Localization dose and time of antigens determine immune reactivity

DermaVir: a plasmid DNA-based nanomedicine therapeutic vaccine for the treatment of HIV/AIDS

The HIV global pandemic continues to rage with over 33 million people living with the disease. Although multidrug therapy has improved the prognosis for those infected by the virus, it has not eradicated the infection. Immunological therapies, including therapeutic vaccines, are needed to supplement drug therapy in the search for a 'functional cure' for HIV. DermaVir (Genetic Immunity Kft, Budapest, Hungary and McLean, Virginia, USA), an experimental HIV/AIDS therapeutic vaccine, combines three key elements of rational therapeutic vaccine design: a single plasmid DNA (pDNA) immunogen expressing 15 HIV antigens, a synthetic pDNA nanomedicine formulation and a dendritic cell-targeting topical-vaccine administration. DermaVir's novel mechanism of action, natural transport by epidermal Langerhans cells to the lymph nodes to express the pDNA-encoded HIV antigens and induce precursor/memory T cells with high proliferation capacity, has been consistently demonstrated in mouse, rabbit, primate and human subjects. Safety, immunogenicity and preliminary efficacy of DermaVir have been clinically demonstrated in HIV-infected human subjects. The DermaVir technology platform for dendritic cell-based therapeutic vaccination might offer a new treatment paradigm for cancer and infectious diseases.

Innate defense regulator peptide synergizes with CpG ODN for enhanced innate intestinal immune responses in neonate piglets

The in vivo immunoadjuvant effects of the combination of CpG oligodeoxynucleotide (CpG ODN) and innate defense-regulator peptides (IDRs) have been studied in mice. However, little is known about the efficacy of these molecules in stimulating the innate intestinal immune system in neonatal piglets. In this study, we observed that intranasal (IN) administration of CpG-IDR (peptide HH2 (VQLRIRVAVIRA)) complex significantly increased intestinal mRNA expression of Th1 cytokines, CC chemokines and CXC chemokines when compared to HH2 and CpG ODN alone. Also an obvious cellular infiltration was observed in the intestine of CpG-HH2-treated neonatal piglets, which was associated with increased protection against Enterotoxigenic Escherichia coli (ETEC). Moreover, we showed that pro-inflammatory cytokine TNF-α was inhibited when CpG ODN combined with HH2. This was the first report that deciphered the role played by CpG-HH2 complex in the intestine of neonatal piglets. This work clearly demonstrated that efficiency of the IN route inducing intestinal responses in neonatal piglets might be taken into consideration for further vaccine development against neonatal intestinal diseases.

Enforced viral replication activates adaptive immunity and is essential for the control of a cytopathic virus

The innate immune system limits viral replication via type I interferon and also induces the presentation of viral antigens to cells of the adaptive immune response. Using infection of mice with vesicular stomatitis virus, we analyzed how the innate immune system inhibits viral propagation but still allows the presentation of antigen to cells of the adaptive immune response. We found that expression of the gene encoding the inhibitory protein Usp18 in metallophilic macrophages led to lower type I interferon responsiveness, thereby allowing locally restricted replication of virus. This was essential for the induction of adaptive antiviral immune responses and, therefore, for preventing the fatal outcome of infection. In conclusion, we found that enforced viral replication in marginal zone macrophages was an immunological mechanism that ensured the production of sufficient antigen for effective activation of the adaptive immune response.

Split immunity: immune inhibition of rat gliomas by subcutaneous exposure to unmodified live tumor cells

Gliomas that grow uninhibited in the brain almost never metastasize outside the CNS. The rare occurrences of extracranial metastasis are usually associated with a suppressed immune system. This observation raises the possibility that some gliomas might not grow outside the CNS due to an inherent immune response, We report in this study that the highly malignant F98 Fischer rat undifferentiated glioma, which grows aggressively in the brain, spontaneously regresses when injected live s.c. We found that this regression is immune-mediated and that it markedly enhances the survival or cures rats challenged with the same tumor intracranially either before or after the s.c. live-cell treatment. Adoptive transfer experiments showed the effect was immune-mediated and that the CD8 T cell fraction, which exhibited direct tumor cytotoxicity, was more effective than the CD4 T cell fraction in mediating resistance to intracranial challenge of naive rats. Brain tumors from treated rats exhibited enhanced CD3(+)CD8(+)CD4(-) and CD3(+)CD4(+)CD8(-) T cell infiltration and IFN-γ secretion. The results in the F98 glioma were corroborated in the Lewis rat CNS-1 astrocytoma. In both tumor models, s.c. treatment with live cells was significantly better than immunization with irradiated cells. We propose in this study a location-based immunotherapeutic phenomenon we term "split immunity": a tumor that thrives in an immune-privileged site may be inhibited by injecting live, unmodified tumor cells into a site that is not privileged, generating protective immunity that spreads back to the privileged site. Split immunity could explain several long-standing paradoxes regarding the lack of overt extracranial metastasis in patients with primary brain tumors.

Vaccine adjuvants - Current status and prospects on controlled release adjuvancity

The strategy of World Health Organization is to develop efficient and inexpensive vaccine against various infectious diseases amongst children's population. Vaccination is considered as the most cost effective health intervention known to public. Since 90 years various substances have been added in vaccine formulation but still alum is considered as the safest adjuvant for human use licensed by United States Food and Drug Administration. MF 59 and ASO4 are the adjuvants were developed recently and approved for human use. Due to poor adjuvancity, conventional vaccines require multiple recall injection at approximately time intervals to attain optimal immune response. For past approximately two decades the vaccine research has been focused towards the alternation of alum type of adjuvant in order to increase the immunogenicity. The development of new vaccines, is more efficacious or easier to deliver, or both have become an area of research that can certainly benefit from controlled release technology. Especially, the conversion of multiple administration vaccine into single administration vaccine may represent an improved advancement towards the betterment of human health care and welfare. Biodegradable polymer microparticles have been evaluated for delivering antigens in native form, sustained release keeping in mind the safety aspects. In this article we review the overall concept of adjuvants in vaccine technology with special focus towards the prospects of controlled release antigens.

