CoPoP liposomes displaying stabilized clade C HIV-1 Env elicit tier 2 multiclade neutralization in rabbits.

One of the strategies towards an effective HIV-1 vaccine is to elicit broadly neutralizing antibody responses that target the high HIV-1 Env diversity. Here, we present an HIV-1 vaccine candidate that consists of cobalt porphyrin-phospholipid (CoPoP) liposomes decorated with repaired and stabilized clade C HIV-1 Env trimers in a prefusion conformation. These particles exhibit high HIV-1 Env trimer decoration, serum stability and bind broadly neutralizing antibodies. Three sequential immunizations of female rabbits with CoPoP liposomes displaying a different clade C HIV-1 gp140 trimer at each dosing generate high HIV-1 Env-specific antibody responses. Additionally, serum neutralization is detectable against 18 of 20 multiclade tier 2 HIV-1 strains. Furthermore, the peak antibody titers induced by CoPoP liposomes can be recalled by subsequent heterologous immunization with Ad26-encoded membrane-bound stabilized Env antigens. Hence, a CoPoP liposome-based HIV-1 vaccine that can generate cross-clade neutralizing antibody immunity could potentially be a component of an efficacious HIV-1 vaccine.

Polymeric nanoparticle-based mRNA vaccine is protective against influenza virus infection in ferrets.

New therapies and vaccines based on nucleic acids combined with an efficient nanoparticle delivery vehicle have a broad applicability for different disease indications. An alternative delivery technology for the successfully applied lipid nanoparticles in mRNA SARS-CoV-2 vaccines are nanoparticles composed of biodegradable poly(amido)amine-based polymers with mRNA payload. To show that these polymeric nanoparticles can efficiently deliver influenza hemagglutinin mRNA to target tissues and elicit protective immune responses, a relevant ferret influenza challenge model was used. In this model, our nanoparticle-based vaccine elicited strong humoral and cellular immune responses in the absence of local and systemic reactogenicity. Upon virus challenge, vaccinated animals exhibited reduced clinical signs and virus load relative to unvaccinated control animals. Based on these findings, further investigation of the polymeric nanoparticles in the context of prophylactic vaccination is warranted. Future studies will focus on optimizing the payload, the nanoparticle stability, the efficacy in the context of pre-existing immunity, and the applicability of the technology to prevent other infectious diseases.

Ad26 vector-based COVID-19 vaccine encoding a prefusion-stabilized SARS-CoV-2 Spike immunogen induces potent humoral and cellular immune responses.

Development of effective preventative interventions against SARS-CoV-2, the etiologic agent of COVID-19 is urgently needed. The viral surface spike (S) protein of SARS-CoV-2 is a key target for prophylactic measures as it is critical for the viral replication cycle and the primary target of neutralizing antibodies. We evaluated design elements previously shown for other coronavirus S protein-based vaccines to be successful, e.g., prefusion-stabilizing substitutions and heterologous signal peptides, for selection of a S-based SARS-CoV-2 vaccine candidate. In vitro characterization demonstrated that the introduction of stabilizing substitutions (i.e., furin cleavage site mutations and two consecutive prolines in the hinge region of S2) increased the ratio of neutralizing versus non-neutralizing antibody binding, suggestive for a prefusion conformation of the S protein. Furthermore, the wild-type signal peptide was best suited for the correct cleavage needed for a natively folded protein. These observations translated into superior immunogenicity in mice where the Ad26 vector encoding for a membrane-bound stabilized S protein with a wild-type signal peptide elicited potent neutralizing humoral immunity and cellular immunity that was polarized towards Th1 IFN-γ. This optimized Ad26 vector-based vaccine for SARS-CoV-2, termed Ad26.COV2.S, is currently being evaluated in a phase I clinical trial (ClinicalTrials.gov Identifier: NCT04436276).

CCL22 Prevents Rejection of Mouse Islet Allografts and Induces Donor-Specific Tolerance.

