Brigitte Fritz

Reduced suppressive effect of CD4+CD25high regulatory T cells on the T cell immune response against myelin oligodendrocyte glycoprotein in patients with multiple sclerosis

Immunoregulatory T cells of CD4+CD25+ phenotype suppress T cell function and protect rodents from organ‐specific autoimmune disease. The human counterpart of this subset of T cells expresses high levels of CD25 and its role in human autoimmune disorders is currently under intense investigation. In multiple sclerosis (MS), a chronic inflammatory disease of the central nervous system (CNS), the activation of circulating self‐reactive T cells with specificity for myelin components is considered to be an important disease initiating event. Here, we investigated whether MS is associated with an altered ability of CD4+CD25high regulatory T cells (Treg) to confer suppression of myelin‐specific immune responses. Whereas Treg frequencies were equally distributed in blood and cerebrospinal fluid of MS patients and did not differ compared to healthy controls, the suppressive potency of patient‐derived CD4+CD25high T lymphocytes was impaired. Their inhibitory effect on antigen‐specific T cell proliferation induced by human recombinant myelin oligodendrocyte protein as well as on immune responses elicited by polyclonal and allogeneic stimuli was significantly reduced compared to healthy individuals. The effect was persistent and not due to responder cell resistance or altered survival of Treg, suggesting that a defective immunoregulation of peripheral T cells mediated by CD4+CD25high T lymphocytes promotes CNS autoimmunity in MS.

Prevalence of Newly Generated Naive Regulatory T Cells (Treg) Is Critical for Treg Suppressive Function and Determines Treg Dysfunction in Multiple Sclerosis

The suppressive function of regulatory T cells (Treg) is impaired in multiple sclerosis (MS) patients. The mechanism underlying the Treg functional defect is unknown. Treg mature in the thymus and the majority of cells circulating in the periphery rapidly adopt a memory phenotype. Because our own previous findings suggest that the thymic output of T cells is impaired in MS, we hypothesized that an altered Treg generation may contribute to the suppressive deficiency. We therefore determined the role of Treg that enter the circulation as recent thymic emigrants (RTE) and, unlike their CD45RO+ memory counterparts, express CD31 as typical surface marker. We show that the numbers of CD31+-coexpressing CD4+CD25+CD45RA+CD45RO−FOXP3+ Treg (RTE-Treg) within peripheral blood decline with age and are significantly reduced in MS patients. The reduced de novo generation of RTE-Treg is compensated by higher proportions of memory Treg, resulting in a stable cell count of the total Treg population. Depletion of CD31+ cells from Treg diminishes the suppressive capacity of donor but not patient Treg and neutralizes the difference in inhibitory potencies between the two groups. Overall, there was a clear correlation between Treg-mediated suppression and the prevalence of RTE-Treg, indicating that CD31-expressing naive Treg contribute to the functional properties of the entire Treg population. Furthermore, patient-derived Treg, but not healthy Treg, exhibit a contracted TCR Vβ repertoire. These observations suggest that a shift in the homeostatic composition of Treg subsets related to a reduced thymic-dependent de novo generation of RTE-Treg with a compensatory expansion of memory Treg may contribute to the Treg defect associated with MS.

Interferon Beta–Induced Restoration of Regulatory T-Cell Function in Multiple Sclerosis Is Prompted by an Increase in Newly Generated Naive Regulatory T Cells

BACKGROUND Naturally occurring regulatory T (T(reg)) cells are functionally impaired in patients with relapsing-remitting multiple sclerosis. We recently showed that prevalences of newly generated CD31-coexpressing naive T(reg) cells (recent thymic emigrant-T(reg) cells) are critical for suppressive function of circulating T(reg) cells, and a shift in the homeostatic composition of T(reg)-cell subsets related to a reduced de novo generation of recent thymic emigrant-T(reg) cells may contribute to the multiple sclerosis (MS)-related T(reg)-cell dysfunction. Interferon beta, an immunomodulatory agent with established efficacy in MS, lowers relapse rates and slows disease progression. Emerging evidence suggests that T(reg)-cell suppressive capacity may increase in patients with MS undergoing treatment with interferon beta, although the mechanisms mediating this effect are uncertain. OBJECTIVE To evaluate the effect of interferon beta treatment on the suppressive activity and the homeostasis of circulating T(reg) cells in patients with MS. PARTICIPANTS Twenty patients with relapsing-remitting MS and 18 healthy control subjects. INTERVENTIONS Administration of interferon beta. MAIN OUTCOME MEASURES Effect of interferon beta on T(reg)-cell homeostasis and suppressive capacity. RESULTS Suppressive capacities of T(reg) cells were consistently upregulated at 3 and 6 months after treatment with interferon beta. The restoration of T(reg)-cell function was paralleled by increased naive recent thymic emigrant-T(reg) cells and a coincidental reduction in memory T(reg) cells. CONCLUSION The increase in T(reg)-cell inhibitory capacity mediated by interferon beta treatment can be explained by its effect on the homeostatic balance within the T(reg) cell compartment.