Sequential administration of bovine and human adenovirus vectors to overcome vector immunity in an immunocompetent mouse model of breast cancer

The potential of a bovine adenovirus serotype 3 (BAd3)-based vector to bypass the human adenoviral serotype 5 (HAd5)-specific neutralizing immune response was evaluated in an immunocompetent mouse model of breast cancer. Initially we monitored vector biodistribution, genome persistence, transgene expression, and potential toxicity of HAd-GFP [HAd5 vector expressing green fluorescent protein (GFP)] or BAd-GFP (BAd3 vector expressing GFP) in FVB/n mice bearing tumors. A comparable biodistribution pattern for BAd-GFP and HAd-GFP was evident. In addition, following the development of vector-specific immune responses, animals were inoculated intratumorally (i.t.) with HAd-GFP or BAd-GFP. HAd-GFP immunity did not hamper the transduction and persistence of BAd-GFP into the tumors and other organs, and, similarly, BAd-GFP immunity did not hamper the transduction and persistence of HAd-GFP. Both BAd3 and HAd5 vectors showed relatively higher transgene expression in the presence of heterologous vector immunity. In contrast, the homologous vector immunity was associated with a rapid vector clearance and decline in transgene expression levels. Histopathological changes in BAd-GFP inoculated animals were generally mild with some acute but recoverable hepatic perturbations. Overall, the data suggest the importance of BAd3 vectors for sequential vector administration in overcoming the vector immunity for cancer gene therapy.

Topical and mucosal liposomes for vaccine delivery

Mucosal (and in minor extent transcutanous) stimulation can induce local or distant mucosa secretory IgA. Liposomes and other vesicles as mucosal and transcutaneous adjuvants are attractive alternatives to parenteral vaccination. Liposomes can be massively produced under good manufacturing practices and stored for long periods, at high antigen/vesicle mass ratios. However, their uptake by antigen-presenting cells (APC) at the inductive sites remains as a major challenge. As neurotoxicity is a major concern in intranasal delivery, complexes between archaeosomes and calcium as well as cationic liposomes complexed with plasmids encoding for antigenic proteins could safely elicit secretory and systemic antigen-specific immune responses. Oral bilosomes generate intense immune responses that remain to be tested against challenge, but the admixing with toxins or derivatives is mandatory to reduce the amount of antigen. Most of the current experimental designs, however, underestimate the mucus blanket 100- to 1000-fold thicker than a 100-nm diameter liposome, which has first to be penetrated to access the underlying M cells. Overall, designing mucoadhesive chemoenzymatic resistant liposomes, or selectively targeted to M cells, has produced less relevant results than tailoring the liposomes to make them mucus penetrating. Opposing, the nearly 10 µm thickness stratum corneum interposed between liposomes and underlying APC can be surpassed by ultradeformable liposomes (UDL), with lipid matrices that penetrate up to the limit with the viable epidermis. UDL made of phospholipids and detergents, proved to be better transfection agents than conventional liposomes and niosomes, without the toxicity of ethosomes, in the absence of classical immunomodulators.

CpG oligodeoxynucleotide synergizes innate defense regulator peptide for enhancing the systemic and mucosal immune responses to pseudorabies attenuated virus vaccine in piglets in vivo

Oligonucleotides containing CpG motifs (CpG ODN) are strong adjuvants for humoral and cellular immune responses in mice, and innate defense-regulator peptides (IDRs) are known to facilitate the uptake of antigens into antigen presenting cells (APCs), but data on synergistic effects of CpG and IDRs in piglets are scarce. In this report, the combination of porcine-specific CpG ODN and HH2 (a kind of IDR which was selected for its better synergy with CpG ODN) was used as immunoadjuvant to enhance the immune responses of the newborn piglets to Pseudorabies attenuated virus (PRV) vaccine. The titers of specific antibodies and serum IgG1/IgG2 subtypes to PRV vaccine, interferon-γ (IFN-γ), tumor necrosis factor-α (TNF-α), IL-12 and IL-4 were examined to identify the immune responses of the newborn piglets. The results showed that piglets immunized intranasally (IN) and subcutaneously (SC) with PRV vaccine and CpG-HH2 complex both presented high titers of PRV-specific antibodies and IgG2 isotype, a Th1-dominated (IFN-γ and IL-12) cytokine profiles, high levels of IgA in saliva, broncheoalveolar lavage (BAL) and intestinal washings. The results suggested that, CpG-HH2 complex augmented systemic (IgG in serum) and mucosal (IgA in saliva, BAL and intestinal washings) immune responses against antigen. CpG-HH2 complex stimulated both T-helper type1 (Th1) (IgG2) and Th2 (IgA) responses when delivered IN, and IN route could induce stronger mucosal immune responses than SC route. All these data indicate that CpG-HH2 complex is a potential effective adjuvant for the PRV vaccine in newborn piglets.

Intralymphatic immunotherapy: from the rationale to human applications

Allergen specific immunotherapy (SIT) is the only treatment of IgE mediated allergies that is causative and has a long-term effect. Classically, SIT requires numerous subcutaneous injections of the allergen during 3-5 years. Over the last decade sublingual allergen applications have established as an alternative, but treatment duration could not be shortened. This review focuses on direct administration of vaccines in general and of allergens in particular into lymph nodes with the aim to enhance immunotherapy. Several studies have found that direct injection of antigens into lymph nodes enhanced immune responses. Recently we have focused on intralymphatic allergen administration in order to enhance SIT. Data in mouse models and in clinical trials showed that intralymphatic allergen administration strongly enhanced SIT, so that the number of allergen injections could be reduced to three, and the allergen dose could be reduced 10-100 fold. Intralymphatic injections proved easy, practically painless and safe. In mice and men, intralymphatic immunotherapy injecting allergens into a subcutaneous lymph node markedly enhances the protective immune response, so that both the dose and number of allergen injections can be reduced, making SIT safer and faster, which enhances patient convenience and compliance.

Mucosal vaccination using claudin-4-targeting

Mucosa-associated lymphoid tissue (MALT) plays pivotal roles in mucosal immune responses. Efficient delivery of antigens to MALT is a critical issue for the development of mucosal vaccines. Although claudin-4 is preferentially expressed in MALT in the gut, a claudin-4-targeting approach for mucosal vaccination has never been developed. In the present study, we found that claudin-4 is expressed in nasal MALT, and we prepared a fusion protein of ovalbumin (OVA) as a model antigen with a claudin-4-binder, the C-terminal fragment of Clostridium perfringens enterotoxin (C-CPE) (OVA-C-CPE). Nasal immunization with OVA-C-CPE, but not a mixture of OVA and C-CPE, induced the production of OVA-specific serum IgG and nasal, vaginal and fecal IgA. Deletion of the claudin-4-binding region in OVA-C-CPE attenuated the induction of the immune responses. OVA-C-CPE immunization activated both Th1 and Th2 responses, and nasal immunization with OVA-C-CPE showed anti-tumor activity in mice inoculated with OVA-expressing thymoma cells. These results indicate that the claudin-4-targeting may be a potent strategy for nasal vaccination.

