Long-Lived Plasma Cells Are Contained within the CD19(-)CD38(hi)CD138(+) Subset in Human Bone Marrow

Heterohybridomas producing human immunoglobulin light chains using CD138-selected bone marrow cells

Background

Light chain research is hampered by lack of mammalian cell lines producing human light chains (FLC). Therefore, we used heterohybridoma (HH) technology to produce clones making FLC thereby providing tools to study light chain behavior.

Methods

Marrow CD138+ cells from patients with multiple myeloma (MM) and polyclonal gammopathy (PG) were selected, fused with B5-6 T cells and cultured in hypoxanthine-aminopterin-thymidine medium (HAT). HH clones were selected based on ELISA for human immunoglobulins and flow cytometry for intracellular (IC) FLC. We compared marrow cell counts and HH yields by diagnosis, evaluated clones making only FLC by flow and by dimer/monomer (D/M) ratios in vitro and in vivo, and sequenced FLC genes with RT-PCR.

Results

Marrows from 13 patients with active disease, 10 MM and 3 PG, were no different in mononuclear or CD138-selected cell counts. HH FLC clones (7 λ, 1 κ) were obtained from 5/10 MM and 2/3 PG; one PG case produced 2 HH FLC clones (one λ and one κ). Of the 10 MM cases, 8 had high risk cytogenetic features and 4 of the 8 produced HH clones while of the 3 PG cases 2 had negative cytogenetics and 1 had loss of IgH identified and produced an HH clone. Mononuclear (MNC) and CD138-selected cell numbers were markedly higher in the samples that enabled productive fusions. Median MFI for the 8 HH clones by IC flow for FLC was 9849 (range, 5344-27451) and median percentage of cells IC positive was 88 % (69-95). Medians of in vitro and in vivo FLC production were 47 μg/mL (9-80) per million cells after 2 days of culture and 66.4 μg/mL (16-1100) in NOD-SCID γ (NSG) mice 14 days after intraperitoneal (IP) implants of 2 × 106 HH cells. Dimer/monomer ratio medians were 0.575 (0.08-0.939) in vitro and 0.91 (0.82-2.7) in vivo, values that were correlated (R2 = 0.565) by two-tailed paired t-test with P < 0.05.

Conclusions

B5-6 T HH producing human FLC were obtained from 50 % of MM and PG cases. High numbers of MNC and CD138+ cells enabled productive fusions. The HH clones produced FLC with easily appreciated dimers and monomers in vitro and in vivo. With IP in vivo implants after 2 weeks more dimers were seen than in short term cultures in vitro. These HH clones will be made available for study of FLC metabolism and testing of therapeutics designed to abrogate FLC production or enable FLC clearance in vivo.

KLF2 expression in IgG plasma cells at their induction site regulates the migration program

Newly generated plasma cells in secondary lymphoid organs migrate to niches in the bone marrow, wherein they survive as long-lived plasma cells (LLPCs). Although LLPCs have been extensively characterized, it is still unclear what the key determinant(s) are for plasma cell longevity. One model postulates that plasma cell heterogeneity is established at the induction site, thereby instructing their longevity. Here, we found that, among newly generated IgG plasma cells, integrin β7hi marks plasma cells predisposed to home to the bone marrow, whereas integrin β7lo cells remain in secondary lymphoid organs. Mechanistically, this egress-prone fraction had a higher expression of the KLF2 transcription factor, the loss of which resulted in defective egress by downregulating S1PR1 and CD11b. Disruption of plasma cell egress results in defective antibody durability, thereby making mice more susceptible to influenza reinfection. Thus, the migration program of plasma cells established at the induction site plays a critical role in determining antibody durability.

Development of Methods to Produce SARS CoV-2 Virus-Like Particles at Scale

The devastating global toll precipitated by the SARS CoV-2 outbreak and the profound impact of vaccines in stemming that outbreak has established the need for molecular platforms capable of rapidly delivering effective, safe and accessible medical interventions in pandemic preparedness. We describe a simple, efficient and adaptable process to produce SARS CoV-2 virus-like particles (VLPs) that can be readily scaled for manufacturing. A rapid but gentle method of tangential flow filtration using a 100 kDa semi-permeable membrane concentrates and buffer exchanges 0.5 L of SARS CoV-2 VLP containing supernatant into low salt and optimal pH for anion exchange chromatography. VLPs are washed, eluted under high salt, dialyzed into physiological buffer, sterile filtered and aliquoted for storage at -80°C. Purification is completed in less than 2 days. A simple quality control process includes Western blot for coincident detection of Spike, Membrane and Envelope protein as a proxy for intact VLP, ELISA to detect conformationally sensitive Spike using readily available anti-Spike and/or anti-RBD antibodies, and negative stain and immunogold electron microscopy to validate particulate, Spike crowned VLPs. This process to produce SARS CoV-2 VLPs for preclinical studies serves as a roadmap for preparation of more distantly related VLPs for pandemic preparedness.

Syndecans and glycosaminoglycans influence B-cell development and activation

Syndecans (SDCs) are glycosaminoglycan-containing cell surface proteins with diverse functions in the immune system with SDC1 (CD138) and SDC4 expressed in B-lineage cells. Here, we show that stem cells lacking either molecule generate fewer B-cell progenitors but give rise to mature B cells in vivo. Deletion of the plasma cell "marker" CD138 has no effect on homeostatic or antigen-induced plasma cell formation. Naive B cells express high SDC4 and encounter with cognate antigen results in transient CD138 upregulation and SDC4 loss, both further modulated by IL-4, IL-21, and CD40 ligation. SDC4 is downregulated on germinal center B cells and absent on most memory B cells. Glycosaminoglycans such as those attached to SDCs, and heparin, a commonly used therapeutic, regulate survival and activation of naive B cells by limiting responsiveness to cognate antigen. Conversely, ablation of SDC4 results in increased baseline and antigen-induced B-cell activation. Collectively, our data reveal B-cell activation- and subset-dependent SDC expression and show that SDC4 and GAGs can limit antigen-induced activation to promote B-cell survival and expansion.

Lung-resident memory B cells maintain allergic IgE responses in the respiratory tract

Although allergen-specific immunoglobulin E (IgE) is a key mediator of allergic asthma, IgE-expressing B cells fail to form memory B cells (MBCs). Here, we studied the cellular mechanisms supporting IgE production in the respiratory tract. Allergen inhalation induced B cell infiltration into the lungs and IgE in the airway. Tracking B cells poised to class switch to IgE in reporter mice revealed predominant IgE class switching in the lung and identified IgG1+ MBCs as precursors of IgE-producing cells, which was supported by B cell receptor (BCR) repertoire sequencing. B cells localized with CD4+ T cells in peribronchiolar lymphoid aggregates. In coculture, interleukin-4 from lung Th2 cells induced lung MBCs to class switch to IgE. Lung-resident MBCs expanded after antigen rechallenge, concurrent with the emergence of IgE-secreting plasma cells (PCs), and the production of IgE in the airway was independent of systemic IgE in circulation, as indicated by parabiosis. Thus, lung-resident IgG1+ MBCs are cellular precursors for IgE-secreting PCs in the respiratory mucosa.

Satralizumab after inebilizumab treatment in a patient with recurrent neuromyelitis optica spectrum disorder: A case report

RATIONALE

Neuromyelitis optica spectrum disorder (NMOSD) comprises a group of rare and severe autoimmune inflammatory diseases affecting the central nervous system, mainly the optic nerves and spinal cord. Phase III studies have shown that the incidence of relapse is significantly reduced in aquaporin (AQP) 4 antibody-positive patients after treatment with satralizumab, a humanized monoclonal recycling antibody that blocks interleukin (IL)-6 signaling pathways, in conjunction with inebilizumab, a B-cell-depleting agent. Here, we report our experience with a patient who presented with pain associated with NMOSD.

PATIENT CONCERNS

A 40-year-old woman initially presented with acute thoracic myelitis. Magnetic resonance imaging revealed a demyelinating lesion in the spinal cord spanning from T2 to T10, along with enhancement and a positive serum AQP4-immunoglobulin G (IgG) titer.

DIAGNOSIS

NMOSD.

INTERVENTIONS

The patient initially received adequate long-term immunotherapy with inebilizumab and corticosteroids. Satralizumab was administered after treatment failure.

