Surface densities of Langerhans cells in relation to rodent epidermal sites with special immunologic properties

HER2/neu DNA vaccination by intradermal gene delivery in a mouse tumor model: Gene gun is superior to jet injector in inducing CTL responses and protective immunity

DNA vaccines are potential tools for the induction of immune responses against both infectious disease and cancer. The dermal application of DNA vaccines is of particular interest since the epidermal and dermal layers of the skin are characterized by an abundance of antigen-presenting cells (APCs). The aim of our study was to compare tumor protection as obtained by two different methods of intradermal DNA delivery (gene gun and jet injector) in a well-established HER2/neu mouse tumor model. BALB/c mice were immunized twice with a HER2/neu-coding plasmid by gene gun or jet injector. Mice were then subcutaneously challenged with HER2/neu⁺ syngeneic D2F2/E2 tumor cells. Protection against subsequent challenges with tumor cells as well as humoral and T-cell immune responses induced by the vaccine were monitored. Gene gun immunization was far superior to jet injector both in terms of tumor protection and induction of HER2/neu-specific immune responses. After gene gun immunization, 60% of the mice remained tumor-free until day 140 as compared with 25% after jet injector immunization. Furthermore, gene gun vaccination was able to induce both a strong T_H1-polarized T-cell response with detectable cytotoxic T-lymphocyte (CTL) activity and a humoral immune response against HER2/neu, whereas the jet injector was not. Although the disadvantages that were associated with the use of the jet injector in our model may be overcome with methodological modifications and/or in larger animals, which exhibit a thicker skin and/or subcutaneous muscle tissue, we conclude that gene gun delivery constitutes the method of choice for intradermal DNA delivery in preclinical mouse models and possibly also for the clinical development of DNA-based vaccines.

Combination therapy for melanoma with BRAF/MEK inhibitor and immune checkpoint inhibitor: a mathematical model

BACKGROUND

The B-raf gene is mutated in up to 66% of human malignant melanomas, and its protein product, BRAF kinase, is a key part of RAS-RAF-MEK-ERK (MAPK) pathway of cancer cell proliferation. BRAF-targeted therapy induces significant responses in the majority of patients, and the combination BRAF/MEK inhibitor enhances clinical efficacy, but the response to BRAF inhibitor and to BRAF/MEK inhibitor is short lived. On the other hand, treatment of melanoma with an immune checkpoint inhibitor, such as anti-PD-1, has lower response rate but the response is much more durable, lasting for years. For this reason, it was suggested that combination of BRAF/MEK and PD-1 inhibitors will significantly improve overall survival time.

RESULTS

This paper develops a mathematical model to address the question of the correlation between BRAF/MEK inhibitor and PD-1 inhibitor in melanoma therapy. The model includes dendritic and cancer cells, CD 4+ and CD 8+ T cells, MDSC cells, interleukins IL-12, IL-2, IL-6, IL-10 and TGF- β, PD-1 and PD-L1, and the two drugs: BRAF/MEK inhibitor (with concentration γ B ) and PD-1 inhibitor (with concentration γ A ). The model is represented by a system of partial differential equations, and is used to develop an efficacy map for the combined concentrations (γ B ,γ A ). It is shown that the two drugs are positively correlated if γ B and γ A are at low doses, that is, the growth of the tumor volume decreases if either γ B or γ A is increased. On the other hand, the two drugs are antagonistic at some high doses, that is, there are zones of (γ B ,γ A ) where an increase in one of the two drugs will increase the tumor volume growth, rather than decrease it.

CONCLUSIONS

It will be important to identify, by animal experiments or by early clinical trials, the zones of (γ B ,γ A ) where antagonism occurs, in order to avoid these zones in more advanced clinical trials.

Gene Expression Architecture of Mouse Dorsal and Tail Skin Reveals Functional Differences in Inflammation and Cancer

Inherited germline polymorphisms can cause gene expression levels in normal tissues to differ substantially between individuals. We present an analysis of the genetic architecture of normal adult skin from 470 genetically unique mice, demonstrating the effect of germline variants, skin tissue location, and perturbation by exogenous inflammation or tumorigenesis on gene signaling pathways. Gene networks related to specific cell types and signaling pathways, including sonic hedgehog (Shh), Wnt, Lgr family stem cell markers, and keratins, differed at these tissue sites, suggesting mechanisms for the differential susceptibility of dorsal and tail skin to development of skin diseases and tumorigenesis. The Pten tumor suppressor gene network is rewired in premalignant tumors compared to normal tissue, but this response to perturbation is lost during malignant progression. We present a software package for expression quantitative trait loci (eQTL) network analysis and demonstrate how network analysis of whole tissues provides insights into interactions between cell compartments and signaling molecules.

Codominant Role of Interferon-γ- and Interleukin-17-Producing T Cells During Rejection in Full Facial Transplant Recipients

Facial transplantation is a life-changing procedure for patients with severe composite facial defects. However, skin is the most immunogenic of all transplants, and better understanding of the immunological processes after facial transplantation is of paramount importance. Here, we describe six patients who underwent full facial transplantation at our institution, with a mean follow-up of 2.7 years. Seum, peripheral blood mononuclear cells, and skin biopsy specimens were collected prospectively, and a detailed characterization of their immune response (51 time points) was performed, defining 47 immune cell subsets, 24 serum cytokines, anti-HLA antibodies, and donor alloreactivity on each sample, producing 4269 data points. In a nonrejecting state, patients had a predominant T helper 2 cell phenotype in the blood. All patients developed at least one episode of acute cellular rejection, which was characterized by increases in interferon-γ/interleukin-17-producing cells in peripheral blood and in the allograft's skin. Serum monocyte chemotactic protein-1 level was significantly increased during rejection compared with prerejection time points. None of the patients developed de novo donor-specific antibodies, despite a fourfold expansion in T follicular helper cells at 1 year posttransplantation. In sum, facial transplantation is frequently complicated by a codominant interferon-γ/interleukin-17-mediated acute cellular rejection process. Despite that, medium-term outcomes are promising with no evidence of de novo donor-specific antibody development.

