Michela Locci

Human Circulating PD-1+CXCR3−CXCR5+ Memory Tfh Cells Are Highly Functional and Correlate with Broadly Neutralizing HIV Antibody Responses

The vast majority of currently licensed human vaccines work on the basis of long-term protective antibody responses. It is now conceivable that an antibody-dependent HIV vaccine might be possible, given the discovery of HIV broadly neutralizing antibodies (bnAbs) in some HIV-infected individuals. However, these antibodies are difficult to develop and have characteristics indicative of a high degree of affinity maturation in germinal centers (GCs). CD4⁺ T follicular helper (Tfh) cells are specialized for B cell help and necessary for GCs. Therefore, the development of HIV bnAbs might depend on Tfh cells. Here, we identified in normal individuals a subpopulation of circulating memory PD-1⁺CXCR5⁺CD4⁺ T cells that are resting memory cells most related to bona fide GC Tfh cells by gene expression profile, cytokine profile, and functional properties. Importantly, the frequency of these cells correlated with the development of bnAbs against HIV in a large cohort of HIV⁺ individuals.

Bcl6 and Maf Cooperate To Instruct Human Follicular Helper CD4 T Cell Differentiation

Follicular helper CD4 T (Tfh) cells provide B cells with signals that are important for the generation of high-affinity Abs and immunological memory and, therefore, are critical for the protective immunity elicited by most human vaccines. Transcriptional regulators of human Tfh cell differentiation are poorly understood. In this article, we demonstrate that Bcl6 controls specific gene modules for human Tfh cell differentiation. The introduction of Bcl6 expression in primary human CD4 T cells resulted in the regulation of a core set of migration genes that enable trafficking to germinal centers: CXCR4, CXCR5, CCR7, and EBI2. Bcl6 expression also induced a module of protein expression critical for T–B interactions, including SAP, CD40L, PD-1, ICOS, and CXCL13. This constitutes direct evidence for Bcl6 control of most of these functions and includes three genes known to be loci of severe human genetic immunodeficiencies (CD40L, SH2D1A, and ICOS). Introduction of Bcl6 did not alter the expression of IL-21 or IL-4, the primary cytokines of human Tfh cells. We show in this article that introduction of Maf (c-Maf) does induce the capacity to express IL-21. Surprisingly, Maf also induced CXCR5 expression. Coexpression of Bcl6 and Maf revealed that Bcl6 and Maf cooperate in the induction of CXCR4, PD-1, and ICOS. Altogether, these findings reveal that Bcl6 and Maf collaborate to orchestrate a suite of genes that define core characteristics of human Tfh cell biology.

Evidence for Long-term Efficacy and Safety of Gene Therapy for Wiskott–Aldrich Syndrome in Preclinical Models

Wiskott-Aldrich Syndrome (WAS) is a life-threatening X-linked disease characterized by immunodeficiency, thrombocytopenia, autoimmunity, and malignancies. Gene therapy could represent a therapeutic option for patients lacking a suitable bone marrow (BM) donor. In this study, we analyzed the long-term outcome of WAS gene therapy mediated by a clinically compatible lentiviral vector (LV) in a large cohort of was(null) mice. We demonstrated stable and full donor engraftment and Wiskott-Aldrich Syndrome protein (WASP) expression in various hematopoietic lineages, up to 12 months after gene therapy. Importantly, we observed a selective advantage for T and B lymphocytes expressing transgenic WASP. T-cell receptor (TCR)-driven T-cell activation, as well as B-cells ability to migrate in response to CXCL13, was fully restored. Safety was evaluated throughout the long-term follow-up of primary and secondary recipients of WAS gene therapy. WAS gene therapy did not affect the lifespan of treated animals. Both hematopoietic and nonhematopoietic tumors arose, but we excluded the association with gene therapy in all cases. Demonstration of long-term efficacy and safety of WAS gene therapy mediated by a clinically applicable LV is a key step toward the implementation of a gene therapy clinical trial for WAS.

