Class-Switched B Cells Display Response to Therapeutic B-Cell Depletion in Rheumatoid Arthritis
Class-Switched B Cells Display Response to Therapeutic B-Cell Depletion in Rheumatoid Arthritis
Introduction Reconstitution of peripheral blood (PB) B cells after therapeutic depletion with the chimeric anti-CD20 antibody rituximab (RTX) mimics lymphatic ontogeny. In this situation, the repletion kinetics and migratory properties of distinct developmental B-cell stages and their correlation to disease activity might facilitate our understanding of innate and adaptive B-cell functions in rheumatoid arthritis (RA).
Methods Thirty-five 'RTX-naïve' RA patients with active arthritis were treated after failure of tumour necrosis factor blockade in an open-label study with two infusions of 1,000 mg RTX. Prednisone dose was tapered according to clinical improvement from a median of 10 mg at baseline to 5 mg at 9 and 12 months. Conventional disease-modifying antirheumatic drugs were kept stable. Subsets of CD19 B cells were assessed by flow cytometry according to their IgD and CD27 surface expression. Their absolute number and relative frequency in PB were followed every 3 months and were determined in parallel in synovial tissue (n = 3) or synovial fluid (n = 3) in the case of florid arthritis.
Results Six of 35 patients fulfilled the European League Against Rheumatism criteria for moderate clinical response, and 19 others for good clinical response. All PB B-cell fractions decreased significantly in number (P < 0.001) after the first infusion. Disease activity developed independently of the total B-cell number. B-cell repopulation was dominated in quantity by CD27IgD 'naïve' B cells. The low number of CD27IgD class-switched memory B cells (MemB) in the blood, together with sustained reduction of rheumatoid factor serum concentrations, correlated with good clinical response. Class-switched MemB were found accumulated in flaring joints.
Conclusions The present data support the hypothesis that control of adaptive immune processes involving germinal centre-derived, antigen, and T-cell-dependently matured B cells is essential for successful RTX treatment.
B-cell depletion with the chimeric anti-human CD20 IgG1 antibody rituximab (RTX) represents a novel target-specific treatment option for active rheumatoid arthritis (RA). RTX leads to almost total depletion of peripheral blood (PB) B cells for several months. The subsequent clinical course follows the autoantibody kinetics more closely than the B-cell numbers in the blood. Despite its specific mode of action on B cells, clinical response to RTX is not restricted to rheumatoid factor (RF)-positive or otherwise autoantibody-positive RA patients. Important innate immune functions of B cells such as antigen presentation and cytokine production, but also B-cell-dependent adaptive autoimmune processes that were not represented by standard autoantibodies, are alternative explanations for this phenomenon.
Up to five repetitive B-cell depletion courses appear safe in RA, but the risk of secondary immunodeficiency with more repetitive RTX courses is still not ruled out. This uncertainty may cause restriction in re-treatment scheduling and requires at least ongoing surveillance. There is a large variability in duration of response after RTX administration. Fixed short re-treatment intervals neglect the potential of saving immunosuppression and costs provided by this variability, whereas long intervals imply the risk of avoidable relapses and disease progression. Previous experimental studies indicated a rationale for repetitive RTX scheduling based on B-cell kinetics, but variable time lag between B-cell repopulation and clinical flare limited the immediate clinical application of B-cell repletion monitoring. Individual re-treatment intervals, therefore, are still recommended on the basis of the clinical course.