Infracommunity dynamics of chiggers (Trombiculidae) parasitic on a rodent

We studied the structure of chigger mite (Trombiculidae) communities parasitic on a South African rodent, Rhabdomys pumilio. We aimed to determine whether: (a) different chigger species differ in preferences for certain body areas of a host and (b) chigger assemblages among body areas of the same host individual, are structured and if so, whether the structure of these assemblages is aggregative or segregative. Rhabdomys pumilio is parasitized by seven chigger species belonging to six genera. The three most abundant species (Leptotrombidium sp. nr. muridium, Schoutedenichia sp. and Neoschoengastia sp. A) displayed a non-random distribution across the host body, with the two most abundant species (L. sp. nr. muridium and Schoutedenichia sp.) significantly associated with the tail area. In addition, whenever non-randomness of chigger co-occurrence in the same body area was recorded, it indicated positive but not negative co-occurrences of different species. This might be due to similarity of chigger species in resource needs and strategies to avoid host defence efforts.

DC3-decorated polyplexes for targeted gene delivery into dendritic cells

Dendritic cells (DCs) are a family of specialized antigen presenting cells (APCs) that detect antigens and initiate a wide spectrum of immune responses against them. These characteristics make them promising candidates for immunotherapy manipulations. In this study we designed and synthesized DC-targeted block copolymers composed of linear polyethylenimine (PEI) conjugated to hydrophilic polyethylene glycol (PEG) installed with a DC-targeting peptide (DC3, primary sequence FYPSYHSTPQRP). Two different conjugation procedures (basic and modified) were employed to synthesize the DC3-PEG-b-PEI and the control SCRM-PEG-b-PEI (with a scrambled DC3 peptide sequence) by one-pot synthesis, in two steps. In the first, basic conjugation procedure, PEG with N-hydroxysuccinimide (NHS) ester and maleimide (MAL) groups (NHS-PEG-MAL, 3.5 kDa) was first coupled to linear PEI (25 kDa) via the NHS group to yield the intermediate MAL-PEG-b-PEI, that was then conjugated to N-terminus-cysteine harboring peptides DC3 or SCRM via the MAL double bond to yield the final DC3-PEG-b-PEI or SCRM-PEG-b-PEI copolymers, respectively. In the second, modified conjugation procedure, Fmoc-cysteine harboring DC3 or SCRM peptides were first conjugated to NHS-PEG-MAL via the MAL group followed by coupling to linear PEI via the NHS functional group. Fmoc cleavage yielded the same final product as in the basic procedure. The modified conjugation procedure was capable of yielding block copolymers richer with peptides, as determined by (1)H NMR analysis. Self-assembly of DC3-PEG-b-PEI copolymers and DNA molecules yielded nanosized polyion complexes (polyplexes), with lower surface charge and limited cytotoxicity when compared to the PEI building block. Significant transfection efficiency of the DC-targeted polyplexes by murine dendritic DC2.4 cells was observed only in DC3-PEG-b-PEI/DNA polyplexes synthesized by the modified conjugation procedure. These polyplexes, with higher peptide-load, showed greater transfection capability in DC2.4 cells relative to the control nontargeted SCRM-PEG-b-PEI/DNA polyplexes, but not in endothelial cells. The transfection efficiency was comparable to or higher than that of the PEI/DNA positive control. The results indicate that PEGylated-PEI polyplexes show significant transfection efficiency into DCs when decorated with DC3 peptide, and are attractive candidates for immunotherapy via DCs.

Disparate hypervariable region-1 of mitochondrial DNA did not induce skin allograft rejection in cloned porcine models

INTRODUCTION

Alloantigen recognition in skin transplantation is the bane for surgeons. Several studies have mainly focused on the immunogenicity of major histocompatibility (MHC) antigens and H-Y minor histocompatibility antigens. However, the roles of the mitochondrial DNA (mtDNA) encorded miHA have not been identified. Therefore, we sought to address the antigenicity of the hypervariable region 1 (HV-1) of mtDNA in skin transplantation using cloned pig models.

METHODS

Swine leukocyte antigen and HV-1 of mtDNA were analyzed using sequencing methods. Skin transplantation was performed between MHC-matched, mtDNA-mismatched cloned miniature pigs. Full-thickness skin was grafted between cloned pigs without any immunosuppressants. The grafted tissues were observed for 3 months and evaluated histologically.

RESULTS

The cloned pigs shared identical MHC but mtDNA mismatched at 9 positions. Skin grafts between the cloned pigs were accepted and hair growth maintained, whereas MHC-mismatched grafts showed acute rejection within 7 days after transplantation and were replaced by hairless scar tissue.

CONCLUSIONS

HV-1 disparate skin grafts were not recognized as alloantigenic by MHC-matched cloned pigs.

Lessons and limits of mouse models

Seminal studies in rabbits and rodent transplantation models by Peter Medawar revealed that cellular processes, rather than humoral antibodies, are central to the acute rejection of transplanted organs, and much of basic transplantation research continues to be focused on the biology and control of these cells, which were subsequently shown to be T cells. However, the success of current immunosuppression at controlling T-cell-mediated rejection has resulted in an increasing awareness of antibody-mediated rejection in the clinic. This, in turn, has fueled an emerging interest in the biology of allospecific antibodies, the B cells that produce these antibodies, and the development of mouse models that allow their investigation. Here we summarize some of the more widely used mouse models that have been developed to study the immunobiology of alloreactivity, transplantation rejection and tolerance, and used to identify therapeutic strategies that modulate these events.

Epicutaneous/transcutaneous allergen-specific immunotherapy: rationale and clinical trials

PURPOSE OF REVIEW

IgE-mediated allergies, such as allergic rhinoconjunctivitis and asthma, have become highly prevalent, today affecting up to 35% of the population in industrialized countries. Allergen immunotherapy (also called hyposensitization therapy, desensitization or allergen-specific immunotherapy), the administration of gradually increasing amounts of an allergen, either subcutaneously or via the sublingual or oral route is effective. However, only few allergy patients (<5%) choose immunotherapy, as treatment duration is over years and because allergen administrations are associated with local and in some cases even systemic allergic side effects due to allergen accidentally reaching the circulation. Therefore, ideally the allergen should be administered to a site that contains high numbers of potent antigen-presenting cells in order to enhance efficacy and shorten treatment duration, and ideally that site should also be nonvascularized in order to prevent both systemic distribution of the allergen and systemic allergic side effects. The epidermis, a nonvascularized multilayer epithelium that contains high numbers of potent antigen-presenting Langerhans cells, could therefore be an interesting administration route.

