Deciphering the importance of culture pH on CD22 CAR T-cells characteristics

BACKGROUND

Chimeric antigen receptor (CAR) T-cells have demonstrated significant efficacy in targeting hematological malignancies, and their use continues to expand. Despite substantial efforts spent on the optimization of protocols for CAR T-cell manufacturing, critical parameters of cell culture such as pH or oxygenation are rarely actively monitored during cGMP CAR T-cell generation. A comprehensive understanding of the role that these factors play in manufacturing may help in optimizing patient-specific CAR T-cell therapy with maximum benefits and minimal toxicity.

METHODS

This retrospective study examined cell culture supernatants from the manufacture of CAR T-cells for 20 patients with B-cell malignancies enrolled in a phase 1/2 clinical trial of anti-CD22 CAR T-cells. MetaFLEX was used to measure supernatant pH, oxygenation, and metabolites, and a Bio-Plex assay was used to assess protein levels. Correlations were assessed between the pH of cell culture media throughout manufacturing and cell proliferation as well as clinical outcomes. Next-generation sequencing was conducted to examine gene expression profiles of the final CAR T-cell products.

RESULTS

A pH level at the lower range of normal at the beginning of the manufacturing process significantly correlated with measures of T-cell expansion and metabolism. Stable or rising pH during the manufacturing process was associated with clinical response, whereas a drop in pH was associated with non-response.

CONCLUSIONS

pH has potential to serve as an informative factor in predicting CAR T-cell quality and clinical outcomes. Thus, its active monitoring during manufacturing may ensure a more effective CAR T-cell product.

CD22 is a potential target of CAR-NK cell therapy for esophageal squamous cell carcinoma

BACKGROUND

Chimeric antigen receptor NK (CAR-NK) cell therapy is one of the most promising immunotherapies. Although it has shown a significant therapeutic effect in hematologic malignancies, few successes have been obtained in solid tumors including esophageal squamous cell carcinoma (ESCC). The major reasons are lack of specific cell surface antigens and complex tumor microenvironment. Here we identify CD22, a well-known tumor surface marker in hematologic malignancies, is expressed in ESCC, possibly serving as a potential target of CAR-NK cell therapy.

METHODS

The expression of 13 tumor cell surface antigens used clinically was analyzed in patients from The Cancer Genome Atlas (TCGA) database. Also, mRNA expression were detected in 2 ESCC cell lines and 2 patients samples by qCPR. Then according to Venn diagram, CD22 was selected for further investigation. Following this, the expression of CD22 by immunofluorescence (IF) in ESCC cell lines and by immunohistochemistry (IHC) in 87 cases of human ESCC samples was detected respectively. On the basis of H-score results, the correlation between CD22 expression and clinical parameters was analyzed. As a proof, the efficacy of CD22-targeted CAR-NK cells against ESCC cell lines was performed by a real-time cell analyzer (RTCA) platform.

RESULTS

KYSE-140 and KYSE-150 cell lines displayed surface expression of CD22. IHC showed an 80.46% (70/87) positive rate in ESCC patient samples. Among these, cell membranous expression of CD22 was observed in 27.59% (24/87) patient samples. Through chi-square test, expression of CD22 in ESCC was associated with lymph node metastasis while it was no related to the depth of tumor invasion and clinical stage. Engineered CD22-targeted CAR-NK cells exhibited inhibitory growth capability against ESCC cell lines (p < 0.0001).

CONCLUSIONS

CD22 is a potential tumor surface antigen capable of being targeted by CAR-NK cells in ESCC. And potential therapeutics for ESCC may be developed based on immune cells expressing anti-CD22 CAR. The study also indicates that CD22 CAR-NK cells could be used in other cancers and more in vivo experiments are needed.

CD22 blockade modulates microglia activity to suppress neuroinflammation following intracerebral hemorrhage

Microglia are first responders to acute brain insults and initiate neuroinflammation to drive secondary tissue injury. Yet the key molecular switches in control of the inflammatory activity of microglia remain poorly understood. Intracerebral hemorrhage (ICH) is a devastating stroke subtype whereby a hematoma is formed within the brain parenchyma and associated with high mortality. Using a mouse model of ICH, we found upregulation of CD22 that predominantly occurred in microglia. Antibody blockade of CD22 led to a reduction in neurological deficits, brain lesion and hematoma volume. This was accompanied by reduced inflammatory activity, increased expression of alternative activation markers (CD206 and IL-10) and enhanced phagocytosis activity in microglia after ICH. CD22 blockade also led to an increase of phosphorylated SYK and AKT after ICH. Notably, the benefits of CD22 blockade were ablated in ICH mice subjected to microglial depletion with a colony-stimulating factor 1 receptor inhibitor PLX5622. Additionally, the protective effects of CD22 blockade was diminished in ICH mice receiving a SYK inhibitor R406. Together, our findings highlight CD22 as a key molecular switch to control the detrimental effects of microglia after acute brain injury, and provide a novel strategy to improve the outcome of ICH injury.

Siglec cis-ligands and their roles in the immune system

Sialic acid-binding immunoglobulin-like lectins are a family of membrane molecules primarily expressed in immune cells. Most of them are inhibitory receptors containing immunoreceptor tyrosine-based inhibition motifs in the cytoplasmic tail. On the cell surface, sialic acid-binding immunoglobulin-like lectins are mostly bound by sialylated glycans on membrane molecules expressed in the same cell (cis-ligands). Although ligands of sialic acid-binding immunoglobulin-like lectins are not efficiently identified by conventional methods such as immunoprecipitation, in situ labeling including proximity labeling is useful in identifying both cis-ligands and the sialylated ligands expressed by other cells (trans-ligands) of sialic acid-binding immunoglobulin-like lectins. Interaction of the inhibitory sialic acid-binding immunoglobulin-like lectins with cis-ligands including both those with and without signaling function modulates the inhibitory activity of sialic acid-binding immunoglobulin-like lectins by multiple different ways. This interaction also modulates signaling function of the cis-ligands. So far, little is known about the role of the interaction between sialic acid-binding immunoglobulin-like lectins and the cis-ligands. Nonetheless, recent studies showed that the inhibitory activity of CD22 (also known as Siglec-2) is regulated by endogenous ligands, most likely cis-ligands, differentially in resting B cells and those in which B-cell antigen receptor is ligated. This differential regulation plays a role in quality control of signaling-competent B cells and also partial restoration of B-cell antigen receptor signaling in immunodeficient B cells.

Impact of Siglecs on autoimmune diseases

Autoimmune diseases affect tens of millions of people just in the United States alone. Most of the available treatment options are aimed at reducing symptoms but do not lead to cures. Individuals affected with autoimmune diseases suffer from the imbalance between tolerogenic and immunogenic functions of their immune system. Often pathogenesis is mediated by autoreactive B and T cells that escape central tolerance and react against self-antigens attacking healthy tissues in the body. In recent years Siglecs, sialic-acid-binding immunoglobulin (Ig)-like lectins, have gained attention as immune checkpoints for therapeutic interventions to dampen excessive immune responses and to restore immune tolerance in autoimmune diseases. Many Siglecs function as inhibitory receptors suppressing activation signals in various immune cells through binding to sialic acid ligands as signatures of self. In this review, we highlight potential of Siglecs in suppressing immune responses causing autoimmune diseases. In particular, we cover the roles of CD22 and Siglec-G/Siglec-10 in regulating autoreactive B cell responses. We discuss several functions of Siglec-10 in the immune modulation of other immune cells, and the potential of therapeutic strategies for restoring immune tolerance by targeting Siglecs and expanding regulatory T cells. Finally, we briefly review efforts evaluating Siglec-based biomarkers to monitor autoimmune diseases.

Deciphering prognostic value of CD22 and its contribution to suppression of proinflammatory cytokines production in patients with IgA nephropathy

BACKGROUND

CD22, mainly expressed in mature B cells, could negatively regulate the function of B cells by binding to sialic acid-positive IgG (SA-IgG). Soluble CD22 (sCD22) is generated by the cleavage of the extracellular domain of CD22 on the membrane surface. However, the role of CD22 in IgA nephropathy (IgAN) remains unknown.

METHODS

A total of 170 IgAN patients with a mean follow-up of 18 months were included in this study. The sCD22, TGF-β, IL-6 and TNF-α were detected using commercial ELISA kits. SA-IgG were purified to stimulate peripheral blood mononuclear cells (PBMCs) from IgAN patients.

