Natalizumab treatment perturbs memory‐ and marginal zone‐like B‐cell homing in secondary lymphoid organs in multiple sclerosis

Abstract

Natalizumab, an antibody against the a4 subunit of a4 integrins, has been approved for multiple sclerosis (MS) therapy based on its high efficacy and safety profile. However, natalizumab has been associated with the development of progressive multifocal leukoencephalopathy (PML), a disorder caused by JC virus (JCV) infection. In order to improve our understanding of the mechanism of action of natalizumab and to identify possible risk factors for PML development, we have characterized in detail the cell blood composition in MS patients treated with natalizumab for more than 30 months. Natalizumab induced the release of lymphoid-but not myeloid precursor cells, which resulted in a chronic increase of T-, NK-and particularly B cells. While the percentage of recent thymic emigrants (RTE), naïve, effector or memory T cells remained unchanged during treatment, a higher percentage of memory-and marginal zone (MZ)-like, but not of naïve B cells, was observed, which most likely is due to a decreased retention of these cells within the splenic MZ. The ability of natalizumab to influence B-cell migration and homeostasis through the splenic MZ, where JCV has been detected, adds to the list of natalizumab effects and may contribute to PML development by disseminating JCV.Key words: B cells . Multiple sclerosis . Natalizumab . Progressive multifocal leukoencephalopathy Supporting Information available online Introduction Natalizumab, a monoclonal antibody against the a4 subunit (CD49d) of a4 integrins (a4b1 and a4b7), has been approved for multiple sclerosis (MS) therapy based on its high efficacy and good safety profile. The a4b1 integrin is expressed by all leukocytes except neutrophils and serves as an adhesion molecule mediating attachment to endothelial cells. Natalizumab prevents transmigration of leukocytes across the blood-brain barrier by blocking a4b1 integrin/vascular cell adhesion molecule-1 (VCAM-1) interaction [1][2][3][4][5]. a4b1 integrin also serves as a retention signal for hematopoietic precursor cells in the BM, and consequently it has been demonstrated that natalizumab mobilizes hematopoietic precursor cells from the BM [6][7][8]. Natalizumab treatment also induces significant phenotypic changes in the immune cell composition of peripheral blood such as an increase Eur. J. Immunol. 2012. 42: 790-798 790 in T-, NK-and especially B cells and a decrease in monocytes [9][10][11][12]. These changes have been attributed to a higher release of hematopoietic precursor cells from the BM as well as a reduced migration of leukocytes into the central nervous system (CNS). However, since a4 integrin ligands are also expressed in secondary lymphoid tissues, such as spleen and gut-associated lymphoid tissue, natalizumab may influence the immune cell composition in the blood by affecting homeostasis, homing and migration of leukocytes through secondary lymphoid organs as well.Natalizumab treatment can lead to progressive multifocal leukoencephalopathy (PML), a demyelinating disorder of the CNS caused by JC virus (JCV...

Peripheral accumulation of newly produced T and B lymphocytes in natalizumab-treated multiple sclerosis patients

“…Instead, by using the TREC and KREC assay we found that newly produced T and B lymphocytes were significantly increased in peripheral blood of patients treated for 6 and 12 months with natalizumab, thus indicating that the drug may influence the lymphocyte release from production sites. The increased production of new T and B lymphocytes was confirmed by flow cytometry that also demonstrated an augmented number of RTE and naïve CD4 + cells in treated patients while, as also shown by Planas et al [6], the percentage of these cell subsets remained unmodified.…”

“…Nevertheless, the majority of B cells in peripheral blood of treated patients were unswitched and switched memory B cells, which are known to undergo an antigen-independent (homeostatic) proliferation [14]. However, the comparable average number of B-cell divisions we have found before and after therapy supports the hypothesis that the natalizumab-induced increase of memory B cells is due to an inhibited retention in the spleen [6] more than a peripheral proliferation.…”

“…Natalizumab treatment has been shown to reduce the migration of leukocytes into the CNS [1,6,11,16,17], to inhibit the retention of memory-and marginal zone-like B cells within the spleen [6] and to induce a sequestration of lymphocytes, in particular activated T cells [18], and of immature B cells [4] in the peripheral circulation of MS-treated patients. However, considering the scarcity of leukocytes in the CNS compared to the periphery and the slight contribution of memory-and marginal zone-like B cells on the composition of the lymphocyte pool, it is unlikely that the reduced migration of leukocytes into the CNS and the decreased retention of specific B-cell subsets in the spleen can quantitatively affect peripheral lymphocyte count or fully explain the increase of lymphocytes observed during natalizumab therapy.…”

“…Its mechanism of action is thought to be mediated through the block of the binding between the α4 subunit of the α4β1 (very late antigen-4; VLA-4) and α4β7 integrins on the lymphocytes of systemic circulation with their ligand, the vascular cell adhesion molecule 1 (VCAM-1), on vascular endothelium. Natalizumab also induces a continuous decrease of α4 expression [3] that results in a reduced transmigration of inflammatory cells across the bloodbrain barrier (BBB) into the central nervous system (CNS) and in an enhancement of the number of B cells, in particular immature B lymphocytes, CD8 + , CD4 + and NK cells in peripheral blood [4][5][6][7]. In treated patients, the increase of CD34 + precursor cells [8], together with the transient increase of nucleated immature red cells [9] and immature B lymphocytes [4] has suggested that natalizumab can preferentially mobilize immature cell subsets, probably because of its interference with the binding between VLA-4 and the VCAM-1 on the bone marrow (BM) stromal cells [8].…”

Immunomonitoring Lymphocyte Subpopulations in Multiple Sclerosis Patients

“…The effect of natalizumab on lymphocyte subpopulations is not fully defined, although it has been described that memory T-cells would be increased in peripheral blood and would induce changes in memory B-cells (90)(91)(92). Moreover, natalizumab treatment interferes with the mechanisms of bone marrow egress of hematopoietic stem cells, inducing an increase of CD34 + cells in peripheral blood, specifically lymphoid progenitors, transitional B-cells, and RTEs (17,91,(93)(94)(95)(96)(97).…”