Reaching macs-imum potential.

Single-cell profiling of prenatal samples reveals multiple macrophage types and states, including microglia-like cells in non-neuronal tissues.

Antibodies elicited in humans upon chimeric hemagglutinin-based influenza virus vaccination confer FcγR-dependent protection in vivo.

Antibody responses against highly conserved epitopes on the stalk domain of influenza virus hemagglutinin (HA) confer broad protection; however, such responses are limited. To effectively induce stalk-specific immunity against conserved HA epitopes, sequential immunization strategies have been developed based on chimeric HA (cHA) constructs featuring different head domains but the same stalk regions. Immunogenicity studies in small animal models, as well as in humans, revealed that cHA immunogens elicit stalk-specific IgG responses with broad specificity against heterologous influenza virus strains. However, the mechanisms by which these antibodies confer in vivo protection and the contribution of their Fc effector function remain unclear. To characterize the role of Fc-FcγR (Fcγ receptor) interactions to the in vivo protective activity of IgG antibodies elicited in participants in a phase I trial of a cHA vaccine candidate, we performed passive transfer studies of vaccine-elicited IgG antibodies in mice humanized for all classes of FcγRs, as well as in mice deficient for FcγRs. IgG antibodies elicited upon cHA vaccination completely protected FcγR humanized mice against lethal influenza virus challenge, while no protection was evident in FcγR-deficient mice, suggesting a major role for FcγR pathways in the protective function of vaccine-elicited IgG antibodies. These findings have important implications for influenza vaccine development, guiding the design of vaccination approaches with the capacity to elicit IgG responses with optimal Fc effector function.

An arrayed CRISPR screen of primary B cells reveals the essential elements of the antibody secretion pathway.

Background: Humoral immunity depends on the differentiation of B cells into antibody secreting cells (ASCs). Excess or inappropriate ASC differentiation can lead to antibody-mediated autoimmune diseases, while impaired differentiation results in immunodeficiency. Methods: We have used CRISPR/Cas9 technology in primary B cells to screen for regulators of terminal differentiation and antibody production. Results: We identified several new positive (Sec61a1, Hspa5) and negative (Arhgef18, Pold1, Pax5, Ets1) regulators that impacted on the differentiation process. Other genes limited the proliferative capacity of activated B cells (Sumo2, Vcp, Selk). The largest number of genes identified in this screen (35) were required for antibody secretion. These included genes involved in endoplasmic reticulum-associated degradation and the unfolded protein response, as well as post-translational protein modifications. Discussion: The genes identified in this study represent weak links in the antibody-secretion pathway that are potential drug targets for antibody-mediated diseases, as well as candidates for genes whose mutation results in primary immune deficiency.

Generation of a CRISPR activation mouse that enables modelling of aggressive lymphoma and interrogation of venetoclax resistance.

CRISPR technologies have advanced cancer modelling in mice, but CRISPR activation (CRISPRa) methods have not been exploited in this context. We establish a CRISPRa mouse (dCas9a-SAMKI) for inducing gene expression in vivo and in vitro. Using dCas9a-SAMKI primary lymphocytes, we induce B cell restricted genes in T cells and vice versa, demonstrating the power of this system. There are limited models of aggressive double hit lymphoma. Therefore, we transactivate pro-survival BCL-2 in Eµ-MycT/+;dCas9a-SAMKI/+ haematopoietic stem and progenitor cells. Mice transplanted with these cells rapidly develop lymphomas expressing high BCL-2 and MYC. Unlike standard Eµ-Myc lymphomas, BCL-2 expressing lymphomas are highly sensitive to the BCL-2 inhibitor venetoclax. We perform genome-wide activation screens in these lymphoma cells and find a dominant role for the BCL-2 protein A1 in venetoclax resistance. Here we show the potential of our CRISPRa model for mimicking disease and providing insights into resistance mechanisms towards targeted therapies.

Epigenetic modulators of B cell fate identified through coupled phenotype-transcriptome analysis.

High-throughput methodologies are the cornerstone of screening approaches to identify novel compounds that regulate immune cell function. To identify novel targeted therapeutics to treat immune disorders and haematological malignancies, there is a need to integrate functional cellular information with the molecular mechanisms that regulate changes in immune cell phenotype. We facilitate this goal by combining quantitative methods for dissecting complex simultaneous cell phenotypic effects with genomic analysis. This combination strategy we term Multiplexed Analysis of Cells sequencing (MAC-seq), a modified version of Digital RNA with perturbation of Genes (DRUGseq). We applied MAC-seq to screen compounds that target the epigenetic machinery of B cells and assess altered humoral immunity by measuring changes in proliferation, survival, differentiation and transcription. This approach revealed that polycomb repressive complex 2 (PRC2) inhibitors promote antibody secreting cell (ASC) differentiation in both murine and human B cells in vitro. This is further validated using T cell-dependent immunization in mice. Functional dissection of downstream effectors of PRC2 using arrayed CRISPR screening uncovered novel regulators of B cell differentiation, including Mybl1, Myof, Gas7 and Atoh8. Together, our findings demonstrate that integrated phenotype-transcriptome analyses can be effectively combined with drug screening approaches to uncover the molecular circuitry that drives lymphocyte fate decisions.