Synthetic innate defence regulator peptide enhances in vivo immunostimulatory effects of CpG-ODN in newborn piglets

The in vivo immunoadjuvant effects of CpG oligodeoxynucleotides (CpG-ODN) have been studied extensively in mice and relatively fewer studies have been done in piglets. But so far, the innate immunostimulatory effects of CpG-ODN combination with innate defense-regulator peptides (IDRs) have not been demonstrated. The purpose of this study is to determine the potential effects of CpG-ODN with IDR in newborn piglets. The immunostimulatory abilities of four selected IDRs were compared, among them HH2 showed best immunostimulatory effects in newborn piglets. Hereafter, the abilities of CpG-ODN combined with HH2 to enhance innate immune responses were examined in newborn piglets. The complex of HH2 and CpG-ODN could induce much stronger Th1 cytokine and chemokine responses than HH2 or CpG-ODN alone. HH2-CpG-ODN immunized piglets showed higher B cell percentage in PBMCs than CpG-ODN alone. These in vivo data demonstrated for the first time that subcutaneously (SC) administration of CpG-ODN combined with HH2 is efficient to stimulate innate immune system in newborn piglets.

Cell density plays a critical role in ex vivo expansion of T cells for adoptive immunotherapy

The successful ex vivo expansion of a large numbers of T cells is a prerequisite for adoptive immunotherapy. In this study, we found that cell density had important effects on the process of expansion of T cells in vitro. Resting T cells were activated to expand at high cell density but failed to be activated at low cell density. Activated T cells (ATCs) expanded rapidly at high cell density but underwent apoptosis at low cell density. Our studies indicated that low-cell-density related ATC death is mediated by oxidative stress. Antioxidants N-acetylcysteine, catalase, and albumin suppressed elevated reactive oxygen species (ROS) levels in low-density cultures and protected ATCs from apoptosis. The viability of ATCs at low density was preserved by conditioned medium from high-density cultures of ATCs in which the autocrine survival factor was identified as catalase. We also found that costimulatory signal CD28 increases T cell activation at lower cell density, paralleled by an increase in catalase secretion. Our findings highlight the importance of cell density in T cell activation, proliferation, survival and apoptosis and support the importance of maintaining T cells at high density for their successful expansion in vitro.

Intralymphatic immunotherapy

PURPOSE OF REVIEW

IgE-mediated allergy can be treated by subcutaneous allergen-specific immunotherapy (SCIT). However, the percentage of allergic patients undergoing SCIT is low, mainly due to the long duration of the therapy and the risk of severe systemic allergic reactions associated with the allergen administration. Typically, SCIT requires dozens of subcutaneous allergen injections that stretch over 3-5 years. Over the last decade, sublingual immunotherapy has been established as an alternative to SCIT, but treatment duration and dosing frequencies could not be reduced. Recently, immunotherapy by direct administration of the allergen into lymph nodes [intralymphatic immunotherapy (ILIT)] has proven a promising alternative and this method is the focus of the present review.

RECENT FINDINGS

Several studies on animals and on humans have shown that direct injection into lymph nodes enhanced immune responses to protein, peptide, and naked DNA vaccines. Moreover, ILIT strongly improved allergen immunotherapy, so that the number of allergen administrations as well as the allergen dose could be reduced. As ILIT was also well tolerated, practically painless, and easy to perform, patient compliance was improved as compared with SCIT.

SUMMARY

Direct ILIT into a subcutaneous lymph node markedly enhances protective immune responses, so that both the dose and the number of allergen injections can be reduced, making ILIT safer and faster than other forms of immunotherapy, and most importantly, this enhances patient convenience and compliance.

Modular antigen-translocation as a novel vaccine strategy for allergen-specific immunotherapy

PURPOSE OF REVIEW

The purpose of the present review is to describe recent approaches aimed at improving the treatment of allergic diseases through allergen-specific immunotherapy (SIT). Special emphasis will be given to the approach based on specific targeting of the major histocompatibility complex (MHC) class-II antigen-presentation pathway.

RECENT FINDINGS

It is well recognized that IgE-mediated allergic diseases including rhinitis, atopic eczema and allergic asthma are increasing worldwide to a pandemic dimension. The only curative treatment remains allergen-SIT, which, however, requires a long treatment time of 3-5 years with up to 80 injections to confer protection. Recent findings strongly indicate that the treatment time and the number of injections could be drastically reduced by turning immunotherapy to a true vaccination. Direct injection of allergen extracts into the inguinal lymph nodes and targeting the MHC class-II antigen-presentation pathway by recombinant modular antigen-translocating vaccines have the potential to cure allergic diseases in a very short time.

SUMMARY

The mechanisms of allergic inflammation can be divided into four distinct stages: T cell activation, organ-selective homing, survival/reactivation and effector functions. On the basis of this new knowledge several novel concepts aimed at treating allergic diseases have been developed. The area of allergen-SIT is experiencing exciting developments. Reciprocal regulation of effector and regulatory T cell subsets is being more and more used to develop novel strategies for immunomodulation.

Nanogram doses of alum-adjuvanted HBs antigen induce humoral immune response in mice when orally administered

Mucosal immunity elicited by plant-based and other orally administered vaccines can serve as the first line of defense against most pathogens infecting through mucosal surfaces, but it is also considered for systemic immunity against blood-borne diseases such as hepatitis B (HB). Previous oral immunization trials based on multiple administration of high doses of HBs antigen elicited an immune response; however, a reproducible and long-lasting immunization protocol was difficult to design. The objective of this study was to evaluate the effect of dose and timing of orally delivered alum-adsorbed antigen on the magnitude of the anti-HBs humoral response. Mice were immunized orally by gavage intubation or parenterally by intramuscular injection three times, once every 2 weeks, with doses of 5, 50, or 500 ng alum-adjuvanted HBsAg. A low dose (10 ng) of HBsAg was orally administered three times in different time intervals: 2, 4, 6, and 8 weeks. The three consecutive 5-ng oral doses of the antigen induced immune response at the protective level (>or=10 mIU/ml), significantly higher than the reaction elicited by three 50 or 500 ng doses. In contrast, intramuscular delivery of these doses did not differ significantly; however, they induced a five to six times higher immune response than oral immunization. The 8-week period between each of the three oral immunizations appeared to be favorable to the anti-HBs humoral responses compared with the shorter schedules. The results presented here clearly identify the importance of low doses of antigen administered orally in extended intervals for a significantly higher anti-HBs response. This finding provides some indications concerning the strategy of orally administered vaccines, including plant-based ones.