Which B-cell subset should be monitored? Long-lived plasma cells currently are believed to play a pivotal role in chronic autoimmunity. They derive from short-lived plasma cells and undergo apoptosis unless they find survival niches of limited number in the bone marrow. Their progenitors, the CD19 plasmablasts, have undergone class switch on their differentiation pathway to further develop to antibody-producing CD19 plasma cells. Plasmablasts draw a dynamic picture of ongoing autoimmune response in animal models. They share CD27 positivity and IgD negativity with germinal centre (GC)-derived, affinity matured, CD27IgD immunoglobulin (Ig) class-switched memory B cells (MemB). However, splenic long-lived plasma cells may also derive from extrafollicular maturation. As long-lived plasma cells are primarily resistant to RTX due to a lack of CD20 expression, they currently are hard to be directly extinguished by any available therapeutic modality. Plasma cells, in principle, are able to persist in tertiary immune organs, as it may be under certain circumstances the inflamed synovium. Their number indeed was reported to be unchanged in the synovium 4 weeks after RTX but strongly reduced later on. Plasma cell numbers are very low after RTX in the PB, with a transient peak early in the reconstitution. However, no correlation of plasma cell kinetics to time to relapse could be shown, which limits their usage for clinical monitoring.
Another candidate B-cell subset of relapsing autoimmunity might be CD27IgD non-switched MemB, which according to their surface marker expression are reported to correspond to splenic CD27IgD(IgM) marginal zone B cells in rodents. Cells of this developmental stage are able to undergo CD27-mediated co-stimulation but have not yet switched their Ig receptor isotype. They are not prone to the GC-related processes of antigen-dependent maturation but may undergo T-cell-independent maturation outside a lymphoid follicle. CD27IgD B cells are centrally involved in the processes of innate host defense, but on the other hand, they also represent several features that argue for a role in autoimmunity. Their number was associated with RA relapse in the regenerating B-cell compartment in previous studies. Like switched MemB, they may also develop to plasmablasts, which are able to secrete RF.
In this study, we questioned whether the advantage of individual RTX scheduling could be achieved by combining serological and cytological monitoring strategies. We confirm the previously reported importance of RF kinetics. In addition, we found that, by using a B-cell monitoring strategy in CD45CD19 B cells (Additional data file 1), sustained depletion of CD27IgD class-switched MemB from the blood was associated with good clinical response to RTX treatment. We found also that the same B-cell subset, but not the CD27IgD non-switched MemB or the CD27IgD 'naïve' B cells, were preferentially accumulated in actively inflamed joints.
Abstract and Introduction
Abstract
Introduction Reconstitution of peripheral blood (PB) B cells after therapeutic depletion with the chimeric anti-CD20 antibody rituximab (RTX) mimics lymphatic ontogeny. In this situation, the repletion kinetics and migratory properties of distinct developmental B-cell stages and their correlation to disease activity might facilitate our understanding of innate and adaptive B-cell functions in rheumatoid arthritis (RA).
Methods Thirty-five 'RTX-naïve' RA patients with active arthritis were treated after failure of tumour necrosis factor blockade in an open-label study with two infusions of 1,000 mg RTX. Prednisone dose was tapered according to clinical improvement from a median of 10 mg at baseline to 5 mg at 9 and 12 months. Conventional disease-modifying antirheumatic drugs were kept stable. Subsets of CD19 B cells were assessed by flow cytometry according to their IgD and CD27 surface expression. Their absolute number and relative frequency in PB were followed every 3 months and were determined in parallel in synovial tissue (n = 3) or synovial fluid (n = 3) in the case of florid arthritis.
Results Six of 35 patients fulfilled the European League Against Rheumatism criteria for moderate clinical response, and 19 others for good clinical response. All PB B-cell fractions decreased significantly in number (P < 0.001) after the first infusion. Disease activity developed independently of the total B-cell number. B-cell repopulation was dominated in quantity by CD27IgD 'naïve' B cells. The low number of CD27IgD class-switched memory B cells (MemB) in the blood, together with sustained reduction of rheumatoid factor serum concentrations, correlated with good clinical response. Class-switched MemB were found accumulated in flaring joints.
Conclusions The present data support the hypothesis that control of adaptive immune processes involving germinal centre-derived, antigen, and T-cell-dependently matured B cells is essential for successful RTX treatment.
