IgA Class Switching Research Articles

Metabolic rewiring controlled by HIF-1α tunes IgA-producing B-cell differentiation and intestinal inflammation.

Germinal centers where B cells undergo clonal expansion and antibody affinity maturation are hypoxic microenvironments. However, the function of hypoxia-inducible factor (HIF)-1α in immunoglobulin production remains incompletely characterized. Here, we demonstrated that B cells lacking HIF-1α exhibited significantly lower glycolytic metabolism and impaired IgA production. Loss of HIF-1α in B cells affects IgA-producing B-cell differentiation and exacerbates dextran sodium sulfate (DSS)-induced colitis. Conversely, promoting HIF-1α stabilization via a PHD inhibitor roxadustatenhances IgA class switching and alleviates intestinal inflammation. Mechanistically, HIF-1α facilitates IgA class switching through acetyl-coenzyme A (acetyl-CoA) accumulation, which is essential for histone H3K27 acetylation at the Sα region. Consequently, supplementation with acetyl-CoA improved defective IgA production in Hif1a-deficient B cells and limited experimental colitis. Collectively, these findings highlight the critical importance of HIF-1α in IgA class switching and the potential for targeting the HIF-1α-dependent metabolic‒epigenetic axis to treat inflammatory bowel diseases and other inflammatory disorders.

B cell targeting in IgA nephropathy.

The "multi-hit theory/4-hit theory" pathogenesis hypothesis is widely accepted and IgA nephropathy (IgAN) is understood to be a disease originating from Hit 1, galactose deficient IgA1 (GdIgA1). The chronic repetitive activation of the complement pathway (alternative and lectin pathways) and the subsequent inflammation results in progressive glomerular damage that spills over into increased intraglomerular pressure and other hemodynamic changes, increased urinary protein, glomerulosclerosis, and tubulointerstitial fibrosis. The basic pathophysiology of this disease is the progression of a mixture of such acute and chronic pathologies. Currently, a number of new drugs has emerged as promising agents, such as complement regulators, endothelin receptor antagonists, and SGLT2 inhibitors, which are associated with each pathological step after glomerular deposition of GdIgA1/immune complexes. On the other hand, the molecular mechanisms of GdIgA1 production are gradually being elucidated, and the development of several novel therapeutic agents targeting the responsible B cells and their international clinical trials are progressing. These agents that inhibit or control the production of the Hit1, GdIgA1, are highly expected as essential therapies for this disease. The large body of clinical and basic research findings to date strongly suggest that nephritogenic GdIgA1 is a polymeric IgA1 of mucosal origin. In addition, the B cells involved in its nephritogenic GdIgA1 production are mainly differentiated mature B cells such as plasma cells, which may migrate to the bone marrow as well as the mucosa. The innate immune system in the mucosa, especially Toll-like receptors (TLRs), is thought to be involved in their production. Among TLRs, TLT9 and TLR7, which recognize bacterial and viral unmethylated DNA and RNA, have been reported to be involved. The mucosal activation of these TLRs is associated with the production of APRIL (A Proliferation Inducing Ligand) and BAFF (B cell activating factor), which are TNF superfamily cytokines involved in B cell maturation, survival, and IgA class switching, and may also be involved in the production of nephritogenic GdIgA1. It is still inconclusive whether APRIL or BAFF is more closely involved in the production of nephritogenic GdIgA1. Phenotypes in transgenic animal models suggest BAFF involvement, however, a genome wide association study (GWAS) analysis of human IgAN has identified APRIL, not BAFF, as a candidate gene. Based on the above background, several international clinical trials are underway for drugs such as TLR regulators (hydroxychloroquine), anti-APRIL drugs, anti-BAFF drugs, APRIL/BAFF receptor (TACI) binding inhibitors, and cytoreductive drugs (proteasome inhibitors, anti-CD38 antibodies) to inhibit nephritogenic GdIgA1 production in responsible B cells. This session will provide an overview of the responsible B cells, their GdIgA1 production mechanism, and ongoing drugs.

B-Cell Epigenetic Modulation of IgA Response by 5-Azacytidine and IgA Nephropathy.

IgA nephropathy is an important global cause of kidney failure. Dysregulation of IgA production is thought to play a key role in IgA nephropathy pathogenesis, however, little is known about the epigenetic mechanisms such as RNA 5- methylcytosine (5mC) modification in regulating IgA synthesis. To decipher the role of RNA 5mC in regulation of IgA class switch, the miR-23b-/- and LCWE induced Kawasaki disease mice were treated with 5-azacytidine. Trdmt1-/- and double Trdmt1-/-/ miR-23b-/- mice, Aid-/- mice or Aid-/-/ miR-23b-/- mice were also employed. We showed that miR-23b down regulated expression of Transfer RNA Aspartic Acid Methyltransferase 1 (Trdmt1) and consequently reduced 5-methylcytosine (m5C) RNA modification and IgA synthesis in B cells. Inhibition of m5C RNA modification normalised serum IgA levels and ameliorated progression of the IgA nephropathy-like kidney disease in miR-23b-/- and Kawasaki disease mice while mesangial IgA and C3 deposition failed to develop in Trdmt1-/-miR-23b-/- mice. By contrast, increased m5C RNA modification resulted in an exaggerated IgA nephropathy phenotype. miR-23b regulation of serum IgA levels and the development of an IgA nephropathy-like kidney disease in miR-23b-/- and Kawasaki disease mice is likely mediated through TRDMT1 driven 5-methylcytosine RNA modification in B cells, resulting in impaired activation-induced cytidine deaminase activity and IgA class switch recombination. This study revealed TRDMT1 induced RNA 5mC methylation regulate IgA class switch and inhibition of RNA 5mC by 5-Azacytidine could ameliorate progression of IgA nephropathy.