DNA vaccines for autoimmune diseases

Autoimmune diseases represent a group of disorders in which there exists a large unmet medical need for effective treatments, but also where there exists a tremendous responsibility among physicians and drug developers to maintain adequate and acceptable patient safety. Several drugs have been approved and many others are about to be approved for the treatment of autoimmune diseases, but in pushing the envelope of therapeutic efficacy, concerns have been raised about the long-term safety of these new therapies. DNA vaccines provide a method of treating autoimmune diseases in a highly specific manner, and could therefore overcome these safety concerns while still maintaining comparable efficacy. The numerous reports of DNA vaccines in animal models of autoimmune diseases and results from three recent human trials of DNA vaccines in autoimmune diseases are reviewed here.

Recent development in carbohydrate-based cancer vaccines

Tumor-associated carbohydrate antigens (TACAs) are important molecular markers on the cancer cell surface, useful for the development of therapeutic cancer vaccines or cancer immunotherapies. However, because of their poor immunogenicity and/or immunotolerance, most TACAs fail to induce T cell-mediated immunity that is critical for cancer therapy. This review summarizes the recent effort to overcome this problem via constructing TACA conjugates with improved immunogenicity, such as by covalently coupling TACAs to proper carrier molecules to form clustered or multi-epitopic conjugate vaccines, coupling TACAs to a T cell peptide epitope and/or an immunostimulant epitope to form fully synthetic multi-component glycoconjugate vaccines, and developing vaccines based on chemically modified TACAs, which is combined with metabolic engineering of cancer cells.

The amino acid sequences flanking an antigenic determinant can strongly affect MHC class I cross-presentation without altering direct presentation

Direct presentation (DP) and cross presentation (CP) on MHC I by professional APCs are defined by the internal or external source of the Ag, respectively. Although some Ags are substrates for both DP and CP, others are only substrates for DP. The reasons for this difference remain largely unknown. In this study, we studied in tissue culture and also in vivo, the effects of altering the length and sequence of the amino acid chains flanking an MHC class I restricted determinant (the chicken OVA OVA(258-265), SIINFEKL) that is normally a good substrate for both DP and CP. We demonstrate that CP but not DP strictly requires flanking N and C-terminal extensions of minimal length. Furthermore, we show that removal but not replacement of just one amino acid 22 residues downstream from the determinant is sufficient to strongly affect CP without affecting either protein stability or DP. Thus, our work shows that the flanking residues of an antigenic determinant can differentially affect CP and DP, and that features of the Ag other than half-life can have a major impact in CP. Our studies may have implications for understanding CP in viral infections and possibly for the design of new vaccines.

Vaccine adjuvants: current challenges and future approaches

For humans, companion animals, and food producing animals, vaccination has been touted as the most successful medical intervention for the prevention of disease in the twentieth century. However, vaccination is not without problems. With the development of new and less reactogenic vaccine antigens, which take advantage of molecular recombinant technologies, also comes the need for more effective adjuvants that will facilitate the induction of adaptive immune responses. Furthermore, current vaccine adjuvants are successful at generating humoral or antibody mediated protection but many diseases currently plaguing humans and animals, such as tuberculosis and malaria, require cell mediated immunity for adequate protection. A comprehensive discussion is presented of current vaccine adjuvants, their effects on the induction of immune responses, and vaccine adjuvants that have shown promise in recent literature.

Foot-and-mouth disease virus can induce a specific and rapid CD4+ T-cell-independent neutralizing and isotype class-switched antibody response in naïve cattle

The role of T-lymphocyte subsets in recovery from foot-and-mouth disease virus (FMDV) infection in calves was investigated by administering subset-specific monoclonal antibodies. The depletion of circulating CD4(+) or WC1(+) gammadelta T cells was achieved for a period extending from before challenge to after resolution of viremia and peak clinical signs, whereas CD8(+) cell depletion was only partial. The depletion of CD4(+) cells was also confirmed by analysis of lymph node biopsy specimens 5 days postchallenge. Depletion with anti-WC1 and anti-CD8 antibodies had no effect on the kinetics of infection, clinical signs, and immune responses following FMDV infection. Three of the four CD4(+) T-cell-depleted calves failed to generate an antibody response to the nonstructural polyprotein 3ABC but generated a neutralizing antibody response similar to that in the controls, including rapid isotype switching to immunoglobulin G antibody. We conclude that antibody responses to sites on the surface of the virus capsid are T cell independent, whereas those directed against the nonstructural proteins are T cell dependent. CD4 depletion was found to substantially inhibit antibody responses to the G-H peptide loop VP1(135-156) on the viral capsid, indicating that responses to this particular site, which has a more mobile structure than other neutralizing sites on the virus capsid, are T cell dependent. The depletion of CD4(+) T cells had no adverse effect on the magnitude or duration of clinical signs or clearance of virus from the circulation. Overall, we conclude that CD4(+) T-cell-independent antibody responses play a major role in the resolution of foot-and-mouth disease in cattle.

Nanoparticles for nasal vaccination

The great interest in mucosal vaccine delivery arises from the fact that mucosal surfaces represent the major site of entry for many pathogens. Among other mucosal sites, nasal delivery is especially attractive for immunization, as the nasal epithelium is characterized by relatively high permeability, low enzymatic activity and by the presence of an important number of immunocompetent cells. In addition to these advantageous characteristics, the nasal route could offer simplified and more cost-effective protocols for vaccination with improved patient compliance. The use of nanocarriers provides a suitable way for the nasal delivery of antigenic molecules. Besides improved protection and facilitated transport of the antigen, nanoparticulate delivery systems could also provide more effective antigen recognition by immune cells. These represent key factors in the optimal processing and presentation of the antigen, and therefore in the subsequent development of a suitable immune response. In this sense, the design of optimized vaccine nanocarriers offers a promising way for nasal mucosal vaccination.