OUTCOMES

The patient experienced recurrences of the disorder despite the initial immunotherapy, including pain and immobility from neurological dysfunction. Furthermore, her serum AQP4-IgG titer remained elevated (1:320), her B-cell proportion remained at 0, and her symptoms were not adequately relieved. She was then administered satralizumab, after which her serum AQP4-IgG and IL-6 levels decreased, the radiological appearance of spinal cord demyelination improved, her pain and other symptoms were alleviated, and her neurological function gradually recovered.

LESSONS

In patients with clinical episodes of NMOSD that recur despite treatment with a B-cell-depleting agent, satralizumab may help alleviate myelitis-associated pain. Further investigations are warranted to establish IL-6 as a therapeutic target for the treatment of neuropathic pain, and may help address the unmet medical need in the management of NMOSD-associated neuropathic pain. As exemplified by the present case, individualized management, and therapy for patients with NMOSD are essential. Our case report provides new ideas for the management of patients with refractory NMOSD and patients with subsequent severe neuropathic pain.

Protein sequence modelling with Bayesian flow networks

Exploring the vast and largely uncharted territory of amino acid sequences is crucial for understanding complex protein functions and the engineering of novel therapeutic proteins. Whilst generative machine learning has advanced protein sequence modelling, no existing approach is proficient in both unconditional and conditional generation. In this work, we propose that Bayesian Flow Networks (BFNs), a recently introduced framework for generative modelling, can address these challenges. We present ProtBFN, a 650M parameter model trained on protein sequences curated from UniProtKB, which generates natural-like, diverse, structurally coherent, and novel protein sequences, significantly outperforming leading autoregressive and discrete diffusion models. Further, we fine-tune ProtBFN on heavy chains from the Observed Antibody Space to obtain an antibody-specific model, AbBFN, which we use to evaluate zero-shot conditional generation capabilities. AbBFN is found to be competitive with or better than antibody-specific BERT-style models when applied to predicting individual framework or complimentary determining regions.

Immune training enhances anti-viral responses and improves outcomes in Pax5-/+ mice susceptible to chronic infection

Viral infections pose a significant global burden. Host susceptibility to pathogens is determined by many factors including genetic variation that can lead to immunodeficient or dysregulated antiviral immune responses. Pax5 heterozygosity (Pax5-/+), resulting in reduced PAX5 levels in mice, mimics germline or somatic PAX5 dysregulation contributing to diseases such as childhood B-cell precursor acute lymphoblastic leukemia (B-ALL). In contrast to the well-characterized roles of PAX5 during early B-cell development, little is known about how Pax5 heterozygosity impacts antiviral responses. We infected Pax5-/+ mice with the noncytopathic Lymphocytic Choriomeningitis Virus (LCMV) and found that infection with the chronic Docile strain resulted in decreased survival of Pax5-/+ mice. While early adaptive CD8+ T-cell (CTL) immunity was robust in Pax5-/+ mice, LCMV-specific neutralizing antibody production was compromised leading to impaired long-term viral clearance and a pro-inflammatory milieu in the bone marrow (BM). Here we show that survival outcomes were improved upon prophylactic treatment with the β-glucan immune trainer through induction of heterologous protection against chronic infection. β-Glucan enhanced viral clearance, CTL immunity, neutralizing antibody production and reduced monocyte immunosuppression in multiple LCMV-resident host organs. New insight from this study will help design effective prophylactic treatment strategies against chronic viral infections, particularly in genetically predisposed susceptible hosts.

Maternal obesity associates with altered humoral immunity in blood and colostrum

Maternal obesity is a condition with increasing prevalence worldwide, that correlates with negative infant outcomes. Here we performed an observational cross-sectional study, where peripheral blood and colostrum samples from 37 mothers with BMI between 18.5-25 or > 30 kg/m2 (21 and 16 mothers, respectively) were collected 24-48 h postpartum. B lymphocyte subpopulations were investigated using flow cytometry. IgG, IgA, and IgM concentrations, and antibody production from colostrum-resident B cells were quantified. Overall, naïve B lymphocytes were the most abundant subtype in peripheral blood, while CD27-IgD- double-negative B cells were the most frequent in colostrum. The colostrum from mothers with BMI > 30 kg/m2 contained significantly more IgG-secreting colostrum-resident B cells, more total IgG, and less total IgA. Mothers with BMI > 30 kg/m2 who had been vaccinated with the Pfizer BioNTech bivalent vaccine during the third trimester of pregnancy (n = 8) did not show higher IgA or IgG antibody responses against SARS-CoV-2 RBD in either tissue types compared to unvaccinated mothers, contrasting with mother of BMI between 18.5-25 kg/m2 (n = 7). This is the first characterization of B lymphocyte subpopulations and antibodies in the colostrum of mothers with obesity. This work uncovers maternal obesity as a possible modifier of humoral immune components in colostrum.

SARS-CoV-2: The Interplay Between Evolution and Host Immunity

The persistence of SARS-CoV-2 infections at a global level reflects the repeated emergence of variant strains encoding unique constellations of mutations. These variants have been generated principally because of a dynamic host immune landscape, the countermeasures deployed to combat disease, and selection for enhanced infection of the upper airway and respiratory transmission. The resulting viral diversity creates a challenge for vaccination efforts to maintain efficacy, especially regarding humoral aspects of protection. Here, we review our understanding of how SARS-CoV-2 has evolved during the pandemic, the immune mechanisms that confer protection, and the impact viral evolution has had on transmissibility and adaptive immunity elicited by natural infection and/or vaccination. Evidence suggests that SARS-CoV-2 evolution initially selected variants with increased transmissibility but currently is driven by immune escape. The virus likely will continue to drift to maintain fitness until countermeasures capable of disrupting transmission cycles become widely available.

Long-term B cell memory emerges at uniform relative rates in the human immune response

B cells generate pathogen-specific antibodies and play an essential role in providing adaptive protection against infection. Antibody genes are modified in evolutionary processes acting on the B cell populations within an individual. These populations proliferate, differentiate, and migrate to long-term niches in the body. However, the dynamics of these processes in the human immune system are primarily inferred from mouse studies. We addressed this gap by sequencing the antibody repertoire and transcriptomes from single B cells in four immune-rich tissues from six individuals. We find that B cells descended from the same pre-B cell ("lineages") often colocalize within the same tissue, with the bone marrow harboring the largest excess of lineages without representation in other tissues. Within lineages, cells with different levels of somatic hypermutation are uniformly distributed among tissues and functional states. This suggests that the relative probabilities of localization and differentiation outcomes change negligibly during affinity maturation, and quantitatively agrees with a simple dynamical model of B cell differentiation. While lineages strongly colocalize, we find individual B cells nevertheless appear to make independent differentiation decisions. Proliferative antibody-secreting cells, however, deviate from these global patterns. These cells are often clonally expanded, their clones appear universally distributed among all sampled organs, and form lineages with an excess of cells of the same type. Collectively, our findings show the limits of peripheral blood monitoring of the immune repertoire, and provide a probabilistic model of the dynamics of antibody memory formation in humans.

A genome wide CRISPR screen reveals novel determinants of long-lived plasma cell secretory capacity

Plasma cell subsets vary in their lifespans and ability to sustain humoral immunity. We conducted a genome-wide CRISPR-Cas9 screen in a myeloma cell line for factors that promote surface expression of CD98, a marker of longevity in primary mouse plasma cells. A large fraction of genes found to promote CD98 expression in this screen are involved in secretory and other vesicles, including many subunits of the V-type ATPase complex. Chemical inhibition or genetic ablation of V-type ATPases in myeloma cells reduced antibody secretion. Primary mouse and human long-lived plasma cells had greater numbers of acidified vesicles than did their short-lived counterparts, and this correlated with increased secretory capacity of IgM, IgG, and IgA. The screen also identified PI4KB, which promoted acidified vesicle numbers and secretory capacity, and DDX3X, an ATP-dependent RNA helicase, the deletion of which reduced immunoglobulin secretion independently of vesicular acidification. Finally, we report a plasma-cell intrinsic function of the signaling adapter MYD88 in both antibody secretion and plasma cell survival in vivo. These data reveal novel regulators of plasma cell secretory capacity, including those that also promote lifespan.