TGF-β1 impairs IgA class switch recombination and production in porcine Peyer's patches B cells.

Secretory IgA is crucial for preventing the invasion of entero-pathogens via intestinal mucosa. While it is well-established that Transforming growth factor β1 (TGF-β1) regulates IgA production in human and mouse B cells, our previous investigation revealed different functions of TGF-β1 in IgA generation in pigs compared with humans and mice, with the underlying mechanism remaining elusive. In this study, IgM+ B cells from porcine Peyer's patches (PPs) were isolated and stimulated with recombinant porcine TGF-β1 to evaluate the effect of TGF-β1 on pigs. The results showed that antibody production from B cells of PPs was impaired by TGF-β1 ex vivo. Furthermore, TGF-β1 treatment led to a decrease in the expression of germ-line transcript αand postswitch transcript α. Moreover, we observed that TGF-β1 predominantly inhibited the phosphorylation of p38-mitogen-activated protein kinases (MAPK), confirming the involvement of the p38-MAPK pathway in porcine IgA generation and IgA class switch recombination. The application of p38-MAPK inhibitor resulted in decreased B-cell differentiation levels. Collectively, this study demonstrates that exogenous TGF-β1 restrains the production and class switch recombination of IgA antibodies by inhibiting p38-MAPK signaling in porcine PPs B cells, which may constitute a component of TGF-β1-mediated inhibition of B-cell activation.

Metabolic fitness of IgA+ plasma cells in the gut requires DOCK8

Dedicator of cytokinesis 8 (DOCK8) mutations lead to a primary immunodeficiency associated with recurrent gastrointestinal infections and poor antibody responses but, paradoxically, heightened IgE to food antigens, suggesting that DOCK8 is central to immune homeostasis in the gut. Using Dock8-deficient mice, we found that DOCK8 was necessary for mucosal IgA production to multiple T cell-dependent antigens, including peanut and cholera toxin. Yet DOCK8 was not necessary in T cells for this phenotype. Instead, B cell-intrinsic DOCK8 was required for maintenance of antigen-specific IgA-secreting plasma cells (PCs) in the gut lamina propria. Unexpectedly, DOCK8 was not required for early B cell activation, migration, or IgA class switching. An unbiased interactome screen revealed novel protein partners involved in metabolism and apoptosis. Dock8-deficient IgA+ B cells had impaired cellular respiration and failed to engage glycolysis appropriately. These results demonstrate that maintenance of the IgA+ PC compartment requires DOCK8 and suggest that gut IgA+ PCs have unique metabolic requirements for long-term survival in the lamina propria.

Molecular Mechanism of Fasting-Mimicking Diet in Inhibiting Colorectal Cancer Progression: Implications for Immune Therapy and Metabolic Regulation.

Recently, fasting-mimicking diet and caloric restriction have been shown to improve antitumor immunity. In this issue of Cancer Research, Zhong and colleagues provide insights into the molecular mechanism of fasting-mimicking diet-mediated metabolic reprogramming in colorectal cancer progression. The authors performed comprehensive mechanistic experiments in mouse models to show that fasting-mimicking diet prevents colorectal cancer progression by lowering intratumoral IgA+ B cells by accelerating fatty acid oxidation to inhibit B-cell IgA class switching. In addition, they found that fatty acid oxidation-dependent acetylation prevents IgA class switching and that IgA+ B cells interfere with the anticancer effects of fasting-mimicking diet in colorectal cancer. Overall, their study establishes that fasting-mimicking diet has the potential to activate anticancer immunity and to induce tumor regression in colorectal cancer. See related article by Zhong et al., p. 3529.

Fasting-mimicking diet drives antitumor immunity against colorectal cancer by reducing IgA-producing cells.

As a safe, feasible, and inexpensive dietary intervention, fasting-mimicking diet (FMD) exhibits excellent antitumor efficacy by regulating metabolism and boosting antitumor immunity. A better understanding of the specific mechanisms underlying the immunoregulatory functions of FMD could help improve and expand the clinical application of FMD-mediated immunotherapeutic strategies. In this study, we aimed to elucidate the role of metabolic reprogramming induced by FMD in activation of antitumor immunity against colorectal cancer (CRC). Single-cell RNA sequencing (scRNA-seq) analysis of intratumoral immune cells revealed that tumor-infiltrating IgA+ B cells were significantly reduced by FMD treatment, leading to the activation of antitumor immunity and tumor regression in murine CRC models. Mechanistically, FMD delayed tumor growth by repressing B cell class switching to IgA. Therefore, FMD-induced reduction of IgA+ B cells overcame the suppression of CD8+ T cells. The immunoregulatory and antitumor effects of FMD intervention were reversed by IgA+ B cell transfer. Moreover, FMD boosted fatty acid oxidation (FAO) to trigger RUNX3 acetylation, thus inactivating Cα gene transcription and IgA class switching. IgA+ B cell expansion was also impeded in patients placed on FMD, while B cell expression of CPT1A, the rate-limiting enzyme of FAO, was increased. Furthermore, CPT1A expression was negatively correlated with both IgA+ B cells and IgA secretion within CRC. Together, these results highlight that FMD holds great promise for treating CRC. Furthermore, the degree of IgA+ B cell infiltration and FAO-associated metabolic status are potential biomarkers for evaluating FMD efficacy.