Aspirin and the induction of tolerance by dendritic cells

Tolerance is maintained by central and peripheral regulatory mechanisms and is essential to prevent autoimmunity. In the setting of solid organ or haematopoietic transplantation, the indirect pathway of allorecognition is a significant driver of chronic rejection. Chronic rejection proceeds despite effective immunosuppressive therapy, therefore achieving immunological tolerance to control the indirect pathway is a desirable goal. Tolerance induction may be achieved by vaccination with modified antigen presenting cells (APCs). Mature dendritic cells (DCs) are potent APCs, but immature DCs have been shown to have a reduced allo-stimulatory capacity and can be tolerogenic. Drug treatment has been shown to decrease the allo-stimulatory capacity of DC compared to immature DC. Dexamethasone and vitamin D3 have been established as having potent effects on dendritic cell immunogenicity.The effects of aspirin, a non-steroidal anti-inflammatory, on DCs have not previously been so extensively studied and here we will review the work which has been carried out using aspirin to induce tolerogenic DCs.We have examined the mechanisms of tolerance induction using human DCs and T cells. It has been possible to demonstrate that in aspirin treated, human DCs there is inhibition of the nuclear factor K-B (NFKB) signalling pathway, modified cytokine production, reduced expression of co-stimulatory molecules (CD40, CD80, and CD86) and increased expression of immunoglobulin-like transcript-3 (ILT3). The decreased expression of co-stimulatory molecules is maintained following cytokine or lipopolysaccharide (LPS) challenge. Drug treatment of DCs increases the expression of immunoglobulin-like transcript 3 (ILT3) when compared with immature DCs (iDCs), and these high levels of expression are maintained when the cells are challenged with a maturational stimulus. Aspirin also reduces the allo-stimulatory capacity of human DCs, and induces hypo-responsiveness and regulatory activity in responder T cells. These regulatory T-cells were CD4(+) CD25(+) FOXP3(+) and by studying CD25(-) or CD45RA populations, it was possible to determine that these regulatory T cells were generated de novo rather than requiring the expansion of naturally occurring Tregs. Aspirin continues therefore to be of interest with regard its wider effects on immune regulation, other than that mediated by direct inhibition of cyclo-oxygenase, in particular its ability to induce tolerogenic DCs at therapeutic concentrations in humans.

Neutralizing antibodies to therapeutic enzymes: considerations for testing, prevention and treatment

Lysosomal storage diseases are characterized by deficiencies in lysosomal enzymes, allowing accumulation of target substrate in cells and eventually causing cell death. Enzyme replacement therapy is the principal treatment for most of these diseases. However, these therapies are often complicated by immune responses to the enzymes, blocking efficacy and causing severe adverse outcomes by neutralizing product activity. It is thus crucial to understand the relationships between genetic mutations, endogenous residual enzyme proteins (cross-reactive immunologic material), development of neutralizing antibodies and their impact on clinical outcomes of lysosomal storage diseases. For patients in whom neutralizing antibodies may cause severe adverse clinical outcomes, it is paramount to develop tolerance inducing protocols to preclude, where predictable, or treat such life-threatening responses.

Phase 2 trial of a DNA vaccine encoding myelin basic protein for multiple sclerosis

OBJECTIVE

To evaluate the efficacy and safety of BHT-3009 in relapsing-remitting multiple sclerosis (MS) and to confirm that BHT-3009 causes immune tolerance.

METHODS

BHT-3009 is a tolerizing DNA vaccine for MS, encoding full-length human myelin basic protein. Relapsing-remitting MS patients were randomized 1:1:1 into three groups: placebo, 0.5 mg BHT-3009, or 1.5 mg BHT-3009, given intramuscularly at weeks 0, 2, 4, and every 4 weeks thereafter until week 44. The primary end point was the 4-week rate of occurrence of new gadolinium-enhancing lesions on brain magnetic resonance images from weeks 28 to 48. Protein microarrays were used to measure levels of anti-myelin autoantibodies.

RESULTS

Compared with placebo, in the 267 patient analysis population the median 4-week rate of new enhancing lesions during weeks 28 to 48 was 50% lower with 0.5 mg BHT-3009 (p = 0.07) and during weeks 8 to 48 was 61% lower with 0.5 mg BHT-3009 (p = 0.05). The mean volume of enhancing lesions at week 48 was 51% lower on 0.5 mg BHT-3009 compared with placebo (p = 0.02). No significant improvement in magnetic resonance imaging lesion parameters was observed with 1.5 mg BHT-3009. Dramatic reductions in 23 myelin-specific autoantibodies in the 0.5 mg BHT-3009 arm were observed, but not with placebo or 1.5 mg BHT-3009.

CONCLUSIONS

In relapsing-remitting MS patients, treatment with the lower dose (0.5 mg) of BHT-3009 for 44 weeks nearly attained the primary end point for reduction of the rate of new enhancing magnetic resonance imaging lesions (p = 0.07) and achieved several secondary end points including a reduction of the rate of enhancing magnetic resonance imaging lesions from weeks 8 to 48 (p = 0.05). Immunological data in a preselected subgroup of patients also indicated that treatment with 0.5 mg induced antigen-specific immune tolerance. The greater dose was ineffective.

The immunologic constant of rejection

The complexity underlying a pathologic process does not necessarily require a complex explanation. The biology determining allograft or cancer rejection, autoimmunity or tissue damage during pathogen infections is complex; however, common patterns are emerging that lead to a common final outcome. For instance, tissue destruction occurs with resolution of the pathogenic process (cancer, infection) or tissue damage and organ failure (autoimmunity, allograft rejection). Observations in humans based on transcriptional profiling converge into what we call an 'immunologic constant of rejection' that characterizes such occurrences. This constant includes the coordinate activation of interferon-stimulated genes (ISGs) and immune effector functions (IEFs). Understanding this final effector pathway may suggest novel strategies for the induction or inhibition of tissue-specific destruction with therapeutic intent in cancer and other immune pathologies.

Spontaneous and treatment-induced cancer rejection in humans

BACKGROUND

Experimental observations suggest that human cancer cells actively interact with normal host cells and this cross-talk results, in most instances, in an increased potential of cancer cells to survive. On the other hand, it is also well documented that on rare occasions tumors can be dramatically destroyed by the host's immune response.

OBJECTIVE

In this review, we argue that understanding the mechanisms that bring about the immune response and lead to cancer destruction is of paramount importance for the design of future rational therapies.

METHODS

Here we summarize the present understanding of the phenomenology leading to cancer regression in humans and propose novel strategies for a more efficient study of human cancer under natural conditions and during therapy.

CONCLUSION

The understanding of tumor/host interactions within the tumor microenvironment is a key component of the study of tumor immunology in humans, much can be learned by a dynamic study of such interactions at time points related to the natural history of the disease or its response to therapy. Such understanding will eventually lead to novel and more effective therapies.

