Regulatory T cells (Tregs) are a small yet critical subset of CD4+ T cells, which have the role of maintaining immune homeostasis by, for example, regulating self-tolerance, tumor immunity, anti-microbial resistance, allergy and transplantation rejection. The suppressive mechanisms by which Tregs function are varied and pleiotropic. The ability of Tregs to maintain self-tolerance means they are critical for the control and prevention of autoimmune diseases. Irregularities in Treg function and number can result in loss of tolerance and autoimmune disease. Restoring immune homeostasis and tolerance through the promotion, activation or delivery of Tregs has emerged as a focus for therapies aimed at curing or controlling autoimmune diseases. Such therapies have focused on the Treg cell subset by using drugs to suppress T effector cells and promote Tregs. Other approaches have trialed inducing tolerance by administering the autoantigen via direct administration, by transient expression using a DNA vector, or by antigen-specific nanoparticles. More recently, cell-based therapies have been developed as an approach to directly or indirectly enhance Treg cell specificity, function and number. This can be achieved indirectly by transfer of tolerogenic dendritic cells, which have the potential to expand antigen-specific Treg cells. Treg cells can be directly administered to treat autoimmune disease by way of polyclonal Tregs or Tregs transduced with a receptor with high affinity for the target autoantigen, such as a high affinity T cell receptor (TCR) or a chimeric antigen receptor (CAR). This review will discuss the strategies being developed to redirect autoimmune responses to a state of immune tolerance, with the aim of the prevention or amelioration of autoimmune disease.

Antigen-specific regulatory T cells (Tregs) suppress pathogenic autoreactivity and are potential therapeutic candidates for autoimmune diseases such as systemic lupus erythematosus (SLE). Lupus nephritis is associated with autoreactivity to the Smith (Sm) autoantigen and the human leucocyte antigen (HLA)-DR15 haplotype; hence, we investigated the potential of Sm-specific Tregs (Sm-Tregs) to suppress disease. Here we identify a HLA-DR15 restricted immunodominant Sm T cell epitope using biophysical affinity binding assays, then identify high-affinity Sm-specific T cell receptors (TCRs) using high-throughput single-cell sequencing. Using lentiviral vectors, we transduce our lead Sm-specific TCR into Tregs derived from patients with SLE who are anti-Sm and HLA-DR15 positive. Compared with polyclonal mock-transduced Tregs, Sm-Tregs potently suppress Sm-specific pro-inflammatory responses in vitro and suppress disease progression in a humanized mouse model of lupus nephritis. These results show that Sm-Tregs are a promising therapy for SLE.

Autoreactivity to myeloperoxidase (MPO) causes anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV), with rapidly progressive glomerulonephritis. Here, we show that a Staphylococcus aureus peptide, homologous to an immunodominant MPO T-cell epitope (MPO_409–428), can induce anti-MPO autoimmunity. The peptide (6PGD_391–410) is part of a plasmid-encoded 6-phosphogluconate dehydrogenase found in some S. aureus strains. It induces anti-MPO T-cell autoimmunity and MPO-ANCA in mice, whereas related sequences do not. Mice immunized with 6PGD_391–410, or with S. aureus containing a plasmid expressing 6PGD_391–410, develop glomerulonephritis when MPO is deposited in glomeruli. The peptide induces anti-MPO autoreactivity in the context of three MHC class II allomorphs. Furthermore, we show that 6PGD_391–410 is immunogenic in humans, as healthy human and AAV patient sera contain anti-6PGD and anti-6PGD_391–410 antibodies. Therefore, our results support the idea that bacterial plasmids might have a function in autoimmune disease.

Memory T cells form from the adaptive immune response to historic infections or vaccinations. Some memory T cells have the potential to recognise unrelated pathogens like severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and generate cross-reactive immune responses. Notably, such T cell cross-reactivity has been observed between SARS-CoV-2 and other human coronaviruses. T cell cross-reactivity has also been observed between SARS-CoV-2 variants from unrelated microbes and unrelated vaccinations against influenza A, tuberculosis and measles, mumps and rubella. Extensive research and debate is underway to understand the mechanism and role of T cell cross-reactivity and how it relates to Coronavirus disease 2019 (COVID-19) outcomes. Here, we review the evidence for the ability of pre-existing memory T cells to cross-react with SARS-CoV-2. We discuss the latest findings on the impact of T cell cross-reactivity and the extent to which it can cross-protect from COVID-19.

Background: Several lines of evidence implicate that there are distinct differences between patients with myeloperoxidase (MPO)-antineutrophil cytoplasmic antibody (ANCA) and anti-glomerular basement membrane (GBM) antibody double-seropositive patients (DPPs) and single-positive patients. Hence, we conducted a retrospective study from a single center in China to analyze the clinical and pathological features, and prognosis of DPPs.Methods: 109 patients with MPO-ANCA-associated vasculitis (MPO-AAV), 20 DPPs and 23 patients diagnosed with anti-GBM disease from a large center in China were included in this study. The ratio of patients with renal biopsy in three groups were 100%, 50% and 100%, respectively. Their clinical and pathological characteristics, and outcomes were analyzed. The intensity of immune deposits in the kidney at diagnosis was detected by immunofluorescence (IF). Furthermore, multivariate Cox hazard model analysis was used to assess the clinical and histological predictors of end-stage renal disease (ESRD) and death for DPPs.Results: In our study, we found that patients in the DPPs group were older than the other two groups (p = 0.007, MPO-AAV vs. DPPs; p < 0.001, DPPs vs. anti-GBM). The DPPs group had a higher value of serum creatinine (p = 0.041) and lower estimated glomerular filtration rate (eGFR) (p = 0.032) compared with MPO-AAV patients. On the contrary, the DPPs group had a lower serum creatinine (p = 0.003) compared with patients with anti-GBM group. The proportion of patients with cardiac system involvement in the DPPs group was higher than anti-GBM patients (p = 0.014). Cellular crescents could be generally observed in renal biopsy of DPPs and patients with anti-GBM glomerulonephritis. In addition, Bowman’s capsule rupture was more common in DPPs than MPO-AAV patients (p = 0.001). MPO-AAV had a better renal and overall survival outcome than DPPs (p < 0.001). There was no significant difference of renal and overall survival outcome between DPPs and patients with anti-GBM disease. The incidence of ESRD in DPPs was negatively associated with lymphocyte count (HR 0.153, 95% CI 0.027 to 0.872, p = 0.034) and eGFR (HR 0.847, 95% CI 0.726 to 0.989, p = 0.036). Elevated serum creatinine was confirmed as a risk factor of both renal (HR 1.003, 95% CI 1.000 to 1.005, p = 0.019) and patient survival in DPPs (HR1.461, 95% CI 1.050 to 2.033, p = 0.024).Conclusion: In summary, compared with anti-GBM disease, DPPs tended to involve multi-organ damage rather than limited to the kidney. It is highlighted that serologic DPPs have a worse renal and patient prognosis than MPO-AAV. Moreover, we found that the risk factors of renal survival of DPPs include low lymphocyte count, elevated serum creatinine and reduced eGFR, and serum creatinine can predict patient survival.