Biomarker expression level changes within rectal gut-associated lymphoid tissues in spinal cord-injured rats

Neurogenic bowel dysfunction (NBD) is common after spinal cord injury (SCI). Gut-associated lymphoid tissue (GALT), an organized structure within the mucosal immune system, is important for the maintenance of gut homeostasis and body health and serves as the first line barrier/defense against diet antigens, commensal microbiota, pathogens, and toxins in mucosal areas. The current study examined gene expression levels along six segments of anorectal tissue using real-time polymerase chain reaction (RT-PCR) in uninjured rats (28-day sham surgical controls) and at both 28- and 42-days post-T9 contusion injury. Consistent with our previous report of functional regional differences in the ano-rectum, we demonstrate the existence of GALTs located primarily within the segment at 3-4.5 cm from the rectal dentate line (termed rectal GALTs-rGALTs) in shams with upregulated gene expression levels of multiple biomarkers, including B cell and T cell-related genes, major histocompatibility complex (MHC) class II molecules, and germinal center (GC)-related genes, which was further confirmed by histologic examination. In the same rectal tissue segment following T9 SCI, inflammation-related genes were upregulated at 28 days post-injury (DPI) indicating that microbial infection and inflammation of rGALTs modified structure and function of rGALTs, while at 42 DPI rGALTs exhibited resolution of inflammation and impaired structure/function for extrafollicular B cell responses. Taken together, our data suggest that rGALTs exists in rat rectum for homeostasis of gut microbiota/barrier. SCI induces microbial infection and inflammation in rectal tissues containing rGALTs, which could contribute to development of SCI-related gut microbiome dysbiosis, NBD, and systemic diseases.

Immunologic and inflammatory consequences of SARS-CoV-2 infection and its implications in renal disease

The emergence of the COVID-19 pandemic made it critical to understand the immune and inflammatory responses to the SARS-CoV-2 virus. It became increasingly recognized that the immune response was a key mediator of illness severity and that its mechanisms needed to be better understood. Early infection of both tissue and immune cells, such as macrophages, leading to pyroptosis-mediated inflammasome production in an organ system critical for systemic oxygenation likely plays a central role in the morbidity wrought by SARS-CoV-2. Delayed transcription of Type I and Type III interferons by SARS-CoV-2 may lead to early disinhibition of viral replication. Cytokines such as interleukin-1 (IL-1), IL-6, IL-12, and tumor necrosis factor α (TNFα), some of which may be produced through mechanisms involving nuclear factor kappa B (NF-κB), likely contribute to the hyperinflammatory state in patients with severe COVID-19. Lymphopenia, more apparent among natural killer (NK) cells, CD8+ T-cells, and B-cells, can contribute to disease severity and may reflect direct cytopathic effects of SARS-CoV-2 or end-organ sequestration. Direct infection and immune activation of endothelial cells by SARS-CoV-2 may be a critical mechanism through which end-organ systems are impacted. In this context, endovascular neutrophil extracellular trap (NET) formation and microthrombi development can be seen in the lungs and other critical organs throughout the body, such as the heart, gut, and brain. The kidney may be among the most impacted extrapulmonary organ by SARS-CoV-2 infection owing to a high concentration of ACE2 and exposure to systemic SARS-CoV-2. In the kidney, acute tubular injury, early myofibroblast activation, and collapsing glomerulopathy in select populations likely account for COVID-19-related AKI and CKD development. The development of COVID-19-associated nephropathy (COVAN), in particular, may be mediated through IL-6 and signal transducer and activator of transcription 3 (STAT3) signaling, suggesting a direct connection between the COVID-19-related immune response and the development of chronic disease. Chronic manifestations of COVID-19 also include systemic conditions like Multisystem Inflammatory Syndrome in Children (MIS-C) and Adults (MIS-A) and post-acute sequelae of COVID-19 (PASC), which may reflect a spectrum of clinical presentations of persistent immune dysregulation. The lessons learned and those undergoing continued study likely have broad implications for understanding viral infections' immunologic and inflammatory consequences beyond coronaviruses.

IL-21-STAT3 axis negatively regulates LAIR1 expression in B cells

LAIR1 is an inhibitory receptor broadly expressed on human immune cells, including B cells. LAIR1 has been shown to modulate BCR signaling, however, it is still unclear whether its suppressive activity can be a negative regulator for autoreactivity. In this study, we demonstrate the LAIR1 expression profile on human B cells and prove its regulatory function and relationships to B cell autoreactivity. We show that both the frequency and level of LAIR1 expression decreases during B cell differentiation. LAIR1 expressing (LAIR1 + ) switched memory (SWM) B cells have a transcriptional profile less differentiated toward a plasma cell (PC) phenotype, harbor more autoreactive B cells and exhibit less PC differentiation in vitro than the LAIR1 negative (LAIR1 - ) counterpart. These data suggests that LAIR1 functions as a B cell tolerance checkpoint. We confirm previous data showing that patients with systemic lupus erythematosus (SLE) express less LAIR1 on B cells, implying a breakdown of the checkpoint, consistent with the enhanced PC differentiation seen in SLE. We further demonstrate that LAIR1 expression is down-regulated through the IL-21/STAT3 pathway which is known to be upregulated in SLE. These data suggest therapeutic targets that might decrease the aberrant PC differentiation observed in SLE.

Interferon activation in bone marrow long-lived plasma cells in systemic lupus erythematosus

While durable antibody responses from long-lived plasma cell (LLPC) populations are important for protection against pathogens, LLPC may be harmful if they produce antibodies against self-proteins or self-nuclear antigens as occurs in autoimmune diseases such as systemic lupus erythematosus (SLE). Thus, the elimination of autoreactive LLPC may improve the treatment of antibody-driven autoimmune diseases. However, LLPC remain a challenging therapeutic target. Here, we compare the matched bone marrow (BM) and peripheral blood (PBL) plasma cell (PC) compartments of SLE and healthy donors (HD). We show a similar distribution of CD138- and CD138+ PC, including putative LLPC (CD19- CD138+ CD38+), between SLE and HD BM. For both SLE and HD, CD138+ PC are at a higher frequency in BM than PBL. Expression of Ki-67 associates with the PBL compartment where it is found on all PC subsets regardless of CD19 or CD138 expression. Transcriptomic analysis identifies an interferon (IFN) gene signature in transitional B cells in the SLE BM, but surprisingly also in the BM PC derived from SLE. BM PC and B cells phosphorylate STAT1 in response to type I IFN stimulation in vitro, but with decreased fold change compared to those from the PBL. While BM PC bind type I IFN receptor-blocking antibody anifrolumab, it is to a lesser degree than circulating B cells. Anti-nuclear autoantibodies (ANA) are found in the BM supernatant and PBL serum of SLE patients. Both SLE and HD BM-derived PC have increased survival compared to their PBL counterparts when treated with verdinexor. In summary, these findings show evidence of IFN activation in BM PC from SLE.

Survival of Human Bone Marrow Plasma Cells In Vitro Depends on the Support of the Stromal Cells, PI3K, and Canonical NF-kappaB Signaling

Contrary to short-lived plasma cells, which survive only 3-5 days, long-lived plasma cells (LLPCs) contribute to the humoral memory of the body and thus also to many antibody-related diseases. The ability of plasma cells to persist over months, years, and even a lifetime has been demonstrated in vivo. Yet, the in vitro culture of human primary bone marrow-derived plasma cells has been limited to a few days. Here, we establish culture conditions for human primary bone marrow-derived plasma cells for 21 days. Plasma cells and stromal cells are isolated from human bone marrow and cultured in 2D or a 3D ceramic scaffold. The plasma cells' survival and antibody secretion depend on direct contact with stromal cells. The culture promotes CD19-negative PCs. Inhibition of the PI3K or NF-kappaB pathways using chemical inhibitors reduced the survival of the plasma cells. These results underline the supportive role of the stromal cells for the survival of the LLPC and confirm mechanisms that were identified in mouse LLPCs also for human LLPCs. The culture described here will promote further studies to deepen our understanding of the human LLPC.