The role of ST8Sia6 in braking inflammation in Inflammatory Bowel Disease

Abstract Inflammatory bowel disease (IBD) including ulcerative colitis (UC) and Crohn’s disease (CD) affects between 1–3 million people in the United States and costs an estimated $11–28 billion in national healthcare costs. Patients present with symptoms including diarrhea, rectal bleeding, and fatigue. Characterization of molecules that regulate IBD is critical in understanding pathogenesis. ST8Sia6 is a sialic acid transferase that adds terminal a2,8 disialic acids to cell surface glycoproteins, and we have found that ST8Sia6 knockout (KO) mice exhibit increased spontaneous small bowel (SB) lamina propria CD4 T H1 polarization, increased inflammatory cytokine production, decreased IgA class switching of SB plasma cells, and alterations of the SB innate lymphoid cells, indicative of gut inflammation. Moreover, adult ST8Sia6 KO mice have shortened small and large bowels, likely due to baseline inflammation. These mice do not exhibit overt baseline symptoms, but ST8Sia6 KO mice exhibit increased weight loss and decreased survival when challenged with dextran sodium sulfate (DSS)-induced colitis, which was also enhanced when co-housed with wildtype (WT) mice. DSS-challenged ST8Sia6 KO mice exhibit increased histological damage and immune infiltration of the gut as compared to WT controls. Accelerated DSS-induced colitis is also observed when ST8Sia6-deficient bone marrow is transplanted into WT recipients, indicating that the effect is mediated specifically by immune cells. This data demonstrates a role for ST8Sia6 in regulating the host immune response to IBD, and further elucidating this role will aid in developing a mechanistic understanding of IBD pathogenesis and in understanding potential immunotherapies for the disease. R01CA243545, 5T32DK124190-03

Cutting Edge: Neutrophil Complement Receptor Signaling Is Required for BAFF-Dependent Humoral Responses in Mice.

T cell-independent (TI) B cell responses to nonprotein Ags involve multiple cues from the innate immune system. Neutrophils express complement receptors and activated neutrophils can release BAFF, but mechanisms effectively linking neutrophil activation to TI B cell responses are incompletely understood. Using germline and conditional knockout mice, we found that TI humoral responses involve alternative pathway complement activation and neutrophil-expressed C3a and C5a receptors (C3aR1/C5aR1) that promote BAFF-dependent B1 cell expansion and TI Ab production. Conditional absence of C3aR1/C5aR1 on neutrophils lowered serum BAFF levels, led to fewer Peyer's patch germinal center B cells, reduced germinal center B cells IgA class-switching, and lowered fecal IgA levels. Together, the results indicate that sequential activation of complement on neutrophils crucially supports humoral TI and mucosal IgA responses through upregulating neutrophil production of BAFF.

High antibody levels and reduced cellular response in children up to one year after SARS-CoV-2 infection

The COVID-19 course and immunity differ in children and adults. We analyzed immune response dynamics in 28 families up to 12 months after mild or asymptomatic infection. Unlike adults, the initial response is plasmablast-driven in children. Four months after infection, children show an enhanced specific antibody response and lower but detectable spike 1 protein (S1)-specific B and T cell responses than their parents. While specific antibodies decline, neutralizing antibody activity and breadth increase in both groups. The frequencies of S1-specific B and T cell responses remain stable. However, in children, one year after infection, an increase in the S1-specific IgA class switch and the expression of CD27 on S1-specific B cells and T cell maturation are observed. These results, together with the enhanced neutralizing potential and breadth of the specific antibodies, suggest a progressive maturation of the S1-specific immune response. Hence, the immune response in children persists over 12 months but dynamically changes in quality, with progressive neutralizing, breadth, and memory maturation. This implies a benefit for booster vaccination in children to consolidate memory formation.

MO212: Updated Interim Results of A Phase 1/2 Study to Investigate the Safety, Tolerability, Pharmacokinetics, Pharmacodynamics and Clinical Activity of BION-1301 in Patients With IGA Nephropathy