Antigen kinetics determines immune reactivity

A current paradigm in immunology is that the strength of T cell responses is governed by antigen dose, localization, and costimulatory signals. This study investigates the influence of antigen kinetics on CD8 T cell responses in mice. A fixed cumulative antigen dose was administered by different schedules to produce distinct dose-kinetics. Antigenic stimulation increasing exponentially over days was a stronger stimulus for CD8 T cells and antiviral immunity than a single dose or multiple dosing with daily equal doses. The same was observed for dendritic cell vaccination, with regard to T cell and anti-tumor responses, and for T cells stimulated in vitro. In conclusion, stimulation kinetics per se was shown to be a separate parameter of immunogenicity. These findings warrant a revision of current immunization models and have implications for vaccine development and immunotherapy.

'Immunization' against airborne tuberculosis by an earlier primary response to a concurrent intravenous infection

Tuberculosis in mice is a lung disease. Airborne infection of this host species with Mycobacterium tuberculosis (Mtb) resulted in 20 days of Mtb growth in the lungs before further growth was inhibited and the level of infection stabilized. Inhibition of Mtb growth was associated with the production of interferon-gamma (IFN-gamma)-producing T cells in the lymph nodes and spleen and with the progressive accumulation of these cells in the lungs. Production of IFN-gamma-producing T cells was not discernable until about day 15 of infection, presumably because Mtb did not disseminate from the lungs to the draining lymph nodes and spleen until after an approximate 10-day delay. By contrast, in mice infected via the intravenous (i.v.) route, the spleen became infected almost immediately, resulting in much earlier production of IFN-gamma-producing T cells and earlier control of spleen and lung infection. In mice infected concurrently via both routes, earlier generation of immunity to the i.v. infection resulted in earlier accumulation of IFN-gamma-producing T cells in the lungs and earlier control of lung infection that was initiated via the airborne route. This protection against airborne infection afforded by an earlier primary immune response is equivalent to that expressed by mice vaccinated with bacillus Calmette-Guérin or certain other vaccines.

Digital NFATc2 activation per cell transforms graded T cell receptor activation into an all-or-none IL-2 expression

The expression of interleukin-2 (IL-2) is a key event in T helper (Th) lymphocyte activation, controlling both, the expansion and differentiation of effector Th cells as well as the activation of regulatory T cells. We demonstrate that the strength of TCR stimulation is translated into the frequency of memory Th cells expressing IL-2 but not into the amount of IL-2 per cell. This molecular switch decision for IL-2 expression per cell is located downstream of the cytosolic Ca²⁺ level. Here we show that in a single activated Th cell, NFATc2 activation is digital but NF-κB activation is graded after graded T cell receptor (TCR) signaling. Subsequently, NFATc2 translocates into the nucleus in an all-or-none fashion per cell, transforming the strength of TCR-stimulation into the number of nuclei positive for NFATc2 and IL-2 transcription. Thus, the described NFATc2 switch regulates the number of Th cells actively participating in an immune response.

The immune response to lentiviral-delivered transgene is modulated in vivo by transgene-expressing antigen-presenting cells but not by CD4+CD25+ regulatory T cells

Systemic delivery of lentiviral vector (LV) in immunocompetent mice leads to efficient in vivo cell transduction and expression of the encoded protein under the control of the ubiquitous promoter of human cytomegalovirus (CMV). However, antitransgene immune response results in clearance of transduced cells 4 weeks after injection. T regulatory cells (Tregs), which have been demonstrated to control immune responses in vivo, were tested for their ability to suppress antitransgene response leading to stable long-term expression. Adoptive transfer of natural CD4(+)CD25(+) Tregs (nTregs) isolated from wild type (wt) mice or from transgene tolerant transgenic (tg) mice did not suppress the antitransgene immune response after LV delivery. These data demonstrate that neither increasing the endogenous pool of natural Tregs nor transferring nTregs selected in a transgene-expressing thymus can modulate the immune response and mediate sustained transgene expression. Conversely, adoptive transfer of antigen-presenting cells (APCs) isolated from transgene-tolerant tg mice efficiently reduced the immune response leading to stable LV-encoded protein expression in vivo. Reduction of CD8(+) effector T cells was observed in LV-treated mice coinjected with transgene-expressing APCs compared with control mice. These data indicate that antitransgene immune response can be modulated by transgene-expressing APCs possibly through deletion of effector T cells.

The early protective thymus-independent antibody response to foot-and-mouth disease virus is mediated by splenic CD9+ B lymphocytes

Infection of mice with cytopathic foot-and-mouth disease virus (FMDV) induces a rapid and specific thymus-independent (TI) neutralizing antibody response that promptly clears the virus. Herein, it is shown that FMDV-infected dendritic cells (DCs) directly stimulate splenic innate-like CD9(+) B lymphocytes to rapidly (3 days) produce neutralizing anti-FMDV immunoglobulin M antibodies without T-lymphocyte collaboration. In contrast, neither follicular (CD9(-)) B lymphocytes from the spleen nor B lymphocytes from lymph nodes efficiently respond to stimulation with FMDV-infected DCs. The production of these protective neutralizing antibodies is dependent on DC-derived interleukin-6 (IL-6) and on CD9(+) cell-derived IL-10 secretion. In comparison, DCs loaded with UV-inactivated FMDV are significantly less efficient in directly stimulating B lymphocytes to secrete TI antibodies. A critical role of the spleen in the early production of anti-FMDV antibodies in infected mice was also demonstrated in vivo. Indeed, either splenectomy or functional disruption of the marginal zone of the spleen delays and reduces the magnitude of the TI anti-FMDV antibody response in infected mice. Together, these results indicate that in addition to virus localization, the FMDV-mediated modulation of DC functionality is a key parameter that collaborates in the induction of a rapid and protective TI antibody response against this virus.

Persistent expression of hF.IX After tolerance induction by in utero or neonatal administration of AAV-1-F.IX in hemophilia B mice

The major complication associated with protein replacement therapy currently used in the treatment of hemophilia B (HB) is the development of antibodies to the infused human Factor IX (hF.IX). We hypothesized that vector-mediated expression of hF.IX, either at a prenatal stage or early in life may lead to tolerance to hF.IX and long-term transgene expression. Fetal, neonatal, and adult F.IX-deficient mice were injected with AAV-1-hF.IX, and the hF.IX levels as well as antibodies to hF.IX in the circulation were assayed. In utero injection followed by postnatal re-administration of adeno-associated virus 1 (AAV-1) vector achieved persistent expression of hF.IX in all animals, with no cellular or humoral immune response to F.IX. Similar results were seen after initial injection in neonatal mice followed by re-administration, whereas all mice injected at the adult stage developed antibodies to hF.IX. In contrast, after administration of AAV-2-hF.IX in the neonatal period, antibodies to hF.IX were formed in all the injected animals. We conclude that in utero or neonatal-stage injection of AAV-1-hF.IX can lead to long-term expression and absence of immune response. The differences in immune response between the AAV-1 and AAV-2 groups suggests that tolerance may be related to differences in bio-distribution, timing of expression, and/or the initial levels of hF.IX expression. This supports the concept of a narrow "window of opportunity" for tolerance induction.