RESULTS

The plasma levels of sCD22 were lower in IgAN patients in comparison with healthy control. Furthermore, CD22 mRNA levels in PBMCs from patients with IgAN were significantly lower than those of healthy controls. The plasma levels of sCD22 were positively correlated to the mRNA levels of CD22. We found that patients with higher sCD22 levels had a lower level of serum creatinine and a higher level of eGFR on the time of renal biopsy and a higher remission rate of proteinuria and a lower risk of kidney events at the end of follow-up. The logistic regression analysis showed sCD22 was associated with an increased odd of proteinuria remission after being adjusted for eGFR, proteinuria, and SBP. After adjusting for confounding variables, sCD22 was a borderline significant predictor of less kidney composite endpoint. In addition, the sCD22 levels were positively associated with SA-IgG in plasma. The experimental results in vitro showed that addition of SA-IgG enhanced the release of sCD22 in cell supernatant and the phosphorylation of CD22 in PBMCs, further inhibiting the production of IL-6, TNF-α, and TGF-β in cell supernatant in a dose-dependent manner. Pretreatment with CD22-antibody significantly increased the expression of cytokines in PBMCs.

CONCLUSIONS

This is the first study to demonstrate that lower plasma soluble CD22 in IgAN patients and high soluble CD22 levels are associated with an increased odd of proteinuria remission and a decreased odd of kidney endpoint. The interaction between CD22 and SA-IgG can inhibit proliferation and inflammation release in PBMCs from IgAN patients.

Polymer-tethered glycosylated gold nanoparticles recruit sialylated glycoproteins into their protein corona, leading to off-target lectin binding

Upon exposure to biological fluids, the fouling of nanomaterial surfaces results in non-specific capture of proteins, which is particularly important when in contact with blood for in vivo and ex vivo applications. It is crucial to evaluate not just the protein components but also the glycans attached to those proteins. Polymer-tethered glycosylated gold nanoparticles have shown promise for use in biosensing/diagnostics, but the impact of the glycoprotein corona has not been established. Here we investigate how polymer-tethered glycosylated gold nanoparticles interact with serum proteins and demonstrate that the protein corona introduces new glycans and hence off-specific targeting capability. Using a panel of RAFT-derived polymers grafted to the gold surface, we show that the extent of corona formation is not dependent on the type of polymer. In lectin-binding assays, a glycan (galactose) installed on the chain-end of the polymer was available for binding even after protein corona formation. However, using sialic-acid binding lectins, it was found that there was significant off-target binding due to the large density of sialic acids introduced in the corona, confirmed by western blotting. To demonstrate the importance, we show that the nanoparticles can bind Siglec-2, an immune-relevant lectin post-corona formation. Pre-coating with (non-glycosylated) bovine serum albumin led to a significant reduction in the total glycoprotein corona. However, sufficient sialic acids were still present in the residual corona to lead to off-target binding. These results demonstrate the importance of the glycans when considering the protein corona and how 'retention of the desired function' does not rule out 'installation of undesired function' when considering the performance of glyco-nanomaterials.

The CD22-IGF2R interaction is a therapeutic target for microglial lysosome dysfunction in Niemann-Pick type C

Lysosome dysfunction is a shared feature of rare lysosomal storage diseases and common age-related neurodegenerative diseases. Microglia, the brain-resident macrophages, are particularly vulnerable to lysosome dysfunction because of the phagocytic stress of clearing dying neurons, myelin, and debris. CD22 is a negative regulator of microglial homeostasis in the aging mouse brain, and soluble CD22 (sCD22) is increased in the cerebrospinal fluid of patients with Niemann-Pick type C disease (NPC). However, the role of CD22 in the human brain remains unknown. In contrast to previous findings in mice, here, we show that CD22 is expressed by oligodendrocytes in the human brain and binds to sialic acid–dependent ligands on microglia. Using unbiased genetic and proteomic screens, we identify insulin-like growth factor 2 receptor (IGF2R) as the binding partner of sCD22 on human myeloid cells. Targeted truncation of IGF2R revealed that sCD22 docks near critical mannose 6-phosphate–binding domains, where it disrupts lysosomal protein trafficking. Interfering with the sCD22-IGF2R interaction using CD22 blocking antibodies ameliorated lysosome dysfunction in human NPC1 mutant induced pluripotent stem cell–derived microglia-like cells without harming oligodendrocytes in vitro. These findings reinforce the differences between mouse and human microglia and provide a candidate microglia-directed immunotherapeutic to treat NPC.

A CD22-Shp1 phosphatase axis controls integrin β7 display and B cell function in mucosal immunity

The integrin α4β7 selectively regulates lymphocyte trafficking and adhesion in the gut and gut-associated lymphoid tissue (GALT). Here, we describe unexpected involvement of the tyrosine phosphatase Shp1 and the B cell lectin CD22 (Siglec-2) in the regulation of α4β7 surface expression and gut immunity. Shp1 selectively inhibited β7 endocytosis, enhancing surface α4β7 display and lymphocyte homing to GALT. In B cells, CD22 associated in a sialic acid-dependent manner with integrin β7 on the cell surface to target intracellular Shp1 to β7. Shp1 restrained plasma membrane β7 phosphorylation and inhibited β7 endocytosis without affecting β1 integrin. B cells with reduced Shp1 activity, lacking CD22 or expressing CD22 with mutated Shp1-binding or carbohydrate-binding domains displayed parallel reductions in surface α4β7 and in homing to GALT. Consistent with the specialized role of α4β7 in intestinal immunity, CD22 deficiency selectively inhibited intestinal antibody and pathogen responses.

Glycoengineering of NK Cells with Glycan Ligands of CD22 and Selectins for B-Cell Lymphoma Therapy

CD22, a member of Siglec family of sialic acid binding proteins, has restricted expression on B cells. Antibody-based agents targeting CD22 or CD20 on B lymphoma and leukemia cells exhibit clinical efficacy for treating these malignancies, but also attack normal B cells leading to immune deficiency. Here, we report a chemoenzymatic glycocalyx editing strategy to introduce high-affinity and specific CD22 ligands onto NK-92MI and cytokine-induced natural killer cells to achieve tumor-specific CD22 targeting. These CD22-ligand modified cells exhibited significantly enhanced tumor cell binding and killing in vitro without harming healthy B cells. For effective lymphoma cell killing in vivo, we further functionalized CD22 ligand-modified NK-92MI cells with the E-selectin ligand sialyl Lewis X to promote trafficking to bone marrow. The dual-functionalized cells resulted in the efficient suppression of B lymphoma in a xenograft model. Our results suggest that natural killer cells modified with glycan ligands to CD22 and selectins promote both targeted killing of B lymphoma cells and improved trafficking to sites where the cancer cells reside, respectively.

Identification of a moderate affinity CD22 binding peptide and in vitro optimization of peptide-targeted nanoparticles for selective uptake by CD22+ B-cell malignancies

B cell malignancies, such as B cell leukemia and lymphoma, have CD22 overexpression with ∼7% of patients. A short CD22 binding peptide (PV3) with a moderate affinity (Kd ∼ 9 μM) was identified by screening multiple peptide candidates determined through analysis of CD22-epratuzumab complex crystal structure. PV3 binding specificity was confirmed via competitive binding inhibition, then was used as the targeting moiety on CD22-targeted liposomal nanoparticle (TNPPV3) formulations. To maximize the potential therapeutic outcome of TNPPV3 formulation, nanoparticle design parameters, such as peptide hydrophilicity, ethylene glycol linker length, valency, and particle size were optimized for maximum selective cellular uptake by CD22+ malignant cancer cells. The effects of altering design parameters one at a time on TNP uptake were evaluated using flow cytometry, and the optimal parameters for TNPPV3 were determined to be 8% peptide density, EG18 linker, and 3 lysines of 100 nm nanoparticles. This optimally designed TNPPV3 achieved ∼4 and 40-fold enhancement of cellular uptake by CD22+ Raji cells over CD22- Jurkat and MOLT-4 cells, respectively, demonstrating selectivity for malignant cells with CD22 overexpression. Overall, this study establishes PV3 to be CD22 binding peptide with proven effectiveness as a targeting element. In future, the optimal TNPPV3 formulation will potentially achieve maximal in vivo therapeutic outcomes by efficiently targeting CD22+ blood cancer cells in vivo.