Abstract BACKGROUND AND AIMS Immunoglobulin A nephropathy (IgAN) is the leading cause of primary glomerulonephritis worldwide with limited treatment options, especially for high-risk patients [1]. BION-1301 is a novel humanized monoclonal antibody that blocks a proliferation-inducing ligand (APRIL), a soluble factor that has been shown to be elevated in patients with IgAN and is correlated with poorer outcomes, including increased proteinuria and decreased eGFR [2, 3]. APRIL promotes IgA class switching, the survival of IgA-secreting plasma cells and the excess production of a galactose-deficient variant form of IgA1 (Gd-IgA1), which is an initiating step in IgAN pathogenesis. This leads to the generation of anti-Gd-IgA1 autoantibodies, considered to be the first ‘hit’ in the multi-hit pathogenesis of IgAN, and the formation of nephritogenic immune complexes that deposit in the kidney, resulting in inflammation and damage [2–4]. Blocking APRIL with BION-1301 is a novel approach to address the underlying pathogenesis of IgAN by reducing circulating levels of Gd-IgA1 and preventing the formation of pathogenic immune complexes. In a Phase 1/2 study of BION-1301 in healthy volunteers (HV), BION-1301 was well-tolerated with no serious adverse events (SAEs), demonstrated a pharmacokinetic (PK) half-life > 30 days and durable dose-dependent reductions in free APRIL (fAPRIL), Gd-IgA1, IgA and IgM, with a lesser effect on IgG [5]. Here we present updated interim results from Part 3 of the study that characterize the safety, PK/PD profile and preliminary efficacy of BION-1301 initially administered intravenously (IV), then subcutaneously (SC), in patients with IgAN. METHOD Parts 1 and 2 of the Phase 1/2 study (NCT03945318) assessing single and multiple ascending doses of BION-1301 in HV are complete. Part 3 is an ongoing, open-label, multicohort design in patients with IgAN treated with BION-1301 for up to 1 year. Key eligibility criteria for Part 3 include: (i) biopsy-verified diagnosis of IgAN within the past 10 years, (ii) baseline urine protein excretion ≥ 0.5 g/24 h or UPCR ≥ 0.5 g/g and (iii) stable/optimized dose of ACE-I/ARB (or intolerant). Cohort 1 receives 450 mg of BION-1301 administered IV every 2 weeks. After at least 24 weeks of IV dosing, patients’ transition to 600 mg of BION-1301 administered SC every 2 weeks. Cohort 2 receives 600 mg of BION-1301 SC every 2 weeks. To evaluate PK/PD effects of BION-1301, serum levels of BION-1301, fAPRIL, anti-drug antibodies (ADA), neutralizing antibodies (NAbs) and Gd-IgA1 were quantitated using ELISA-based immunoassays. RESULTS Updated data from Cohort 1 will be reported. BION-1301 was well-tolerated in patients with IgAN receiving a 450 mg IV dose every 2 weeks for at least 24 weeks, with no SAEs or early terminations due to AEs. Durable reductions in serum levels of fAPRIL and immunoglobulins were observed in patients with IgAN. Clinically meaningful reductions in proteinuria were seen as early as 12 weeks and were associated with the reduction in Gd-IgA1 levels. CONCLUSION BION-1301 offers disease-modifying potential by directly targeting the initiating mechanisms underlying the multi-hit immune pathogenesis of IgAN, which is not addressed with currently available treatments. Promising early mechanistic biomarker and clinical activity responses support the therapeutic potential of BION-1301 in IgAN.

MO207: A Phase 1/2, Multicenter Study to Investigate the Safety, Tolerability, Pharmacokinetics and Pharmacodynamics of BION-1301 in Healthy Volunteers and Adults with IGA Nephropathy

Abstract BACKGROUND AND AIMS Immunoglobulin A nephropathy (IgAN) is the leading cause of primary glomerulonephritis worldwide with limited treatment options, especially for high-risk patients [1]. BION-1301 is a novel humanized monoclonal antibody that blocks a proliferation-inducing ligand (APRIL), a soluble factor that has been shown to be elevated in patients with IgAN and is correlated with poorer outcomes, including increased proteinuria and decreased eGFR [2, 3]. APRIL promotes IgA class switching, the survival of IgA-secreting plasma cells and the excess production of a galactose-deficient variant form of IgA1 (Gd-IgA1), which is an initiating step in the multi-hit pathogenesis of IgAN. This leads to the generation of anti-Gd-IgA1 autoantibodies and the formation of nephritogenic immune complexes that deposit in the kidney, resulting in inflammation and damage [2–4]. Blocking APRIL with BION-1301 is a novel approach to address the underlying pathogenesis of IgAN by reducing circulating levels of Gd-IgA1 and preventing the formation of pathogenic immune complexes. The primary objective of this Phase 1/2 study is to assess the safety and tolerability of BION-1301 in healthy volunteers (HV) and patients with IgAN, and secondarily to assess the PK, PD, immunogenicity and preliminary clinical activity. METHOD The Phase 1/2 study (NCT03945318) is comprised of three parts. Parts 1 and 2 were blinded, placebo-controlled single and multiple ascending dose designs in HV and have been completed. Part 3 is a multicenter (USA, UK, South Korea), multicohort, open-label study in up to 40 patients with IgAN. Patients in Cohort 1 receive 450 mg of BION-1301 administered IV every 2 weeks for up to 1 year. After completing at least 24 weeks of IV dosing, patients in Cohort 1 transitioned from receiving 450 mg of BION-1301 IV to receiving 600 mg of BION-1301 SC every 2 weeks. Patients in Cohort 2 receive 600 mg of BION-1301 SC every 2 weeks for up to 1 year. Additional cohorts may be added to explore other doses and dosing schedules. Key eligibility criteria for Part 3 include: (1) biopsy-verified diagnosis of IgAN within 10 years, (2) baseline urine protein excretion ≥ 0.5 g/24 h or UPCR ≥ 0.5 g/g and (3) stable/optimized dose of ACE-I/ARB (or intolerant). RESULTS Final HV data from Parts 1 and 2 have been presented at earlier conferences [5]. Part 3 is on-going and updated interim data from patients with IgAN in Cohort 1 who received BION-1301 IV as well as patients who transitioned to SC dosing are planned to be presented at the 59th ERA Congress. CONCLUSION The current design of the Phase 1/2 study incorporating SC dosing provides for an improved patient experience and will enable the generation of extended safety, PK, PD, immunogenicity and preliminary efficacy data for the potential use of BION-1301 in patients with IgAN.

