Khalid Muhammad

In Vivo Effects of the Anti―Interleukin-6 Receptor Inhibitor Tocilizumab on the B Cell Compartment

OBJECTIVE Interleukin-6 (IL-6) receptor inhibition by tocilizumab was recently licensed for the treatment of rheumatoid arthritis (RA). IL-6 induces in vitro differentiation of B cells into antibody-forming cells; however, the in vivo effects of IL-6 inhibition on the B cell compartment are currently not known. The purpose of this study was to examine this feature. METHODS Sixteen patients with active RA were treated in an open-label study with tocilizumab (8 mg/kg every 4 weeks). Immunophenotyping was performed at baseline, week 12, and week 24. RESULTS Memory B cell subsets declined significantly during tocilizumab therapy. Preswitch memory B cells decreased from a median of 19.6% to 12.3% at week 24 and postswitch memory B cells declined from a median of 18.6% to 15.0% at week 24 (P = 0.04). In parallel, CD19+IgA+ and CD19+IgG+ B cells decreased significantly. The proportion of IgA-expressing B cells fell from a median of 9.2% at baseline to 4.3% at week 12 and to 3.6% at week 24 (P = 0.01). IgG+ B cells declined from a median of 6.7% at baseline to 4.9% at week 12 (P = 0.007) and 2.8% at week 24 (P = 0.01). In parallel, serum levels of IgA and IgG were significantly diminished at week 24 (P < 0.05). There was a good correlation between relative and absolute numbers of IgA+ B cells with serum IgA at week 24. CONCLUSION Tocilizumab induced a significant reduction in the frequency of peripheral preswitch and postswitch memory B cells. In addition, the number of IgG+ and IgA+ B cells declined and correlated well with reduced serum immunoglobulin levels. The data indicate that IL-6 blockade affects the B cell hyperreactivity in RA patients.

Impact of IL-6 receptor inhibition on human memory B cells in vivo: impaired somatic hypermutation in preswitch memory B cells and modulation of mutational targeting in memory B cells

Objective Interleukin 6 (IL-6) receptor (IL-6R) inhibition by tocilizumab is a novel anti-inflammatory therapy for rheumatoid arthritis (RA) patients. As IL-6 is a late differentiation factor of B cells the authors asked if IL-6R inhibition impacts on the mutational differentiation of human memory B-cell antigen receptors in vivo. Methods 1733 immunoglobulin receptors (IgR) of single cell sorted preswitch and postswitch memory B cells were prospectively analysed from 11 RA patients under IL-6R inhibition (7 patients) or tumour necrosis factor (TNF) inhibition (4 patients). Results The results show a reduced mutational frequency in IgR of preswitch memory B cells (p=0.0001) during week 12, week 24 and 1 year of tocilizumab therapy. Mutational hotspot RGYW/WRCY motifs indicated significantly decreased targeting (p<0.05) in preswitch and postswitch memory B cells. Anti-TNFα therapy had no effect on mutational frequency and mutational hotspot targeting motifs in memory B-cell subsets. Conclusions These data suggest that preswitch and postswitch memory B cells are susceptible to IL-6R inhibition in vivo. Acquisition of mutations was substantially altered in preswitch memory B cells, while targeting of mutational hotspots affected preswitch and postswitch memory B cells. The results indicate that preswitch and postswitch memory B cells have a differential dependence on the IL-6/IL-6R system for differentiation, which can be influenced by tocilizumab in vivo.

NFATc1 Induction in Peripheral T and B Lymphocytes

NFAT transcription factors control the proliferation and survival of peripheral lymphocytes. We have reported previously that the short isoform NFATc1/αA whose generation is induced by immune receptor stimulation supports the proliferation and inhibits the activation-induced cell death of peripheral T and B cells. We will show in this study that in novel bacterial artificial chromosome transgenic mice that express EGFP under the control of entire Nfatc1 locus the Nfatc1/Egfp transgene is expressed as early as in double-negative thymocytes and in nonstimulated peripheral T and B cells. Upon immune receptor stimulation, Nfatc1/Egfp expression is elevated in B, Th1, and Th2 cells, but only weakly in T regulatory, Th9, and Th17 cells in vitro whose generation is affected by TGFβ. In naive lymphocytes, persistent immune receptor signals led to a 3–5 increase in NFATc1/αA RNA levels during primary and secondary stimulation, but a much stronger induction was observed at the protein level. Whereas anti-CD3+CD28 stimulation of primary T cells induces both NFATc1/αA and their proliferation and survival, anti-IgM stimulation of B cells induces NFATc1/αA and proliferation, but activation-induced cell death after 3-d incubation in vitro. The anti-IgM–mediated activation-induced cell death induction of B cells in vitro is suppressed by anti-CD40–, LPS-, and CpG-mediated signals. In addition to inducing NF-κB factors, together with anti-IgM, these signals also support the generation of NFATc1/αA. According to these data and the architecture of its promoter region, the Nfatc1 gene resembles a primary response gene whose induction is affected at the posttranscriptional level.

