) and noninfectious (CGD and Crohn disease) diseases that have been associated with intestinal inflammation. Methods Phenotypic and transcriptional analyses were performed on cells isolated from the blood and colon. Results IgA-secreting CCR10-expressing PCs predominated in the guts of healthy subjects, whereas in patients with HIV, CGD, and Crohn disease, there was a significant increase in the proportion of IgG-secreting PCs. Where intestinal inflammation was present, IgG-secreting PCs expressed reduced levels of CCR10 and increased levels of CXCR4. The intensity of CXCR4 expression correlated with the frequency of IgG-expressing PCs and the frequency of CXCR4 + /IgG + PCs was associated with the severity of intestinal inflammatory disease yet distinct from PCs and plasmablasts circulating in the blood. Conclusions These findings suggest that regardless of the underlying disease, the presence of CXCR4 + /IgG + PCs in the gut is a strong yet localized indicator of intestinal inflammation. Furthermore, our findings suggest that CXCR4 + /IgG + PCs might play a role in immune cell homeostasis during inflammatory processes of the gut.

CD27+ memory B cells are reduced in the blood of patients with chronic granulomatous disease (CGD) for reasons and consequences that remain unclear. Here we confirm not only decreased CD27+ but also IgG+ B cells in the blood of CGD patients compared with healthy donors (HDs). However, among IgG+ B cells, the ratio of CD27− to CD27+ was significantly higher in CGD patients compared with HDs. Similar to conventional memory B cells, CD27−IgG+ B cells of CGD patients expressed activation markers and had undergone somatic hypermutation, albeit at levels lower than their CD27+ counterparts. Functional analyses revealed slight reductions in frequencies of total IgG but not influenza-specific memory B-cell responses, as measured by Elispot in CGD patients compared with HDs. Serum IgG levels and influenza-specific antibodies were also normal in these CGD patients. Finally, we provide evidence that influenza-specific memory B cells can be present within the CD27−IgG+ B-cell compartment. Together, these findings show that, despite reduced circulating CD27+ memory B cells, CGD patients maintain an intact humoral immunologic memory, with potential contribution from CD27− B cells.

Chronic lymphocytic leukemia (CLL) is a common malignancy characterized by the accumulation of B lymphocytes with an antigen-experienced activated CD19(+)CD5(+) clonal phenotype. Clinically, ∼50% of cases will behave more aggressively. Here, we investigate the role of the major B-cell transcription factor E2A, a known regulator of B-cell survival and proliferation, to CLL persistence. We show that E2A is elevated at the mRNA and protein levels relative to normal B-cell subsets. E2A silencing in primary CLL cells leads to a significant increase in spontaneous apoptosis in both CD38(+) (aggressive) and CD38(-) (indolent) cases. Moreover, E2A knockdown synergizes with the immunomodulatory drug lenalidomide to reduce CLL viability. E2A is known to restrain the proliferation of primary B and T lymphocytes at multiple stages of maturation and we report that targeted E2A disruption increases the frequency of Ki-67(+) CLL cells in the absence of effects on de novo proliferation. At the molecular level, E2A siRNA-treated CLL cells display reduced expression of key genes associated with survival and cell cycling including p27, p21 and mcl-1, of which the former two are known E2A target genes. Thus, E2A, a key transcription factor associated with the B-cell activation profile, regulates apoptosis in CLL and may contribute to disease pathology.

CCAAT/enhancer-binding protein β (C/EBPβ), also known as nuclear factor–interleukin-6 (NF-IL6), is a transcription factor that plays an important role in the regulation of growth and differentiation of myeloid and lymphoid cells. Mice deficient in C/EBPβ show impaired generation of B lymphocytes. We show that C/EBPβ regulates transcription factors critical for proliferation and survival in multiple myeloma. Multiple myeloma cell lines and primary multiple myeloma cells strongly expressed C/EBPβ, whereas normal B cells and plasma cells had little or no detectable levels of C/EBPβ. Silencing of C/EBPβ led to down-regulation of transcription factors such as IRF4, XBP1, and BLIMP1 accompanied by a strong inhibition of proliferation. Further, silencing of C/EBPβ led to a complete down-regulation of antiapoptotic B-cell lymphoma 2 (BCL2) expression. In chromatin immunoprecipitation assays, C/EBPβ directly bound to the promoter region of IRF4, BLIMP1, and BCL2. Our data indicate that C/EBPβ is involved in the regulatory network of transcription factors that are critical for plasma cell differentiation and survival. Targeting C/EBPβ may provide a novel therapeutic strategy in the treatment of multiple myeloma.