Regulation of Inflammatory Bowel Disorder by ST8Sia6

Abstract Inflammatory bowel disorders (IBD) including ulcerative colitis (UC) and Crohn’s disease (CD) affect between 1–3 million people in the United States with prevalence on the rise. Patients present with symptoms including diarrhea, abdominal cramps, and weight loss. Many factors are implicated in pathogenesis, including host immune response. Identification of molecules that regulate IBD is critical in understanding pathogenesis. ST8Sia6 is a sialic acid transferase that adds terminal a2,8 disialic acids to cell surface glycoproteins, and we have found that ST8Sia6 knockout (KO) mice exhibit increased spontaneous small bowel lamina propria CD4 TH1 polarization, increased inflammatory cytokine production, and decreased IgA class switching of Peyer’s patch B cells, indicative of inflammation. Additionally, adult ST8Sia6 KO mice have shortened small bowels, likely due to baseline inflammation. These mice do not exhibit obvious baseline symptoms, but ST8Sia6 KO mice exhibit increased weight loss and decreased survival when challenged with dextran sodium sulfate (DSS)-induced colitis, which was also enhanced when co-housed with wildtype (WT) mice and after antibiotic treatment. These DSS-challenged ST8Sia6 KO mice exhibit increased histological damage and immune infiltration of the gut as compared to WT controls. The accelerated DSS-colitis is also observed when ST8Sia6-deficient bone marrow is transplanted into WT recipients, indicating that the effect is mediated specifically by immune cells. This data demonstrates a role for ST8Sia6 in regulating the host immune response to inflammatory bowel disorders, and further elucidating this role will aid in developing a mechanistic understanding of IBD pathogenesis. Supported by grants from NIH R01 CA243545

Parenteral vaccination strategies target protective immunity to the small and large intestine mucosa

Abstract Prophylactic vaccines are most commonly given by a parenteral route. However, this strategy often confers poor protection against GI pathogens because antigens are primarily presented in peripheral lymph nodes, which do not provide the prerequisite ‘tissue imprinting signals’ to target memory T and B cells to the gut. Here, we describe a platform that enables parenteral vaccines to target protection to the GI tract. This was achieved by subcutaneous (s.c.) delivery of compounds known to imprint gut tropism onto lymphocytes. Am80, a retinoic acid receptor agonist, targeted immunity to the small intestine through up-regulation of gut-homing receptors α4β7 and CCR9, and promotion of IgA class-switching. S.c. injection of OVA + CpG combined with repeated injections of Am80 generated significantly higher and durable fecal anti-OVA IgA titers, compared to OVA + CpG without Am80. Vaccination with Am80 also increased antigen-specific CD4 and CD8 T cell trafficking to the small intestine and generated tissue resident memory T (Trm) cells. To overcome the need for multiple doses of Am80, which can cause tissue toxicity at the injection site and hinder clinical translation, we developed a polymeric nanocarrier that showed equivalent imprinting efficacy upon a single injection, lowering the cumulative dose to one-third. Furthermore, we also developed a modified vaccination strategy that could augment effector and memory T cell responses not only in the small intestine, but also in the cecum, colon and rectum, conferring protection to the entire intestinal tract. We conclude that supplementation with mucosal imprinting signals is a promising approach to enhance parenteral vaccines by generating mucosal protection against GI infections. Supported by the Bill & Melinda Gates Foundation

POS-109 INTERIM RESULTS OF PHASE 1 AND 2 TRIALS TO INVESTIGATE THE SAFETY, TOLERABILITY, PHARMACOKINETICS, PHARMACODYNAMICS, AND CLINICAL ACTIVITY OF BION-1301 IN PATIENTS WITH IgA NEPHROPATHY