CD22 blockade restores homeostatic microglial phagocytosis in ageing brains

Microglia maintain homeostasis in the central nervous system through phagocytic clearance of protein aggregates and cellular debris. This function deteriorates during ageing and neurodegenerative disease, concomitant with cognitive decline. However, the mechanisms of impaired microglial homeostatic function and the cognitive effects of restoring this function remain unknown. We combined CRISPR-Cas9 knockout screens with RNA sequencing analysis to discover age-related genetic modifiers of microglial phagocytosis. These screens identified CD22, a canonical B cell receptor, as a negative regulator of phagocytosis that is upregulated on aged microglia. CD22 mediates the anti-phagocytic effect of α2,6-linked sialic acid, and inhibition of CD22 promotes the clearance of myelin debris, amyloid-β oligomers and α-synuclein fibrils in vivo. Long-term central nervous system delivery of an antibody that blocks CD22 function reprograms microglia towards a homeostatic transcriptional state and improves cognitive function in aged mice. These findings elucidate a mechanism of age-related microglial impairment and a strategy to restore homeostasis in the ageing brain.

Integrated machine learning pipeline for aberrant biomarker enrichment (i-mAB): characterizing clusters of differentiation within a compendium of systemic lupus erythematosus patients

Clusters of differentiation (CD) are cell surface biomarkers that denote key biological differences between cell types and disease state. CD-targeting therapeutic monoclonal antibodies (mABs) afford rich trans-disease repositioning opportunities. Within a compendium of systemic lupus erythematous (SLE) patients, we applied the Integrated machine learning pipeline for aberrant biomarker enrichment (i-mAB) to profile de novo gene expression features affecting CD20, CD22 and CD30 gene aberrance. First, a novel Relief-based algorithm identified interdependent features(p=681) predicting treatment-naïve SLE patients (balanced accuracy=0.822). We then compiled CD-associated expression profiles using regularized logistic regression and pathway enrichment analyses. On an independent general cell line model system data, we replicated associations (in silico) of BCL7A (padj=1.69e-9) and STRBP(padj=4.63e-8) with CD22; NCOA2(padj=7.00e-4), ATN1 (padj=1.71e-2), and HOXC4(padj=3.34e-2) with CD30; and PHOSPHO1, a phosphatase linked to bone mineralization, with both CD22(padj=4.37e-2) and CD30(padj=7.40e-3). Utilizing carefully aggregated secondary data and leveraging a priori hypotheses, i-mAB fostered robust biomarker profiling among interdependent biological features.

Flow Cytometric Monitoring for Residual Disease in B Lymphoblastic Leukemia Post T Cell Engaging Targeted Therapies

The use of targeted therapy is growing in the setting of hematopoietic neoplasms. Flow cytometry is a cornerstone of residual disease monitoring post therapy in this group of malignancies. Often, there is overlap between antigens targeted by immunotherapies and gating reagents utilized for population identification by flow cytometry. Such overlap can render a previously excellent gating reagent inadequate for disease detection. Recently, several anti-CD19 T cell-engaging immunotherapeutic agents and an anti-CD22 immunotoxin have been FDA approved for use in B lymphoblastic leukemia (B-LL), with an anti-CD22 T cell-engaging agent in development. In the setting of such targeted therapies, CD19 and CD22 expression may be altered, compromising the use of these reagents for identification of abnormal blasts. We describe herein a strategy for flow cytometric monitoring for residual disease in patients with B-LL post T cell-engaging anti-CD19 and anti-CD22 therapies. © 2018 by John Wiley & Sons, Inc.

Galectin-9 suppresses B cell receptor signaling and is regulated by I-branching of N-glycans

Leukocytes are coated with a layer of heterogeneous carbohydrates (glycans) that modulate immune function, in part by governing specific interactions with glycan-binding proteins (lectins). Although nearly all membrane proteins bear glycans, the identity and function of most of these sugars on leukocytes remain unexplored. Here, we characterize the N-glycan repertoire (N-glycome) of human tonsillar B cells. We observe that naive and memory B cells express an N-glycan repertoire conferring strong binding to the immunoregulatory lectin galectin-9 (Gal-9). Germinal center B cells, by contrast, show sharply diminished binding to Gal-9 due to upregulation of I-branched N-glycans, catalyzed by the β1,6-N-acetylglucosaminyltransferase GCNT2. Functionally, we find that Gal-9 is autologously produced by naive B cells, binds CD45, suppresses calcium signaling via a Lyn-CD22-SHP-1 dependent mechanism, and blunts B cell activation. Thus, our findings suggest Gal-9 intrinsically regulates B cell activation and may differentially modulate BCR signaling at steady state and within germinal centers.

Decreased CD22 expression and intracellular signaling aberrations in B cells of patients with systemic sclerosis

The objective of the study was to explore the phenotype and intracellular signaling events of B cells in patients with systemic sclerosis (SSc). Peripheral blood B cell surface markers CD19 and CD22 were evaluated by flow cytometry in 23 patients with SSc and seven healthy individuals. Levels of intracellular kinases Lyn, Syk and P-Y 348 Syk along with phosphatase SHP-1 were examined with Western immunoblotting in selected patients. P-Y 822 CD22 was subsequently evaluated flow cytometrically in antigen receptor stimulated B cells. A statistically significant decrease in CD22 B cell surface expression was found in the diffuse subset of patients (median CD22 MFI ± SD was 5.90 ± 2.35 vs 10.20 ± 1.88 for patients vs healthy controls respectively; p = 0.021), while no statistically significant change was found regarding CD19. CD22 underexpression was more pronounced when interstitial lung disease (ILD) was present (median CD22 MFI ± SD was 5.90 ± 2.25 vs 10.20 ± 1.88 for patients with ILD vs healthy controls respectively; p = 0.011). CD22 phosphorylation following B cell receptor (BCR) stimulation was also found to be impaired in patients with diffuse SSc (median change in MFI ± SD was 0.28 ± 0.09 vs 0.38 ± 0.08 for patients vs healthy controls respectively; p = 0.034). Low CD22 expression was arithmetically correlated with kinase Lyn underexpression (Pearson coefficient 0.926; p = ns) in B cells from a small sample of patients. These results suggest that CD22 underexpression and impaired phosphorylation along with implications for Lyn kinase aberrations could contribute to the activated B cell phenotype in SSc.

A Chemical Biology Solution to Problems with Studying Biologically Important but Unstable 9-O-Acetyl Sialic Acids

9-O-Acetylation is a common natural modification on sialic acids (Sias) that terminate many vertebrate glycan chains. This ester group has striking effects on many biological phenomena, including microbe-host interactions, complement action, regulation of immune responses, sialidase action, cellular apoptosis, and tumor immunology. Despite such findings, 9-O-acetyl sialoglycoconjugates have remained largely understudied, primarily because of marked lability of the 9-O-acetyl group to even small pH variations and/or the action of mammalian or microbial esterases. Our current studies involving 9-O-acetylated sialoglycans on glycan microarrays revealed that even the most careful precautions cannot ensure complete stability of the 9-O-acetyl group. We now demonstrate a simple chemical biology solution to many of these problems by substituting the oxygen atom in the ester with a nitrogen atom, resulting in sialic acids with a chemically and biologically stable 9-N-acetyl group. We present an efficient one-pot multienzyme method to synthesize a sialoglycan containing 9-acetamido-9-deoxy-N-acetylneuraminic acid (Neu5Ac9NAc) and compare it to the one with naturally occurring 9-O-acetyl-N-acetylneuraminic acid (Neu5,9Ac2). Conformational resemblance of the two molecules was confirmed by computational molecular dynamics simulations. Microarray studies showed that the Neu5Ac9NAc-sialoglycan is a ligand for viruses naturally recognizing Neu5,9Ac2, with a similar affinity but with much improved stability in handling and study. Feeding of Neu5Ac9NAc or Neu5,9Ac2 to mammalian cells resulted in comparable incorporation and surface expression as well as binding to 9-O-acetyl-Sia-specific viruses. However, cells fed with Neu5Ac9NAc remained resistant to viral esterases and showed a slower turnover. This simple approach opens numerous research opportunities that have heretofore proved intractable.