RECENT FINDINGS

We have recently reintroduced transcutaneous or epicutaneous allergen-specific immunotherapy (EPIT) as treatment option for IgE-mediated allergies. This method was found efficacious and safe. Few applications of allergens using skin patches with a treatment duration of a few weeks were sufficient to achieve lasting relief.

SUMMARY

This review gives an overview on the history, the rationale, and the mechanisms of transcutaneous/epicutaneous immunotherapy.

Epicutaneous allergen administration as a novel method of allergen-specific immunotherapy

BACKGROUND

Subcutaneous allergen-specific immunotherapy is an effective treatment of IgE-mediated allergies, but it requires repeated allergen injections with a risk of systemic allergic reactions. Transcutaneous immunotherapy may improve patient compliance and safety.

OBJECTIVE

To assess the safety and efficacy of epicutaneous allergen immunotherapy.

METHODS

This monocentric, placebo-controlled, double-blind trial was conducted from March 2006 to December 2007 at the University Hospital Zurich. Thirty-seven adult patients with positive skin prick and nasal provocation tests to grass pollen were randomized to receive patches containing either allergen (n = 21) or placebo (n = 16). Treatment took place before and during the pollen season 2006, and follow-up visits took place before (n = 26) and after the pollen season 2007 (n = 30). The primary outcome measures were nasal provocation tests.

RESULTS

Allergen-treated patients showed significantly decreased scores in nasal provocation tests in the first (P < .001) and second year (P = .003) after treatment. In contrast, placebo-treated patients had decreased scores in the first treatment year, 2006 (P = .03), but the effect diminished in the second year (P = .53). Although improvement of nasal provocation test scores was not significantly better in the verum versus placebo group, the overall treatment success was rated significantly higher by the allergen-treated group than by the placebo group (2006, P = .02; 2007, P = .005). No severe adverse events were observed. Occurrence of eczema after allergen patch applications proved stimulation of specific T-cell responses, but was noted as an adverse effect of the treatment.

CONCLUSION

Epicutaneous allergen immunotherapy is a promising strategy to treat allergies and merits further investigation.

Skin allograft rejection

Skin allograft rejection is a test of the competence of T lymphocytes to mediate in vivo tissue destruction, which in turn reflects their role in critical functions such as anti-viral and tumor immunity. The tail-skin graft procedure described in this unit is useful predominantly because of the ease of preparation and resistance to ischemic (nonspecific) necrosis. Additionally, it is not necessary to sacrifice the donor mouse. However, rejection of tail-skin grafts should not be used to test for genetic homogeneity in breeding experiments or to detect minor histocompatibility (minor-H) antigens because tail skin is less sensitive than trunk skin in detecting such differences.

Gender differences in skin: a review of the literature

BACKGROUND

There has been increasing interest in studying gender differences in skin to learn more about disease pathogenesis and to discover more effective treatments. Recent advances have been made in our understanding of these differences in skin histology, physiology, and immunology, and they have implications for diseases such as acne, eczema, alopecia, skin cancer, wound healing, and rheumatologic diseases with skin manifestations.

OBJECTIVE

This article reviews advances in our understanding of gender differences in skin.

METHODS

Using the PubMed database, broad searches for topics, with search terms such as gender differences in skin and sex differences in skin, as well as targeted searches for gender differences in specific dermatologic diseases, such as gender differences in melanoma, were performed. Additional articles were identified from cited references. Articles reporting gender differences in the following areas were reviewed: acne, skin cancer, wound healing, immunology, hair/alopecia, histology and skin physiology, disease-specific gender differences, and psychological responses to disease burden.

RESULTS

A recurring theme encountered in many of the articles reviewed referred to a delicate balance between normal and pathogenic conditions. This theme is highlighted by the complex interplay between estrogens and androgens in men and women, and how changes and adaptations with aging affect the disease process. Sex steroids modulate epidermal and dermal thickness as well as immune system function, and changes in these hormonal levels with aging and/or disease processes alter skin surface pH, quality of wound healing, and propensity to develop autoimmune disease, thereby significantly influencing potential for infection and other disease states. Gender differences in alopecia, acne, and skin cancers also distinguish hormonal interactions as a major target for which more research is needed to translate current findings to clinically significant diagnostic and therapeutic applications.

CONCLUSIONS

The published findings on gender differences in skin yielded many advances in our understanding of cancer, immunology, psychology, skin histology, and specific dermatologic diseases. These advances will enable us to learn more about disease pathogenesis, with the goal of offering better treatments. Although gender differences can help us to individually tailor clinical management of disease processes, it is important to remember that a patient's sex should not radically alter diagnostic or therapeutic efforts until clinically significant differences between males and females arise from these findings. Because many of the results reviewed did not originate from randomized controlled clinical trials, it is difficult to generalize the data to the general population. However, the pressing need for additional research in these areas becomes exceedingly clear, and there is already a strong foundation on which to base future investigations.

Expression of langerin/CD207 reveals dendritic cell heterogeneity between inbred mouse strains

Langerin/CD207 is expressed by a subset of dendritic cells (DC), the epithelial Langerhans cells. However, langerin is also detected among lymphoid tissue DC. Here, we describe striking differences in langerin-expressing cells between inbred mouse strains. While langerin+ cells are observed in comparable numbers and with comparable phenotypes in the epidermis, two distinct DC subsets bear langerin in peripheral, skin-draining lymph nodes of BALB/c mice (CD11c(high) CD8alpha(high) and CD11c(low) CD8alpha(low)), whereas only the latter subset is present in C57BL/6 mice. The CD11c(high) subset is detected in mesenteric lymph nodes and spleen of BALB/c mice, but is virtually absent from C57BL/6 mice. Similar differences are observed in other mouse strains. CD11c(low) langerin+ cells represent skin-derived Langerhans cells, as demonstrated by their high expression of DEC-205/CD205, maturation markers, and recruitment to skin-draining lymph nodes upon imiquimod-induced inflammation. It will be of interest to determine the role of lymphoid tissue-resident compared to skin-derived langerin+ DC.

