Background T follicular helper (Tfh) cells underpin T-cell dependent humoral immunity and the success of most vaccines. Tfh cells also contribute to human immune disorders such as autoimmunity, immunodeficiency and malignancy. Understanding the molecular requirements for the generation and function of Tfh cells will provide strategies for targeting these cells to modulate their behavior in the setting of these immunological abnormalities. Objective To determine the signaling pathways and cellular interactions required for the development and function of Tfh cells in humans. Methods Human primary immunodeficiencies (PIDs) resulting from monogenic mutations provide a unique opportunity to assess the requirement for particular molecules in regulating human lymphocyte function. Circulating Tfh (cTfh) cell subsets, memory B cells and serum Ig levels were quantified and functionally assessed in healthy controls as well as patients with PIDs resulting from mutations in STAT3, STAT1, TYK2, IL21, IL21R, IL10R, IFNGR1/2, IL12RB1, CD40LG, NEMO, ICOS or BTK. Results Loss-of function (LOF) mutations in STAT3, IL10R, CD40LG, NEMO, ICOS or BTK reduced cTfh frequencies. STAT3, IL21/R LOF and STAT1 gain-of function mutations skewed cTfh differentiation towards a phenotype characterized by over-expression of IFNγ and programmed death -1 (PD-1). IFNγ inhibited cTfh function in vitro and in vivo, corroborated by hypergammaglobulinemia in patients with IFNGR1/2, STAT1 and IL12RB1 LOF mutations. Conclusion Specific mutations impact the quantity and quality of cTfh cells, highlighting the need to assess Tfh cells in patients by multiple criteria, including phenotype and function. Furthermore, IFNγ functions in vivo to restrain Tfh-induced B cell differentiation. These findings shed new light on Tfh biology and the integrated signaling pathways required for their generation, maintenance and effector function, and explain compromised humoral immunity in some PIDs.

Heterozygosity for human STAT3 dominant-negative (DN) mutations underlies an autosomal dominant form of hyper-IgE syndrome (HIES). We describe patients with an autosomal recessive form of HIES due to loss-of-function mutations of a previously uncharacterized gene, ZNF341. ZNF341 is a transcription factor that resides in the nucleus, where it binds a specific DNA motif present in various genes, including, most notably the STAT3 promoter. The patients’ cells have low basal levels of STAT3 mRNA and protein. The auto-induction of STAT3 production, activation, and function by STAT3-activating cytokines is particularly strongly impaired. Like patients with STAT3 DN mutations, ZNF341-deficient patients lack Th17 cells, have an excess of Th2 cells, and low memory B cells, due to the tight dependence of STAT3 activity on ZNF341 in lymphocytes. Their milder extra-hematopoietic manifestations and stronger inflammatory responses reflect the lower ZNF341-dependence of STAT3 activity in other cell types. Human ZNF341 is essential for the STAT3 transcription-dependent auto-induction and sustained activity of STAT3.

Inherited IL-12Rβ1 and TYK2 deficiencies impair both IL-12- and IL-23-dependent IFN-γ immunity and are rare monogenic causes of tuberculosis, each found in about 1/100,000 individuals. We show that homozygosity for the common TYK2 P1104A allele, which is found in about 1/600 Europeans and 1/2,500 other individuals, is much more frequent in patients with tuberculosis than in ethnicity-adjusted controls (p = 8.37×10−8, odds ratio = 89.31 [95%CI: 14.7–1,725]). We also show that the frequency of P1104A in Europeans has decreased significantly, from about 9% to 4.2%, over the last 4,000 years, consistent with purging of this variant by endemic tuberculosis. Moreover, we show that catalytically inactive P1104A impairs cellular responses to IL-23, but not to IFN-α, IL-10, or even IL-12, which, like IL-23, induces IFN-γ via activation of TYK2 and JAK2. Finally, we show that catalytically competent TYK2 is critical for IL-23 but not IL-12 responses, whereas catalytically competent JAK2 is redundant for both. Homozygosity for the P1104A missense variant of TYK2 selectively disrupts the induction of IFN-γ by IL-23 and is a common monogenic etiology of tuberculosis.

Gain-of-function (GOF) mutations in , encoding the p110δ subunit of phosphatidylinositide 3-kinase (PI3K), cause a primary immunodeficiency. Affected individuals display impaired humoral immune responses following infection or immunization. To establish mechanisms underlying these immune defects, we studied a large cohort of patients with GOF mutations and established a novel mouse model using CRISPR/Cas9-mediated gene editing to introduce a common pathogenic mutation in In both species, hyperactive PI3K severely affected B cell development and differentiation in the bone marrow and the periphery. Furthermore, PI3K GOF B cells exhibited intrinsic defects in class-switch recombination (CSR) due to impaired induction of activation-induced cytidine deaminase (AID) and failure to acquire a plasmablast gene signature and phenotype. Importantly, defects in CSR, AID expression, and Ig secretion were restored by leniolisib, a specific p110δ inhibitor. Our findings reveal key roles for balanced PI3K signaling in B cell development and long-lived humoral immunity and memory and establish the validity of treating affected individuals with p110δ inhibitors.

In two complementary papers, Casanova, Malissen, and collaborators report the discovery of human RLTPR deficiency, the first primary immunodeficiency of the human CD28 pathway in T cells. Together, the two studies highlight the important and largely (but not completely) overlapping roles of RLTPR in T and B cells of humans and mice.

Tangye and collaborators use a series of mutants to elucidate the pathways required to generate distinct subsets of human effector CD4+ T cells.

No abstract

No abstract