Down-regulation of B cell-related genes in peripheral blood leukocytes of Parkinson's disease patients with and without GBA mutations

Parkinson's disease (PD) is a common neurodegenerative disorder, caused by aging, genetic and environmental factors. Many genes and genetic loci have been implicated in autosomal dominant and recessive PD, among them SNCA, LRRK2, GBA, Parkin, DJ1 and PINK1. Mutations in the LRRK2 and GBA genes are especially common among PD patients of Ashkenazi-Jewish (AJ) origin, accounting for over a third of the patient population. We aimed to identify genes and cellular pathways that may be involved in GBA-associated PD. Whole genome expression analysis was performed using peripheral blood leukocytes (PBLs) of PD patients with mutations in the GBA gene (PD-GBA, n = 59) compared to healthy controls (n = 59). Significant expression changes were detected in 26 genes, most of them were down-regulated in patients and annotated to B cell or immune-related functions. The expression levels of five membrane-bound B cell genes (FCRL1, CD19, CD22, CD79A and CD180) were further analyzed in four distinct populations: (1) Healthy controls (n = 20), (2) PD-GBA (n = 20), (3) PD patients who do not carry LRRK2 or GBA mutations (PD-NC, n = 20), (4) Asymptomatic 1st degree family members, with (n = 15) or without (n = 15) GBA mutations. In qRT-PCR analysis, all five genes were down-regulated in patients (PD-GBA and PD-NC) compared to controls. These changes in expression were not observed when comparing family members who carry GBA mutations to non-carrier family members. Furthermore, these expression levels were disease-duration dependent: the most significant decreased expression occurred after the first two years of onset, and remained steady after 6 years. These results further support the involvement of B cell-related genes in PD and correlate the level of reduced expression to disease duration.

Systematic comparison of single-chain Fv antibody-fusion toxin constructs containing Pseudomonas Exotoxin A or saporin produced in different microbial expression systems

BACKGROUND

Antibodies raised against selected antigens over-expressed at the cell surface of malignant cells have been chemically conjugated to protein toxin domains to obtain immunotoxins (ITs) able to selectively kill cancer cells. Since latest generation immunotoxins are composed of a toxic domain genetically fused to antibody fragment(s) which confer on the IT target selective specificity, we rescued from the hydridoma 4KB128, a recombinant single-chain variable fragment (scFv) targeting CD22, a marker antigen expressed by B-lineage leukaemias and lymphomas. We constructed several ITs using two enzymatic toxins both able to block protein translation, one of bacterial origin (a truncated version of Pseudomonas exotoxin A, PE40) endowed with EF-2 ADP-ribosylation activity, the other being the plant ribosome-inactivating protein saporin, able to specifically depurinate 23/26/28S ribosomal RNA. PE40 was selected because it has been widely used for the construction of recombinant ITs that have already undergone evaluation in clinical trials. Saporin has also been evaluated clinically and has recently been expressed successfully at high levels in a Pichia pastoris expression system. The aim of the present study was to evaluate optimal microbial expression of various IT formats.

RESULTS

An anti-CD22 scFv termed 4KB was obtained which showed the expected binding activity which was also internalized by CD22+ target cells and was also competed for by the parental monoclonal CD22 antibody. Several fusion constructs were designed and expressed either in E. coli or in Pichia pastoris and the resulting fusion proteins affinity-purified. Protein synthesis inhibition assays were performed on CD22+ human Daudi cells and showed that the selected ITs were active, having IC50 values (concentration inhibiting protein synthesis by 50% relative to controls) in the nanomolar range.

CONCLUSIONS

We undertook a systematic comparison between the performance of the different fusion constructs, with respect to yields in E. coli or P. pastoris expression systems and also with regard to each constructs specific killing efficacy. Our results confirm that E. coli is the system of choice for the expression of recombinant fusion toxins of bacterial origin whereas we further demonstrate that saporin-based ITs are best expressed and recovered from P. pastoris cultures after yeast codon-usage optimization.

Cancer stem cells biomarkers in triple negative invasive carcinoma of the breast and associated in situ lesions

Triple negative breast cancer (TNBC) [negative for expression of estrogen and progesterone receptors (ER, PR) and HER2÷neu protein] represent a subtype of breast cancer associated with poor prognosis and highly aggressive behavior. The characterization of stem cell in this type of carcinoma could determine the appearance of new ideas concerning origin and evolution. There is an impressive amount of data in the literature related to TNBC and a growing interest for stem cell research during the past years, but there are no data concerning the genetic characterization of stem cells in the context of cell biology of TNBC as compared with associated DCIS. We performed immunohistochemical studies for the expression and distribution of several stem cell-related antigens, focusing on the association of TNBC with DCIS and comparing the presence of stem cells in the invasive and in the in situ component. Optimization of detection, identification and characterization of tumorigenic breast cancer stem cells might permit further identification of targeted treatment.

Kinetics of MDR transport in tumor-initiating cells

Multidrug resistance (MDR) driven by ABC (ATP binding cassette) membrane transporters is one of the major causes of treatment failure in human malignancy. MDR capacity is thought to be unevenly distributed among tumor cells, with higher capacity residing in tumor-initiating cells (TIC) (though opposite finding are occasionally reported). Functional evidence for enhanced MDR of TICs was previously provided using a "side population" assay. This assay estimates MDR capacity by a single parameter - cell's ability to retain fluorescent MDR substrate, so that cells with high MDR capacity ("side population") demonstrate low substrate retention. In the present work MDR in TICs was investigated in greater detail using a kinetic approach, which monitors MDR efflux from single cells. Analysis of kinetic traces obtained allowed for the estimation of both the velocity (V max) and affinity (K M) of MDR transport in single cells. In this way it was shown that activation of MDR in TICs occurs in two ways: through the increase of V max in one fraction of cells, and through decrease of K M in another fraction. In addition, kinetic data showed that heterogeneity of MDR parameters in TICs significantly exceeds that of bulk cells. Potential consequences of these findings for chemotherapy are discussed.

IgG4 subclass antibodies impair antitumor immunity in melanoma

Host-induced antibodies and their contributions to cancer inflammation are largely unexplored. IgG4 subclass antibodies are present in IL-10-driven Th2 immune responses in some inflammatory conditions. Since Th2-biased inflammation is a hallmark of tumor microenvironments, we investigated the presence and functional implications of IgG4 in malignant melanoma. Consistent with Th2 inflammation, CD22+ B cells and IgG4(+)-infiltrating cells accumulated in tumors, and IL-10, IL-4, and tumor-reactive IgG4 were expressed in situ. When compared with B cells from patient lymph nodes and blood, tumor-associated B cells were polarized to produce IgG4. Secreted B cells increased VEGF and IgG4, and tumor cells enhanced IL-10 secretion in cocultures. Unlike IgG1, an engineered tumor antigen-specific IgG4 was ineffective in triggering effector cell-mediated tumor killing in vitro. Antigen-specific and nonspecific IgG4 inhibited IgG1-mediated tumoricidal functions. IgG4 blockade was mediated through reduction of FcγRI activation. Additionally, IgG4 significantly impaired the potency of tumoricidal IgG1 in a human melanoma xenograft mouse model. Furthermore, serum IgG4 was inversely correlated with patient survival. These findings suggest that IgG4 promoted by tumor-induced Th2-biased inflammation may restrict effector cell functions against tumors, providing a previously unexplored aspect of tumor-induced immune escape and a basis for biomarker development and patient-specific therapeutic approaches.

Targeting of CD22-positive B-cell lymphoma cells by synthetic divalent sialic acid analogues

CD22 is an inhibitory co-receptor of the B-cell receptor (BCR) on B cells. Since CD22 is ubiquitously expressed in the B-cell lineage and CD22 endocytosis can be triggered efficiently, antibodies and antibody-based immunotoxins against CD22 are used to target B cells both in B-cell lymphomas and leukemias, as well as in autoimmune diseases. CD22 recognizes α2,6-linked sialic acids as endogenous ligands. We have developed new synthetic sialosides as ligands for human CD22. These sialosides bind CD22 on human B cells with high affinity and can efficiently enhance IgM-triggered Ca(2+) signaling. We coupled these sialosides to Pseudomonas exotoxin A to generate a novel CD22 ligand-based immunotoxin. This sialoside-exotoxin-A construct can specifically kill CD22-positive B-cell lymphoma cells. It binds specifically to CD22-positive B-cell lymphoma cells and is dominant over endogenous cis-ligands on the B-cell surface. The sialoside-exotoxin-A construct is efficiently internalized by endocytosis into B-cell lymphoma cell lines. Thus we show the development of a new therapeutic compound for targeting CD22 on human B cells, both for B-cell lymphoma, as well as for B-cell-mediated autoimmune diseases.