The gene regulatory network controlling plasma cell function.

Antibodies are an essential element of the immune response to infection, and in long-term protection upon re-exposure to the same micro-organism. Antibodies are produced by plasmablasts and plasma cells, the terminally differentiated cells of the B lymphocyte lineage. These relatively rare populations, collectively termed antibody secreting cells (ASCs), have developed highly specialized transcriptional and metabolic pathways to facilitate their extraordinarily high rates of antibody synthesis and secretion. In this review, we discuss the gene regulatory network that controls ASC identity and function, with a particular focus on the processes that influence the transcription, translation, folding, modification and secretion of antibodies. We will address how ASCs have adapted their transcriptional, metabolic and protein homeostasis pathways to sustain such high rates of antibody production, and the roles that the major ASC regulators, the transcription factors, Irf4, Blimp-1 and Xbp1, play in co-ordinating these processes.

Mining the Plasma Cell Transcriptome for Novel Cell Surface Proteins.

Antibody Secreting Cells (ASCs) are a fundamental component of humoral immunity, however, deregulated or excessive antibody production contributes to the pathology of autoimmune diseases, while transformation of ASCs results in the malignancy Multiple Myeloma (MM). Despite substantial recent improvements in treating these conditions, there is as yet no widely used ASC-specific therapeutic approach, highlighting a critical need to identify novel methods of targeting normal and malignant ASCs. Surface molecules specifically expressed by the target cell population represent ideal candidates for a monoclonal antibody-based therapy. By interrogating the ASC gene signature that we previously defined we identified three surface proteins, Plpp5, Clptm1l and Itm2c, which represent potential targets for novel MM treatments. Plpp5, Clptm1l and Itm2c are highly and selectively expressed by mouse and human ASCs as well as MM cells. To investigate the function of these proteins within the humoral immune system we have generated three novel mouse strains, each carrying a loss-of-function mutation in either Plpp5, Clptm1l or Itm2c. Through analysis of these novel strains, we have shown that Plpp5, Clptm1l and Itm2c are dispensable for the development, maturation and differentiation of B-lymphocytes, and for the production of antibodies by ASCs. As adult mice lacking either protein showed no apparent disease phenotypes, it is likely that targeting these molecules on ASCs will have minimal on-target adverse effects.

Characterization of Blimp-1 function in effector regulatory T cells.

Regulatory T (Treg) cells maintain immunological tolerance in steady-state and after immune challenge. Activated Treg cells can undergo further differentiation into an effector state that highly express genes critical for Treg cell function, including ICOS, TIGIT and IL-10, although how this process is controlled is poorly understood. Effector Treg cells also specifically express the transcriptional regulator Blimp-1 whose expression overlaps with many of the canonical markers associated with effector Treg cells, although not all ICOS+TIGIT+ Treg cells express Blimp-1 or IL-10. In this study, we addressed the role of Blimp-1 in effector Treg cell function. Mice lacking Blimp-1 specifically in Treg cells mature normally, but succumb to a multi-organ inflammatory disease later in life. Blimp-1 is not required for Treg cell differentiation, with mutant mice having increased numbers of effector Treg cells, but regulated a suite of genes involved in cell signaling, communication and survival, as well as being essential for the expression of the immune modulatory cytokine IL-10. Thus, Blimp-1 is a marker of effector Treg cells in all contexts examined and is required for the full functionality of these cells during aging.

Environmental sensing by mature B cells is controlled by the transcription factors PU.1 and SpiB.

Humoral immunity requires B cells to respond to multiple stimuli, including antigen, membrane and soluble ligands, and microbial products. Ets family transcription factors regulate many aspects of haematopoiesis, although their functions in humoral immunity are difficult to decipher as a result of redundancy between the family members. Here we show that mice lacking both PU.1 and SpiB in mature B cells do not generate germinal centers and high-affinity antibody after protein immunization. PU.1 and SpiB double-deficient B cells have a survival defect after engagement of CD40 or Toll-like receptors (TLR), despite paradoxically enhanced plasma cell differentiation. PU.1 and SpiB regulate the expression of many components of the B cell receptor signaling pathway and the receptors for CD40L, BAFF and TLR ligands. Thus, PU.1 and SpiB enable B cells to appropriately respond to environmental cues.