Peripheral memory B cells in multiple sclerosis vs. double negative B cells in neuromyelitis optica spectrum disorder: disease driving B cell subsets during CNS inflammation

B cells are fundamental players in the pathophysiology of autoimmune diseases of the central nervous system, such as multiple sclerosis (MS) and neuromyelitis optica spectrum disorder (NMOSD). A deeper understanding of disease-specific B cell functions has led to the differentiation of both diseases and the development of different treatment strategies. While NMOSD is strongly associated with pathogenic anti-AQP4 IgG antibodies and proinflammatory cytokine pathways, no valid autoantibodies have been identified in MS yet, apart from certain antigen targets that require further evaluation. Although both diseases can be effectively treated with B cell depleting therapies, there are distinct differences in the peripheral B cell subsets that influence CNS inflammation. An increased peripheral blood double negative B cells (DN B cells) and plasmablast populations has been demonstrated in NMOSD, but not consistently in MS patients. Furthermore, DN B cells are also elevated in rheumatic diseases and other autoimmune entities such as myasthenia gravis and Guillain-Barré syndrome, providing indirect evidence for a possible involvement of DN B cells in other autoantibody-mediated diseases. In MS, the peripheral memory B cell pool is affected by many treatments, providing indirect evidence for the involvement of memory B cells in MS pathophysiology. Moreover, it must be considered that an important effector function of B cells in MS may be the presentation of antigens to peripheral immune cells, including T cells, since B cells have been shown to be able to recirculate in the periphery after encountering CNS antigens. In conclusion, there are clear differences in the composition of B cell populations in MS and NMOSD and treatment strategies differ, with the exception of broad B cell depletion. This review provides a detailed overview of the role of different B cell subsets in MS and NMOSD and their implications for treatment options. Specifically targeting DN B cells and plasmablasts in NMOSD as opposed to memory B cells in MS may result in more precise B cell therapies for both diseases.

Differential Effects of Fingolimod and Natalizumab on B Cell Repertoires in Multiple Sclerosis Patients

Natalizumab and fingolimod are effective multiple sclerosis (MS) therapies that disrupt lymphocyte migration but have differential effects on B cell maturation and trafficking. We investigated their effects on peripheral blood (PB) and cerebrospinal fluid (CSF) B cell repertoires using next-generation deep sequencing. Paired CSF and PB B cell subsets (naïve, CD27+ memory, and CD27-IgD- double-negative B cells and plasmablasts) were collected by applying flow cytometry at baseline and after 6 months of treatment and their respective heavy-chain variable region repertoires assessed by Illumina MiSeq. Treatment with fingolimod contracted, whereas natalizumab expanded circulating PB B cells. CSF B cell numbers remained stable following fingolimod treatment but decreased with natalizumab therapy. Clonal overlap between CSF and PB B cells was reduced with natalizumab treatment but remained stable with fingolimod therapy. Lineage analyses of pre- and posttreatment CSF B cell repertoires revealed large, clonally expanded B cell clusters in natalizumab-treated MS patients but no intrathecal clonal expansion following fingolimod therapy. Our findings suggest that natalizumab diminishes the exchange of peripheral and intrathecal B cells without impacting intrathecal clonal expansion. In contrast, fingolimod treatment fails to alter blood-brain barrier B cell exchange but diminishes intrathecal clonal expansion. Sphingosine-1 phosphate receptor inhibition may alter intrathecal B cell biology in MS.

Differential effects of disease modifying drugs on peripheral blood B cell subsets: A cross sectional study in multiple sclerosis patients treated with interferon-β, glatiramer acetate, dimethyl fumarate, fingolimod or natalizumab

Background

Several disease modifying drugs (DMDs) have been approved for the treatment of multiple sclerosis (MS), however, little is known about their differential impact on peripheral blood (PB) B cell subsets.

Methods

We performed a cross sectional study on PB B cells in MS patients treated with interferon-β (n = 25), glatiramer acetate (n = 19), dimethyl fumarate (n = 15), fingolimod (n = 16) or natalizumab (n = 22), untreated MS patients (n = 20), and in patients with non-inflammatory neurological diseases (n = 12). Besides analyzing routine laboratory data, flow cytometry was performed to analyze naïve B cells (CD19+CD20+CD27-IgD+), non-class switched (CD19+CD20+CD27+IgD+) and class-switched memory B cells (CD19+CD20+CD27+IgD-), double negative B cells (CD19+CD20lowCD27-IgD-) and plasmablasts (CD19+CD20lowCD27+CD38++).

Results

Treatment associated changes were found for the overall B cell pool as well as for all B cell subsets. Natalizumab increased absolute numbers and percentage of all B cells mainly by expanding the memory B cell pool. Fingolimod decreased absolute numbers of all B cell subsets and the percentage of total B cells. Fingolimod, dimethyl fumarate and interferon-β treatments were associated with an increase in the fraction of naïve B cells while class switched and non-class switched memory B cells showed decreased percentages.

Conclusion

Our results highlight differential effects of DMDs on the PB B cell compartment. Across the examined treatments, a decreased percentage of memory B cells was found in dimethyl fumarate, interferon-β and fingolimod treated patients which might contribute to the drugs’ mode of action in MS. Further studies are necessary to decipher the exact role of B cell subsets during MS pathogenesis.

Differential effects of fingolimod (FTY720) on immune cells in the CSF and blood of patients with MS

BACKGROUND

The oral immunomodulator fingolimod (FTY720) has recently been shown to be highly effective in relapsing-remitting multiple sclerosis (MS). Fingolimod is a functional antagonist of the sphingosine-1-phosphate receptor 1 and thereby inhibits sphingosine-1-phosphate-dependent lymphocyte egress from secondary lymphoid tissues, resulting in a pronounced lymphopenia in the peripheral blood. The effects of fingolimod treatment on the CSF of patients with MS have not been studied so far.

METHODS

We analyzed the leukocyte count, albumin quotient, immunoglobulin G (IgG) index, and oligoclonal bands in the CSF of fingolimod-treated patients with MS. Moreover, we performed immunophenotyping of CSF and peripheral blood leukocytes by flow cytometry. The results were compared to those from treatment-naive or natalizumab-treated patients with MS and patients with other inflammatory and noninflammatory neurologic diseases.

RESULTS

Fingolimod therapy significantly decreased CSF leukocyte counts, but had little impact on the extent of intrathecal IgG synthesis and presence of oligoclonal bands in the CSF. Fingolimod decreased the proportion of CSF CD4+ T cells but to a lesser extent than in the peripheral blood. While fingolimod strongly reduced B cells in the periphery, it had little impact on B cells in the CSF. The percentage of CSF CD8+ T cells, NK cells, and monocytes increased compared to treatment-naive patients. The CD4+/CD8+ T-cell ratio in CSF reversed in most of the patients.

CONCLUSION

Fingolimod treatment has a profound impact on CSF, which to some extent differs from the peripheral effects of the drug.