IgA nephropathy (IgAN) is an autoimmune disease with no approved treatments. A critical step in IgAN pathogenesis is the production of galactose-deficient IgA1 (Gd-IgA1) leading to the generation of anti-Gd-IgA1 autoantibodies and the formation of immune complexes that result in kidney inflammation and damage. A Proliferation-Inducing Ligand (APRIL), a soluble factor that regulates B cell differentiation, proliferation and survival of plasma cells, and IgA class-switching is elevated in patients with IgAN. IgAN patients with high plasma APRIL levels are reported as having higher levels of Gd-IgA1 and proteinuria and lower estimated glomerular filtration rates compared to those with lower plasma APRIL levels. BION-1301 is a novel humanized blocking antibody targeting APRIL that has been evaluated in a Phase 1 study of healthy volunteers (HV). In that study, BION-1301 was well-tolerated with no serious adverse events (SAEs), a pharmacokinetic (PK) half life >30 days and demonstrated dose-dependent pharmacodynamic (PD) effects characterized by durable reductions in serum levels of free April (fAPRIL), IgA and Gd-IgA1, IgM, and to a lesser extent IgG. Here we present interim results from Part 3 of the Phase 1 and the Phase 2 Open-Label Extension (OLE) trials that characterize the safety, PK and PD profile, and preliminary efficacy of BION-1301 in patients with IgAN. The Phase 1 study (NCT03945318) comprises 3 parts. Parts 1 and 2 assessed single- and multiple ascending doses of BION-1301 in HV from 10mg to 1350mg and 50mg to 450mg once every 2 weeks for one month, respectively. Part 3 is an ongoing, open-label, two cohort design in approximately 20 IgAN patients with BION-1301 at 450mg once every 2 weeks for a total of 12 weeks. Key eligibility criteria for Part 3 include: (1) biopsy-verified diagnosis of IgAN within the past 10 years,(2) urine protein ≥0.5 g/24h or baseline UPCR ≥0.5 g/g, and (3) stable/optimized dose of ACE-I/ARB (or intolerant). Patients completing Part 3 are eligible to enroll in the Phase 2 OLE study (NCT04684745) to receive BION-1301 for an additional 2 years. To evaluate PK and PD effects of BION-1301, serum levels of BION-1301, fAPRIL, antidrug antibodies (ADA), neutralizing antibodies (NAbs), and Gd-IgA1 were quantitated using ELISA-based immunoassays. Serum levels of IgA, IgG, and IgM were measured by immunoturbidimetry. UPCR was assessed from 24-hour urine collections. BION-1301 has been well tolerated in IgAN patients receiving a 450mg IV dose every two weeks for 12+ weeks with no SAEs or treatment related AE’s. Consistent with PD responses reported in HVs, durable reductions in serum levels of fAPRIL and immunoglobulins were observed in IgAN patients. Clinically meaningful reductions in proteinuria were seen as early as 12 weeks and were associated with the reduction in Gd-IgA1 levels. Additional data from patients receiving long-term treatment will be updated. This abstract was also submitted for the 58thERA-EDTA Congress. BION-1301 offers disease modifying potential by directly targeting the underlying multi-hit immune pathogenesis of IgAN, which is not addressed with the current standard of care treatment. Promising early biomarker and clinical activity responses support the continued development of BION-1301 in IgAN.

Human Cord Blood B Cells Differ from the Adult Counterpart by Conserved Ig Repertoires and Accelerated Response Dynamics.

Neonatal and infant immune responses are characterized by a limited capability to generate protective Ab titers and memory B cells as seen in adults. Multiple studies support an immature or even impaired character of umbilical cord blood (UCB) B cells themselves. In this study, we provide a comprehensive molecular and functional comparison of B cell subsets from UCB and adult peripheral blood. Most UCB B cells have a mature, naive B cell phenotype as seen in adults. The UCB Ig repertoire is highly variable but interindividually conserved, as BCR clonotypes are frequently shared between neonates. Furthermore, UCB B cells show a distinct transcriptional program that confers accelerated responsiveness to stimulation and facilitated IgA class switching. Stimulation drives extensive differentiation into Ab-secreting cells, presumably limiting memory B cell formation. Humanized mice suggest that the distinctness of UCB versus adult B cells is already reflected by the developmental program of hematopoietic precursors, arguing for a layered B-1/B-2 lineage system as in mice, albeit our findings suggest only partial comparability to murine B-1 cells. Our study shows that UCB B cells are not immature or impaired but differ from their adult mature counterpart in a conserved BCR repertoire, efficient IgA class switching, and accelerated, likely transient response dynamics.

MO286DESIGN OF A PH1, MULTICENTER TRIAL TO INVESTIGATE THE SAFETY, TOLERABILITY, PK/PD OF BION-1301 IN HEALTHY VOLUNTEERS AND ADULTS WITH IGAN AND A MULTICENTER, OPEN-LABEL EXTENSION STUDY FOR IGAN PATIENTS WHO PARTICIPATED IN A PRIOR TRIAL OF BION-1301