Activin A programs the differentiation of human TFH cells

SUMMARY Follicular helper T (TFH) cells are CD4+ T cells specialized in helping B cells and are associated both with protective antibody responses and autoimmune diseases. The promise of targeting TFH cells therapeutically has been limited by fragmentary understanding of extrinsic signals regulating human TFH cell differentiation. A screen of a human protein library identified activin A as new regulator of TFH cell differentiation. Activin A orchestrated expression of multiple TFH-associated genes, independently or in concert with additional signals. TFH programming by activin A was antagonized by the cytokine IL-2. Activin A’s capacity to drive TFH cell differentiation in vitro was conserved for non-human primates but not mice. Finally, activin A-induced TFH programming was dependent on SMAD2 and SMAD3 signaling and blocked by pharmacological inhibitors.Follicular helper T cells (TFH cells) are CD4+ T cells specialized in helping B cells and are associated both with protective antibody responses and autoimmune diseases. The promise of targeting TFH cells therapeutically has been limited by fragmentary understanding of extrinsic signals that regulate the differentiation of human TFH cells. A screen of a human protein library identified activin A as a potent regulator of TFH cell differentiation. Activin A orchestrated the expression of multiple genes associated with the TFH program, independently or in concert with additional signals. TFH cell programming by activin A was antagonized by the cytokine IL-2. Activin As ability to drive TFH cell differentiation in vitro was conserved in non-human primates but not in mice. Finally, activin-A-induced TFH programming was dependent on signaling via SMAD2 and SMAD3 and was blocked by pharmacological inhibitors.

Lentiviral-mediated gene therapy leads to improvement of B-cell functionality in a murine model of Wiskott-Aldrich syndrome

BACKGROUND Wiskott-Aldrich syndrome (WAS) is an X-linked primary immunodeficiency characterized by thrombocytopenia, eczema, infections, autoimmunity, and lymphomas. Transplantation of hematopoietic stem cells from HLA-identical donors is curative, but it is not available to all patients. We have developed a gene therapy (GT) approach for WAS by using a lentiviral vector encoding for human WAS promoter/cDNA (w1.6W) and demonstrated its preclinical efficacy and safety. OBJECTIVE To evaluate B-cell reconstitution and correction of B-cell phenotype in GT-treated mice. METHODS We transplanted Was(-/-) mice sublethally irradiated (700 rads) with lineage marker-depleted bone marrow wild-type cells, Was(-/-) cells untransduced or transduced with the w1.6W lentiviral vector and analyzed B-cell reconstitution in bone marrow, spleen, and peritoneum. RESULTS Here we show that WAS protein(+) B cells were present in central and peripheral B-cell compartments from GT-treated mice and displayed the strongest selective advantage in the splenic marginal zone and peritoneal B1 cell subsets. After GT, splenic architecture was improved and B-cell functions were restored, as demonstrated by the improved antibody response to pneumococcal antigens and the reduction of serum IgG autoantibodies. CONCLUSION WAS GT leads to improvement of B-cell functions, even in the presence of a mixed chimerism, further validating the clinical application of the w1.6W lentiviral vector.

Reversible Reprogramming of Circulating Memory T Follicular Helper Cell Function during Chronic HIV Infection

Despite the overwhelming benefits of antiretroviral therapy (ART) in curtailing viral load in HIV-infected individuals, ART does not fully restore cellular and humoral immunity. HIV-infected individuals under ART show reduced responses to vaccination and infections and are unable to mount an effective antiviral immune response upon ART cessation. Many factors contribute to these defects, including persistent inflammation, especially in lymphoid tissues, where T follicular helper (Tfh) cells instruct and help B cells launch an effective humoral immune response. In this study we investigated the phenotype and function of circulating memory Tfh cells as a surrogate of Tfh cells in lymph nodes and found significant impairment of this cell population in chronically HIV-infected individuals, leading to reduced B cell responses. We further show that these aberrant memory Tfh cells exhibit an IL-2–responsive gene signature and are more polarized toward a Th1 phenotype. Treatment of functional memory Tfh cells with IL-2 was able to recapitulate the detrimental reprogramming. Importantly, this defect was reversible, as interfering with the IL-2 signaling pathway helped reverse the abnormal differentiation and improved Ab responses. Thus, reversible reprogramming of memory Tfh cells in HIV-infected individuals could be used to enhance Ab responses. Altered microenvironmental conditions in lymphoid tissues leading to altered Tfh cell differentiation could provide one explanation for the poor responsiveness of HIV-infected individuals to new Ags. This explanation has important implications for the development of therapeutic interventions to enhance HIV- and vaccine-mediated Ab responses in patients under ART.

A distinct subpopulation of CD25− T-follicular regulatory cells localizes in the germinal centers