B cells undergo unique compartmentalized redistribution in multiple sclerosis

Increasing evidence fosters the role of B cells (BC) in multiple sclerosis (MS). The compartmentalized distribution of BC in blood and cerebrospinal fluid (CSF) is incompletely understood. In this study, we analyzed BC-patterns and BC-immunoreactivity at these sites during active and during stable disease and the impact of disease modifying drugs (DMD) on peripheral BC-homeostasis. For this purpose we assessed BC-subsets in blood and CSF from patients with clinically isolated syndrome (CIS), relapsing remitting MS (RRMS), rheumatoid arthritis (RA), and healthy controls (HC) by flow cytometric detection of whole (W-BC), naïve, transitional (TN-BC), class-switched memory (CSM-BC), unswitched memory (USM-BC), double-negative memory (DNM-BC) BC-phenotypes, plasma blasts (PB), and plasma cells (PC). FACS-data were correlated with BC-specific chemotactic activities in CSF, intrathecal CXCL13-levels, and immunoreactivity of peripheral W-BC. Our study revealed that frequencies of systemic CSM-BC/USM-BC became contracted in active CIS/MS while proportions of naive BC, TN-BC and DNM-BC were reciprocally expanded. Moreover, the shifted BC-composition promoted reduced immunoreactivity of W-BC and resolved during remission. Cross-over changes in CSF included privileged accumulation of CSM-BC linked to intrathecal CXCL13-concentrations and expansion of PB/PC. Treatment with interferon-beta and natalizumab evoked distinct though differing redistribution of circulating BC-subsets. We conclude that symptomatic CIS and MS are accompanied by distinctive changes in peripheral and CSF BC-homeostasis. The privileged reciprocal distribution between naïve versus CSM-phenotypes in both compartments together with the marked chemotactic driving force towards BC prompted by CSF supernatants renders it likely that CSF BC are mainly recruited from peripheral blood during active CIS/MS, whereas constantly low percentages of circulating PB/PC and their failure to respond to migratory stimuli favors intrathecal generation of antibody secreting cells. Notably, BC-redistribution closely resembles alterations detectable in systemic autoimmunity associated with active RA and impacts BC-function Together with unique effects of DMDs on BC-homeostasis these findings underline the important role of BC in MS.

A specific CD4 epitope bound by tregalizumab mediates activation of regulatory T cells by a unique signaling pathway

CD4+CD25+ regulatory T cells (Tregs) represent a specialized subpopulation of T cells, which are essential for maintaining peripheral tolerance and preventing autoimmunity. The immunomodulatory effects of Tregs depend on their activation status. Here we show that, in contrast to conventional anti‐CD4 monoclonal antibodies (mAbs), the humanized CD4‐specific monoclonal antibody tregalizumab (BT‐061) is able to selectively activate the suppressive properties of Tregs in vitro. BT‐061 activates Tregs by binding to CD4 and activation of signaling downstream pathways. The specific functionality of BT‐061 may be explained by the recognition of a unique, conformational epitope on domain 2 of the CD4 molecule that is not recognized by other anti‐CD4 mAbs. We found that, due to this special epitope binding, BT‐061 induces a unique phosphorylation of T‐cell receptor complex‐associated signaling molecules. This is sufficient to activate the function of Tregs without activating effector T cells. Furthermore, BT‐061 does not induce the release of pro‐inflammatory cytokines. These results demonstrate that BT‐061 stimulation via the CD4 receptor is able to induce T‐cell receptor‐independent activation of Tregs. Selective activation of Tregs via CD4 is a promising approach for the treatment of autoimmune diseases where insufficient Treg activity has been described. Clinical investigation of this new approach is currently ongoing.