Manipulation of regulatory T cell (Treg) migration by islet expression of the chemokine CCL22 prevents diabetes in NOD mice and delays recurrent autoimmunity in syngeneic islet transplants. We sought to determine whether attracting Tregs with CCL22 also prevents islet allograft rejection. Isolated Bl/6 mouse islets were transduced overnight with adenovirus expressing CCL22 (Ad-CCL22) downstream of the CMV promoter. Islets were transplanted under the renal capsule of Balb/c recipients made diabetic by streptozotocin. To assess immunologic tolerance, graft-bearing kidneys from recipients of CCL22-expressing islet grafts were removed, and mice received a second transplant of naive islets from the same donor strain or third-party islets into the contralateral kidney. Adenoviral expression of CCL22 conferred prolonged protection of islet allografts in MHC-mismatched, diabetic recipients, maintaining normoglycemia in 75% of recipients for at least 80 days. Increased frequency of Treg cells was observed in islet grafts transduced with Ad-CCL22 compared with untreated grafts. Normoglycemic recipients of CCL22-expressing islet grafts showed complete absence of antidonor antibodies and no lymphocyte proliferation after exposure to donor splenocytes. After removal of the primary graft at day 80, mice that received a second transplant with untreated islets from the same donor strain did not reject the grafts, suggesting the development of tolerance. Expression of CCL22 recruits Treg cells to transplanted islets, prevents activation of alloreactive T-cells and islet allograft failure and induces alloantigen-specific tolerance. Manipulation of Treg cells by CCL22 in transplanted islets may be a novel therapeutic strategy for diabetes.

Toll-like receptor 5 deficiency protects from wasting disease in a T cell transfer colitis model in T cell receptor-ß-deficient mice.

BACKGROUND: Toll-like receptor 5 (TLR5) is implicated in the innate and adaptive immune responses that are associated with inflammatory bowel disease (IBD). In humans TLR5 is expressed on CD4(+) T cells and costimulation with flagellin potentiates effector and regulatory T cell responses. The aim of this study was to determine the role of TLR5 in CD4(+) T cell subsets versus other cells in induction of disease in a model of T cell-dependent colitis. METHODS: TLR5 expression on CD4(+) T cells was assessed by real-time reverse-transcriptase polymerase chain reaction (RT-PCR). Wildtype (WT) or TLR5-deficient (5-/-) CD4(+) T conventional cells (Tconv) and T regulatory cells (Treg) were compared for their ability to induce and suppress T cell transfer colitis, respectively. In addition, the role of TLR5 expression in recipient mice was analyzed. RESULTS: TLR5 is preferentially expressed on mouse Treg compared to Tconv, although expression levels were low. The colitogenic capacity of WT and 5-/- Tconv was found to be similar and Treg from WT or 5-/- donor animals both prevented T cell transfer colitis in TLR-competent hosts. TLR5 deficiency in recipient mice, however, did affect the disease process, as T cell receptor-ß (TCRß) 5-/- recipients had decreased weight loss compared to TCRß recipient mice when WT Tconv were used. CONCLUSIONS: TLR5 expression on T cells is not required for induction of or protection from T cell-dependent colitis. Expression of TLR5 in non-T cells has a pathogenic role, since TLR5 deficiency in recipient mice protects against weight loss induced by WT T cells.

Prevention of murine autoimmune diabetes by CCL22-mediated Treg recruitment to the pancreatic islets.

Type 1 diabetes is characterized by destruction of insulin-producing ß cells in the pancreatic islets by effector T cells. Tregs, defined by the markers CD4 and FoxP3, regulate immune responses by suppressing effector T cells and are recruited to sites of action by the chemokine CCL22. Here, we demonstrate that production of CCL22 in islets after intrapancreatic duct injection of double-stranded adeno-associated virus encoding CCL22 recruits endogenous Tregs to the islets and confers long-term protection from autoimmune diabetes in NOD mice. In addition, adenoviral expression of CCL22 in syngeneic islet transplants in diabetic NOD recipients prevented ß cell destruction by autoreactive T cells and thereby delayed recurrence of diabetes. CCL22 expression increased the frequency of Tregs, produced higher levels of TGF-ß in the CD4+ T cell population near islets, and decreased the frequency of circulating autoreactive CD8+ T cells and CD8+ IFN-γ­producing T cells. The protective effect of CCL22 was abrogated by depletion of Tregs with a CD25-specific antibody. Our results indicate that islet expression of CCL22 recruits Tregs and attenuates autoimmune destruction of ß cells. CCL22-mediated recruitment of Tregs to islets may be a novel therapeutic strategy for type 1 diabetes.