Skin tolerance: in search of the Holy Grail

In 1943, Gibson and Medawar opened the modern era of transplantation research with a paper on the problem of skin allograft rejection. Ten years later Billingham, Brent and Medawar demonstrated that it was possible to induce selective immune acceptance of skin grafts in mice, a state of tolerance. After over six decades, however, the precise mechanism of skin allograft rejection remains still ill-defined. Furthermore, it has not been possible to achieve reliably clinical tolerance allowing the widespread application of skin allotransplantation techniques. The first successful applications of skin allotransplantation have included the hand and face. However, complications from the chronic immunosuppression regimens limit the application of these techniques. Induction of tolerance to skin (and the other tissues in the allograft) would be the most effective way to overcome all these difficulties, but this is yet to be achieved reliably, stimulating some to look for other ways to surmount the current limitations. This paper summarizes alternatives to enlarge the scope of skin allotransplantation techniques, current understanding of mechanisms of skin rejection, and the utility and limitations of animal models used to study skin rejection and tolerance induction. Finally, manipulation strategies to achieve skin tolerance are outlined.

Epidermal langerhans cells are dispensable for humoral and cell-mediated immunity elicited by gene gun immunization

Gene gun immunization, i.e., bombardment of skin with DNA-coated particles, is an efficient method for the administration of DNA vaccines. Direct transfection of APC or cross-presentation of exogenous Ag acquired from transfected nonimmune cells enables MHC-I-restricted activation of CD8(+) T cells. Additionally, MHC-II-restricted presentation of exogenous Ag activates CD4(+) Th cells. Being the principal APC in the epidermis, Langerhans cells (LC) seem ideal candidates to accomplish these functions. However, the dependence on LC of gene gun-induced immune reactions has not yet been demonstrated directly. This was primarily hampered by difficulties to discriminate the contributions of LC from those of other dermal dendritic cells. To address this problem, we have used Langerin-diphtheria toxin receptor knockin mice that allow for selective inducible ablation of LC. LC deficiency, even over the entire duration of experiments, did not affect any of the gene gun-induced immune functions examined, including proliferation of CD4(+) and CD8(+) T cells, IFN-gamma secretion by spleen cells, Ab production, CTL activity, and development of protective antitumor immunity. Together, our data show that gene gun immunization is capable of inducing humoral and cell-mediated immune reactions independently of LC.

CD4 T cell-induced, bid-dependent apoptosis of cutaneous dendritic cells regulates T cell expansion and immune responses

The fate of dendritic cells (DCs) after Ag presentation may be DC subset-specific and controlled by many factors. The role of activation-induced apoptosis in regulating DC function is not clear. We investigated the fate of cutaneous DCs (cDCs), specifically Langerhans cells (LCs), and observed that they undergo apoptosis after successful Ag presentation to CD4 T cells. Caspase-specific inhibitors revealed that LC lines use a type II apoptosis pathway in response to CD4 T cells. In support of this, BH3-interacting domain (Bid) protein was present at high levels and specifically cleaved in the presence of Ag-specific T cells. Significant resistance to apoptosis by OT-2 CD4 cells was also observed for Bid knockout (KO) LCs in vitro. To test whether Bid was required to regulate LC function in vivo, we measured contact sensitization and topical immunization responses in Bid KO mice and observed markedly enhanced ear swelling and proliferation responses compared with wild-type mice. Furthermore, when Ag-pulsed Bid KO migratory cDCs were inoculated into wild-type recipients, an increase in both the rate and percentage of expanded OT-2 T cells expressing IFN-gamma was observed. Thus, enhanced Ag presentation function was intrinsic to Bid KO cDCs. Therefore, Bid is an important regulator of LC viability and Ag presentation function.

Uptake characteristics of NGR-coupled stealth PEI/pDNA nanoparticles loaded with PLGA-PEG-PLGA tri-block copolymer for targeted delivery to human monocyte-derived dendritic cells

We have investigated the in vitro uptake, toxicity, phenotypic consequences and transfection efficiency of a stealth NGR/PEG/PDBA-coupled-SHA-PEI/pDNA targeting polyplex loaded with PLGA-PEG-PLGA tri-block copolymer in human monocyte-derived dendritic cells (DCs). Modification with PEG effectively shielded and reduced non-specific phagocytosis by immature DCs to approximately 20%. Coupling the NGR cell-specific peptide to the PEGylated polyplex (NGR/PEG/PDBA-SHA-PEI/pDNA) however resulted in specific and enhanced phagocytosis in DCs without any observable toxicity at the optimum concentration of 0.25% of the copolymer. DNase treatment had no effect on DNA integrity in the encapsulated polyplex. Confocal microscopy confirmed intracellular localization of the targeting NGR/PEG/PDBA-SHA-PEI/pDNA microparticles, resulting in more enhanced uptake of the radiolabeled plasmid DNA and approximately 5- and 10-fold increase over the control tri-block Pluronic F68 copolymer and the non-targeting polyplex, respectively. More importantly, phagocytosis of the targeting microparticles neither altered the functionality of immature DCs nor the phenotypic expression of DC-specific cell surface molecules, CD80, CD86, CD40 and CD54 (ICAM-1), suggesting that uptake of the targeting microparticles by themselves did not induce DC maturation. Taken together, these results suggest that PLGA-PEG-PLGA encapsulation of this stealth targeting polyplex has no negative effects on key properties of immature DCs and should pave the way for targeting DCs for vaccination purposes.

Nonviral delivery of cancer genetic vaccines

The potential use of genetic vaccines to address numerous diseases including cancer is promising, but currently unrealized. Here, we review advances in the nonviral delivery of antigen-encoded plasmid DNA for the purpose of treating cancer through the human immune system, as this disease has drawn the most attention in this field to date. Brief overviews of dendritic cell immunobiology and the mechanism of immune activation through genetic vaccines set the stage for the desirability of delivery technology. Several promising nonviral delivery techniques are discussed along with a mention of targeting strategies aimed at improving the potency of vaccine formulations. Implications for the future of genetic vaccines are also presented.

Downregulation of IgE antibody and allergic responses in the lung by epidermal biolistic microparticle delivery

BACKGROUND

Biolistic injections provide a needle-free delivery of antigen-laden microparticles to the epithelium. The precision of the injection preferentially targets the Langerhans cell network, which, although ideal for vaccination, might not be suitable for the downregulation of immune responses in immunotherapy.