TRAIL and DR5 promote thyroid follicular cell apoptosis in iodine excess-induced experimental autoimmune thyroiditis in NOD mice

Death receptor-mediated apoptosis has been implicated in target organ destruction in patients with chronic autoimmune thyroiditis. Several apoptosis signaling pathways, such as Fas ligand and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), have been shown to be active in thyroid cells and may be involved in destructive thyroiditis. Thyroid toxicity of iodide excess has been demonstrated in animals fed with an iodide-rich diet, but its pathogenic role remains unclear. The effects of excessive iodine on TRAIL and its death receptor expression in thyroid were investigated. Experimental autoimmune thyroiditis (EAT) was induced by excessive iodine and thyroglobulin (Tg) in non-obese diabetic mice. The expression of TRAIL and its death receptor DR5 was detected by immunofluorescence staining. Following administration of excessive iodine alone, Tg, and excessive iodine combined with Tg, TRAIL-positive cells appear not only in follicular cells but also in lymphocytes infiltrated in the thyroid, whereas DR5-positive cells appear only in follicular cells. Large numbers of CD3-positive cells and a few CD22-positive cells were detected in thyroid. A great amount of follicular cells were labeled specifically by terminal deoxynucleotide transferase-mediated deoxynucleotide triphosphate nick-end labeling assay. Taken together, our results suggest that excessive iodine could induce TRAIL and DR5 abnormal expression in thyroid. TRAIL band with DR5 to promote follicular cells apoptosis thus mediate thyroid destruction in EAT.

Amplified B lymphocyte CD40 signaling drives regulatory B10 cell expansion in mice

BACKGROUND

Aberrant CD40 ligand (CD154) expression occurs on both T cells and B cells in human lupus patients, which is suggested to enhance B cell CD40 signaling and play a role in disease pathogenesis. Transgenic mice expressing CD154 by their B cells (CD154(TG)) have an expanded spleen B cell pool and produce autoantibodies (autoAbs). CD22 deficient (CD22(-/-)) mice also produce autoAbs, and importantly, their B cells are hyper-proliferative following CD40 stimulation ex vivo. Combining these 2 genetic alterations in CD154(TG)CD22(-/-) mice was thereby predicted to intensify CD40 signaling and autoimmune disease due to autoreactive B cell expansion and/or activation.

METHODOLOGY/PRINCIPAL FINDINGS

CD154(TG)CD22(-/-) mice were assessed for their humoral immune responses and for changes in their endogenous lymphocyte subsets. Remarkably, CD154(TG)CD22(-/-) mice were not autoimmune, but instead generated minimal IgG responses against both self and foreign antigens. This paucity in IgG isotype switching occurred despite an expanded spleen B cell pool, higher serum IgM levels, and augmented ex vivo B cell proliferation. Impaired IgG responses in CD154(TG)CD22(-/-) mice were explained by a 16-fold expansion of functional, mature IL-10-competent regulatory spleen B cells (B10 cells: 26.7×10(6)±6 in CD154(TG)CD22(-/-) mice; 1.7×10(6)±0.4 in wild type mice, p<0.01), and an 11-fold expansion of B10 cells combined with their ex vivo-matured progenitors (B10+B10pro cells: 66×10(6)±3 in CD154(TG)CD22(-/-) mice; 6.1×10(6)±2 in wild type mice, p<0.01) that represented 39% of all spleen B cells.

CONCLUSIONS/SIGNIFICANCE

These results demonstrate for the first time that the IL-10-producing B10 B cell subset has the capacity to suppress IgG humoral immune responses against both foreign and self antigens. Thereby, therapeutic agents that drive regulatory B10 cell expansion in vivo may inhibit pathogenic IgG autoAb production in humans.

Bioengineering a unique deimmunized bispecific targeted toxin that simultaneously recognizes human CD22 and CD19 receptors in a mouse model of B-cell metastases

A drug of high potency and reduced immunogenicity is needed to develop a targeted biological drug that when injected systemically can penetrate to malignant B cells. Therefore, a novel deimmunized bispecific ligand-directed toxin targeted by dual high-affinity single-chain Fvs (scFv) spliced to PE38 with a KDEL COOH-terminus was genetically engineered. The aims were to reduce toxin immunogenicity using mutagenesis, measure the ability of mutated drug to elicit antitoxin antibody responses, and show that mutated drug was effective against systemic B-cell lymphoma in vivo. Both human anti-CD22 scFv and anti-CD19 scFv were cloned onto the same single-chain molecule with truncated pseudomonas exotoxin (PE38) to create the drug. Site-specific mutagenesis was used to mutate amino acids in seven key epitopic toxin regions that dictate B-cell generation of neutralizing antitoxin antibodies. Bioassays were used to determine whether mutation reduced potency, and ELISAs were done to determine whether antitoxin antibodies were reduced. Finally, a powerful genetically altered luciferase xenograft model was used that could be imaged in real time to determine the effect on systemic malignant human B-cell lymphoma, Raji-luc. Patient B-lineage acute lymphoblastic leukemia, B-cell chronic lymphocytic leukemia, and B lymphoma were high in CD22 and CD19 expression. 2219KDEL7mut was significantly effective against systemic Raji-luc in mice and prevented metastatic spread. Mutagenesis reduced neutralizing antitoxin antibodies by approximately 80% with no apparent loss in in vitro or in vivo activity. Because 2219KDEL7mut immunogenicity was significantly reduced and the drug was highly effective in vivo, we can now give multiple drug treatments with targeted toxins in future clinical trials.

Autoantibody-mediated regulation of B cell responses by functional anti-CD22 autoantibodies in patients with systemic sclerosis

Studies have demonstrated that B cells play important roles in systemic sclerosis (SSc), especially through the CD19/CD22 autoimmune loop. CD22 is a B cell-specific inhibitory receptor that dampens B cell antigen receptor (BCR) signalling via tyrosine phosphorylation-dependent mechanism. In this study, we examined the presence and functional property of circulating autoantibodies reacting with CD22 in systemic sclerosis. Serum samples from 10 tight skin (TSK/+) mice and 50 SSc patients were assessed for anti-CD22 autoantibodies by enzyme-linked immunosorbent assays using recombinant mouse or human CD22. The association between anti-CD22 antibodies and clinical features was also investigated in SSc patients. Furthermore, the influence of SSc serum including anti-CD22 autoantibodies for CD22 tyrosine phosphorylation was examined by Western blotting using phosphotyrosine-specific antibodies reacting with four major tyrosine motifs of CD22 cytoplasmic domain. Anti-CD22 autoantibodies were positive in 80% of TSK/+ mice and in 22% of SSc patients. Patients positive for anti-CD22 antibodies showed significantly higher modified Rodnan skin thickness score compared with patients negative for anti-CD22 antibodies. Furthermore, anti-CD22 antibodies from patients' sera were capable of reducing phosphorylation of all four CD22 tyrosine motifs, while sera negative for anti-CD22 antibodies did not affect CD22 phosphorylation. Thus, a subset of SSc patients possessed autoantibodies reacting with a major inhibitory B cell response regulator, CD22. Because these antibodies can interfere CD22-mediated suppression onto B cell activation in vitro, SSc B cells produce functional autoantibodies that can enhance their own activation. This unique regulation may contribute to the autoimmune aspect of SSc.

Change you can B(cell)eive in: recent progress confirms a critical role for B cells in type 1 diabetes

PURPOSE OF REVIEW

Here we review extant recent findings regarding the multiple roles of B cells in type 1 diabetes (T1D) and discuss how autoreactive B cells may become activated by a breach in B cell tolerance, and thereby initiate disease. Finally, we discuss the use of B cell-targeted therapies for treatment of autoimmunity.

RECENT FINDINGS

Anti-CD20-specific depletion of B cells prevents and reverses diabetes in human CD20/non-obese diabetic (NOD) mice. Correspondingly, in nontransgenic NOD mice, B cells are effectively depleted with high dose antimouse CD20 mAbs of varying isotypes, and this also prevents diabetes in more than 60% of the mice when administered early, and significantly delays disease in 15-week-old animals. A separate study revealed that targeting B cells with anti-CD22/cal monoclonal antibody therapy delays diabetes onset in prediabetic NOD mice and restores normoglycemia in new-onset hyperglycemic NOD mice. In humans, a clinical trial of rituximab in new onset type 1 diabetics has yielded promising preliminary findings.

SUMMARY

B cells are major players in T1D in humans, and clearly essential for disease development in the NOD mouse model of T1D. In this review, we discuss the silencing of autoreactive B cells and how failure of this process may contribute to autoimmunity. Further, we describe the most recent advances in studies of therapeutic effects of B cell depletion in T1D, and provide recent data indicating the diverse functions by which B cells may mediate disease.