Enhancing the Deformability of the Adjuvant: Achieving Lymph Node Targeted Delivery to Elicit a Long-Lasting Immune Protection

A key challenge in vaccine development is to induce an effective and durable immune response. Live virus vaccines induce lifelong antibody responses; however, the immune responses induced by inactivated or subunit vaccines decrease gradually. Activation of the germinal center (GC) reaction, which generates long-lived plasma cells (LLPCs), is a key mediator of long-term antibody responses. To enhance the activation of GC, lymph node-targeted delivery of the vaccine is promoted by enhancing the deformability of the delivery vector. In this study, a double emulsion is designed with strong deformability and containing chitosan nanoparticles (CSNP) in the internal aqueous phase (WNP) for efficient antigen loading, called WNP/O/W. The flexible oil layer and the internally loaded positively charged particles endow the emulsion with strong deformability, continuously enrich model antigen ovalbumin (OVA) in the lymph nodes, activate germinal center B (GC B) cells and T follicular helper (TFH) cells, induce LLPCs, and obtain high-level antibody persistence for more than 5 months, which is significantly better than the traditional oil emulsion adjuvant. Concurrently, it also improves the immune-protective effect in aged mice. Altogether, these results indicate that WNP/O/W achieves lymph node targeted delivery by strengthening deformability, generating high-intensity antibody responses, and long-lasting immune protection.

SARS-CoV-2-specific plasma cells are not durably established in the bone marrow long-lived compartment after mRNA vaccination

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mRNA vaccines are effective at protecting from severe disease, but the protective antibodies wane rapidly even though SARS-CoV-2-specific plasma cells can be found in the bone marrow (BM). Here, to explore this paradox, we enrolled 19 healthy adults at 2.5-33 months after receipt of a SARS-CoV-2 mRNA vaccine and measured influenza-, tetanus- or SARS-CoV-2-specific antibody-secreting cells (ASCs) in long-lived plasma cell (LLPC) and non-LLPC subsets within the BM. Only influenza- and tetanus-specific ASCs were readily detected in the LLPCs, whereas SARS-CoV-2 specificities were mostly absent. The ratios of non-LLPC:LLPC for influenza, tetanus and SARS-CoV-2 were 0.61, 0.44 and 29.07, respectively. In five patients with known PCR-proven history of recent infection and vaccination, SARS-CoV-2-specific ASCs were mostly absent from the LLPCs. We show similar results with measurement for secreted antibodies from BM ASC culture supernatant. While serum IgG titers specific for influenza and tetanus correlated with IgG LLPCs, serum IgG levels for SARS-CoV-2, which waned within 3-6 months after vaccination, were associated with IgG non-LLPCs. In all, our studies suggest that rapid waning of SARS-CoV-2-specific serum antibodies could be accounted for by the absence of BM LLPCs after these mRNA vaccines.

Contribution of long-lived plasma cells to antibody-mediated allograft rejection

Persistent alloantigens derived from allograft tissues can be recognized by the host's alloreactive immune system. This process enables cognate B cells to differentiate into plasma cells, which secrete donor-specific antibodies that are key drivers of antibody-mediated allograft rejection. A subset of these plasma cells can survive for extended periods in a suitable survival niche and mature into long-lived plasma cells (LLPCs), which are a cellular component of humoral memory. The current understanding of LLPCs is limited due to their scarcity, heterogeneity, and absence of unique markers. However, accumulating evidence indicates that LLPCs, unlike conventional short-lived plasma cells, can respond to extrinsic signals from their survival niches and can resist cell death associated with intracellular stress through cell-intrinsic mechanisms. Notably, they are refractory to traditional immunosuppressants and B cell depletion therapies. This resistance, coupled with their longevity, may explain why current treatments targeting antibody-mediated rejection are often ineffective. This review offers insights into the biology of LLPCs and discusses ongoing therapeutic trials that target LLPCs in the context of antibody-mediated allograft rejection.

Targeting human plasma cells using regulated BCMA CAR T cells eliminates circulating antibodies in humanized mice

Pathogenic long-lived plasma cells (LLPCs) secrete autoreactive antibodies, exacerbating autoimmune diseases and complicating solid organ transplantation. Targeted elimination of the autoreactive B cell pool represents a promising therapeutic strategy, yet current treatment modalities fall short in depleting mature PCs. Here, we demonstrate that chimeric antigen receptor (CAR) T cells, targeting B cell maturation antigen (BCMA) utilizing a split-receptor design, offer a controlled and effective therapeutic strategy against LLPCs. Dimerizing agent-regulated immune-receptor complex (DARIC) T cells demonstrated robust rapamycin-dependent targeting of tumor and PCs. Notably, in humanized mouse models, DARIC T cells regulated peripheral human immunoglobulin levels through specific elimination of human LLPCs from the bone marrow. Furthermore, DARIC constructs were efficiently integrated into the T cell receptor α constant (TRAC) locus while maintaining potent antigen-specific cytotoxicity. These findings underscore the potential of split-receptor CAR T cells in autoimmune and transplant medicine, highlighting their versatility in applications beyond oncology.

Advancements in the design and function of bispecific CAR-T cells targeting B Cell-Associated tumor antigens

Single-targeted CAR-T has exhibited notable success in treating B-cell tumors, effectively improving patient outcomes. However, the recurrence rate among patients remains above fifty percent, primarily attributed to antigen escape and the diminished immune persistence of CAR-T cells. Over recent years, there has been a surge of interest in bispecific CAR-T cell therapies, marked by an increasing number of research articles and clinical applications annually. This paper undertakes a comprehensive review of influential studies on the design of bispecific CAR-T in recent years, examining their impact on bispecific CAR-T efficacy concerning disease classification, targeted antigens, and CAR design. Notable distinctions in antigen targeting within B-ALL, NHL, and MM are explored, along with an analysis of how CAR scFv, transmembrane region, hinge region, and co-stimulatory region design influence Bi-CAR-T efficacy across different tumors. The summary provided aims to serve as a reference for designing novel and improved CAR-Ts, facilitating more efficient treatment for B-cell malignant tumors.

Immunomolecular and reactivity landscapes of gut IgA subclasses in homeostasis and inflammatory bowel disease

The human gut includes plasma cells (PCs) expressing immunoglobulin A1 (IgA1) or IgA2, two structurally distinct IgA subclasses with elusive regulation, function, and reactivity. We show here that intestinal IgA1+ and IgA2+ PCs co-emerged early in life, comparably accumulated somatic mutations, and were enriched within short-lived CD19+ and long-lived CD19- PC subsets, respectively. IgA2+ PCs were extensively clonally related to IgA1+ PCs and a subset of them presumably emerged from IgA1+ precursors. Of note, secretory IgA1 (SIgA1) and SIgA2 dually coated a large fraction of mucus-embedded bacteria, including Akkermansia muciniphila. Disruption of homeostasis by inflammatory bowel disease (IBD) was associated with an increase in actively proliferating IgA1+ plasmablasts, a depletion in long-lived IgA2+ PCs, and increased SIgA1+SIgA2+ gut microbiota. Such increase featured enhanced IgA1 reactivity to pathobionts, including Escherichia coli, combined with depletion of beneficial A. muciniphila. Thus, gut IgA1 and IgA2 emerge from clonally related PCs and show unique changes in both frequency and reactivity in IBD.

Therapeutic potentials of adoptive cell therapy in immune-mediated neuropathy

Immune-mediated neuropathy (IMN) is a group of heterogenous neuropathies caused by intricate autoimmune responses. For now, known mechanisms of different IMN subtypes involve the production of autoantibodies, complement activation, enhanced inflammation and subsequent axonal/demyelinating nerve damages. Recent therapeutic studies mainly focus on specific antibodies and small molecule inhibitors previously approved in rheumatoid diseases. Initial strategies based on the pathophysiologic features of IMN should be explored. Adoptive cell therapy (ACT) refers to the emerging immunotherapies in which circulating immunocytes are collected from peripheral blood and modified with killing and immunomodulatory capacities. It consists of chimeric antigen receptor-T cell therapy, T cell receptor-engineered T cell, CAR-Natural killer cell therapy, and others. In the last decade, ACT has demonstrated extraordinary potentials in treating cancers, infectious diseases and autoimmune diseases. Versatile combinations of targets, chimeric domains and effector cells greatly empower ACT to treat complicated immune disorders. In this review, we summarized the advances of ACT and envisioned suitable strategies for different IMN subtypes.