OBJECTIVE

We sought to determine the ability of biolistic injection of antigen into the epithelium of sensitized mice to inhibit IgE antibody and lung inflammatory responses produced by further exposure to antigen.

METHODS

Mice were sensitized by means of a needle injection of ovalbumin (OVA) in alum and given a series of biolistic injections of OVA or vehicle control, followed by a boost of OVA in alum. Serum IgE and IgG antibodies were measured before and after the boost. The mice were then challenged intranasally, and the infiltration of inflammatory cells was measured by means of bronchoalveolar lavage. Airway reactivity of the challenged mice was measured by examining responses to methacholine with forced oscillatory techniques.

RESULTS

Biolistic injection of OVA into the dorsal skin of sensitized mice markedly inhibited IgE and IgG1 antibody responses induced by boosting. IgG2a antibody responses were reduced rather than stimulated. The eosinophilic inflammation in the bronchoalveolar lavage fluid induced by intranasal challenge was also markedly inhibited. Lung hyperreactivity showed an initial increase and then a decrease of responsiveness to methacholine, with elastance returning to the level of unsensitized mice. Biolistic injection into the buccal epithelium was also inhibitory.

CONCLUSIONS

Biolistic injection of allergen inhibited the boosting of IgE antibody and eosinophilic lung inflammatory responses without inducing T(H)1 immunity.

Transfection of a mouse dendritic cell line by plasmid DNA-loaded PLGA microparticles in vitro

Targeting of DC for DNA vaccination may be achieved by DNA-loaded poly(lactide-co-glycolide) (PLGA) biodegradable microparticles, since DC efficiently capture these microparticles in vitro and in vivo. DNA was encapsulated in PLGA microparticles by spray-drying. Various additives were tested and process parameters adjusted in order to prevent degradation of the DNA during encapsulation. The highest degree of supercoiled DNA was maintained by adding a strong buffering agent, such as PBS or NaHCO(3), whereas the cryoprotective lactose did not show a significant protective effect. DNA-containing PLGA microparticles were administered to a mouse DC line. Transfection efficacy was compared with commonly employed cationic transfectants and was visually assessed by green fluorescent protein expression. Transfection rate was very low in DC for all microparticle formulations and was comparable with commonly used cationic transfectants. It is concluded that the transfection of DC using PLGA microparticles is feasible, but efforts need to be undertaken to improve transfection efficiency in vitro, which may in addition lead to improved immune responses in vivo.

"Hijacking" the thyrotropin receptor: A chimeric receptor-lysosome associated membrane protein enhances deoxyribonucleic acid vaccination and induces Graves' hyperthyroidism

Naked DNA vaccination with the TSH receptor (TSHR) does not, in most studies, induce TSHR antibodies and never induces hyperthyroidism in BALB/c mice. Proteins expressed endogenously by vaccination are preferentially presented by major histocompatibility complex class I, but optimal T cell help for antibody production requires lysosomal processing and major histocompatibility complex class II presentation. To divert protein expression to lysosomes, we constructed a plasmid with the TSHR ectodomain spliced between the signal peptide and transmembrane-intracellular region of lysosome-associated membrane protein (LAMP)-1, a lysosome-associated membrane protein. BALB/c mice pretreated with cardiotoxin were primed intramuscularly using this LAMP-TSHR chimera and boosted twice with DNA encoding wild-type TSHR, TSHR A-subunit, or LAMP-TSHR. With each protocol, spleen cells responded to TSHR antigen by secreting interferon-gamma, and 60% or more mice had TSHR antibodies detectable by ELISA. TSH binding inhibitory activity was present in seven, four, and two of 10 mice boosted with TSHR A-subunit, LAMP-TSHR, or wild-type TSHR, respectively. Importantly, six of 30 mice had elevated T4 levels and goiter (5 of 6 with detectable thyroid-stimulating antibodies). Injecting LAMP-TSHR intradermally without cardiotoxin pretreatment induced TSHR antibodies detectable by ELISA but not by TSH binding inhibitory activity, and none became hyperthyroid. These findings are consistent with a role for cardiotoxin-recruited macrophages in which (unlike in fibroblasts) LAMP-TSHR can be expressed intracellularly and on the cell surface. In conclusion, hijacking the TSHR to lysosomes enhances T cell responses and TSHR antibody generation and induces Graves'-like hyperthyroidism in BALB/c mice by intramuscular naked DNA vaccination.

Langerhans cells activate naive self-antigen-specific CD8 T cells in the steady state

TCR transgenic mice that express a peptide antigen in keratinocytes develop a lethal CD8 T cell-dependent autoimmune disease. We employed an adoptive transfer system to understand this disease and show that transfer of low numbers of naive CD8 T cells into peptide transgenic mice caused chronic skin disease. The antigen-presenting cell that initiated this response was the epidermal Langerhans cell. Naive CD8 T cells proliferated extensively, migrated to tissues, developed effector function, and were capable of making a recall response. These features are very different from the abortive activation of CD8 T cells that occurred in response to the same antigen presented by APC from other tissues. Furthermore, tolerance was dominant when the antigen was presented by both Langerhans cells and other APC. These data suggest that Langerhans cells do not have tolerogenic properties in the steady state.

Epicutaneous application of CpG oligodeoxynucleotides with peptide or protein antigen promotes the generation of CTL

Immunostimulatory oligodeoxynucleotides (ODN) are effective adjuvants in the induction of humoral and cellular immune responses when administered parenterally with antigen. The skin has recently become a target organ for the design of non-invasive vaccine technologies. Using ovalbumin (OVA) as a model antigen, we demonstrate that the application of ODN sequences to tape-stripped skin promotes the induction of potent cytotoxic T lymphocyte (CTL) responses to co-administered peptide. Induction of peptide-specific CTL required the presence of CpG motifs within the ODN. CTL afforded tumor protection against a tumor expressing an immunodominant OVA CTL epitope. CTL could also be induced to whole protein administered onto the skin. Differential CpG sequence activity was noted with respect to the induction of CTL to epicutaneous protein with an ODN sequence containing a poly-G motif having an optimal effect. Peptide-specific CTL could be detected in the peripheral blood as early as 6 d after a single immunization. These results highlight the potential of the bare skin as a route for vaccine development and indicate an important role for immunostimulatory ODN as adjuvants to generate functional CTL with the help of the skin immune system.