Down-modulation of B cell signal transduction by ligation of mucins to CD22

Epithelial cancer cells secrete mucins carrying carbohydrate antigens such as a sialyl-Tn antigen into cancer tissues and/or the bloodstream, in which mucins may interact with CD22 (Siglec-2). Mucins isolated from colon cancer cells and bovine submaxillary mucins bound to CD22 cDNA transfectants and a human B cell line, Daudi cell, and the binding of soluble recombinant CD22 to the mucins was confirmed by means of a plate assay. The binding specificity was demonstrated by the fact that the mucins bound to the recombinant CD22 with an intact ectodomain but not to that with a mutated ectodomain. Daudi cells were stimulated with anti-IgM F(ab')(2) in the presence or absence of mucins. Ligation of mucins to CD22 decreased the phosphorylation of CD22 and SHP-1 recruitment, and the phosphorylation of ERK-1/2 prominently. The in vivo effect of mucins on splenic B cells in the tumor-bearing state was investigated using mucin-producing (TA3-Ha) and non-producing (TA3-St) mammary adenocarcinoma-bearing mice. When fluorescence-labeled epiglycanins were administered to normal mice, a portion of them was taken up by the spleen and became associated with splenic B cells. We found that splenic B cells were reduced in TA3-Ha-bearing mice but not in TA3-St-bearing ones. These results suggest that in the tumor-bearing state a portion of the mucins in the bloodstream was taken up by the spleen and ligated to CD22 expressed on splenic B cells, which may have led to down-regulation of signal transduction.

On-virus construction of polyvalent glycan ligands for cell-surface receptors

Glycans arrayed on the exterior of virus particles were used as substrates for glycosyltransferase reactions to build di- and trisaccharides from the virus surface. The resulting particles exhibited tight and specific associations with cognate receptors on beads and cells, in one example defeating in cis cell-surface interactions in a manner characteristic of polyvalent binding. Combined with the ability of viruses to provide structurally well-defined attachment points, the methodology provides a convenient and powerful way to prepare complex carbohydrate ligands for clustered receptors.

Human B-lymphocytes express alpha2-6-sialylated 6-sulfo-N-acetyllactosamine serving as a preferred ligand for CD22/Siglec-2

CD22/Siglec-2, an important inhibitory co-receptor on B-lymphocytes, is known to recognize alpha2-6-sialylated glycan as a specific ligand. Here we propose that the alpha2-6-sialylated and 6-GlcNAc-sulfated determinant serves as a preferred ligand for CD22 because the binding of a human B-cell line to CD22 was almost completely abrogated after incubating the cells with NaClO3, an inhibitor of cellular sulfate metabolism, and was also significantly inhibited by a newly generated monoclonal antibody specific to the alpha2-6-sialylated 6-sulfo-N-acetyllactosamine (LacNAc) determinant (KN343, murine IgM). The alpha2-6-sialylated 6-sulfo-LacNAc determinant defined by the antibody was significantly expressed on a majority of normal human peripheral B-lymphocytes as well as follicular B-lymphocytes in peripheral lymph nodes. The determinant was also expressed in endothelial cells of high endothelial venules of secondary lymphoid tissues, including lymph nodes, tonsils, and intestine-associated lymphoid tissues, more strongly than on B-lymphocytes, suggesting a role for CD22 in B-cell interaction with blood vessels and trafficking. These results indicate that the alpha2-6-sialylated 6-sulfo-LacNAc determinant serves as an endogenous ligand for human CD22 and suggest the possibility that 6-GlcNAc sulfation as well as alpha2-6-sialylation may regulate CD22/Siglec-2 functions in humans.

Synthetic glycan ligand excludes CD22 from antigen receptor-containing lipid rafts

CD22/Siglec-2 is a B cell membrane-bound lectin that recognizes glycan ligands containing alpha2,6-linked sialic acid, and negatively regulates signaling through the B cell antigen receptor (BCR). Previous studies demonstrated that synthetic sialosides that bind to CD22 augment BCR signaling by inhibiting CD22-mediated BCR regulation. Here we demonstrate that, after antigen stimulation, CD22 forms a cap together with BCR, and translocates to lipid rafts. Both co-capping of CD22 with BCR and translocation of CD22 to lipid rafts were markedly blocked by a synthetic alpha2,6-linked sialic acid, Neu5Gcalpha2-6GalbetaSE. These results strongly suggest that synthetic glycan ligand excludes CD22 from BCR-containing lipid rafts. Because CD22-mediated signal regulation requires phosphorylation of CD22 by Lyn that localizes in lipid rafts and is activated by BCR, synthetic glycan ligand regulates localization of CD22 crucial for signal regulation.

Distinct endocytic mechanisms of CD22 (Siglec-2) and Siglec-F reflect roles in cell signaling and innate immunity

Sialic acid-binding immunoglobulin-like lectins (siglecs) are predominately expressed on immune cells. They are best known as regulators of cell signaling mediated by cytoplasmic tyrosine motifs and are increasingly recognized as receptors for pathogens that bear sialic acid-containing glycans. Most siglec proteins undergo endocytosis, an activity tied to their roles in cell signaling and innate immunity. Here, we investigate the endocytic pathways of two siglec proteins, CD22 (Siglec-2), a regulator of B-cell signaling, and mouse eosinophil Siglec-F, a member of the rapidly evolving CD33-related siglec subfamily that are expressed on cells of the innate immune system. CD22 exhibits hallmarks of clathrin-mediated endocytosis and traffics to recycling compartments, consistent with previous reports demonstrating its localization to clathrin domains. Like CD22, Siglec-F mediates endocytosis of anti-Siglec-F and sialoside ligands, a function requiring intact tyrosine-based motifs. In contrast, however, we find that Siglec-F endocytosis is clathrin and dynamin independent, requires ADP ribosylation factor 6, and traffics to lysosomes. The results suggest that these two siglec proteins have evolved distinct endocytic mechanisms consistent with roles in cell signaling and innate immunity.

Siglecs and their roles in the immune system

Cell surfaces in the immune system are richly equipped with a complex mixture of glycans, which can be recognized by diverse glycan-binding proteins. The Siglecs are a family of sialic-acid-binding immunoglobulin-like lectins that are thought to promote cell-cell interactions and regulate the functions of cells in the innate and adaptive immune systems through glycan recognition. In this Review, we describe recent studies on signalling mechanisms and discuss the potential role of Siglecs in triggering endocytosis and in pathogen recognition. Finally, we discuss the postulated functions of the recently discovered CD33-related Siglecs and consider the factors that seem to be driving their rapid evolution.

IgG1 B cell receptor signaling is inhibited by CD22 and promotes the development of B cells whose survival is less dependent on Ig alpha/beta

We describe a mouse strain in which B cell development relies either on the expression of membrane-bound immunoglobulin (Ig) gamma1 or mu heavy chains. Progenitor cells expressing gamma1 chains from the beginning generate a peripheral B cell compartment of normal size with all subsets, but a partial block is seen at the pro- to pre-B cell transition. Accordingly, gamma1-driven B cell development is disfavored in competition with developing B cells expressing a wild-type (WT) IgH locus. However, the mutant B cells display a long half-life and accumulate in the mature B cell compartment, and even though partial truncation of the Ig alpha cytoplasmic tail compromises their development, it does not affect their maintenance, as it does in WT cells. IgG1-expressing B cells showed an enhanced Ca(2+) response upon B cell receptor cross-linking, which was not due to a lack of inhibition by CD22. The enhanced Ca(2+) response was also observed in mature B cells that had been switched from IgM to IgG1 expression in vivo. Collectively, these results suggest that the gamma1 chain can exert a unique signaling function that can partially replace that of the Ig alpha/beta heterodimer in B cell maintenance and may contribute to memory B cell physiology.

Enhancement and suppression of signaling by the conserved tail of IgG memory-type B cell antigen receptors

Immunological memory is characterized by heightened immunoglobulin (Ig) G antibody production caused in part by enhanced plasma cell formation conferred by conserved transmembrane and cytoplasmic segments in isotype-switched IgG B cell receptors. We tested the hypothesis that the IgG tail enhances intracellular B cell antigen receptor (BCR) signaling responses to antigen by analyzing B cells from Ig transgenic mice with IgM receptors or chimeric IgMG receptors containing the IgG tail segment. The IgG tail segment enhanced intracellular calcium responses but not tyrosine or extracellular signal–related kinase (ERK) phosphorylation. Biochemical analysis and crosses to CD22-deficient mice established that IgG tail enhancement of calcium and antibody responses, as well as marginal zone B cell formation, was not due to diminished CD22 phosphorylation or inhibitory function. Microarray profiling showed no evidence for enhanced signaling by the IgG tail for calcium/calcineurin, ERK, or nuclear factor κB response genes and little evidence for any enhanced gene induction. Instead, almost half of the antigen-induced gene response in IgM B cells was diminished 50–90% by the IgG tail segment. These findings suggest a novel “less-is-more” hypothesis to explain how switching to IgG enhances B cell memory responses, whereby decreased BCR signaling to genes that oppose marginal zone and plasma cell differentiation enhances the formation of these key cell types.