Delayed acquisition of somatic hypermutations in repopulated IGD+CD27+ memory B cell receptors after rituximab treatment.

OBJECTIVE Transient B cell depletion by rituximab has been used with clinical efficacy in the treatment of patients with rheumatoid arthritis (RA). Previous studies of B cell repopulation have shown long-term numerical reduction in memory B cells. Non-class-switched IgD+CD27+ memory B cells, in particular, repopulate slowly. This study was undertaken to determine whether mutational acquisition in individual B cell receptors in repopulating class-switched and non-class-switched memory B cells is affected by rituximab. METHODS Cells obtained from 16 RA patients, 4 healthy donors, and 3 patients who underwent allogeneic stem cell transplantation (ASCT) were analyzed using single B cell sorting followed by nested polymerase chain reaction and Ig V(H)3 sequencing. RESULTS There was a delayed acquisition of mutations in Ig receptors of IgD+ memory B cells over a period of 6 years after a single course of rituximab. One year after rituximab treatment, 84% of single repopulating IgD+CD27+ B cells were unmutated, and no highly mutated Ig receptors were found (compared with 52% before therapy). Over time, increasing numbers of mutations were detected. Even 6 years after rituximab treatment, however, mutations in IgD+ memory B cells were still significantly reduced. In contrast, class-switched memory B cells repopulated with quantitatively normal mutations. In comparison, in patients undergoing ASCT, IgD+ memory cells repopulated earlier with higher mutations in Ig receptors. CONCLUSION Our data suggest that IgD+ memory B cells are particularly susceptible to the effects of rituximab, with delayed acquisition of mutations in their Ig receptors still evident 6 years after a single course of rituximab. Our findings indicate that these cells have different requirements for mutational acquisition compared with class-switched memory B cells.

RF positivity has substantial influence on the peripheral memory B-cell compartment and its modulation by TNF inhibition

Objectives: The role of B cells in rheumatoid arthritis (RA) has been well established with the advent of B-cell targeted therapies. Alterations of peripheral B-cell subsets in RA and heterogeneous modulations of the B-cell compartment under tumour necrosis factor (TNF) inhibition have been described. In this study we examined the influence of rheumatoid factor (RF) positivity on the peripheral B-cell compartment and its modulation under TNF blockade. Methods: Consecutive patients with RA and inadequate response to methotrexate (MTX) were stratified according to RF status and a subset of them was included in a prospective study of weekly etanercept treatment. Results: At baseline, RF-negative patients had a significant higher percentage of overall CD27+ B cells compared to healthy controls (HC) and RF-positive patients. In detail, RF-negative patients had 46.6% (range 15.7–86.8%) CD27+ B cells compared to 31.3% (12.9–56.9%, p = 0.026) in HC and 29.8% (19–73.3%, p = 0.04) in RF-positive patients. Within the CD27+ compartment, CD27+/immunoglobulin (Ig)D+ memory B cells were significantly increased to 26.4% (range 5.9–54.7%) in RF-negative patients compared to 14.9% (4.1–27.3%, p = 0.006) in HC and 10.5% (3.4–41.1%, p = 0.003) in RF-positive patients. During anti-TNF therapy, memory B cells increased significantly in relative and absolute numbers only in RF-negative patients. Conclusions: In RF-negative patients, we observed an enhanced frequency of peripheral memory B cells and an accumulation of pre-switch memory B cells. During anti-TNF therapy, memory B cells increased significantly only in RF-negative patients, suggesting that the peripheral memory B-cell compartment is more amenable to TNF inhibition in these patients.

Architecture and expression of the Nfatc1 gene in lymphocytes

In lymphocytes, the three NFAT factors NFATc1 (also designated as NFAT2), NFATc2 (NFAT1), and NFATc3 (NFAT4 or NFATx) are expressed and are the targets of immune receptor signals, which lead to a rapid rise of intracellular Ca++, the activation of phosphatase calcineurin, and to the activation of cytosolic NFATc proteins. In addition to rapid activation of NFAT factors, immune receptor signals lead to accumulation of the short NFATc1/αA isoform in lymphocytes which controls their proliferation and survival. In this mini-review, we summarize our current knowledge on the structure and transcription of the Nfatc1 gene in lymphocytes, which is controlled by two promoters, two poly A addition sites and a remote downstream enhancer. The Nfatc1 gene resembles numerous primary response genes (PRGs) induced by LPS in macrophages. Similar to the PRG promoters, the Nfatc1 promoter region is organized in CpG islands, forms DNase I hypersensitive sites, and is marked by histone tail modifications before induction. By studying gene induction in lymphocytes in detail, it will be important to elucidate whether the properties of the Nfatc1 induction are not only typical for the Nfatc1 gene but also for other transcription factor genes expressed in lymphocytes.