Transcutaneous immunization induces mucosal CTLs and protective immunity by migration of primed skin dendritic cells

Transcutaneous immunization (TCI), the application of vaccines on the skin, induces robust systemic and mucosal antibodies in animal models and in humans. The means by which mucosal immune responses to vaccine antigens are elicited by TCI has not been well characterized. We examined the effect of TCI with an HIV peptide vaccine on the induction of mucosal and systemic CTL responses and protective immunity against mucosal challenge with live virus in mice. Robust HIV-specific CTL responses in the spleen and in the gut mucosa were detected after TCI. The responses were dependent upon the addition of an adjuvant and resulted in protection against mucosal challenge with recombinant vaccinia virus encoding HIV gp160. Although it is clear that adjuvant-activated DCs migrated mainly to draining lymph nodes, coculture with specific T cells and flow cytometry studies with DCs isolated from Peyer's patches after TCI suggested that activated DCs carrying skin-derived antigen also migrated from the skin to immune-inductive sites in gut mucosa and presented antigen directly to resident lymphocytes. These results and previous clinical trial results support the observation that TCI is a safe and effective strategy for inducing strong mucosal antibody and CTL responses.

Optimization of epicutaneous immunization for the induction of CTL

The immune system of the skin has recently been exploited for the development of non-invasive vaccine technologies. However, one of the limitations of current vaccine protocols is the inefficient priming of cytotoxic T lymphocytes (CTL). In this study, we report that the application of either an immunodominant class I MHC restricted ovalbumin peptide or whole ovalbumin protein, to tape-stripped skin together with the co-application of the bacterial enterotoxin cholera toxin (CT) induces antigen-specific CTL. Tape-stripping (TS) was found to enhance the magnitude of antibody responses to co-administered protein and to promote the generation of antigen-specific IgG(2a) responses. As well, both cholera toxin and tape-stripping enhanced epidermal dendritic cell (DC) immigration into draining lymph nodes. The adjuvant effect of co-administered cholera toxin and tape-stripping in promoting CTL priming was not dependent on IL-12. Epicutaneous immunization has previously been shown to induce robust antibody responses to administered protein antigen. We now demonstrate the induction of robust and persistent CTL responses to epicutaneously administered protein antigen. Epicutaneous immunization is cheap, simple and effective. These findings suggest the potential use of the skin for the generation of protective immune responses to both viral and tumor challenge.

Species differences in the structure and function of the immune system

With the recent publication of regulatory guidelines from both the FDA and the CPMP addressing the investigation of immunotoxicity of new chemical entities has come the requisite increased application of immunotoxicology protocols. Importantly, the fulfillment of these protocols may require the use of different species, and while in many cases information concerning the structure and function of the immune system can be readily translated across species, there are numerous and significant species differences that need to be considered. In some cases, the generation of meaningful immunotoxicology data can be adversely affected by the choice of a species that does not adequately share the immune function of concern with man. Likewise immunotoxicology testing in one species may produce negative data in one species but positive data in another. Knowing the mechanistic basis through an understanding of species differences in the structure and function of the immune system is pivotal to success. This becomes especially true as pharmaceutical companies design and develop highly specific immunomodulatory molecules that demonstrate species-specific pharmacology. This review is an exploration of various species differences in the structure and function of the immune system and an attempt to identify those differences that may be important in the conduct of immunotoxicity tests.

Drug-inducible, dendritic cell-based genetic immunization

Determining the mechanism of Ag loading of Langerhans cells (LC) for genetic immunization (GI) is complicated by the inability to distinguish between the response generated by direct transfection of LC from that due to exogenous uptake. To unravel this mechanism, we examined the impact of gene gun treatment on LC with respect to their activation and migration from skin, transgene expression, and ability to initiate humoral and cellular immune responses upon transfer to naive mice. To assess responses generated by direct LC transfection, an RU486-inducible expression system was used as a GI vector. In vitro skin organ cultures were developed from gene gun immunized mouse ear specimens to obtain LC. Gene gun treatment markedly augmented (3-fold) LC migration from ear skin, and these LC expressed the transgene at RNA and protein levels. Transfer of 2 x 10(5) migratory cells resulted in identical cellular responses to, but 10-fold lower humoral responses than, standard GI. Using an RU486-inducible system, we were able to measure responses generated by directly transfected LC. Our results indicate that direct transfection is a predominant pathway for LC Ag loading. The ability to regulate transgene expression with inducible DC-based vaccines demonstrates a new level of immunological control.

The potential of antibody-based immunosuppressive agents for corneal transplantation

Corneal transplantation is a sight-restorative procedure but its success is limited by irreversible graft rejection, which accounts for up to 50 per cent of failures. The normal eye is an immune-privileged site. Multiple mechanisms maintain ocular privilege, including the blood-eye barrier, the lack of blood vessels and lymphatics in the normal cornea, the relative paucity of mature antigen-presenting cells in the central cornea, the presence of immunomodulatory factors in ocular fluids, and the constitutive expressive of CD95L (Fas ligand) within the eye. However, privilege can be eroded by the sequelae of inflammation and neovascularization. Corneal graft rejection in humans is currently suppressed with topical glucocorticosteroids, which are moderately effective. Systemically administered immunosuppressive therapy is of limited efficacy and may be accompanied by unacceptable morbidity. Alternative therapies are needed to improve outcomes. Corneal graft rejection is primarily a cell-mediated response controlled by the CD4+ T cell, and thus CD4 and costimulatory molecule blockade are appealing targets for new therapeutic interventions. A number of monoclonal antibodies have shown promise as immunosuppressants to prolong corneal graft survival in experimental animal models, and may eventually prove to be useful adjuncts to corticosteroids.

Langerhans cell-like dendritic cells in the cornea, tongue and oesophagus of the chicken (Gallus gallus)

Langerhans cells are dendritic leucocytes which reside mainly within stratified squamous epithelia of skin and mucosa. Their visualization requires the use of ATPase histochemistry, electron microscopy for identifying the unique trilaminar cytoplasmic organelles (the Langerhans cell granules or Birbeck granules), and the expression of major histocompatibility complex class II molecules. Following uptake of antigen, Langerhans cells migrate via the afferent lymphatics to the lymph nodes and undergo differentiation from an antigen-processing cell to an antigen-presenting cell. Using the same approach as that employed in previous studies for the identification of chicken epidermal Langerhans cells, we show here the presence of ATPase-positive and major histocompatibility complex class II-positive Langerhans cell-like dendritic cells at the mucosal surface of the eye, tongue and oesophagus of the chicken. Ultrastructurally, these cells qualified as Langerhans cells except that they lack Langerhans cell granules. Thus, as in mammalian skin and mucosa, chicken mucosa contains mucosal dendritic cells with morphological and phenotypical features for the engagement of incoming antigens within epithelium and lamina propria.

