An agonistic anti-signal regulatory protein α antibody for chronic inflammatory diseases.

Signal regulatory protein (SIRPα) is an immune inhibitory receptor expressed by myeloid cells to inhibit immune cell phagocytosis, migration, and activation. Despite the progress of SIRPα and CD47 antagonist antibodies to promote anti-cancer immunity, it is not yet known whether SIRPα receptor agonism could restrain excessive autoimmune tissue inflammation. Here, we report that neutrophil- and monocyte-associated genes including SIRPA are increased in inflamed tissue biopsies from patients with rheumatoid arthritis and inflammatory bowel diseases, and elevated SIRPA is associated with treatment-refractory ulcerative colitis. We next identify an agonistic anti-SIRPα antibody that exhibits potent anti-inflammatory effects in reducing neutrophil and monocyte chemotaxis and tissue infiltration. In preclinical models of arthritis and colitis, anti-SIRPα agonistic antibody ameliorates autoimmune joint inflammation and inflammatory colitis by reducing neutrophils and monocytes in tissues. Our work provides a proof of concept for SIRPα receptor agonism for suppressing excessive innate immune activation and chronic inflammatory disease treatment.

Proinflammatory IgG Fc structures in patients with severe COVID-19.

Severe acute respiratory syndrome coronavirus 2 infections can cause coronavirus disease 2019 (COVID-19), which manifests with a range of severities from mild illness to life-threatening pneumonia and multi-organ failure. Severe COVID-19 is characterized by an inflammatory signature, including high levels of inflammatory cytokines, alveolar inflammatory infiltrates and vascular microthrombi. Here we show that patients with severe COVID-19 produced a unique serologic signature, including an increased likelihood of IgG1 with afucosylated Fc glycans. This Fc modification on severe acute respiratory syndrome coronavirus 2 IgGs enhanced interactions with the activating Fcγ receptor FcγRIIIa; when incorporated into immune complexes, Fc afucosylation enhanced production of inflammatory cytokines by monocytes, including interleukin-6 and tumor necrosis factor. These results show that disease severity in COVID-19 correlates with the presence of proinflammatory IgG Fc structures, including afucosylated IgG1.

Blimp-1 is essential for allergen-induced asthma and Th2 cell development in the lung.

A Th2 immune response is central to allergic airway inflammation, which afflicts millions worldwide. However, the mechanisms that augment GATA3 expression in an antigen-primed developing Th2 cell are not well understood. Here, we describe an unexpected role for Blimp-1, a transcriptional repressor that constrains autoimmunity, as an upstream promoter of GATA3 expression that is critical for Th2 cell development in the lung to inhaled but not systemically delivered allergens but is dispensable for TFH function and IgE production. Mechanistically, Blimp-1 acts through Bcl6, leading to increased GATA3 expression in lung Th2 cells. Surprisingly, the anti-inflammatory cytokine IL-10, but not the pro-inflammatory cytokines IL-6 or IL-21, is required via STAT3 activation to up-regulate Blimp-1 and promote Th2 cell development. These data reveal a hitherto unappreciated role for an IL-10-STAT3-Blimp-1 circuit as an initiator of an inflammatory Th2 response in the lung to allergens. Thus, Blimp-1 in a context-dependent fashion can drive inflammation by promoting rather than terminating effector T cell responses.

Bcl6 and Blimp1 reciprocally regulate ST2+ Treg-cell development in the context of allergic airway inflammation.

BACKGROUND: Bcl6 is required for the development of T follicular helper cells and T follicular regulatory (Tfr) cells that regulate germinal center responses. Bcl6 also affects the function of regulatory T (Treg) cells. OBJECTIVE: The goal of this study was to define the functions of Bcl6 in Treg cells, including Tfr cells, in the context of allergic airway inflammation. METHODS: We used a model of house dust mite sensitization to challenge wild-type, Bcl6fl/fl Foxp3-Cre, and Prdm1 (Blimp1)fl/fl Foxp3-Cre mice to study the reciprocal roles of Bcl6 and Blimp1 in allergic airway inflammation. RESULTS: In the house dust mite model, Tfr cells repress the production of IgE and Bcl6+ Treg cells suppress the generation of type 2 cytokine-producing cells in the lungs. In mice with Bcl6-deficient Treg cells, twice as many ST2+ (IL-33R+) Treg cells develop as are observed in wild-type mice. ST2+ Treg cells in the context of allergic airway inflammation are Blimp1 dependent, express type 2 cytokines, and share features of visceral adipose tissue Treg cells. Bcl6-deficient Treg cells are more susceptible, and Blimp1-deficient Treg cells are resistant, to acquiring the ST2+ Treg-cell phenotype in vitro and in vivo in response to IL-33. Bcl6-deficient ST2+ Treg cells, but not Bcl6-deficient ST2+ conventional T cells, strongly promote allergic airway inflammation when transferred into recipient mice. Lastly, ST2 is required for the exacerbated allergic airway inflammation in Bcl6fl/fl Foxp3-Cre mice. CONCLUSIONS: During allergic airway inflammation, Bcl6 and Blimp1 play dual roles in regulating Tfr-cell activity in the germinal center and in the development of ST2+ Treg cells that promote type 2 cytokine responses.

Follicular regulatory T cells inhibit the development of granzyme B-expressing follicular helper T cells.