Enhanced Prenatal and Postnatal Development Study in Marmoset Monkeys Following Administration of Felzartamab

Felzartamab is a recombinant fully human immunoglobulin G1 anti-CD38 monoclonal antibody under clinical investigation for immune-mediated diseases. In support of felzartamab clinical development, toxicology studies were conducted in marmoset monkeys, which was the most relevant species based on CD38 binding affinity, pharmacologic activity, and target expression. The felzartamab toxicology program included an enhanced prenatal and postnatal development (ePPND) study to identify potential reproductive and postnatal development risks. In this ePPND study, pregnant marmoset monkeys were randomized to receive vehicle (0 mg/kg) or felzartamab at two dose levels (15 mg/kg and 75 mg/kg) twice per week until parturition, and maternal animals and infants were evaluated for 6 months thereafter. Felzartamab exposure was confirmed in maternal animals and infants in both dosing groups. Overall, felzartamab was well tolerated by pregnant animals at the evaluated doses, with no effect on body weight or body weight gain during pregnancy. No felzartamab-related effects on pregnancy loss or stillbirth rate were observed, and litter counts and numbers of liveborn infants were similar between the vehicle and felzartamab groups. Among infants, there were no felzartamab-related malformations or variations in external anatomy or skeletal morphology and no felzartamab-related observations in histopathology, hematologic and immune cell development, or humoral immune response to vaccination. In conclusion, among pregnant marmoset monkeys dosed with felzartamab, the lack of reproductive toxicity and felzartamab-related effects on offspring supports the clinical evaluation of felzartamab in women of childbearing potential and further demonstrates the suitability of the marmoset monkey for ePPND studies.

Survivorship in Chimeric Antigen Receptor T-Cell Therapy Recipients: Infections, Secondary Malignancies, and Non-Relapse Mortality

BACKGROUND

Chimeric antigen receptor (CAR) T-cell therapy has significantly advanced the treatment of hematologic malignancies, offering curative potential for patients with relapsed or refractory disease. However, the long-term survivorship of these patients is marked by unique challenges, particularly immune deficits and infectious complications, second primary malignancies (SPMs), and non-relapse mortality (NRM). Understanding and addressing these risks is paramount to improving patient outcomes and quality of life.

SUMMARY

This review explores the incidence and risk factors for NRM and long-term complications following CAR T-cell therapy. Infections are the leading cause of NRM, accounting for over 50% of cases, driven by neutropenia, hypogammaglobulinemia, and impaired cellular immunity. SPMs, including secondary myeloid and T-cell malignancies, are increasingly recognized, prompting the FDA to issue a black box warning, although their direct link to CAR T cells remains disputed. While CAR T-cell-specific toxicities like cytokine release syndrome and immune effector cell-associated neurotoxicity syndrome contribute to morbidity, they represent only a minority of NRM cases. The management of these complications is critical as CAR T-cell therapy is being evaluated for broader use, including in earlier treatment lines and for non-malignant conditions like autoimmune diseases.

KEY MESSAGES

CAR T-cell therapy has revolutionized cancer treatment, but survivorship is complicated by infections, SPMs, and ultimately endangered by NRM. Prophylactic strategies, close monitoring, and toxicity management strategies are key to improving long-term outcomes.

Effects of early intervention in neuromyelitis optica spectrum disorder patients with seropositive AQP4 antibodies

Background

The impact of early intervention with immunosuppressive treatment (IST) in anti-Aquaporin4-antibody (AQP4-ab) seropositive neuromyelitis optica spectrum disorder (NMOSD) has not been thoroughly evaluated.

Objective

This study aims to assess the effects of early IST intervention in patients with NMOSD.

Methods

This retrospective cohort study included 174 treatments from 137 NMOSD patients seropositive for AQP4-antibody, treated with ISTs such as rituximab, mycophenolate mofetil, azathioprine, or tacrolimus. Multiple statistical analyses, including regression discontinuity design (RDD), kaplan-meier analyze, Cox proportional hazards regression model, were employed to evaluate the effects of early IST intervention on annualized relapse rate (ARR) change, Expanded Disability Status Scale (EDSS) change, and time to next relapse.

Results

A total of 174 treatments from 137 patients were analyzed. Patients exhibited significant improvement in ARR[1.95 vs.0, IQR (0.70-6.0 vs. 0-0.42), p<0.001] and EDSS [3.0 vs. 2.5, IQR (2.0-4.0 vs. 1.0-3.0) p<0.001]after IST, although the ARR change was not significant in patients treated with TAC. Early IST initiation was associated with greater improvements in both ARR and EDSS compared to later initiation. RDD analysis demonstrated a time-dependent effect of ARR-change, indicating greater efficacy with early IST intervention.

Conclusions

Early intervention with ISTs in AQP4-antibody-positive NMOSD patients is associated with better outcomes in terms of reducing relapse rate and improving disability. These findings underscore the importance of early treatment in NMOSD.

Chimeric antigen receptor T cell therapy for autoimmune disease

Infusion of T cells engineered to express chimeric antigen receptors (CARs) that target B cells has proven to be a successful treatment for B cell malignancies. This success inspired the development of CAR T cells to selectively deplete or modulate the aberrant immune responses that underlie autoimmune disease. Promising results are emerging from clinical trials of CAR T cells targeting the B cell protein CD19 in patients with B cell-driven autoimmune diseases. Further approaches are being designed to extend the application and improve safety of CAR T cell therapy in the setting of autoimmunity, including the use of chimeric autoantibody receptors to selectively deplete autoantigen-specific B cells and the use of regulatory T cells engineered to express antigen-specific CARs for targeted immune modulation. Here, we highlight important considerations, such as optimal target cell populations, CAR construct design, acceptable toxicities and potential for lasting immune reset, that will inform the eventual safe adoption of CAR T cell therapy for the treatment of autoimmune diseases.

A guide to adaptive immune memory

Immune memory - comprising T cells, B cells and plasma cells and their secreted antibodies - is crucial for human survival. It enables the rapid and effective clearance of a pathogen after re-exposure, to minimize damage to the host. When antigen-experienced, memory T cells become activated, they proliferate and produce effector molecules at faster rates and in greater magnitudes than antigen-inexperienced, naive cells. Similarly, memory B cells become activated and differentiate into antibody-secreting cells more rapidly than naive B cells, and they undergo processes that increase their affinity for antigen. The ability of T cells and B cells to form memory cells after antigen exposure is the rationale behind vaccination. Understanding immune memory not only is crucial for the design of more-efficacious vaccines but also has important implications for immunotherapies in infectious disease and cancer. This 'guide to' article provides an overview of the current understanding of the phenotype, function, location, and pathways for the generation, maintenance and protective capacity of memory T cells and memory B cells.

Lupus nephritis-related chronic kidney disease

Lupus nephritis is a common complication of systemic lupus erythematosus (SLE) and a determinant of overall morbidity and mortality, as lupus nephritis-related chronic kidney disease (CKD) drives cardiovascular disease and secondary immunodeficiency. Two lines of action are required to prevent the progression of lupus nephritis-related CKD: suppression of autoimmune SLE activity, which is a risk factor for immunopathology-related irreversible kidney injury, and management of non-immune risk factors that contribute to CKD progression. As each episode or relapse of active lupus nephritis implicates CKD progression, preventing flares of lupus nephritis is a key treatment target. Non-immune risk factors of CKD mostly include causes of nephron hyperfiltration, such as obesity, hypertension, sodium- or protein-rich diets and type 2 diabetes mellitus, as well as pregnancy. Nephrotoxic agents and smoking also drive kidney cell loss. Intrinsic risk factors for CKD progression include poor nephron endowment because of prematurity at birth, nephropathic genetic variants, ageing, male sex and previous or concomitant kidney diseases. Care for lupus nephritis involves the control of all modifiable risk factors of CKD progression. In addition, remnant nephron overload can be reduced using early dual therapy with inhibitors of the renin-angiotensin system and sodium-glucose transporter-2, whereas further renoprotective drug interventions are underway. As patients with lupus nephritis are at risk of CKD progression, they would all benefit from interdisciplinary care to minimize the risk of kidney failure, cardiovascular disease and infections.

CAR-engineered T cell therapy as an emerging strategy for treating autoimmune diseases

CAR-T therapy has demonstrated great success in treating hematological malignancies, which has led to further research into its potential in treating other diseases. Autoimmune diseases have great potential to be treated with this therapy due to the possibility of specific targeting of pathological immune cells and cells that produce autoantibodies, which could lead to permanent healing and restoration of immunological tolerance. Several approaches are currently under investigation, including targeting and depleting B cells via CD19 in the early stages of the disease, simultaneously targeting B cells and memory plasma cells in later stages and refractory states, as well as targeting specific autoantigens through the chimeric autoantibody receptor (CAAR). Additionally, CAR-engineered T regulatory cells can be modified to specifically target the autoimmune niche and modulate the pathological immune response. The encouraging results from preclinical studies have led to the first successful use of CAR-T therapy in humans to treat autoimmunity. This paved the way for further clinical studies, aiming to evaluate the long-term safety and efficacy of these therapies, potentially revolutionizing clinical use.