Environmental influences on T regulatory cells in inflammatory bowel disease.

Inflammatory bowel disease (IBD) is characterized by chronic, idiopathic inflammation of the intestine. The disease is thought to result from a combination of genetic and environmental factors which ultimately leads to a mucosal immune system that overreacts to normal constituents of the mucosal microbiota. The inflammation in IBD is primarily mediated by inappropriate production of proinflammatory cytokines by CD4(+) T effector cells, effects that are suppressed by CD4(+) T regulatory cells. Defects in both the function of T regulatory cells, and the ability of T effector cells to be suppressed, have been implicated in IBD. In this review we will discuss environmental factors, including cytokines, vitamins A and D, and commensal bacteria, which influence the phenotype and function of regulatory T cells and thereby alter the course of IBD. We will also discuss how these environmental signals can be manipulated therapeutically in order to improve the function of regulatory T cells and ultimately restore mucosal homeostasis in patients with IBD.

TLR5 is not required for flagellin-mediated exacerbation of DSS colitis.

BACKGROUND: The two forms of human inflammatory bowel disease, Crohn's disease (CD) and ulcerative colitis (UC), are both associated with loss of tolerance to gut microbial antigens. The dominant antigen recognized by antibody and T-cell responses in patients with CD is bacterial flagellin. Flagellin is also the only known ligand for Toll-like receptor 5 (TLR5), a key protein in innate immunity. Although flagellin activates TLR5 to produce inflammatory responses in many cell types in the gut, there is conflicting evidence as to whether TLR5 is harmful or protective in CD and murine colitis models. A recent study found that administration of flagellin enemas to mice along with dextran sodium sulfate (DSS) made their colitis worse. METHODS: We sought to determine whether this exacerbation was due to TLR5 ligation, or to TLR5-independent adaptive immune responses to flagellin as an antigen, by using a transposon insertional mutant of the Escherichia coli H18 flagellin, 2H3, which lacks TLR5 stimulatory activity. RESULTS: We found that flagellin enemas produced only a mild exacerbation of DSS colitis, and that 2H3 was equivalent to or worse than wildtype flagellin. Moreover, we found that DSS colitis was more severe in TLR5(-/-) mice than wildtype C57BL/6 mice. CONCLUSIONS: Together, these results suggest that flagellin-mediated exacerbation of colitis is independent of TLR5.

The proteoglycan (heparan sulfate proteoglycan) binding domain of APRIL serves as a platform for ligand multimerization and cross-linking.

A proliferation-inducing ligand (APRIL) (also known as TALL-2 and TRDL-1) is a member of the tumor necrosis factor (TNF) superfamily that has tumorigenic properties but is also important for the induction of humoral immune responses. APRIL binds two TNF receptors: transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI) and B-cell maturation antigen (BCMA) as well as heparan sulfate proteoglycans (HSPGs). The aim of this study was to clarify the role of the HSPG interaction in canonical APRIL signaling, because it has been proposed to act as a docking site and also to play a role in direct signaling. In this study, we generated point mutants of soluble APRIL that lack either the capacity to bind HSPGs or TACI and BCMA and then tested the function of these mutants in mouse B-cell assays. In contrast to previous reports, we found that APRIL alone is sufficient to costimulate B-cell proliferation and drive IgA production and does not require artificial antibody cross-linking. We found no evidence that APRIL requires signaling through HSPGs but, notably, were able to show that binding of APRIL to HSPGs is crucial for mediating natural APRIL cross-linking to allow for optimal activation of murine B cells.