In vivo administration of lentiviral vectors triggers a type I interferon response that restricts hepatocyte gene transfer and promotes vector clearance

Liver gene transfer is a highly sought goal for the treatment of inherited and infectious diseases. Lentiviral vectors (LVs) have many desirable properties for hepatocyte-directed gene delivery, including the ability to integrate into nondividing cells. Unfortunately, upon systemic administration, LV transduces hepatocytes relatively inefficiently compared with nonparenchymal cells, and the duration of transgene expression is often limited by immune responses. Here, we investigated the role of innate antiviral responses in these events. We show that administration of LVs to mice triggers a rapid and transient IFNalphabeta response. This effect was dependent on functional vector particles, and in vitro challenge of antigen-presenting cells suggested that plasmacytoid dendritic cells initiated the response. Remarkably, when LVs were administered to animals that lack the capacity to respond to IFNalphabeta, there was a dramatic increase in hepatocyte transduction, and stable transgene expression was achieved. These findings indicate that, even in the setting of acute delivery of replication-defective vectors, IFNs effectively interfere with transduction in a cell-type-specific manner. Moreover, because disabling a single component of the innate/immune network was sufficient to establish persistent xenoantigen expression, our results raise the hope that the immunologic barriers to gene therapy are less insurmountable than expected.

Improved generation of anti-tumor immunity by antigen dose limitation

Background

The malignant cells of cutaneous T cell lymphoma (CTCL) display immunogenic peptides derived from the clonal T cell receptor (TCR) providing an attractive model for refinement of anti-tumor immunization methodology. To produce a clinically meaningful anti-tumor response, induction of cytotoxic anti-CTCL cells must be maximized while suppressive T regulatory cells (Treg) should be minimized. We have demonstrated that engulfment of apoptotic CTCL cells by dendritic cells (DC) can lead to either CD8 anti-CTCL responses or immunosuppressive Treg induction. Treg generation is favored when the number of apoptotic cells available for ingestion is high.

Methods

In this study, we sought to determine whether the balance between immunity and immunosuppression could be shifted towards a CD8 anti-CTCL response by lowering the ratio of apoptotic CTCL cells available for DC ingestion. CTCL cell apoptosis was produced by engagement of the TCR by anti-CD3 antibody affixed to magnetic beads.

Results

The physical perturbation inherent in passage through a separation column induced monocytes to differentiate into DC, demonstrated by increased expression of class II and CD86 and decreased expression of the monocyte marker CD14. The immature DC internalized and processed apoptotic CTCL cells and could potentially present the tumor-derived peptides in the context of MHC class I and II. As the number of apoptotic cells increased, there was a dose-dependent increase in the expression of Treg markers CTLA-4, CD25, and FoxP3, with a ratio of apoptotic cell/DC loading of > 10:1 corresponding to the greatest Treg induction. These inducible phenotypic Treg also functionally inhibited CD8-mediated perforin expression in vitro. At lower levels of apoptotic cell/DC loading of < 5:1, there was an expansion of the CD8 T cell compartment with increased perforin expression and increased CTCL cell death, indicating anti-tumor activity.

Conclusion

These findings demonstrate that the ratio of apoptotic cells supplied to DC is an important determinant of whether CD8 anti-tumor immunity or immunosuppression is generated.

A Novel Postpriming Regulatory Check Point of Effector/Memory T Cells Dictated through Antigen Density Threshold-Dependent Anergy

CTLs act as the effector arm of the cell-mediated immune system to kill undesirable cells. Two processes regulate these effector cells to prevent self reactivity: a thymic selection process that eliminates autoreactive clones and a multistage activation or priming process that endows them with a license to kill cognate target cells. Hitherto no subsequent regulatory restrictions have been ascribed for properly primed and activated CTLs that are licensed to kill. In this study we show that CTLs possess a novel postpriming regulatory mechanism(s) that influences the outcome of their encounter with cognate target cells. This mechanism gauges the degree of Ag density, whereupon reaching a certain threshold significant changes occur that induce anergy in the effector T cells. The biological consequences of this Ag-induced postpriming control includes alterations in the expression of cell surface molecules that control immunological synapse activity and cytokine profiles and induce retarded cell proliferation. Most profound is genome-wide microarray analysis that demonstrates changes in the expression of genes related to membrane potential, TCR signal transduction, energy metabolism, and cell cycle control. Thus, a discernible and unique gene expression signature for anergy as a response to high Ag density has been observed. Consequently, activated T cells possess properties of a self-referential sensory organ. These studies identify a new postpriming control mechanism of CTL with anergenic-like properties. This mechanism extends our understanding of the control of immune function and regulation such as peripheral tolerance, viral infections, antitumor immune responses, hypersensitivity, and autoimmunity.

Immunotherapy success in prophylaxis cannot predict therapy: prime-boost vaccination against the 5T4 oncofoetal antigen

We have investigated the tumour therapeutic efficacy of homologous and heterologous prime-boost vaccine strategies against the 5T4 oncofoetal antigen, using both replication defective adenovirus expressing human 5T4 (Ad5T4), and retrovirally transduced DC lines (DCh5T4) in a subcutaneous B16 melanoma model (B16h5T4). In naïve mice we show that all vaccine combinations tested can provide significant tumour growth delay. While DCh5T4/Adh5T4 sequence is the best prophylactic regimen (P > 0.0001), it does not demonstrate any therapeutic efficacy in mice with established tumours. In active therapy the Adh5T4/DCh5T4 vaccination sequence is the best treatment regimen (P = 0.0045). In active therapy, we demonstrate that B16h5T4 tumour growth per se induces Th2 polarising immune responses against 5T4, and the success of subsequent vaccination is dependant on altering the polarizing immune responses from Th2 to Th1. We show that the first immunization with Adh5T4 can condition the mice to induce 5T4 specific Th1 immune responses, which can be sustained and subsequently boosted with DCh5T4. In contrast immunisation with DCh5T4 augments Th2 immune responses, such that a subsequent vaccination with Adh5T4 cannot rescue tumour growth. In this case the depletion of CD25(+) regulatory cells after tumour challenge but before immunization can restore therapeutic efficacy. This study highlights that all vaccine vectors are not equal at generating TAA immune responses; in tumour bearing mice the capability of different vaccines to activate the most appropriate anti-tumour immune responses is greatly altered compared to what is found in naïve mice.