Role of cellular effectors in the induction and maintenance of IgA responses leading to protective immunity against enteric bacterial pathogens

The mucosal immune system is a critical first line of defense to infectious diseases, as many pathogens enter the body through mucosal surfaces, disrupting the balanced interactions between mucosal cells, secretory molecules, and microbiota in this challenging microenvironment. The mucosal immune system comprises of a complex and integrated network that includes the gut-associated lymphoid tissues (GALT). One of its primary responses to microbes is the secretion of IgA, whose role in the mucosa is vital for preventing pathogen colonization, invasion and spread. The mechanisms involved in these key responses include neutralization of pathogens, immune exclusion, immune modulation, and cross-protection. The generation and maintenance of high affinity IgA responses require a delicate balance of multiple components, including B and T cell interactions, innate cells, the cytokine milieu (e.g., IL-21, IL-10, TGF-β), and other factors essential for intestinal homeostasis, including the gut microbiota. In this review, we will discuss the main cellular components (e.g., T cells, innate lymphoid cells, dendritic cells) in the gut microenvironment as mediators of important effector responses and as critical players in supporting B cells in eliciting and maintaining IgA production, particularly in the context of enteric infections and vaccination in humans. Understanding the mechanisms of humoral and cellular components in protection could guide and accelerate the development of more effective mucosal vaccines and therapeutic interventions to efficiently combat mucosal infections.

The Divergent Effect of Different Infant Vaccination Schedules of the 13-Valent Pneumococcal Conjugate Vaccine on Serotype-Specific Immunological Memory

Pneumococcal vaccination schedules are traditionally assessed based on the antibody response. The Memory B Cell (MBC) response has been less studied, despite its role in the magnitude and longevity of protection. We compared the immune response to different vaccination schedules with the 13-valent Pneumococcal Conjugate Vaccine (PCV13) and investigated the relationship between MBCs and the antibody response. Total and pneumococcal serotype (PS)-specific MBCs, their subsets and PS-specific IgG antibodies induced by a 3 + 0 (group A), 2 + 1 (group B) or 3 + 1 (group C) schedule in healthy infants were studied before and 1 month after the last PCV13. The relatively immature IgM+IgD+ MBC subset was the predominant subset in all groups but was larger in group A compared to group B and group C, indicating that age might be a significant parameter of the composition of the MBC pool. PS-specific MBCs at baseline were higher in group A, but they increased significantly only in the groups receiving the booster schedules (groups B and C). PS-specific IgM-only MBCs at baseline positively corelated with the antibody response and the PS-specific swIg MBCs post-immunization. Our findings illustrate the importance of a booster dose for the enrichment of PS-specific immunological memory. IgM-only MBCs and swIg MBCs may serve as additional correlates of vaccine-induced protection.

Remodeling the hepatic immune microenvironment and demolishing T cell traps to enhance immunotherapy efficacy in liver metastasis

Immune checkpoint inhibitors (ICIs) exhibit compromised therapeutic efficacy in many patients with advanced cancers, particularly those with liver metastases. Much of this incapability can be ascribed as an irresponsiveness resulting from the "cold" hepatic tumor microenvironment that acts as T cell "traps" for which there currently lack countermeasures. We report a novel nanomedicine that converts the hepatic immune microenvironment to a "hot" phenotype by targeting hepatic macrophage-centric T cell elimination. Using the nanomedicine, composed of KIRA6 (an endothelium reticulum stress inhibitor), α-Tocopherol nanoemulsions, and anti-PD1 antibodies, we found its potency in murine models of orthotopic colorectal tumors and hepatic metastases, restoring immune responses and enhancing anti-tumor effects. A post-treatment scrutiny of the immune microenvironment landscape in the liver reveals repolarization of immunosuppressive hepatic macrophages, upregulation of Th1-like effector CD4+ T cells, and rejuvenation of dendritic cells along with CD8+ T cells. These findings suggest adaptations of liver-centric immune milieu modulation strategies to improve the efficacy of ICIs for a variety of "cold" tumors and their liver metastases.

Phase 1b/2a Study Assessing the Safety and Efficacy of Felzartamab in Anti-Phospholipase A2 Receptor Autoantibody-Positive Primary Membranous Nephropathy

Introduction

Primary membranous nephropathy (PMN) is most often caused by autoantibodies to phospholipase A2 receptor (PLA2R). M-PLACE (NCT04145440) is an open-label, phase 1b/2a study that assessed the safety and efficacy of the fully human anti-CD38 monoclonal antibody felzartamab in high-risk anti-PLA2R+ PMN.

Methods

Patients with newly diagnosed or relapsed PMN (cohort 1 [C1]; n = 18) or PMN refractory to immunosuppressive therapy (IST) (cohort 2 [C2]; n = 13) received 9 infusions of felzartamab 16 mg/kg in the 24-week treatment period, followed by a 28-week follow-up. The primary end point was the incidence and severity of treatment-emergent adverse events (TEAEs).

Results

A total of 31 patients were enrolled and received felzartamab. Twenty-seven patients (87.1%) had TEAEs, including infusion-related reactions (IRRs) (29.0%), hypogammaglobulinemia (25.8%), peripheral edema (19.4%), and nausea (16.1%). Five patients (16.1%) had serious TEAEs that all resolved. Immunologic response (anti-PLA2R titer reduction ≥50%) was achieved by 20 of 26 efficacy-evaluable patients (76.9%) (C1, 13/15 [86.7%]; C2, 7/11 [63.6%]). Anti-PLA2R titer reductions were rapid (week 1 response, 44.0%; response 7 months after last felzartamab dose [end of study, EOS], 53.8%). Partial proteinuria remission (urine protein-to-creatinine ratio [UPCR] reduction ≥50%, UPCR <3.0 g/g, and stable estimated glomerular filtration rate [eGFR]) was achieved by 9 of 26 patients (34.6%) (C1, 7/15 [46.7%]; C2, 2/11 [18.2%]) before or at EOS (median follow-up, 366 days). Serum albumin increased from baseline to EOS in 20 of 26 patients (76.9%) (C1, 12/15 [80.0%]; C2, 8/11 [72.7%]).

Conclusion

In this population with high-risk anti-PLA2R+ PMN, felzartamab was tolerated and resulted in rapid partial and complete immunologic responses and partial improvements in proteinuria and serum albumin in some patients.

Long-Term Immunogenicity Study of an Aluminum Phosphate-Adjuvanted Inactivated Enterovirus A71 Vaccine in Children: An Extension to a Phase 2 Study

Enterovirus A71 (EV-A71) causes hand, foot, and mouth disease in infants and children with potential for fatal complications such as encephalitis and acute flaccid myelitis. This study examined the long-term immunity conferred by EV71vac, an inactivated EV-A71 vaccine adjuvanted with aluminum phosphate, in children from the age of 2 months to <6 years, for up to 5 years after the first immunization. A total of 227 participants between 2 months and <6 years of age who had previously received either EV71vac or placebo in the phase two clinical study were enrolled. Subjects were divided into age groups: 2 years to <6 years (Group 2b), 6 months to <2 years (Group 2c), and 2 months to <6 months (Group 2d). At Year 5, the neutralizing antibody titers against the B4 subgenotype remained high at 621.38 to 978.20, 841.40 to 1159.93, and 477.71 to 745.07 for Groups 2b, 2c, and 2d, respectively. Cross-neutralizing titers at Year 5 remained high against B5 and C4a subgenotypes, respectively. No long-term safety issues were reported. Our study provides novel insights into the long-term immunity conferred by EV71vac in children aged from two months to six years, particularly in those who received EV71vac between two and six months of age.