V(D)J recombinase activity is expressed in bone marrow (BM) multipotent progenitors (MPPs) that retain the potential to differentiate into B cells in BM and T cells in thymus. However, it remains unclear whether MPPs in each organ exhibit distinct transcriptional requirements for recombinase activity, or whether thymic MPPs imprint the requirements of upstream BM MPPs from which they originate. Here we use V(D)J recombination reporter mice to examine transcriptional requirements in BM versus thymic multipotent subsets. Within BM, the frequency of recombinase+ cells increases from 5% in MPPs to 15% in common lymphoid progenitors (CLPs) and 20% in pre-pro B cells. Within thymus, 10% of early thymic progenitors (ETPs) are recombinase+. While the E47 transcription factor is expressed in both BM and thymus, E47 deficiency selectively ablates V(D)J recombination in the former. BM MPPs, CLPs and pre-pro B cells from E47 knockouts lack detectable recombinase activity. In the thymus, E47 deficiency reduces ETP numbers but V(D)J recombinase activity is maintained. Loss of the related E protein HEB does not diminish recombinase activity in ETPs while functional inhibition of E47:HEB complexes leads to a 40% reduction in TCRβ rearrangements. Thus, V(D)J recombinase activity is regulated differently in MPPs in BM and thymus. E protein transcription factors are essential for recombinase activity in multipotent BM MPPs and CLPs but are dispensable in multipotent thymic ETPs.

It is of great interest to understand the mechanisms controlling the development and maintenance of multi-potential bone marrow progenitors, the key hematopoietic compartment that seeds the entire immune system. Using E47 knockout (KO) mice, we found that the transcription factor E47 plays a critical role in the cell cycle regulation and development of the multipotent hematopoietic subsets. Multipotent LSKs (Lineage-Sca-1+c-Kit+) from E47 KO mice had significantly increased BrdU incorporation, decreased proportion of progenitors in G0, and hypersensitivity to a mitotoxin 5-Fluorouracil, suggesting loss of cell cycle quiescence. Total LSKs contain both self-renewing hematopoietic stem cells (HSCs) and non-renewing multipotential progenitors (MPPs). Using three independent phenotypic definitions, we found that E47 KO mice have numerically unperturbed HSCs but a 2-4 fold reduction in the MPPs. Moreover, the residual MPPs in E47 KO mice fail to fully up-regulate flk2 and lack V(D)J rearrangement, suggesting compromised lymphoid differentiation potential. Finally, both loss-of-function and gain-of-function experiments identified a key stem cell regulator, p21, as E47 target in the multipotent LSKs. Taken together, our data define an important role of the transcription factor E47 in controlling the development, differentiation and cell cycle regulation of multipotent hematopoietic progenitors.

Chronic lymphocytic leukemia (CLL) is a common malignancy characterized by the accumulation of B lymphocytes with an antigen-experienced, activated CD19+CD5+ clonal phenotype. Clinically, approximately 50% of cases will behave more aggressively. Here we used siRNA knockdown to investigate the contribution of E2A, a key transcriptional regulator of B cell activation, to CLL survival and proliferation. E2A silencing in primary CLL cells leads to a modest increase in spontaneous apoptosis in both CD38+ (aggressive) and CD38- (indolent) cases. E2A is known to restrain lymphocyte proliferation, and E2A disruption promotes cell cycle progression of aggressive but not indolent CLL. Lenalidomide, an immunomodulatory (IMiD) anticancer drug with pro-apoptotic activity in some B lineage cancers, shows synergistic effects with E2A knockdown. While lenalidomide alone fails to induce detectable apoptosis in CLL, the combined treatment of lenalidomide plus E2A silencing dramatically increases apoptosis beyond either treatment alone. Thus, disruption of a transcription factor associated with the B cell activation profile enhances the anti-tumor potential of lenalidomide, providing the opportunity for improved drug efficacy.