T follicular regulatory (TFR) cells are found in the germinal center (GC) response and help shape the antibody (Ab) response. However, the precise role of TFR cells in the GC is controversial. Here, we addressed TFR cell function using mice with impaired TFR cell development (Bcl6-flox/Foxp3-cre, or Bcl6FC mice), mice with augmented TFR cell development (Blimp1-flox/Foxp3-cre, or Blimp1FC mice), and two different methods of immunization. Unexpectedly, GC B cell levels positively correlated with TFR cell levels. Using a gene profiling approach, we found that TFH cells from TFR-deficient mice showed strong upregulation of granzyme B (Gzmb) and other effector CD8+ T cell genes, many of which were Stat4 dependent. The upregulation of cytotoxic genes was the highest in TFH cells from TFR-deficient mice where Blimp1 was also deleted in Foxp3+ regulatory T cells (Bcl6-flox/Prdm1-flox/Foxp3-cre [DKO] mice). Granzyme B- and Eomesodermin-expressing TFH cells correlated with a higher rate of apoptotic GC B cells. Klrg1+ TFH cells from DKO mice expressed higher levels of Gzmb. Our data show that TFR cells repress the development of abnormal cytotoxic TFH cells, and the presence of cytotoxic TFH cells correlates with a lower GC and Ab response. Our data show what we believe is a novel mechanism of action for TFR cells helping the GC response.

Roles of T Follicular Helper Cells and T Follicular Regulatory Cells in Autoantibody Production in IL-2-Deficient Mice.

Autoantibodies can result from excessive T follicular helper (Tfh) cell activity, whereas T follicular regulatory (Tfr) cells negatively regulate autoantibody production. IL-2 knockout (KO) mice on the BALB/c background have elevated Tfh responses, produce autoantibodies, and develop lethal autoimmunity. We analyzed Tfh and Tfr cells in IL-2 KO mice on the C57BL/6 (B6) genetic background. In B6 IL-2 KO mice, the spontaneous formation of Tfh cells and germinal center B cells was greatly enhanced, along with production of anti-DNA autoantibodies. IL-2 has been reported to repress Tfr cell differentiation; however, Tfr cells were not increased over wild-type levels in the B6 IL-2 KO mice. To assess Tfh and Tfr cell regulation of autoantibody production in IL-2 KO mice, we generated IL-2 KO mice with a T cell-specific deletion of the master Tfh cell transcription factor Bcl6. In IL-2 KO Bcl6 conditional KO (2KO-Bcl6TC) mice, Tfh cells, Tfr cells, and germinal center B cells were ablated. In contrast to expectations, autoantibody IgG titers in 2KO-Bcl6TC mice were significantly elevated over autoantibody IgG titers in IL-2 KO mice. Specific deletion of Tfr cells with Foxp3-cre Bcl6-flox alleles in IL-2 KO mice led to early lethality, before high levels of autoantibodies could develop. We found IL-2+/+ Tfr cell-deficient mice produce significant levels of autoantibodies. Our overall findings provide evidence that Tfh cells are dispensable for high-level production of autoantibodies and also reveal a complex interplay between Tfh and Tfr cells in autoantibody production and autoimmune disease.

Bcl6 promotes follicular helper T-cell differentiation and PD-1 expression in a Blimp1-independent manner in mice.

The transcription factors Bcl6 and Blimp1 have opposing roles in the development of the follicular helper T (TFH ) cells: Bcl6 promotes and Blimp1 inhibits TFH -cell differentiation. Similarly, Bcl6 activates, while Blimp1 represses, expression of the TFH -cell marker PD-1. However, Bcl6 and Blimp1 repress each other's expression, complicating the interpretation of the regulatory network. Here we sought to clarify the extent to which Bcl6 and Blimp1 independently control TFH -cell differentiation by generating mice with T-cell specific deletion of both Bcl6 and Blimp1 (double conditional KO [dcKO] mice). Our data indicate that Blimp1 does not control TFH -cell differentiation independently of Bcl6. However, a population of T follicular regulatory (TFR ) cells developed independently of Bcl6 in dcKO mice. We have also analyzed regulation of IL-10 and PD-1, two genes controlled by both Bcl6 and Blimp1, and observed that Bcl6 regulates both genes independently of Blimp1. We found that Bcl6 positively regulates PD-1 expression by inhibiting the ability of T-bet/Tbx21 to repress Pdcd1 transcription. Our data provide a novel mechanism for positive control of gene expression by Bcl6, and illuminate how Bcl6 and Blimp1 control TFH -cell differentiation.

AMP kinase promotes Bcl6 expression in both mouse and human T cells.

The transcription factor Bcl6 is a master regulator of follicular helper T (TFH) cells, and understanding the signaling pathway that induces Bcl6 and TFH cell differentiation is therefore critical. IL-2 produced during T cell activation inhibits Bcl6 expression but how TFH cells evade IL-2 inhibition is not completely understood. Here we show that Bcl6 is highly up-regulated in activated CD4 T cells following glucose deprivation (GD), and this pathway is insensitive to inhibition by IL-2. Similar to GD, the glucose analog 2-deoxyglucose (2DG) inhibits glycolysis, and 2DG induced Bcl6 expression in activated CD4 T cells. The metabolic sensor AMP kinase (AMPK) is activated when glycolysis is decreased, and the induction of Bcl6 by GD was inhibited by the AMPK antagonist compound C. Additionally, activation of AMPK by the drug AICAR caused Bcl6 up-regulation in activated CD4 T cells. When mice were immunized with KLH using AICAR as an adjuvant, there was a strong TFH-dependent enhancement of KLH-specific antibody (Ab) responses, and higher Bcl6 expression in TFH cells in vivo. Activation of AMPK strongly induced BCL6 and the up-regulation of TFH cell marker expression by human CD4 T cells. Our data reveal a major new pathway for TFH cell differentiation, conserved by both mouse and human T cells. Mature TFH cells are reported to have a lower metabolic state compared to TH1 cells. Our data indicates that decreased metabolism may be deterministic for TFH cell differentiation, and not simply a result of TFH cell differentiation.