Abstract Background and Aims IgA nephropathy (IgAN), the leading cause of primary glomerulonephritis, is an autoimmune disease with no approved treatments.1 Progression to end-stage-renal disease occurs in up to 45% of IgAN patients, requiring dialysis or kidney transplant to manage.2-4 A critical step in IgAN pathogenesis is the production of galactose-deficient IgA1 (Gd-IgA1) leading to the generation of anti-Gd-IgA autoantibodies and the formation of immune complexes that result in kidney inflammation and damage.5 A Proliferation-Inducing Ligand (APRIL), a soluble factor that regulates B cell differentiation, proliferation and survival of plasma cells, and IgA class-switching is elevated in patients with IgAN6, 7. IgAN patients with high plasma APRIL levels are reported as having higher levels of Gd-IgA1 and proteinuria and lower estimated glomerular filtration rates compared to those with lower plasma APRIL levels.7 BION-1301 is a novel humanized blocking antibody targeting APRIL. The primary objective of Study ADU-CL-19 is to assess the short-term safety and tolerability of BION-1301 in Healthy Volunteers (HV) and IgAN patients and to secondarily assess the short-term pharmacokinetics (PK), pharmacodynamics (PD), immunogenicity, and preliminary clinical activity of BION-1301. The primary objective of Study ADU-CL-24 is to characterize the long-term safety of BION-1301 in IgAN patients who completed treatment in ADU-CL-19 while secondarily assessing the long-term PK, PD, immunogenicity, and preliminary clinical activity of BION-1301. Method The Phase 1 study (ADU-CL-19; NCT03945318) comprises 3 parts. Parts 1 and 2 are double-blind, randomized, placebo-controlled single and multiple ascending dose designs in HV; both parts have been completed. Part 3 is an ongoing multicenter (US and UK), multiple-dose, two cohort design in approximately 20 patients with IgAN (10/cohort). Key eligibility criteria for Part 3 includes: (1) urine protein ≥0.5 g/24h or baseline UPCR ≥0.5 g/g, (2) stable/optimized dose of ACE-I/ARB or intolerant to ACE-I/ARB, and (3) biopsy-verified diagnosis of IgAN within the past 10 years. In Part 3, patients in Cohort 1 are receiving BION-1301 at 450mg every 2 weeks for 3 months. The dose and schedule for Cohort 2 will be determined by the Safety Review Team (SRT) based on data from the first 5 patients. After 3 months of treatment, patients continue safety follow-up for approximately 6 months unless deciding to enroll in the open-label extension (OLE) study, withdraw from the study, or are lost to follow up. Study ADU-CL-24 (NCT04684745) is a Phase 2 Open-Label Extension (OLE) of Study ADU-CL-19. Eligibility for the OLE study is restricted to those patients who completed at least 75% of their intended doses as well as the End of Treatment (EOT) visit in Study ADU-CL-19. Patients who enroll directly from the ADU-CL-19 EOT visit are not required to attend an additional screening visit. This is encouraged to maintain un-interrupted dosing. Once enrolled in the OLE, patients receive BION-1301 at the same dose and regimen as assigned in the parent study for up to 2 years. The dose, route, and regimen of BION-1301 may change after review of emergent safety, PK, PD and efficacy data by the SRT. Results Parts 1 and 2 of the Phase 1 study in HV are complete and the data were presented at ASN in 20208 Part 3 of the Phase 1 and the Phase 2 OLE study are ongoing, and interim results from the first dose cohort in IgAN patients are being presented in a separate poster at this meeting. Conclusion The design of the Phase 1 and Phase 2 OLE studies described in HVs and IgAN patients have enabled the generation of short- and long-term safety, PK, PD, immunogenicity and preliminary efficacy data for BION-1301. The Phase 1 short-term data will guide the design of future later-stage trials of BION-1301, while the long-term data from OLE will enable a greater understanding of the potential long-term risk/benefit profile of BION-1301 in IgAN patients.

FC 040INTERIM RESULTS OF PHASE 1 AND 2 TRIALS TO INVESTIGATE THE SAFETY, TOLERABILITY, PHARMACOKINETICS, PHARMACODYNAMICS, AND CLINICAL ACTIVITY OF BION-1301 IN PATIENTS WITH IGA NEPHROPATHY

Abstract Background and Aims IgA nephropathy (IgAN), the leading cause of primary glomerulonephritis, is an autoimmune disease with no approved treatments.1 Progression to end-stage-renal disease occurs in up to 45% of IgAN patients, requiring dialysis or kidney transplant to manage.2-4 A critical step in IgAN pathogenesis is the production of galactose-deficient IgA1 (Gd-IgA1) leading to the generation of anti-Gd-IgA1 autoantibodies and the formation of immune complexes that result in kidney inflammation and damage.5 A Proliferation-Inducing Ligand (APRIL), a soluble factor that regulates B cell differentiation, proliferation and survival of plasma cells, and IgA class-switching is elevated in patients with IgAN6, 7. IgAN patients with high plasma APRIL levels are reported as having higher levels of Gd-IgA1 and proteinuria and lower estimated glomerular filtration rates compared to those with lower plasma APRIL levels.7 BION-1301 is a novel humanized blocking antibody targeting APRIL that has been evaluated in a Phase 1 study of healthy volunteers (HV). In Parts 1 and 2 of the Phase 1 study in HV, we previously reported that BION-1301 was well-tolerated with no serious adverse events (SAEs), a pharmacokinetic (PK) half life >30 days and demonstrated dose-dependent pharmacodynamic (PD) effects characterized by durable reductions in serum levels of free April (fAPRIL), IgA and Gd-IgA1, IgM, and to a lesser extent IgG8. Here we present interim results from Part 3 of the Phase 1 and the Phase 2 Open-Label Extension (OLE) trials that characterize the safety, PK and PD profile, and preliminary efficacy of BION-1301 in patients with IgAN. Method The Phase 1 study (NCT03945318) comprises 3 parts. Parts 1 and 2 assessed single- and multiple ascending doses of BION-1301 in HV from 10mg to 1350mg and 50mg to 450mg once every 2 weeks for one month, respectively. Part 3 is an ongoing, open-label, two cohort design in approximately 20 IgAN patients with BION-1301 at a starting dose and regimen of 450mg once every 2 weeks for a total of 3 months. Key eligibility criteria for Part 3 include: (1) urine protein ≥0.5 g/24h or baseline UPCR ≥0.5 g/g, (2) stable/optimized dose of ACE-I/ARB or be intolerant to ACE-I/ARB, and (3) biopsy-verified diagnosis of IgAN within the past 10 years. Patients completing Part 3 are eligible to enroll in the Phase 2 OLE study (NCT04684745) to receive BION-1301 for up to an additional 2 years. To evaluate PK and PD effects of BION-1301, serum levels of BION-1301, free APRIL (fAPRIL), anti-drug antibodies (ADA), neutralizing antibodies (NAbs), and Gd-IgA1 were quantitated using ELISA-based immunoassays. Serum levels of IgA, IgG, and IgM were measured by immunoturbidimetry. UPCR was assessed from 24-hour urine collections. Results In Part 3 of Phase 1 and the Phase 2 OLE trial to date, BION-1301 has been well tolerated in IgAN patients receiving a 450mg dose every two weeks for 12+ weeks with no SAEs observed. Consistent with PD responses previously reported in HVs, durable reductions in serum levels of fAPRIL and immunoglobulins were also observed in IgAN patients. Clinically meaningful reductions in proteinuria were observed as early as 12 weeks and were associated with the reduction in IgA. Additional data from patients receiving long-term treatment will be updated. Conclusion BION-1301 is a novel humanized anti-APRIL monoclonal antibody being developed as a potential treatment for patients with IgAN. BION-1301 offers disease modifying potential by directly targeting the underlying multi-hit immune pathogenesis of IgAN, which is not addressed with the current standard of care treatment. Promising early biomarker and clinical activity responses support the continued development of BION-1301 in IgAN.