NFATc1 controls the cytotoxicity of CD8+ T cells

Cytotoxic T lymphocytes are effector CD8+ T cells that eradicate infected and malignant cells. Here we show that the transcription factor NFATc1 controls the cytotoxicity of mouse cytotoxic T lymphocytes. Activation of Nfatc1−/− cytotoxic T lymphocytes showed a defective cytoskeleton organization and recruitment of cytosolic organelles to immunological synapses. These cells have reduced cytotoxicity against tumor cells, and mice with NFATc1-deficient T cells are defective in controlling Listeria infection. Transcriptome analysis shows diminished RNA levels of numerous genes in Nfatc1−/− CD8+ T cells, including Tbx21, Gzmb and genes encoding cytokines and chemokines, and genes controlling glycolysis. Nfatc1−/−, but not Nfatc2−/− CD8+ T cells have an impaired metabolic switch to glycolysis, which can be restored by IL-2. Genome-wide ChIP-seq shows that NFATc1 binds many genes that control cytotoxic T lymphocyte activity. Together these data indicate that NFATc1 is an important regulator of cytotoxic T lymphocyte effector functions.NFAT nuclear translocation has been shown to be required for CD8+ T cell cytokine production in response to viral infection. Here the authors show NFATc1 controls the cytotoxicity and metabolic switching of activated CD8+ T cells required for optimal response to bacteria and tumor cells.

NF-κB factors control the induction of NFATc1 in B lymphocytes

In peripheral lymphocytes, the transcription factors (TFs) NF‐κB, NFAT, and AP‐1 are the prime targets of signals that emerge from immune receptors. Upon activation, these TFs induce gene networks that orchestrate the growth, expansion, and effector function of peripheral lymphocytes. NFAT and NF‐κB factors share several properties, such as a similar mode of induction and architecture in their DNA‐binding domain, and there is a subgroup of κB‐like DNA promoter motifs that are bound by both types of TFs. However, unlike NFAT and AP‐1 factors that interact and collaborate in binding to DNA, NFAT, and NF‐κB seem neither to interact nor to collaborate. We show here that NF‐κB1/p50 and c‐Rel, the most prominent NF‐κB proteins in BCR‐induced splenic B cells, control the induction of NFATc1/αA, a prominent short NFATc1 isoform. In part, this is mediated through two composite κB/NFAT‐binding sites in the inducible Nfatc1 P1 promoter that directs the induction of NFATc1/αA by BCR signals. In concert with coreceptor signals that induce NF‐κB factors, BCR signaling induces a persistent generation of NFATc1/αA. These data suggest a tight connection between NFATc1 and NF‐κB induction in B lymphocytes contributing to the effector function of peripheral B cells.

NFATc1 supports imiquimod-induced skin inflammation by suppressing IL-10 synthesis in B cells

Epicutaneous application of Aldara cream containing the TLR7 agonist imiquimod (IMQ) to mice induces skin inflammation that exhibits many aspects of psoriasis, an inflammatory human skin disease. Here we show that mice depleted of B cells or bearing interleukin (IL)-10-deficient B cells show a fulminant inflammation upon IMQ exposure, whereas ablation of NFATc1 in B cells results in a suppression of Aldara-induced inflammation. In vitro, IMQ induces the proliferation and IL-10 expression by B cells that is blocked by BCR signals inducing NFATc1. By binding to HDAC1, a transcriptional repressor, and to an intronic site of the Il10 gene, NFATc1 suppresses IL-10 expression that dampens the production of tumour necrosis factor-α and IL-17 by T cells. These data indicate a close link between NFATc1 and IL-10 expression in B cells and suggest NFATc1 and, in particular, its inducible short isoform, NFATc1/αA, as a potential target to treat human psoriasis.

Effect of ATG-F on B-cell reconstitution after hematopoietic stem cell transplantation

Antithymocyte globulin Fresenius (ATG‐F) is used before hematopoietic stem cell transplantation to prevent graft rejection and graft‐versus‐host disease in patients with HLA‐matched unrelated donors or mismatched volunteers. However, little is known about the effect of ATG‐F on the reconstitution of B‐cell subsets. Sixty‐seven patients were longitudinally studied at day 15, day 30, and then monthly after hematopoietic stem cell transplantation. Conditioning regimes included ATG‐F, which was infused at days 3, 2 and 1 at a dosage of 10 mg/kg/d. Twenty‐seven patients received conditioning regimes without ATG. ATG‐treated patients showed a significant delay of CD19+ B cells in the early recovery period. The absolute numbers of circulating CD19+ B cells were significantly lower (P < 0.05) up to 5 months post‐transplantation compared to non‐ATG patients. The recovery of the memory compartment was delayed in both groups and did not reach normal values 1‐year post‐transplantation. ATG‐treated patient showed significantly lower absolute numbers of circulating CD27+ memory B cells in the first‐month after transplantation compared to non‐ATG patients. In conclusion, treatment with ATG in the conditioning regime of patients undergoing allogeneic hematopoietic stem cell transplantation leads to a significant delay of CD19+ B cells. Thus, ATG seems also to negatively influence B‐cell immune reconstitution.