Alexandra V. Bocharnikov

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by pathologic T cell-B cell interactions and autoantibody production. Defining the T cell populations that drive B cell responses in SLE may enable design of therapies that specifically target pathologic cell subsets. Here, we evaluated the phenotypes of CD4+ T cells in the circulation of 52 SLE patients drawn from multiple cohorts and identified a highly expanded PD-1hiCXCR5-CD4+ T cell population. Cytometric, transcriptomic, and functional assays demonstrated that PD-1hiCXCR5-CD4+ T cells from SLE patients are T peripheral helper (Tph) cells, a CXCR5- T cell population that stimulates B cell responses via IL-21. The frequency of Tph cells, but not T follicular helper (Tfh) cells, correlated with both clinical disease activity and the frequency of CD11c+ B cells in SLE patients. PD-1hiCD4+ T cells were found within lupus nephritis kidneys and correlated with B cell numbers in the kidney. Both IL-21 neutralization and CRISPR-mediated deletion of MAF abrogated the ability of Tph cells to induce memory B cell differentiation into plasmablasts in vitro. These findings identify Tph cells as a highly expanded T cell population in SLE and suggest a key role for Tph cells in stimulating pathologic B cell responses.

OBJECTIVE: Inflammatory arthritides exhibit hallmark patterns of affected and spared joints, but in each individual, arthritis affects only a subset of all possible sites. The purpose of this study was to identify patient-specific patterns of joint flare to distinguish local from systemic drivers of disease chronicity. METHODS: Patients with juvenile idiopathic arthritis followed without interruption from disease onset into adulthood were identified across 2 large academic centers. Joints inflamed at each visit were established by medical record review. Flare was defined as physician-confirmed joint inflammation following documented inactive disease. RESULTS: Among 222 adults with JIA, 95 had complete serial joint examinations dating from disease onset in childhood. Mean follow-up was 12.5 years (interquartile range 7.9-16.7 years). Ninety (95%) of 95 patients achieved inactive disease, after which 81% (73 patients) experienced at least 1 flare. Among 940 joints affected in 253 flares, 74% had been involved previously. In flares affecting easily observed large joint pairs where only 1 side had been involved before (n = 53), the original joint was affected in 83% and the contralateral joint in 17% (P < 0.0001 versus random laterality). However, disease extended to at least 1 new joint in ~40% of flares, a risk that remained stable even decades after disease onset, and was greatest in flares that occurred while patients were not receiving medication (54% versus 36% of flares occurring with therapy; odds ratio 2.09, P = 0.015). CONCLUSION: Arthritis flares preferentially affect previously inflamed joints but carry an ongoing risk of disease extension. These findings confirm joint-specific memory and suggest that prevention of new joint accumulation should be an important target for arthritis therapy.

<h3>Background</h3> Pathologic T cell-B cell interactions and production of autoantibodies are hallmark features of SLE. T follicular helper (Tfh) cells are generally considered the principal T cell population capable of helping B cells. However, distinct T cell populations can augment B cell responses in chronically inflamed peripheral tissues. We recently described a dramatically expanded population of T peripheral helper (Tph) cells that promotes B cell responses in synovium of patients with seropositive RA. Here we evaluate the frequency, phenotype, and clinical associations of Tph cells in the circulation of patients with lupus. <h3>Methods</h3> Mass cytometry data from the Accelerating Medicines Partnership RA/SLE Network were used to quantify cell populations in PBMCs from 27 lupus nephritis patients, 27 RA patients, and 25 non-inflammatory controls. Frequencies of Tph cells (PD-1^hi CXCR5^- CD4⁺ T cells), Tfh cells (PD-1^hi CXCR5⁺ CD4⁺ T cells), and CD21^low CD19⁺ B cells were quantified by standardized gating, and associations with SLEDAI and dsDNA titers were assessed. For <i>in vitro</i> T cell-B cell co-cultures, sorted Tph cells, Tfh cells, or control T cell populations from SLE patients were co-cultured with memory B cells and stimulated with SEB +LPS, and CD38^hi CD27⁺ plasmablasts were quantified at day 5. <h3>Results</h3> We first confirmed that Tph cells (PD-1^hi CXCR5^- CD4⁺ T cells) from SLE patients possess B cell helper function, as we previously observed in RA. Tph cells sorted from blood from 5 different lupus patients strongly induced B cell differentiation into CD38^hi CD27⁺ plasmablasts <i>in vitro</i> (figure 1A, n=5 donors). By mass cytometry, Tph cells are markedly expanded in the circulation of SLE patients compared to non-inflammatory controls (4.3-fold increase, p&lt;0.0001, figure 1B). Tfh cells are also increased in the SLE patients compared to controls (1.9-fold); however, the magnitude of the increase in Tph cells in SLE patients well exceeds that of Tfh cells. Tph cell frequency is higher in lupus nephritis patients with dsDNA titers &gt;50 (p=0.017) and with SELENA-SLEDAI &gt;10 (p=0.046) compared to patients with lower disease activity measures. Similar associations with disease activity were not observed for Tfh cells. Expression of surface receptors on Tph cells from SLE and RA patients was similar. A strong positive correlation emerged between the frequencies of Tph cells and CD21^low B cells, an activated B cell population highly expanded in SLE (Spearman r=0.56, p=0.0026, figure 1C, gray=SLE patients, black=all other patients). In contrast, no correlation was seen between Tfh cells and CD21^low B cells in SLE patients. <h3>Conclusions</h3> Tph cells are markedly expanded in the circulation of patients with SLE and demonstrate robust B cell helper function. The strong and specific positive correlation between Tph cell and CD21^low B cell frequencies suggests that these cells may act coordinately in the pathologic autoimmune response in SLE. <h3>Acknowledgements</h3> We acknowledge the Accelerating Medicines Partnership RA/SLE Network and its members.