Epidermal powder immunization induces both cytotoxic T-lymphocyte and antibody responses to protein antigens of influenza and hepatitis B viruses

Cytotoxic T lymphocytes (CTL) play a vital role in host defense against viral and intracellular bacterial infections. However, nonreplicating vaccines administered by intramuscular injection using a syringe and needle elicit predominantly humoral responses and not CTL responses. Here we report that epidermal powder immunization (EPI), a technology that delivers antigens on 1.5- to 2.5-microm gold particles to the epidermis using a needle-free powder delivery system, elicits CTL responses to nonreplicating antigens. Following EPI, a majority of the antigen-coated gold particles were found in the viable epidermis in the histological sections of the target skin. Further studies using transmission electron microscopy revealed the intracellular localization of the gold particles. Many Langerhans cells (LCs) at the vaccination site contained antigen-coated particles, as revealed by two-color immunofluorescence microscopy, and these cells were found in the draining lymph nodes 20 h later. Immune responses to several viral protein antigens after EPI were studied in mice. EPI with hepatitis B surface antigen (HBsAg) and a synthetic peptide of influenza virus nucleoprotein (NP peptide) elicited antigen-specific CTL responses as well as antibody responses. In an in vitro cell depletion experiment, we demonstrated that the CTL activity against HBsAg elicited by EPI was attributed to CD8(+), not CD4(+), T cells. As controls, needle injections of HBsAg or the NP peptide into deeper tissues elicited solely antibody, not CTL, responses. We further demonstrated that EPI with inactivated A/Aichi/68 (H3N2) or A/Sydney/97 (H3N2) influenza virus elicited complete protection against a mouse-adapted A/Aichi/68 virus. In summary, EPI directly delivers protein antigens to the cytosol of the LCs in the skin and elicits both cellular and antibody responses.

Comparative analysis of dendritic cell density and total number in commonly transplanted organs: morphometric estimation in normal mice

Dendritic cells (DC) are considered to be the major cell type responsible for induction of primary immune responses. While they have been shown to play a critical role in eliciting allosensitization via the direct pathway, there is evidence that maturational and/or activational heterogeneity between DC in different donor organs may be crucial to allograft outcome. Despite such an important perceived role for DC, no accurate estimates of their number in commonly transplanted organs have been reported. Therefore, leukocytes and DC were visualized and enumerated in cryostat sections of normal mouse (C57BL/10, B10.BR, C3H) liver, heart, kidney and pancreas by immunohistochemistry (CD45 and MHC class II staining, respectively). Total immunopositive cell number and MHC class II+ cell density (C57BL/10 mice only) were estimated using established morphometric techniques--the fractionator and disector principles, respectively. Liver contained considerably more leukocytes (approximately 5-20 x 10(6)) and DC (approximately 1-3 x 10(6)) than the other organs examined (pancreas: approximately 0.6 x 10(6) and approximately 0.35 x 10(6); heart: approximately 0.8 x 10(6) and approximately 0.4 x 10(6); kidney approximately 1.2 x 10(6) and 0.65 x 10(6), respectively). In liver, DC comprised a lower proportion of all leukocytes (approximately 15-25%) than in the other parenchymal organs examined (approximately 40-60%). Comparatively, DC density in C57BL/10 mice was heart > kidney > pancreas >> liver (approximately 6.6 x 10(6), 5 x 10(6), 4.5 x 10(6) and 1.1 x 10(6) cells/cm3, respectively). When compared to previously published data on allograft survival, the results indicate that the absolute number of MHC class II+ DC present in a donor organ is a poor predictor of graft outcome. Survival of solid organ allografts is more closely related to the density of the donor DC network within the graft.

Immunobiology of xenogeneic cornea grafts in mouse eyes. I. Fate of xenogeneic cornea tissue grafts implanted in anterior chamber of mouse eyes

BACKGROUND

The cornea is an immune privileged tissue that, when grafted orthotopically, forms the anterior surface of the immune privileged anterior chamber. We have recently reported that allogeneic cornea fragments implanted in the anterior chamber of mouse eyes resist immune rejection, although such graft fragments are rejected outside the eye. We wished to determine the extent to which xenogeneic cornea fragments placed in the eyes of normal mice are vulnerable to immune rejection.

METHODS

Guinea pig corneas, deprived surgically of epithelium, were cut into fragments and inserted into the anterior chamber of eyes of BALB/c and severe combined immune deficient (SCID) mice, adjacent to the central cornea of the recipient. The fate of the grafts was assessed clinically by biomicroscopy and histologically for 8 weeks postimplantation.

RESULTS

The majority of guinea pig cornea fragments devoid of epithelium came to rest with the raw stroma adjacent to recipient endothelium. These fragments remained clear for the 8-week observation interval in both BALB/c and severe combined immune deficient mice. Clear grafts displayed viable guinea pig keratocytes and endothelial cell layers for 4 weeks. The endothelium was then replaced by murine cells by 8 weeks. A minority of guinea pig cornea fragments were oriented with donor endothelium adjacent to recipient endothelium. Although these grafts in severe combined immune deficient eyes eventually acquired an endothelial layer that faces the anterior chamber and remained clear, similar fragments in BALB/c eyes became opaque, failed to acquire a proper lining of endothelium that faces the anterior chamber, and incited an inflammatory reaction in adjacent recipient cornea.

CONCLUSIONS

Immune privilege is afforded to xenografts of guinea pig cornea placed as stromal: endothelial cell fragments in the anterior chamber of mouse eyes, but only if the surface of the fragments that faces the anterior chamber is promptly covered with corneal endothelium. The possible roles of corneal endothelium in promoting immune privilege of corneal xenografts are discussed.