Popliteal lymph node (PLN) assay to study adjuvant effects on respiratory allergy

Different variants of the popliteal lymph node (PLN) assay have been published. Here we describe the adjuvant popliteal lymph node assay, an immune response assay to study the adjuvant activity of soluble substances as well as particulate matter. The substance to be studied for adjuvant activity is injected into the hind footpad of mice or rats together with an antigen. Adjuvant activity is determined as the increase in PLN weight and cell numbers in animals receiving antigen together with the substance under study, compared with PLN weight and cell numbers in animals given the antigen without the substance in question, and animals given the putative adjuvant alone. Because lymph node weight and cell numbers are immunologically non-specific parameters, specific immune response assays like serum antibody responses or antibody-forming cell numbers should additionally be performed. Different antigens and immune response assays may be used, depending on the research question asked. In relation to respiratory (or food) allergy, the assays should as a minimum include determination of specific IgE in serum, and preferably also IgG1 (mouse). Serum specific IgG2a antibody determination may be added to get an indication of the Th1-Th2-balance of the response. The adjuvant PLN assay, with cellular response assays performed in the draining popliteal lymph node and antibody determinations in serum, requires small amounts of test material. The assay offers a practical, sensitive and reproducible method to determine the adjuvant activity of soluble substances as well as particulate material, with the possibility to also perform mechanistic studies.

Transgene expression levels and kinetics determine risk of humoral immune response modeled in factor IX knockout and missense mutant mice

Immune responses leading to antibody-mediated elimination of the transgenic protein are a concern in gene replacement for congenital protein deficiencies, for which hemophilia is an important model. Although most hemophilia B patients have circulating non-functional but immunologically crossreactive factor IX (FIX) protein (CRM+ phenotype), inciting factors for FIX neutralizing antibody (inhibitor) development have been studied in crossreactive material-negative (CRM-) animal models. For this study, determinants of FIX inhibitor development were compared in hemophilia B mice, in which circulating FIX protein is absent (CRM- factor IX knockout (FIXKO) model) or present (CRM+ missense R333Q-hFIX model) modeling multiple potential therapies. The investigations compare for the first time different serotypes of adeno-associated virus (AAV) vectors (AAV2 and AAV1), each at multiple doses, in the setting of two different FIX mutations. The comparisons demonstrate in the FIXKO background (CRM- phenotype) that neither vector serotype nor vector particle number independently determine the inhibitor trigger, which is influenced primarily by the level and kinetics of transgene expression. In the CRM+ missense background, inhibitor development was never stimulated by AAV gene therapy or protein therapy, despite the persistence of lymphocytes capable of responding to FIX with non-inhibitory antibodies. This genotype/phenotype is strongly protective against antibody formation in response to FIX therapy.

The fate of effector CD8 T cells in vivo is controlled by the duration of antigen stimulation

What controls the fate of the T-cell response remains incompletely defined. Gain of effector function facilitated by costimulation has been thought to be a crucial factor in determining the outcome of the T-cell response, i.e. long-term memory in the presence of costimulation versus tolerance induction in the absence of costimulation. In this study, we show that while costimulation or cognate CD4 helps to promote the acquisition of effector function during the initial phase of the CD8 T-cell response, the fate of effector CD8 T cells is controlled by the duration of subsequent antigenic stimulation. Effector CD8 T cells differentiate into memory cells only after clearance of antigen, whereas in the presence of persistent antigen, effector CD8 T cells are tolerized. Furthermore, protective immunity against tumour cannot develop in the persisting antigen environment. These results suggest that removal of persisting antigen by other means might be a prerequisite for effective immunotherapy in cancer.

Dendritic cells in a mature age

A common view supposes that dendritic cells (DCs) exist in two basic functional states: immature DCs induce tolerance to self, whereas mature DCs induce immunity to foreign antigens. However, the term 'mature' is often used not only functionally to designate immunogenic DCs but also as a phenotypic description of DCs expressing high levels of MHC, adhesion and co-stimulatory molecules. The recent realization that DCs can express such markers under non-immunogenic conditions raises the question of whether the two connotations of the term 'mature' should continue to be used interchangeably. Here, I discuss the origins of the maturation model and how terminology is evolving to better accommodate our current understanding of the function of DCs.

IC31, a novel adjuvant signaling via TLR9, induces potent cellular and humoral immune responses

IC31, the combination of a novel immunostimulatory oligodeoxynucleotide containing deoxy-Inosine/deoxy-Cytosine (ODN1a) and the antimicrobial peptide KLKL(5)KLK, represents a promising novel adjuvant signaling via the TLR9/MyD88-dependent pathway of the innate immune system. In mice, IC31 induces potent peptide-specific type 1 cellular immune responses, as well as mainly type 1 dominated protein-specific cellular and humoral immune responses. In addition, cytotoxic T lymphocytes were induced, able to kill efficiently target cells in vivo. Activation of murine dendritic cells by IC31 induced efficiently proliferation of naïve CD4(+) TCR transgenic T cells (DO.11.10) as well as their differentiation into IFN-gamma- and IL-4-producing T cells in vitro.

Lymphoid neogenesis in chronic inflammatory diseases

The frequent observation of organized lymphoid structures that resemble secondary lymphoid organs in tissues that are targeted by chronic inflammatory processes, such as autoimmunity and infection, has indicated that lymphoid neogenesis might have a role in maintaining immune responses against persistent antigens. In this Review, we discuss recent progress in several aspects of lymphoid neogenesis, focusing on the similarities with lymphoid tissue development, the mechanisms of induction, functional competence and pathophysiological significance. As more information on these issues becomes available, a better understanding of the role of lymphoid neogenesis in promoting chronic inflammation might eventually lead to new strategies to target immunopathological processes.

Pediatric hemophagocytic syndromes: a diagnostic and therapeutic challenge

Pediatric hemophagocytic syndrome (HS) is a severe and often fatal clinical disorder. This syndrome is frequently unrecognized, and thus, affected children may receive suboptimal management, leading to an increase in mortality. The purpose of this review is to provide a clinical guide to (1) the recognition of HS based on clinical, biologic, and pathologic features; (2) the identification of the primary cause of HS in a given affected child; and (3) the initiation of effective treatment in a timely manner.