B cell signaling and autoimmune diseases: CD19/CD22 loop as a B cell signaling device to regulate the balance of autoimmunity

Autoimmune diseases, including connective tissue diseases and bullous diseases, may be life-threatening. Recent clinical and experimental approaches have demonstrated that B cells play critical roles in the manifestation of autoimmune disease not only by well-established autoantibody-mediated mechanisms but also by a variety of other functions. These B cell functions are under the regulation of B cell antigen receptor (BCR)-induced signals and by specialized cell surface coreceptors, or "response regulators", which inform B cells of their microenvironment. These response regulators include CD19 and CD22. CD19 and CD22 do not merely regulate BCR signals independently, but they have their own regulatory network. CD19 regulates CD22 phosphorylation by augmenting Lyn kinase activity, while CD22 inhibits CD19 phosphorylation via SHP-1. Importantly, this "CD19/CD22 loop" is significantly related to an autoimmune phenotype in mice. Thus, the CD19/CD22 loop may be a potential therapeutic target in autoimmune disease for modulating B cell signaling.

Epratuzumab (humanised anti-CD22 antibody) in primary Sjögren's syndrome: an open-label phase I/II study

This open-label, phase I/II study investigated the safety and efficacy of epratuzumab, a humanised anti-CD22 monoclonal antibody, in the treatment of patients with active primary Sjögren's syndrome (pSS). Sixteen Caucasian patients (14 females/2 males, 33–72 years) were to receive 4 infusions of 360 mg/m² epratuzumab once every 2 weeks, with 6 months of follow-up. A composite endpoint involving the Schirmer-I test, unstimulated whole salivary flow, fatigue, erythrocyte sedimentation rate (ESR), and immunoglobulin G (IgG) was devised to provide a clinically meaningful assessment of response, defined as a ≥20% improvement in at least two of the aforementioned parameters, with ≥20% reduction in ESR and/or IgG considered as a single combined criterion. Fourteen patients received all infusions without significant reactions, 1 patient received 3, and another was discontinued due to a mild acute reaction after receiving a partial infusion. Three patients showed moderately elevated levels of Human anti-human (epratuzumab) antibody not associated with clinical manifestations. B-cell levels had mean reductions of 54% and 39% at 6 and 18 weeks, respectively, but T-cell levels, immunoglobulins, and routine safety laboratory tests did not change significantly. Fifty-three percent achieved a clinical response (at ≥20% improvement level) at 6 weeks, with 53%, 47%, and 67% responding at 10, 18, and 32 weeks, respectively. Approximately 40%–50% responded at the ≥30% level, while 10%–45% responded at the ≥50% level for 10–32 weeks. Additionally, statistically significant improvements were observed in fatigue, and patient and physician global assessments. Further, we determined that pSS patients have a CD22 over-expression in their peripheral B cells, which was downregulated by epratuzumab for at least 12 weeks after the therapy. Thus, epratuzumab appears to be a promising therapy in active pSS, suggesting that further studies be conducted.

Performance of calibration standards for antigen quantitation with flow cytometry in chronic lymphocytic leukemia

BACKGROUND

The fluorescence intensities of CD3, CD4 on T cells and CD20, CD22 molecules on B cells were quantitatively measured on lymphocytes from chronic lymphocytic leukemia (CLL) patients and healthy donors.

METHODS

The performance of three different types of microbeads was compared, i.e. Quantum molecules of equivalent soluble fluorochrome (Q-MESF), Quantum simply cellular (QSC), and QuantiBRITE (QB). As all PE-conjugates had a F/P ratio of 1:1, the MESF units represented also the antibody binding capacity (ABC).

RESULTS

The ABCs of CD4 and CD20 antigens estimated with QSC (ABC(QSC)) were higher than those assigned with QB (ABC(QB)) with an average difference 49%. Higher numbers of antigenic sites were obtained with Q-MESF than with QSC for CD20 antigen. On the contrary, CD4 antigenic sites numbers estimated with QSC were higher than those estimated with Q-MESF. ABC values estimated with Quantum MESF PE (ABC(Q-MESF)) were approximately 15% higher than ABC(QSC), whereas ABC(Q-MESF) was approximately 49% higher than ABC(QB). Statistically significant correlations were found between the values obtained using various standards. The present study is the first to report down-regulation of CD3 antigen on T cells from patients with CLL.

CONCLUSIONS

This study emphasizes the relevance of quantitative measurement of fluorescence intensity by flow cytometry as a standardized approach to measure and interpret the expression of some CLL markers and reduce variability of results obtained at different sites in multi-center clinical studies.

Peripheral B cell receptor editing may promote the production of high-affinity autoantibodies in CD22-deficient mice

CD22-deficient mice are characterized by B cell hyperactivity and autoimmunity. We have constructed knock-in CD22-/- mice, expressing an anti-DNA heavy (H) chain (D42), alone or combined with Vkappa1-Jkappa1 or Vkappa8-Jkappa5 light (L) chains. The Ig-targeted mice produced a lupus-like serology that was age- and sex-dependent. High-affinity IgG autoantibodies were largely dependent on the selection of B cells with a particular H/L combination, in which a non-transgenic, endogenous L chain was assembled by secondary rearrangements through the mechanism of receptor editing. Moreover, we present evidence that these secondary rearrangements are very prominent in splenic peripheral B cells. Since CD22 is primarily expressed on the surface of peripheral B cells, we propose a model for the development of a lupus-like autoimmune disease by a combination of peripheral receptor editing and abnormal B cell activation.

CD19/22 balance relates to improvement of disease activity in systemic lupus erythematosus

B cells in patients with systemic lupus erythematosus (SLE) are hyperactivated and B-cell receptor signal transduction may be affected by various response regulators. CD19 and CD22 play a major role as regulators of B-cell response. Therefore, we examined CD19 and CD22 expressions on B cells of patients with SLE, and how they were related to disease activity. Thirty-one patients with active SLE were selected and enrolled in this study. Evaluation of CD19 and CD22 expressions on B cells was performed prior to and after treatments with flow cytometry analysis. Disease activity was determined according to the SLE disease activity index score. CD19 and CD22 expressions on B cells in SLE patients revealed no significant differences when compared with the controls. However, improvement of SLE was recognized among patients with an increased ratio of CD22-positive cells. Our results suggest that this balance is a useful marker for determining improvement of SLE disease activity, although the CD19/22 balance does not contribute to the pathogenesis of SLE.

High-affinity ligand probes of CD22 overcome the threshold set by cis ligands to allow for binding, endocytosis, and killing of B cells

CD22 (Siglec-2) is a key regulator of B cell signaling whose function is modulated by interaction with extracellular glycan ligands mediated through its N-terminal Ig domain. Its preferred ligand is the sequence Sia alpha2-6Gal that is abundantly expressed on N-linked glycans of B cell glycoproteins, and by binding to CD22 in cis causes CD22 to appear "masked" from binding to synthetic sialoside probes. Yet, despite the presence of cis ligands, CD22 redistributes to sites of cell contact by binding to trans ligands on neighboring cells. In this study, we demonstrate the dynamic equilibrium that exists between CD22 and its cis and trans ligands, using a high-affinity multivalent sialoside probe that competes with cis ligands and binds to CD22 on native human and murine B cells. Consistent with the constitutive endocytosis reported for CD22, the probes are internalized once bound, demonstrating that CD22 is an endocytic receptor that can carry ligand-decorated "cargo" to intracellular compartments. Conjugation of the sialoside probes to the toxin saporin resulted in toxin uptake and toxin-mediated killing of B lymphoma cell lines, suggesting an alternative approach for targeting CD22 for treatment of B cell lymphomas.

