SLAM family receptors control pro-survival effectors in germinal center B cells to promote humoral immunity

T peripheral helper (Tph) cells, a marker of immune activation in cancer and autoimmune disorders

T peripheral helper (Tph) cells are a newly discovered subtype of CD4+ T cells that have emerged as the counterpart of T follicular helper (Tfh) cells in the peripheral tissues. These two cell types share some common characteristics, such as high levels of PD1 and CXCL13 expression, but differ in the expression of transcription factors and chemokine receptors. Tph cells have been studied in relation to B cells' effector functions, including cytokines production and antibody-mediated immune responses. However, their role in the inflammatory-mediated development of malignancies remains poorly understood. Tph cells were initially identified in the synovium of rheumatoid arthritis patients and have since been found to be expanded in several autoimmune diseases. They have been linked to a worse prognosis in autoimmune conditions, but intriguingly, their presence has been correlated with better outcomes in certain types of cancer. The functions of Tph cells are still being investigated, but recent data suggests their involvement in the assembly of tertiary lymphoid structures (TLS). Furthermore, their interaction with B cells, which have been mainly described as possessing a memory phenotype, promotes their development. In this review, we explore the role of Tph cells in peripheral immune responses during cancer and autoimmune disorders.

SLAMF7 predicts prognosis and correlates with immune infiltration in serous ovarian carcinoma

OBJECTIVE

Signaling lymphocytic activation molecule family members (SLAMFs) play a critical role in immune regulation of malignancies. This study aims to investigate the prognostic value and function of SLAMFs in ovarian cancer (OC).

METHODS

The expression analysis of SLAMFs was conducted based on The Cancer Genome Atlas Ovarian Cancer Collection (TCGA-OV) and Gene Expression Omnibus (GEO) databases. Immunohistochemistry (IHC) was further performed on tissue arrays (n=98) to determine the expression of SLAMF7. Kaplan-Meier plotter and multivariate Cox regression model were used to evaluate the correlation of SLAMF7 expression with survival outcomes of patients. The molecular function of SLAMF7 in OC was further investigated using Gene Set Enrichment Analysis (GSEA).

RESULTS

SLAMF7 mRNA expression were significantly upregulated in OC tumor tissue compared to normal tissue. IHC revealed that SLAMF7 expression was located in the interstitial parts of tumor tissue, and higher SLAMF7 expression was associated with favorable survival outcomes. GSEA demonstrated that SLAMF7 is involved immune-related pathways. Further analysis showed that SLAMF7 had a strong correlation with the T cell-specific biomarker (CD3) but not with the B cell (CD19, CD22, and CD23) and natural killer cell-specific biomarkers (CD85C, CD336, and CD337). Furthermore, IHC analysis confirmed that SLAMF7 was expressed in tumor-infiltrating T cells, and the IHC score of SLAMF7 was positively correlated with CD3 (r=0.85, p<0.001).

CONCLUSION

SLAMF7 is expressed in the interstitial components of clinical OC tissue, and higher SLAMF7 expression indicated a favorable prognosis for patients with OC. Additionally, SLAMF7 is involved in T-cell immune infiltration in OC.

Suppression of adaptive NK cell expansion by macrophage-mediated phagocytosis inhibited by 2B4-CD48

Infection of mice by mouse cytomegalovirus (MCMV) triggers activation and expansion of Ly49H+ natural killer (NK) cells, which are virus specific and considered to be "adaptive" or "memory" NK cells. Here, we find that signaling lymphocytic activation molecule family receptors (SFRs), a group of hematopoietic cell-restricted receptors, are essential for the expansion of Ly49H+ NK cells after MCMV infection. This activity is largely mediated by CD48, an SFR broadly expressed on NK cells and displaying augmented expression after MCMV infection. It is also dependent on the CD48 counter-receptor, 2B4, expressed on host macrophages. The 2B4-CD48 axis promotes expansion of Ly49H+ NK cells by repressing their phagocytosis by virus-activated macrophages through inhibition of the pro-phagocytic integrin lymphocyte function-associated antigen-1 (LFA-1) on macrophages. These data identify key roles of macrophages and the 2B4-CD48 pathway in controlling the expansion of adaptive NK cells following MCMV infection. Stimulation of the 2B4-CD48 axis may be helpful in enhancing adaptive NK cell responses for therapeutic purposes.