Introduction
B-cell depletion with the chimeric anti-human CD20 IgG1 antibody rituximab (RTX) represents a novel target-specific treatment option for active rheumatoid arthritis (RA). RTX leads to almost total depletion of peripheral blood (PB) B cells for several months. The subsequent clinical course follows the autoantibody kinetics more closely than the B-cell numbers in the blood. Despite its specific mode of action on B cells, clinical response to RTX is not restricted to rheumatoid factor (RF)-positive or otherwise autoantibody-positive RA patients. Important innate immune functions of B cells such as antigen presentation and cytokine production, but also B-cell-dependent adaptive autoimmune processes that were not represented by standard autoantibodies, are alternative explanations for this phenomenon.
Up to five repetitive B-cell depletion courses appear safe in RA, but the risk of secondary immunodeficiency with more repetitive RTX courses is still not ruled out. This uncertainty may cause restriction in re-treatment scheduling and requires at least ongoing surveillance. There is a large variability in duration of response after RTX administration. Fixed short re-treatment intervals neglect the potential of saving immunosuppression and costs provided by this variability, whereas long intervals imply the risk of avoidable relapses and disease progression. Previous experimental studies indicated a rationale for repetitive RTX scheduling based on B-cell kinetics, but variable time lag between B-cell repopulation and clinical flare limited the immediate clinical application of B-cell repletion monitoring. Individual re-treatment intervals, therefore, are still recommended on the basis of the clinical course.
Which B-cell subset should be monitored? Long-lived plasma cells currently are believed to play a pivotal role in chronic autoimmunity. They derive from short-lived plasma cells and undergo apoptosis unless they find survival niches of limited number in the bone marrow. Their progenitors, the CD19 plasmablasts, have undergone class switch on their differentiation pathway to further develop to antibody-producing CD19 plasma cells. Plasmablasts draw a dynamic picture of ongoing autoimmune response in animal models. They share CD27 positivity and IgD negativity with germinal centre (GC)-derived, affinity matured, CD27IgD immunoglobulin (Ig) class-switched memory B cells (MemB). However, splenic long-lived plasma cells may also derive from extrafollicular maturation. As long-lived plasma cells are primarily resistant to RTX due to a lack of CD20 expression, they currently are hard to be directly extinguished by any available therapeutic modality. Plasma cells, in principle, are able to persist in tertiary immune organs, as it may be under certain circumstances the inflamed synovium. Their number indeed was reported to be unchanged in the synovium 4 weeks after RTX but strongly reduced later on. Plasma cell numbers are very low after RTX in the PB, with a transient peak early in the reconstitution. However, no correlation of plasma cell kinetics to time to relapse could be shown, which limits their usage for clinical monitoring.
Another candidate B-cell subset of relapsing autoimmunity might be CD27IgD non-switched MemB, which according to their surface marker expression are reported to correspond to splenic CD27IgD(IgM) marginal zone B cells in rodents. Cells of this developmental stage are able to undergo CD27-mediated co-stimulation but have not yet switched their Ig receptor isotype. They are not prone to the GC-related processes of antigen-dependent maturation but may undergo T-cell-independent maturation outside a lymphoid follicle. CD27IgD B cells are centrally involved in the processes of innate host defense, but on the other hand, they also represent several features that argue for a role in autoimmunity. Their number was associated with RA relapse in the regenerating B-cell compartment in previous studies. Like switched MemB, they may also develop to plasmablasts, which are able to secrete RF.
In this study, we questioned whether the advantage of individual RTX scheduling could be achieved by combining serological and cytological monitoring strategies. We confirm the previously reported importance of RF kinetics. In addition, we found that, by using a B-cell monitoring strategy in CD45CD19 B cells (Additional data file 1), sustained depletion of CD27IgD class-switched MemB from the blood was associated with good clinical response to RTX treatment. We found also that the same B-cell subset, but not the CD27IgD non-switched MemB or the CD27IgD 'naïve' B cells, were preferentially accumulated in actively inflamed joints.