CD22 ligand binding regulates normal and malignant B lymphocyte survival in vivo

The CD22 extracellular domain regulates B lymphocyte function by interacting with alpha2,6-linked sialic acid-bearing ligands. To understand how CD22 ligand interactions affect B cell function in vivo, mouse anti-mouse CD22 mAbs were generated that inhibit CD22 ligand binding to varying degrees. Remarkably, mAbs which blocked CD22 ligand binding accelerated mature B cell turnover by 2- to 4-fold in blood, spleen, and lymph nodes. CD22 ligand-blocking mAbs also inhibited the survival of adoptively transferred normal (73-88%) and malignant (90%) B cells in vivo. Moreover, mAbs that bound CD22 ligand binding domains induced significant CD22 internalization, depleted marginal zone B cells (82-99%), and reduced mature recirculating B cell numbers by 75-85%. The CD22 mAb effects were independent of complement and FcRs, and the CD22 mAbs had minimal effects in CD22AA mice that express mutated CD22 that is not capable of ligand binding. These data demonstrate that inhibition of CD22 ligand binding can disrupt normal and malignant B cell survival in vivo and suggest a novel mechanism of action for therapeutics targeting CD22 ligand binding domains.

ST6Gal-I restrains CD22-dependent antigen receptor endocytosis and Shp-1 recruitment in normal and pathogenic immune signaling

The ST6Gal-I sialyltransferase produces Siglec ligands for the B-cell-specific CD22 lectin and sustains humoral immune responses. Using multiple experimental approaches to elucidate the mechanisms involved, we report that ST6Gal-I deficiency induces immunoglobulin M (IgM) antigen receptor endocytosis in the absence of immune stimulation. This coincides with increased antigen receptor colocalization with CD22 in both clathrin-deficient and clathrin-enriched membrane microdomains concurrent with diminished tyrosine phosphorylation of Igalpha/beta, Syk, and phospholipase C-gamma2 upon immune activation. Codeficiency with CD22 restores IgM antigen receptor half-life at the cell surface in addition to reversing alterations in membrane trafficking and immune signaling. Diminished immune responses due to ST6Gal-I deficiency further correlate with constitutive recruitment of Shp-1 to CD22 in unstimulated B cells independent of Lyn tyrosine kinase activity and prevent autoimmune disease pathogenesis in the Lyn-deficient model of systemic lupus erythematosus, resulting in a significant extension of life span. Protein glycosylation by ST6Gal-I restricts access of antigen receptors and Shp-1 to CD22 and operates by a CD22-dependent mechanism that decreases the basal rate of IgM antigen receptor endocytosis in altering the threshold of B-cell immune activation.

High efficacy of combined rituximab and gemcitabine on Epstein–Barr virus-associated human B-cell lymphoma obtained after Hodgkin's xenograft in immunodeficient mice

The objectives were to characterize an Epstein-Barr virus-associated human B-cell lymphoma obtained from Hodgkin's xenograft, and to evaluate the in-vivo combination of rituximab and/or gemcitabine. A lymph node biopsy sample from a patient with Hodgkin's disease was xenografted into Rag gamma(c)(-/-) mice. Immunohistochemical, cytogenetic and genetic analyses were performed on both the human biopsy and xenografted tumor from severe combined immunodeficient mice. Tumor-bearing mice were then treated with rituximab and/or gemcitabine. Histologic features of the patient's biopsy concluded on classical CD15/CD30-positive Hodgkin's disease without expression of Epstein-Barr virus proteins. In contrast, morphologic and immunophenotypic examination of the xenograft showed diffuse proliferation of large B cells with high Epstein-Barr virus protein expression. Comparative genomic hybridization showed a normal pattern in the first case and a gain of chromosomal 12 in the xenografted tumor. Finally, polymerase chain reaction detected an immunoglobulin heavy chain rearrangement in the xenografted tumor. Altogether, these results indicate that the xenograft grew from the patient's Epstein-Barr virus-infected B-lymphoid cells and could be assimilated to posttransplant lymphoproliferative disease. In-vivo treatments of xenografted tumors showed significant tumor growth inhibition induced either by rituximab or gemcitabine alone and an impressive efficacy of combined treatment. This result therefore indicates that combined rituximab and gemcitabine could be an alternative approach in patients with posttransplant lymphoproliferative disease.

Epratuzumab, a CD22-targeting recombinant humanized antibody with a different mode of action from rituximab

Epratuzumab is a humanized anti-CD22 monoclonal antibody currently in clinical trials for treatment of non-Hodgkin lymphoma (NHL) and certain autoimmune diseases. Here we report the results of investigations of epratuzumab's mode of action in comparison to and in combination with the anti-CD20 mAb, rituximab. In vitro cell growth inhibition, induction of apoptosis, and the ability of the mAbs to mediate complement-dependent cytotoxicity (CDC) and antibody-dependent cellular cytotoxicity (ADCC) were evaluated. We also investigated the potential activity of epratuzumab in the regulation of B-cell antigen receptor (BCR) activation. Epratuzumab and rituximab displayed very distinct modes of action; epratuzumab acts as an immunomodulatory agent, while rituximab is an acutely cytotoxic therapeutic antibody. Epratuzumab has distinct effects on cell growth from rituximab. For example, rituximab+anti-human IgG Fcgamma yielded marked inhibition of proliferation in human NHL cell lines, while epratuzumab had little or no effect in this assay. However, when cells were immobilized and stimulated with anti-IgM, epratuzumab, but not rituximab, caused a significant antiproliferative effect. Unlike rituximab, no CDC could be detected, and ADCC was modest but significant with epratuzumab. Importantly, combining rituximab and epratuzumab did not decrease rituximab's ability to induce apoptosis, CDC, and ADCC. In fact, the combination is more effective than rituximab alone in inhibiting proliferation of Daudi Burkitt lymphoma cells in the presence of second antibody, and at least equally effective to rituximab in the absence of crosslinking. These observations suggest that it may be possible to enhance clinical efficacy by combination therapy comprised of anti-CD20 and anti-CD22 mAbs.

B cell antigen receptor and CD40 differentially regulate CD22 tyrosine phosphorylation

Cell surface molecules on lymphocytes positively or negatively modulate the Ag receptor signaling, and thus regulate the fate of the cell. CD22 is a B cell-specific cell surface protein that contains multiple ITIMs in the cytoplasmic tail, and critically regulates B cell activation and survival. CD22 regulation on B cell signaling is complex because CD22 can have both positive and negative roles in various contexts. We generated phosphospecific polyclonal Abs reacting four major CD22 tyrosine motifs (Y762, Y807, Y822, and Y842) and analyzed the pattern and intensity of phosphorylation of these tyrosine residues. The tyrosine motifs, Y762, Y822, and Y842, are considered as ITIM, whereas the other, Y807, is suggested to be important for Grb2 recruitment. Approximately 10% of the four tyrosine residues were constitutively phosphorylated. Upon anti-IgM ligation, CD22 Y762 underwent most rapid phosphorylation, whereas all four tyrosine residues were eventually phosphorylated equally at approximately 35% of all CD22 molecules in the cell. By contrast, anti-CD40 stimulation specifically up-regulated anti-IgM-induced phosphorylation of tyrosines within two ITIM motifs, Y762 and Y842, which was consistent with in vivo finding of the negative role of CD22 in CD40 signaling. Thus, CD22 phosphorylation is not only quantitatively but also qualitatively regulated by different stimulations, which may determine the outcome of B cell signaling.

[Abnormal expression of cCD79a/cCD22 in acute myeloid leukemia with t (8;21)]

OBJECTIVE

To report abnormal expression of cCD79a/cCD22 in four cases of acute myeloid leukemia (AML) with t (8;21).

METHODS

The characteristics of morphology, immunophenotype, chromosome karyotype (MIC) and clinical manifestations of 4 AML patients with t (8;21) expressing cCD79a/cCD22 were analyzed.

RESULTS

The features of the 4 patients were: (1) no difference in gender; (2) young age; (3) exmedullary infiltration may be present; (4) normal number of white blood cells in peripheral blood; (5) morphology showed acute myeloid leukemia with high percentage of blast cells; (6) B-lymphoid and myeloid immunophenotype, and high expression of CD34; (7) frequent depletion of Y chromosome and complex changes of chromosomes; (8) positive for AML1/ETO fusion gene; (9) response well to chemotherapy regimen which simultaneously treated myeloid and lymphocytic leukemia.

CONCLUSION

Abnormal expression of cCD79a/cCD22 in AML with t (8;21) (q22;q22) suggested that this kind of leukemia might be related with abnormal expression gene of B cell.

A photochemical snapshot of CD22 binding

Identification of endogenous glycan-binding ligands for cell-surface receptors has been difficult. Incorporation of a photoactive sialic acid analog into B-cell surface glycoproteins suggests that CD22 molecules may cluster by binding carbohydrate antigens on neighboring CD22 molecules.