Significance T-follicular regulatory (Tfr) cells, a subset of Foxp3-expressing regulatory T (Treg) cells, have a critical role in the control of antibody responses. Whereas Treg cells express CD25 and are dependent on IL-2, Tfr cells also express the transcription factor BCL6 that is inhibited by IL-2 in T-follicular helper (Tfh) cells. In this report, we find that mature Tfr cells in the germinal centers or circulating in human blood down-regulate CD25 and gain a transcriptional signature mixed between Tfh cells and Treg cells while retaining their regulatory function. These cells represent an IL-2–independent branch of effector Treg cells losing CD25 expression but gaining increased expression of Tfh-related markers, such as BCL6 and CXCR5, in both mice and humans. T-follicular helper (Tfh) cells differentiate through a multistep process, culminating in germinal center (GC) localized GC-Tfh cells that provide support to GC-B cells. T-follicular regulatory (Tfr) cells have critical roles in the control of Tfh cells and GC formation. Although Tfh-cell differentiation is inhibited by IL-2, regulatory T (Treg) cell differentiation and survival depend on it. Here, we describe a CD25− subpopulation within both murine and human PD1+CXCR5+Foxp3+ Tfr cells. It is preferentially located in the GC and can be clearly differentiated from CD25+ non–GC-Tfr, Tfh, and effector Treg (eTreg) cells by the expression of a wide range of molecules. In comparison to CD25+ Tfr and eTreg cells, CD25− Tfr cells partially down-regulate IL-2–dependent canonical Treg features, but retain suppressive function, while simultaneously up-regulating genes associated with Tfh and GC-Tfh cells. We suggest that, similar to Tfh cells, Tfr cells follow a differentiation pathway generating a mature GC-localized subpopulation, CD25− Tfr cells.

Dendritic cell functional improvement in a preclinical model of lentiviral-mediated gene therapy for Wiskott-Aldrich syndrome

Wiskott–Aldrich syndrome (WAS) is a rare X-linked primary immunodeficiency caused by the defective expression of the WAS protein (WASP) in hematopoietic cells. It has been shown that dendritic cells (DCs) are functionally impaired in WAS patients and was−/− mice. We have previously demonstrated the efficacy and safety of a murine model of WAS gene therapy (GT), using stem cells transduced with a lentiviral vector (LV). The aim of this study was to investigate whether GT can correct DC defects in was−/− mice. As DCs expressing WASP were detected in the secondary lymphoid organs of the treated mice, we tested the in vitro and in vivo function of bone marrow-derived DCs (BMDCs). The BMDCs showed efficient in vitro uptake of latex beads and Salmonella typhimurium. When BMDCs from the treated mice (GT BMDCs) and the was−/− mice were injected into wild-type hosts, we found a higher number of cells that had migrated to the draining lymph nodes compared with mice injected with was−/− BMDCs. Finally, we found that ovalbumin (OVA)-pulsed GT BMDCs or vaccination of GT mice with anti-DEC205 OVA fusion protein can efficiently induce antigen-specific T-cell activation in vivo. These findings show that WAS GT significantly improves DC function, thus adding new evidence of the preclinical efficacy of LV-mediated WAS GT.

Allergen-specific immunotherapy modulates the balance of circulating Tfh and Tfr cells

Abstract Follicular helper T cells (Tfh cells) are a CD4 T cell subset essential for germinal center formation and B cell responses, although their role in allergy and allergen-specific immunotherapy (AIT) is unclear. Here, we show that AIT-treated patients have a higher ratio of regulatory Tfh cells (Tfr) to follicular T cells (Tfh) and hypothesize an IL-2 dependent mechanism.

CRISPR-Mediated Slamf1Δ/Δ Slamf5Δ/Δ Slamf6Δ/Δ Triple Gene Disruption Reveals NKT Cell Defects but Not T Follicular Helper Cell Defects

SAP (SH2D1A) is required intrinsically in CD4 T cells to generate germinal center responses and long-term humoral immunity. SAP binds to SLAM family receptors, including SLAM, CD84, and Ly108 to enhance cytokine secretion and sustained T cell:B cell adhesion, which both improve T follicular helper (Tfh) cell aid to germinal center (GC) B cells. To understand the overlapping roles of multiple SLAM family receptors in germinal center responses, Slamf1Δ/Δ Slamf5Δ/Δ Slamf6Δ/Δ triple gene disruption (Slamf1,5,6Δ/Δ) mice were generated using CRISPR-Cas9 gene editing to eliminate expression of SLAM (CD150), CD84, and Ly108, respectively. Gene targeting was highly efficient, with 6 of 6 alleles disrupted in 14 of 23 pups and the majority of alleles disrupted in the remaining pups. NKT cell differentiation in Slamf1,5,6Δ/Δ mice was defective, but not completely absent. The remaining NKT cells exhibited substantially increased 2B4 (SLAMF4) expression. Surprisingly, there were no overt defects in germinal center responses to acute viral infections or protein immunizations in Slamf1,5,6Δ/Δ mice, unlike Sh2d1a-/- mice. Similarly, in the context of a competitive environment, SLAM family receptor expressing GC Tfh cell, GC B cell, and plasma cell responses exhibited no advantages over Slamf1,5,6Δ/Δ cells.