The expanding role of APRIL in cancer and immunity.

Proteins of the tumour necrosis factor (TNF) family are implicated in the regulation of essential cell processes such as proliferation, differentiation, survival and cell death. Altered expression of TNF family members is often associated with pathological conditions such as autoimmune disease and cancer. The TNF-like ligand APRIL (A PRoliferation Inducing Ligand), first described in 1998, was named for its capacity to stimulate tumour cell proliferation in vitro. APRIL expression was initially reported in haematopoietic cells in physiological conditions, and it is overexpressed in certain tumour tissues. APRIL is now known to be involved in activation and immune responses of B cells, as well as in B cell malignancies. This review focuses on recent advances in understanding APRIL and its receptors in physiology and tumour pathology, including the accumulating evidence that specific Toll-like receptor ligands can trigger APRIL-mediated responses, and the identification of new sources of APRIL such as epithelial cells and tumour-infiltrating neutrophils.

The role of T-regulatory cells and Toll-like receptors in the pathogenesis of human inflammatory bowel disease.

Two related chronic inflammatory diseases, Crohn's disease and ulcerative colitis, are together often referred to as inflammatory bowel disease (IBD). Current treatment options are not curative, and patients face lifelong therapy and debilitation. IBD is thought to be the product of a combination of genetic and environmental factors that result in the abnormal regulation of immune responses. Experimental models have demonstrated that normal CD4+ T-regulatory (Treg) cell responses and commensal bacteria are required for the maintenance of gut immune homeostasis. Recent evidence that CD4+ T cells express Toll-like receptors (TLRs) and respond directly to TLR ligands, suggests that signals from commensal bacteria may directly affect T-cell responses in the gut. In this review, we focus on evidence that defects in Treg cells may underlie IBD in humans. In addition, we discuss evidence that direct signaling via TLRs to T cells can affect IBD and that T-cell-dependent responses to bacterial proteins, such as flagellin, are central to the aetiology of this disease.

APRIL facilitates viral-induced erythroleukemia but is dispensable for T cell immunity and lymphomagenesis.

The TNF family member, a proliferation-inducing ligand (APRIL), has been suggested to act as a costimulatory molecule in T cell responses. However, studies addressing this role in vivo are largely lacking. Here, we evaluated the effects of APRIL on physiological T cell responses in vivo. Although receptors for APRIL are expressed on a subset of T cells, neither TCR transgenic (Tg) T cell responses nor endogenous TCR responses were affected by Tg APRIL expression in vivo. Moreover, APRIL did not significantly enhance the induction of T cell lymphomas upon Moloney murine leukemia virus (MLV) infection. This clearly contrasts current belief and indicates that APRIL does not serve a major role in T cell immunity or lymphomagenesis. However, we did observe a strong increase in erythroleukemia formation after MLV inoculation of APRIL Tg mice. Strikingly, this erythroleukemia-facilitating property of APRIL was confirmed using the erythroleukemogenic Friend-MLV. Erythroleukemia in APRIL Tg mice was characterized by low hematocrits and grossly enlarged spleens with an increased percentage of erythroid precursors. Altogether, these results unveil new proerythroleukemogenic properties of APRIL.

APRIL affects antibody responses and early leukocyte infiltration, but not influenza A viral control.

A proliferation inducing ligand (APRIL) is implicated in the regulation of class switch recombination to IgA in T-independent B cell responses. Since B cells play an important role in the immunity to influenza A virus and resistance against the virus is partly controlled by T-independent IgA B cell responses, we studied the role of APRIL during an influenza A infection in vivo. APRIL transgenic, wild-type and APRIL deficient mice were intranasally infected with a non-lethal dose of a mouse adapted strain of influenza A. Compared to wild-type mice, APRIL deficient mice showed a twofold reduction in the amount of macrophages in the lungs and a tendency towards decreased granulocyte influx in the early leukocyte recruitment phase. Although the T cell immune response against influenza was unaffected, APRIL Tg mice showed prolonged influenza-specific IgM production and differential class switching. Unexpectedly, the IgA B cell response was completely T helper cell dependent and also not affected by the absence or presence of APRIL. In addition, viral clearance and recovery from the infection was not influenced by APRIL. Combined these results indicate that APRIL affects specific aspects of the anti-influenza response, but plays a limited role in disease recovery.