Epigenetic regulation of IgA class-switching by miR-146a through selective downregulation of Smad2, Smad3 and Smad4

Abstract IgA is the predominant antibody isotype at mucosal surfaces. It plays a critical role in mucosal homeostasis and provides a first line of defense in immune protection. Class switch DNA recombination (CSR) to IgA is initiated by TGF-β, which induces Smad2, Smad3, Smad4 and Runx3 binding to the Iα promoter. This promotes germline Iα-Cα transcription, thereby increasing accessibility to the Igα locus. Epigenetic modifications, such as microRNAs, have been shown to modulate the antibody response, although the role of microRNAs in B cell differentiaton processes, such as guiding CSR to specific Ig isotypes, remains unexplored. miR146a has been shown to regulate T cell, dendritic cell and macrophage functions in innate and adaptive immune responses. Here we show that miR146a, which targets Smad2, Smad3 and Smad4 3′UTRs and is the most abundant miRNA in resting B cells, is significantly downregulated in B cells undergoing CSR to IgA. Deletion of miR146a, as in miR146a−/− B cells, frees Smad2, Smad3 and Smad4 from transcriptional repression, thereby increasing recruitment of these transcription factors to the Iα promoter. This results in increased germline Iα-Cα transcription and CSR to IgA without alterations to Aicda and Prdm1 expression. Accordingly, miR146a−/− mice displayed an elevated gut, systemic IgA responses and kidney IgA deposition, a hallmark of hyper IgA nephropathy. This was recapitulated in μMT/miR146a−/− mixed bone marrow chimera mice, further demonstrating the B cell-intrinsic role of miR146a in the modulation of CSR to IgA. Thus, by silencing Smad2, Smad3 and Smad4 transcription, miR-146a plays an important B cell intrinsic role in the modulation of the IgA response.

POS-144 A PHASE 1, OPEN-LABEL, RANDOMIZED, SINGLE-DOSE, PARALLEL GROUP SAFETY AND BIOAVAILABILITY STUDY OF BION-1301 ADMINISTERED BY INTRAVENOUS (IV) AND SUBCUTANEOUS (SC) ROUTES

IgAN (IgA nephropathy) is the most common primary glomerulonephritis in the world. There are currently no approved treatments and limited off-label treatment options consist largely of supportive measures which do not directly address the underlying immunologic pathogenesis of disease. APRIL (A proliferation-inducing ligand) is critical for IgA class switching, maturation and survival of IgA secreting plasma cells, and production of gd-IgA1 (galactose—deficient IgA1) which is recognized as an auto-antigen leading to the formation of pathogenic IgA immune complexes. BION-1301 is a novel humanized monoclonal antibody that neutralizes APRIL and is currently in Phase 1 development in healthy volunteers and patients with IgAN. In prior Phase 1 studies, BION-1301 was well-tolerated in healthy volunteers and reduced serum levels of free APRIL, IgA, IgM, and to a lesser extent IgG at single doses up to 1350 mg IV and multiple doses up to 450 mg IV every 2 weeks. This study compares pharmacokinetic (PK) and pharmacodynamic (PD) profiles following the administration of BION-1301 300 mg by IV and SC routes in healthy volunteers. Up to 34 healthy volunteers were randomized 1:1 to receive BION-1301 300mg either by IV or SC administration. The primary endpoint was an estimate of the bioavailability of BION-1301 with secondary endpoints of safety, tolerability, PK, PD, and immunogenicity. Subjects were closely monitored during the in-clinic stay through day 8, with in-clinic follow-up visits occurring through the end of study at day 57. PK, PD, and immunogenicity samples were collected periodically throughout the course of the study. BION-1301 continues to be well tolerated with no Grade 3 treatment emergent adverse events or serious adverse event to date. Serum PK profiles; PD profiles including free APRIL, IgA, IgG, and IgM levels; and anti-drug antibody levels will be presented and compared between IV and SC routes. Blockade of APRIL by BION-1301 remains a promising therapeutic approach for the treatment of IgAN. PK and PD data comparing IV and SC administration of BION-1301 will be used to refine the SC dose selection for future global clinical studies of BION-1301 in IgAN.