Characterization of B cells in Multiple Sclerosis patients treated with Ocrelizumab: Role of postbiotics in the resetting of the B cell compartment

Multiple sclerosis (MS) is a chronic inflammatory disease that results in the development of autoimmunity against myelin antigens, which in turn leads to neuroinflammation and neurodegeneration. For many years, it was assumed that T cells were the primary agents responsible for the autoimmune manifestation in MS, given their role in actively targeting myelin antigens. However, recent studies have identified B cells as playing a pivotal role in the pathogenesis and course of MS. They produce autoantibodies and function as antigen-presenting cells, in addition to secreting cytokines and neurotoxic factors. Moreover, they can acquire a regulatory functional state, whereby they produce immuno-modulatory cytokines, such as IL-10 which regulates the immune response by limiting the production of autoantibodies and pro-inflammatory B and T cells activation. Considering the aforementioned factors, several B lymphocyte-directed therapeutic strategies, including the selective depletion of CD20+ B cells by anti-CD20 drugs, have been developed in recent times. Ocrelizumab (OCR), is an anti-CD20 depleting drug and it has been introduced as a therapeutic option for patients with MS since 2018, but follow-up studies are still limited. All patients are treated with the same regimen, with no differentiation in timing or dosage based on their response or disease progression. Nevertheless, prior to rescheduling the dosage of OCR, it is essential to gain a more profound comprehension of the behavior of B cells prior and following depletion. The principal objective of this study was to analyze B cells in MS patients treated with OCR, with a particular focus on B regulatory cells which is beneficial in autoimmune contexts. Firstly, this approach allowed a comprehensive investigation of B cells in MS patients in comparison to healthy individuals, thereby facilitating a deeper understanding of their potential involvement in the pathogenesis and progression of MS. Patients with MS exhibit elevated levels of B lymphocyte activation, proliferation and differentiation. Moreover, MS patients exhibit deficiencies in regulatory IL-10-producing B cells, which appear to originate from a distinct source in comparison with healthy controls. Therefore, an additional objective of this study was to investigate how educate and reset the B cell compartment towards regulatory state. The impact of the intestinal environment and the commensal gut microbiota on the pathogenesis of MS has been substantiated and the potential impact of postbiotics on immune cells represents a well-defined research area. Several studies identified short-chain fatty acids (SCFAs) as key immunoregulators with a particular focus on the skewing of immune cells towards a regulatory state. In this study SCFAs were quantified in fecal samples and were found to be deficient in MS patients compared to healthy controls. They were also tested in vitro in human B cells and the results suggest that SCFAs may potentially exert regulatory effects on B cells. Subsequently, the characterization of B cells before and six months after the initiation of OCR enabled to verify that MS patients respond differently to the therapy according to the phenotype of B cells after treatment. Patients were clustered in two groups: some patients show an incomplete B cell depletion and a concomitant higher abundance of activated, differentiated and proliferating B cells, and thus a slower response associated with a worsening EDSS. Conversely, other patients showed a more rapid response, with the appearance of "new" transitional B cells. This could provide a foundation for the evaluation of a personalized therapy with monitoring and adjustment of OCR injections. Furthermore, given the potential impact of SCFAs on regulatory B cells, a tailored therapy that incorporates SCFAs integration may represent a promising avenue for enhancing the repopulation of B cells towards a regulatory state following OCR depletion.