Human plasma cells engineered to secrete bispecifics drive effective in vivo leukemia killing

Bispecific antibodies are an important tool for the management and treatment of acute leukemias. As a next step toward clinical translation of engineered plasma cells, we describe approaches for secretion of bispecific antibodies by human plasma cells. We show that human plasma cells expressing either fragment crystallizable domain-deficient anti-CD19 × anti-CD3 (blinatumomab) or anti-CD33 × anti-CD3 bispecific antibodies mediate T cell activation and direct T cell killing of B acute lymphoblastic leukemia or acute myeloid leukemia cell lines in vitro. We demonstrate that knockout of the self-expressed antigen, CD19, boosts anti-CD19-bispecific secretion by plasma cells and prevents self-targeting. Plasma cells secreting anti-CD19-bispecific antibodies elicited in vivo control of acute lymphoblastic leukemia patient-derived xenografts in immunodeficient mice co-engrafted with autologous T cells. In these studies, we found that leukemic control elicited by engineered plasma cells was similar to CD19-targeted chimeric antigen receptor-expressing T cells. Finally, the steady-state concentration of anti-CD19 bispecifics in serum 1 month after cell delivery and tumor eradication was comparable with that observed in patients treated with a steady-state infusion of blinatumomab. These findings support further development of ePCs for use as a durable delivery system for the treatment of acute leukemias, and potentially other cancers.

Antibody-secreting cells as a source of NR1-IgGs in N-methyl-D-aspartate receptor-antibody encephalitis

BACKGROUND

The pathogenicity of NR1-IgGs in N-methyl-D-aspartate receptor (NMDAR)-antibody encephalitis is known, but the immunobiological mechanisms underlying their production remain unclear.

METHODS

For the first time, we explore the origin of NR1-IgGs and evaluate the contribution of B-cells to serum NR1-IgGs levels. Peripheral blood mononuclear cells (PBMCs) were obtained from patients and healthy controls (HCs). Naïve, unswitched memory (USM), switched memory B cells (SM), antibody-secreting cells (ASCs), and PBMC depleted of ASCs were obtained by fluorescence-activated cell sorting and cultured in vitro.

RESULTS

For some patients, PBMCs spontaneously produced NR1-IgGs. Compared to the patients in PBMC negative group, the positive group had higher NR1-IgG titers in cerebrospinal fluid and Modified Rankin scale scores. The proportions of NR1-IgG positive wells in PBMCs cultures were correlated with NR1-IgGs titers in serum and CSF. The purified ASCs, SM, USM B cells produced NR1-IgGs in vitro. Compared to the patients in ASCs negative group, the positive group exhibited a worse response to second-line IT at 3-month follow-up. Naïve B cells also produce NR1-IgGs, implicating that NR1-IgGs originate from naïve B cells and a pre-germinal centres defect in B cell tolerance checkpoint in some patients. For HCs, no NR1-IgG from cultures was observed. PBMC depleted of ASCs almost eliminated the production of NR1-IgGs.

CONCLUSIONS

These collective findings suggested that ASCs might mainly contribute to the production of peripheral NR1-IgG in patients with NMDAR-antibody encephalitis in the acute phase. Our study reveals the pathogenesis and helps develop tailored treatments (eg, anti-CD38) for NMDAR-antibody encephalitis.

Ally, adversary, or arbitrator? The context-dependent role of eosinophils in vaccination for respiratory viruses and subsequent breakthrough infections

Eosinophils are a critical type of immune cell and central players in type 2 immunity. Existing literature suggests that eosinophils also can play a role in host antiviral responses, typically type 1 immune events, against multiple respiratory viruses, both directly through release of antiviral mediators and indirectly through activation of other effector cell types. One way to prime host immune responses toward effective antiviral responses is through vaccination, where typically a type 1-skewed immunity is desirable in the context of intracellular pathogens like respiratory viruses. In the realm of breakthrough respiratory viral infection in vaccinated hosts, an event in which virus can still establish productive infection despite preexisting immunity, eosinophils are most prominently known for their link to vaccine-associated enhanced respiratory disease upon natural respiratory syncytial virus infection. This was observed in a pediatric cohort during the 1960s following vaccination with formalin-inactivated respiratory syncytial virus. More recent research has unveiled additional roles of the eosinophil in respiratory viral infection and breakthrough infection. The specific contribution of eosinophils to the quality of vaccine responses, vaccine efficacy, and antiviral responses to infection in vaccinated hosts remains largely unexplored, especially regarding their potential roles in protection. On the basis of current findings, we will speculate upon the suggested function of eosinophils and consider the many potential ways by which eosinophils may exert protective and pathological effects in breakthrough infections. We will also discuss how to balance vaccine efficacy with eosinophil-related risks, as well as the use of eosinophils and their products as potential biomarkers of vaccine efficacy or adverse events.

Deficient Generation of Spike-Specific Long-Lived Plasma Cells in the Bone Marrow After Severe Acute Respiratory Syndrome Coronavirus 2 Infection

Generation of a stable long-lived plasma cell (LLPC) population is the sine qua non of durable antibody responses after vaccination or infection. We studied 20 individuals with a prior coronavirus disease 2019 infection and characterized the antibody response using bone marrow aspiration and plasma samples. We noted deficient generation of spike-specific LLPCs in the bone marrow after severe acute respiratory syndrome coronavirus 2 infection. Furthermore, while the regression model explained 98% of the observed variance in anti-tetanus immunoglobulin G levels based on LLPC enzyme-linked immunospot assay, we were unable to fit the same model with anti-spike antibodies, again pointing to the lack of LLPC contribution to circulating anti-spike antibodies.

MENSA, a Media Enriched with Newly Synthesized Antibodies, to Identify SARS-CoV-2 Persistence and Latent Viral Reactivation in Long-COVID

Post-acute sequelae of SARS-CoV-2 (SARS2) infection (PASC) is a heterogeneous condition, but the main viral drivers are unknown. Here, we use MENSA, Media Enriched with Newly Synthesized Antibodies, secreted exclusively from circulating human plasmablasts, to provide an immune snapshot that defines the underlying viral triggers. We provide proof-of-concept testing that the MENSA technology can capture the new host immune response to accurately diagnose acute primary and breakthrough infections when known SARS2 virus or proteins are present. It is also positive after vaccination when spike proteins elicit an acute immune response. Applying the same principles for long-COVID patients, MENSA is positive for SARS2 in 40% of PASC vs none of the COVID recovered (CR) patients without any sequelae demonstrating ongoing SARS2 viral inflammation only in PASC. Additionally, in PASC patients, MENSAs are also positive for Epstein-Barr Virus (EBV) in 37%, Human Cytomegalovirus (CMV) in 23%, and herpes simplex virus 2 (HSV2) in 15% compared to 17%, 4%, and 4% in CR controls respectively. Combined, a total of 60% of PASC patients have a positive MENSA for SARS2, EBV, CMV, and/or HSV2. MENSA offers a unique antibody snapshot to reveal the underlying viral drivers in long-COVID thus demonstrating the persistence of SARS2 and reactivation of viral herpes in 60% of PASC patients.

New insights into the ontogeny, diversity, maturation and survival of long-lived plasma cells

Plasma cells are unique immune effectors, capable of producing large amounts of high-affinity antibodies that protect against pathogenic infections. Although most plasma cells have short lifespans, certain conditions or vaccinations can give rise to long-lived plasma cells (LLPCs) that provide individuals with lifelong protection against pathogen exposure. The nature of these LLPCs is poorly understood; however, recent studies have shed new light on the ontogeny, diversity, maturation and survival of these unique cells. Whereas LLPCs had been thought to arise preferentially from germinal centres, novel genetic tools have revealed that they can originate from various stages throughout the humoral response. Furthermore, new single-cell analyses have shown that mouse and human plasma cells are heterogeneous and may undergo further maturation in situ in the bone marrow niche. Finally, plasma cells were previously considered to be sessile cells maintained in fixed survival niches, but new data show that plasma cell subsets can differentially migrate and organize into clusters that may be associated with survival niches. These descriptive findings provide new insights into how cell-intrinsic programmes and extrinsic factors may regulate the longevity of plasma cells in various contexts, which suggest new research avenues for their functional validation.

Donor-derived anti-HLA antibodies in a haploidentical hematopoietic cell transplant recipient shortly after transplant

A pediatric patient with acute myeloid leukemia was referred to our institution for investigational therapy after disease relapse following a mismatched unrelated donor hematopoietic cell transplant (HCT). Prior to second HCT, the patient's serum was negative for antibodies to class I and class II HLA. Eight days after receiving a maternal donor haploidentical transplant, the patient became platelet refractory and highly sensitized to multiple class I HLA. Serum from the patient's mother was positive for the strongest antibodies present in the patient, suggesting the antibodies were donor-derived. Patient sera showed magnified and expanded sensitization over time in the context of 100% donor chimerism and despite undetectable circulating B cells. Escalating sensitization suggests active transfer of rituximab-resistant antibody-producing passenger lymphocytes from a haploidentical donor to a transplant recipient at the time of progenitor cell infusion. Evaluation of donor sensitization status may be a consideration prior to HLA mismatched HCT.