Thymus-independent class switch recombination is affected by APRIL.

The tumour necrosis factor (TNF) family member a proliferation-inducing ligand (APRIL) is implicated in various B-cell processes, such as class switch recombination, plasma cell differentiation and plasma cell survival. This was suggested from initial studies analysing B-cell responses in APRIL-deficient and transgenic mice, and mice deficient for the TNF receptors of APRIL, transmembrane activator and CAML interactor (TACI) and B-cell maturation antigen. Here, we present additional evidence for the importance of APRIL in thymus-independent (TI) B-cell responses, using APRIL-deficient and transgenic mice. APRIL-deficient mice show an impaired immunoglobulin A (IgA) response towards TI B-cell antigens, whereas APRIL transgenic mice show exaggerated TI B-cell responses. Moreover, antibody titres to TI antigens were sustained in APRIL transgenic mice for a long time and even increased up to 75 days in the case of IgA against 4-hydroxy-nitrophenacetyl-lipopolysaccharide.

Specific TLR ligands regulate APRIL secretion by dendritic cells in a PKR-dependent manner.

A proliferation inducing ligand (APRIL) and B cell activating factor belonging to the TNF family (BAFF/BLyS) have been implicated in IgA class switch recombination in thymus-independent (TI) B cell responses. Dendritic cells (DC) are thought to regulate Ig class switching in TI B cell responses by providing B cells with cytokines, including APRIL and BAFF. We therefore set out to analyze the regulation of APRIL and BAFF expression by human monocyte-derived DC (moDC). We observed that moDC produce and secrete APRIL, but could not detect expression of BAFF. Importantly, stimulation with the Toll-like receptor ligands CpG and poly I:C specifically induced APRIL production, while other Toll-like receptor ligands were ineffective. The increase in APRIL was dependent on translation, but surprisingly not transcription. Instead, enhanced APRIL production and secretion resulted from activation of protein kinase receptor (PKR), as it was completely inhibited by the specific inhibitor of PKR, 2-aminopurine. This suggests that the specific induction of APRIL by CpG and poly I:C, and the signal integration by PKR, are regulated by translational modification and hint at a role for APRIL in the TI B cell response to viral infections.

APRIL promotes B-1 cell-associated neoplasm.

A tumor-supporting role for the TNF-like ligand APRIL has been suggested. Here we describe that 9- to 12-month-old APRIL transgenic mice develop lymphoid tumors that originate from expansion of the peritoneal B-1 B cell population. Aging APRIL transgenic mice develop progressive hyperplasia in mesenteric lymph nodes and Peyer's patches, disorganization of affected lymphoid tissues, mucosal and capsular infiltration, and eventual tumor cell infiltration into nonlymphoid tissues such as kidney and liver. We detected significantly increased APRIL levels in sera of B cell chronic lymphoid leukemia (B-CLL) patients, indicating that APRIL promotes onset of B-1-associated neoplasms and that APRIL antagonism may provide a therapeutic strategy to treat B-CLL patients.

Dynamic programming of CD8+ T lymphocyte responses.

The initial encounter with an antigen-presenting cell (APC) is the primary force behind the expansion, differentiation and survival of naive T cells. Using an APC that permits temporal control of priming, we examined whether the duration of antigenic stimulation can influence the functional development of CD8+ cytotoxic T lymphocytes (CTLs) in vivo. Whereas CTLs given a 4-h stimulus underwent an abortive clonal expansion with transient surface CD25 expression, those given a 20-h stimulus sustained CD25 up-regulation, proliferated extensively, and efficiently mediated destruction of peripheral target tissues. Our results show that an instructional program preceding the first cell division integrates differences in signal strength into the decision to activate versus tolerize specific CTL clones.