Diana Castaño

Lipid nanoparticles (LNPs) represent the leading delivery platform for mRNA vaccines with advantageous biocompatibility, scalability, adjuvant activity and often an acceptable safety profile. Here we investigate the physicochemical characteristics and adjuvanticity of four-component LNPs. Previous vaccine studies have demonstrated that altering the ionizable lipid influences the adjuvanticity of an LNP; however, the impact of the polyethylene glycol lipid and phospholipid has received less attention. Our mRNA–LNP vaccine formulations utilized different phospholipids and varying ratios of polyethylene glycol lipid, whereas the ionizable lipid and cholesterol remained approximately constant. We demonstrate that such modifications impact the magnitude and quality of the vaccine-elicited immune responses. We also dissect the underlying mechanisms and show that the biodistribution and cellular uptake of LNPs correlate with the magnitude and quality of the immune responses. These findings support the rational design of novel LNPs to tailor immune responses (cellular or humoral focused) based on the vaccine application.

T follicular regulatory (T _fr ) cells can counteract the B cell helper activity of T follicular helper (T _fh ) cells and hinder the production of antibodies against self-antigens or allergens. A mechanistic understanding of the cytokines initiating the differentiation of human regulatory T (T _reg ) cells into T _fr cells is still missing. Herein, we report that low doses of the pro-T _fh cytokine interleukin-12 (IL-12) drive the induction of a T _fr cell program on activated human T _reg cells while also preserving their regulatory function. Mechanistically, we found that IL-12 led to STAT4 (signal transducer and activator of transcription 4) phosphorylation and binding to IL-12–driven follicular signature genes. Patients with inborn errors of immunity in the IL12RB1 gene presented with a strong decrease in circulating T _fr cells and produced higher levels of anti-actin autoantibodies in vivo. Overall, this study unveils IL-12 as an inducer of T _fr cell differentiation in vivo and provides an approach for the in vitro generation of human T _fr -like cells.

Background: B cells are pivotal in systemic lupus erythematosus and autoimmune disease pathogenesis. Materials & methods: To address this, Nile Red-labeled polylactic acid nanoparticles (NR-PLA NPs... Plain language summary In this study, a new approach to treating autoimmune diseases, particularly systemic lupus erythematosus, was investigated by focusing on a type of immune cell called B cells...

Background: Extracellular vesicles are involved in the intercellular communication of the immune system. In rheumatoid arthritis (RA), these structures are considered a source of autoantigens that drive proinflammatory responses of innate immune cells. A high concentration of circulating medium/large size extracellular vesicles (m/lEVs) and m/lEVs forming immune complexes (m/lEV-ICs) have been associated with disease activity and systemic inflammation in patients with RA. B cells are central components of RA immunopathology because of their involvement in the production of autoantibodies, antigen presentation, and cytokine production. However, the effect of m/lEVs on B cell function in the context of RA and other autoimmune diseases remains unknown. Methods: We evaluated the effect of m/lEVs obtained from healthy donors (HD) and patients with RA on B cell responses in vitro. In addition, we evaluated the effect of pre-exposition of monocyte-derived macrophages (MDM) to m/lEVs on activation of autologous B cells from HD and patients. Results: The presence of m/lEVs reduced the frequency of CD69⁺ and CD86⁺ B cells from HD activated by an agonist of antigen receptor. This regulation of the B cell activation markers by m/lEVs was partially dependent on phosphatidylserine binging. These m/lEVs also reduced the proliferation, calcium mobilization, and global phosphorylation of tyrosine. Similar responses were observed in B cells from patients with RA. However, the presence of m/lEVs promoted high antibody levels in B cells cultured with T cell-dependent stimuli by 7 days. In addition, despite the direct inhibitory effect of m/lEVs on early B cell responses, when B cells were cocultured with autologous MDM previously exposed to m/lEVs or m/lEV-ICs, an increased frequency of CD69⁺ B cells from patients with RA was observed, albeit not with cells from HD. Conclusions: These data together suggest that m/lEVs have a direct modulatory effect in early responses of B cells through B cell receptor that can potentially fail in patients with RA because of the impact of these vesicles over cells of the innate immune system. This phenomenon can potentially contribute to the loss of tolerance and disease activity in patients with RA.

Summary: Patients with rheumatoid arthritis (RA) may be classified as seropositive or seronegative according to the presence of autoantibodies. An abnormal B cell phenotype and function could be one of the main components of the immunopathology of seropositive patients; however, there is little information regarding B cell defects in these patients. This study shows a broad characterization of the B cell phenotype and function in patients with seropositive RA. We focused mainly on the evaluation of subsets, the expression of modulatory molecules of cell activation (CD22, FcɣRIIb and FcµR), calcium mobilization, global tyrosine phosphorylation, expression of activation markers, cytokine and immunoglobulin (Ig) production, proliferation and the in-vitro generation of plasma cells. Increased frequency of CD27−IgM−IgD− and CD21− B cells was observed in patients with seropositive RA compared with healthy donors (HD). Decreased expression of CD22 was primarily found in memory B cells of patients with RA regardless of seropositivity. B cells from seropositive patients exhibited normal proliferation, calcium mobilization kinetics and global tyrosine phosphorylation, but showed an increased frequency of CD86+ B cells compared with HD. B cells of seropositive patients secrete less interleukin-10 after in-vitro activation and showed a decreased frequency of plasma cell differentiation and IgM production compared with HD. Our data indicate that patients with seropositive RA have an increased frequency of atypical B cell populations previously associated with chronic activation and antigen exposure. This may result in the observed low responsiveness of these cells in vitro.