Disrupting B and T-cell collaboration in autoimmune disease: T-cell engagers versus CAR T-cell therapy?

B and T cells collaborate to drive autoimmune disease (AID). Historically, B- and T-cell (B-T cell) co-interaction was targeted through different pathways such as alemtuzumab, abatacept, and dapirolizumab with variable impact on B-cell depletion (BCD), whereas the majority of patients with AID including rheumatoid arthritis, systemic lupus erythematosus, multiple sclerosis, and organ transplantation benefit from targeted BCD with anti-CD20 monoclonal antibodies such as rituximab, ocrelizumab, or ofatumumab. Refractory AID is a significant problem for patients with incomplete BCD with a greater frequency of IgD-CD27+ switched memory B cells, CD19+CD20- B cells, and plasma cells that are not directly targeted by anti-CD20 antibodies, whereas most lymphoid tissue plasma cells express CD19. Furthermore, B-T-cell collaboration is predominant in lymphoid tissues and at sites of inflammation such as the joint and kidney, where BCD may be inefficient, due to limited access to key effector cells. In the treatment of cancer, chimeric antigen receptor (CAR) T-cell therapy and T-cell engagers (TCE) that recruit T cells to induce B-cell cytotoxicity have delivered promising results for anti-CD19 CAR T-cell therapies, the CD19 TCE blinatumomab and CD20 TCE such as mosunetuzumab, glofitamab, or epcoritamab. Limited evidence suggests that anti-CD19 CAR T-cell therapy may be effective in managing refractory AID whereas we await evaluation of TCE for use in non-oncological indications. Therefore, here, we discuss the potential mechanistic advantages of novel therapies that rely on T cells as effector cells to disrupt B-T-cell collaboration toward overcoming rituximab-resistant AID.

Temporal dynamics and genomic programming of plasma cell fates

Affinity-matured plasma cells (PCs) of varying lifespans are generated through a germinal center (GC) response. The developmental dynamics and genomic programs of antigen-specific PC precursors remain to be elucidated. Here, using a model antigen in mice, we demonstrate biphasic generation of PC precursors, with those generating long-lived bone marrow PCs preferentially produced in the late phase of GC response. Clonal tracing using single-cell RNA sequencing and B cell antigen receptor sequencing in spleen and bone marrow compartments, coupled with adoptive transfer experiments, reveals a new PC transition state that gives rise to functionally competent PC precursors. The latter undergo clonal expansion, dependent on inducible expression of TIGIT. We propose a model for the proliferation and programming of precursors of long-lived PCs, based on extended antigen encounters in the GC.

Advances and challenges in investigating B-cells via single-cell transcriptomics

Single-cell RNA sequencing (scRNAseq) and Variable, Diversity, Joining (VDJ) profiling have improved our understanding of B-cells. Recent scRNAseq-based approaches have led to the discovery of intermediate B-cell states, including preplasma cells and pregerminal centre B-cells, as well as unveiling protective roles for B-cells within tertiary lymphoid structures in respiratory infections and cancers. These studies have improved our understanding of transcriptional and epigenetic control of B-cell development and of atypical and memory B-cell differentiation. Advancements in temporal profiling in parallel with transcriptomic and VDJ sequencing have consolidated our understanding of the trajectory of B-cell clones over the course of infection and vaccination. Challenges remain in studying B-cell states across tissues in humans, in relating spatial location with B-cell phenotype and function, in examining antibody isotype switching events, and in unequivocal determination of clonal relationships. Nevertheless, ongoing multiomic assessments and studies of cellular interactions within tissues promise new avenues for improving humoral immunity and combatting autoimmune conditions.

B cell-targeting chimeric antigen receptor T cells as an emerging therapy in neuroimmunological diseases

BACKGROUND

Neuroimmunology research and development has been marked by substantial advances, particularly in the treatment of neuroimmunological diseases, such as multiple sclerosis, myasthenia gravis, neuromyelitis optica spectrum disorders, and myelin oligodendrocyte glycoprotein antibody disease. With more than 20 drugs approved for multiple sclerosis alone, treatment has become more personalised. The approval of disease-modifying therapies, particularly those targeting B cells, has highlighted the role of immunotherapeutic interventions in the management of these diseases. Despite these successes, challenges remain, particularly for patients who do not respond to conventional therapies, underscoring the need for innovative approaches.

RECENT DEVELOPMENTS

The approval of monoclonal antibodies, such as ocrelizumab and ofatumumab, which target CD20, and inebilizumab, which targets CD19, for the treatment of various neuroimmunological diseases reflects progress in the understanding and management of B-cell activity. However, the limitations of these therapies in halting disease progression or activity in patients with multiple sclerosis or neuromyelitis optica spectrum disorders have prompted the exploration of cell-based therapies, particularly chimeric antigen receptor (CAR) T cells. Initially successful in the treatment of B cell-derived malignancies, CAR T cells offer a novel therapeutic mechanism by directly targeting and eliminating B cells, potentially overcoming the shortcomings of antibody-mediated B cell depletion. WHERE NEXT?: The use of CAR T cells in autoimmune diseases and B cell-driven neuroimmunological diseases shows promise as a targeted and durable option. CAR T cells act autonomously, penetrating deep tissue and effectively depleting B cells, especially in the CNS. Although the therapeutic potential of CAR T cells is substantial, their application faces hurdles such as complex logistics and management of therapy-associated toxic effects. Ongoing and upcoming clinical trials will be crucial in determining the safety, efficacy, and applicability of CAR T cells. As research progresses, CAR T cell therapy has the potential to transform treatment for patients with neuroimmunological diseases. It could offer extended periods of remission and a new standard in the management of autoimmune and neuroimmunological disorders.

Recruitment of plasma cells from IL-21-dependent and IL-21-independent immune reactions to the bone marrow

Bone marrow plasma cells (BMPC) are the correlate of humoral immunity, consistently releasing antibodies into the bloodstream. It remains unclear if BMPC reflect different activation environments or maturation of their precursors. Here we define human BMPC heterogeneity and track the recruitment of antibody-secreting cells (ASC) from SARS-CoV-2 vaccine immune reactions to the bone marrow (BM). Trajectories based on single-cell transcriptomes and repertoires of peripheral and BM ASC reveal sequential colonisation of BMPC compartments. In activated B cells, IL-21 suppresses CD19 expression, indicating that CD19low-BMPC are derived from follicular, while CD19high-BMPC originate from extrafollicular immune reactions. In primary immune reactions, both CD19low- and CD19high-BMPC compartments are populated. In secondary immune reactions, most BMPC are recruited to CD19high-BMPC compartments, reflecting their origin from extrafollicular reactivations of memory B cells. A pattern also observable in vaccinated-convalescent individuals and upon diphtheria/tetanus/pertussis recall-vaccination. Thus, BMPC diversity reflects the evolution of a given humoral immune response.

Unveiling the proteome-wide autoreactome enables enhanced evaluation of emerging CAR T cell therapies in autoimmunity

Given the global surge in autoimmune diseases, it is critical to evaluate emerging therapeutic interventions. Despite numerous new targeted immunomodulatory therapies, comprehensive approaches to apply and evaluate the effects of these treatments longitudinally are lacking. Here, we leveraged advances in programmable-phage immunoprecipitation methodology to explore the modulation, or lack thereof, of autoantibody profiles, proteome-wide, in both health and disease. Using a custom set of over 730,000 human-derived peptides, we demonstrated that each individual, regardless of disease state, possesses a distinct and complex constellation of autoreactive antibodies. For each individual, the set of resulting autoreactivites constituted a unique immunological fingerprint, or "autoreactome," that was remarkably stable over years. Using the autoreactome as a primary output, we evaluated the relative effectiveness of various immunomodulatory therapies in altering autoantibody repertoires. We found that therapies targeting B cell maturation antigen (BCMA) profoundly altered an individual's autoreactome, while anti-CD19 and anti-CD20 therapies had minimal effects. These data both confirm that the autoreactome comprises autoantibodies secreted by plasma cells and strongly suggest that BCMA or other plasma cell-targeting therapies may be highly effective in treating currently refractory autoantibody-mediated diseases.