CD47 masks pro-phagocytic ligands in cis on tumor cells to suppress antitumor immunity

Cancer cells often overexpress CD47, which triggers the inhibitory receptor SIRPα expressed on macrophages, to elude phagocytosis and antitumor immunity. Pharmacological blockade of CD47 or SIRPα is showing promise as anticancer therapy, although CD47 blockade has been associated with hematological toxicities that may reflect its broad expression pattern on normal cells. Here we found that, in addition to triggering SIRPα, CD47 suppressed phagocytosis by a SIRPα-independent mechanism. This mechanism prevented phagocytosis initiated by the pro-phagocytic ligand, SLAMF7, on tumor cells, due to a cis interaction between CD47 and SLAMF7. The CD47-SLAMF7 interaction was disrupted by CD47 blockade and by a first-in-class agonist SLAMF7 antibody, but not by SIRPα blockade, thereby promoting antitumor immunity. Hence, CD47 suppresses phagocytosis not only by engaging SIRPα, but also by masking cell-intrinsic pro-phagocytic ligands on tumor cells and knowledge of this mechanism may influence the decision between CD47 blockade or SIRPα blockade for therapeutic purposes.

Transcriptional and metabolic programs promote the expansion of follicular helper T cells in lupus-prone mice

The expansion of follicular helper T (Tfh) cells, which is tightly associated with the development of lupus, is reversed by the inhibition of either glycolysis or glutaminolysis in mice. Here we analyzed the gene expression and metabolome of Tfh cells and naive CD4+ T (Tn) cells in the B6.Sle1.Sle2.Sle3 (triple congenic, TC) mouse model of lupus and its congenic B6 control. Lupus genetic susceptibility in TC mice drives a gene expression signature starting in Tn cells and expanding in Tfh cells with enhanced signaling and effector programs. Metabolically, TC Tn and Tfh cells showed multiple defective mitochondrial functions. TC Tfh cells also showed specific anabolic programs including enhanced glutamate metabolism, malate-aspartate shuttle, and ammonia recycling, as well as altered dynamics of amino acid content and their transporters. Thus, our study has revealed specific metabolic programs that can be targeted to specifically limit the expansion of pathogenic Tfh cells in lupus.

Alterations in germinal center formation and B cell activation during severe Orientia tsutsugamushi infection in mice

Scrub typhus is a poorly studied but life-threatening disease caused by the intracellular bacterium Orientia tsutsugamushi (Ot). Cellular and humoral immunity in Ot-infected patients is not long-lasting, waning as early as one-year post-infection; however, its underlying mechanisms remain unclear. To date, no studies have examined germinal center (GC) or B cell responses in Ot-infected humans or experimental animals. This study was aimed at evaluating humoral immune responses at acute stages of severe Ot infection and possible mechanisms underlying B cell dysfunction. Following inoculation with Ot Karp, a clinically dominant strain known to cause lethal infection in C57BL/6 mice, we measured antigen-specific antibody titers, revealing IgG2c as the dominant isotype induced by infection. Splenic GC responses were evaluated by immunohistology, co-staining for B cells (B220), T cells (CD3), and GCs (GL-7). Organized GCs were evident at day 4 post-infection (D4), but they were nearly absent at D8, accompanied by scattered T cells throughout splenic tissues. Flow cytometry revealed comparable numbers of GC B cells and T follicular helper (Tfh) cells at D4 and D8, indicating that GC collapse was not due to excessive death of these cell subtypes at D8. B cell RNAseq analysis revealed significant differences in expression of genes associated with B cell adhesion and co-stimulation at D8 versus D4. The significant downregulation of S1PR2 (a GC-specific adhesion gene) was most evident at D8, correlating with disrupted GC formation. Signaling pathway analysis uncovered downregulation of 71% of B cell activation genes at D8, suggesting attenuation of B cell activation during severe infection. This is the first study showing the disruption of B/T cell microenvironment and dysregulation of B cell responses during Ot infection, which may help understand the transient immunity associated with scrub typhus.

New twists in humoral immune regulation by SLAM family receptors

SLAM family receptors are involved in humoral immune regulation. In this issue of JEM, Zhong et al. (2021. J. Exp. Med.https://doi.org/10.1084/jem.20200756) provide evidence that these receptors collectively suppress germinal center reaction but promote production of antigen-specific antibodies.