Immunobiology of xenogeneic cornea grafts in mouse eyes. II. Immunogenicity of xenogeneic cornea tissue grafts implanted in anterior chamber of mouse eyes

BACKGROUND

Xenogeneic corneal fragments (guinea pig) are highly resistant to immune rejection in the anterior chamber of mouse eyes. Because guinea pigs and mice are discordant (i.e., mouse serum normally contains guinea pig reactive xenoantibodies), we wished to determine the extent to which xenogeneic corneal fragments placed intraocularly in normal and specifically sensitized mice activated xenoreactive T and B cells.

METHODS

Guinea pig corneas, deprived surgically of epithelium, were cut into fragments and inserted into the anterior chamber of eyes of BALB/c mice, adjacent to the central cornea of the recipient. Antibody (immunoglobulin [Ig]M, IgG) and delayed type hypersensitivity (DTH) immune responses of recipient mice to guinea pig xenoantigens were assessed. The fate of xenogeneic cornea implants was assessed in mice immunized systemically to guinea pig antigens.

RESULTS

Guinea pig spleen cells and corneal fragments implanted s.c. induced within 2 weeks of immunization both DTH and IgG antibodies to guinea pig xenoantigens. By contrast, xenogeneic corneal fragments implanted in the anterior chamber of mouse eyes evoked no change in recipient humoral immune status and induced mild guinea pig-specific DTH only after 5 weeks. Presensitization of mice to guinea pig xenoantigens failed to increase the proportion of grafts that were regarded as rejected, but the onset of rejection in failed grafts occurred earlier than in unsensitized recipients. Active systemic immunization of mice bearing intracameral guinea pig corneal fragments failed to curtail the grafts' survival. Guinea pig corneal fragments implanted in the anterior chamber of normal mice failed to induce anterior chamber-associated immune deviation.

CONCLUSIONS

Xenogeneic corneal fragments implanted in the anterior chamber of eyes of normal mice display strikingly reduced immunogenicity, and an inability to induce anterior chamber-associated immune deviation. These properties are discussed in terms of the vulnerability of guinea pig corneal tissue to immune rejection within the eye.

Neural influences on induction of contact hypersensitivity

Contact hypersensitivity (CH)-induction begins when cutaneous antigen-presenting cells (APC) capture hapten that has been applied epicutaneously, and the process prepares hapten for presentation to T-cells. APCs are functionally plastic, are influenced by the microenvironment in which they reside, and their functional properties have a profound effect on the phenotype of the hapten-specific T-cells that they activate. Ultraviolet B radiation (UVR) distorts the cutaneous microenvironment, thereby altering local APC function, and changing the immune outcome from sensitization to unresponsiveness. Although UVR induces keratinocytes to produce TNF alpha and IL-10 (cytokines that have been implicated in failed CH-induction and tolerance, respectively, after UVR), dermal mast cells turn out to be the source of these immunomodulatory cytokines. Mast cell degranulation is triggered by CGRP released from UVR-exposed cutaneous nerve termini. Even in normal skin, cutaneous nerves influence the immune response to haptens. Substance P released from cutaneous nerves acts as an adjuvant, raising the immunogenicity of epicutaneously applied haptens. Thus, the nerves and the neuropeptides that these processes release contribute to the cutaneous microenvironment. By altering APC function, cutaneous nerves can dictate the quality and the quantity of immune responses to antigens of the skin.

Quantitative analysis of the immunopotency of genetically transfected dendritic cells

Dendritic cells (DCs) instruct and activate a naive immune system to mount a response toward foreign proteins. Therefore, it has been hypothesized that an ideal vaccine strategy would be to directly introduce genes encoding antigens into DCs. To test this strategy quantitatively, we have compared the immune response elicited by a genetically transfected DC line to that induced by a fibroblast line, or standard genetic immunization. We observe that a single injection of 500-1,000 transfected DCs can produce a response comparable to that of standard genetic immunization, whereas fibroblasts, with up to 50-fold greater transfection efficiency, were less potent. We conclude that transfection of a small number of DCs is sufficient to initiate a wide variety of immune responses. These results indicate that targeting genes to DCs will be important for controlling and augmenting the immunological outcome in genetic immunization.

alpha beta T cell development is abolished in mice lacking both Lck and Fyn protein tyrosine kinases

Two families of protein tyrosine kinases (PTKs), the Src and Syk/ZAP-70 families, are required for T cell development. Lck is the major Src family member required for thymopoiesis, since there is a severe deficit of CD4+CD8+ thymocytes and mature T cells in its absence. However, some peripheral T cells are evident in these mice, suggesting that additional PTKs may contribute to T cell development. Here we show that the combined disruption of Lck and Fyn (lck(-/-)fyn(-/-)) completely arrests alpha beta T cell development at the CD4-CD8- stage. The development of V gamma 3+ dendritic epidermal T cells is also severely impaired, but natural killer cell development and cytolytic activity is unaffected in lck(-/-)fyn(-/-) mice. These findings reveal the potential for redundant functions mediated by Src family PTKs while emphasizing crucial roles for Lck and Fyn in T cell development.

The hamster cheek pouch: an immunologically privileged site suitable to the study of granulomatous infections

The hamster cheek pouch is an invagination of oral mucosa, characterized histologically as skin-like. In this paper we describe anatomical, histological and embriological features of the pouch and comment on the pouch as an immunologically privileged site since it lacks lymphatic drainage and has few Langerhans cells. We present the review from literature and our observations after inoculation in the pouch of mycobacteriae (BCG, Mycobacterium tuberculosis and Mycobacterium leprae) and a fungus (Paracoccidioides brasiliensis). Lesions in the pouch were granulomatous but smaller and long lasting; even granulomatous, the reaction was inefficient to control the proliferation of agents compared with inoculation in other sites, except for BCG. Appearance of immunity was also delayed or absent and, when it was detected, a sharp decrease in number of agents in pouch lesions was observed. These observations make the pouch an interesting site for the study of the role of immune system in infectious diseases and in granuloma formation.

The pharmacology of immunosuppressant drugs in skin transplant rejection in mice and other rodents

1. Skin transplantation in rodents is a convenient, widely used method, particularly in mice. It is used as much as an indicator of immune responsiveness as for pharmacological studies. 2. Many differences exist in experimental protocols, both for transplantation and drug administration and in this review, the increase in graft survival time with respect to control times is used to indicate drug effects, in an attempt to account for these differences. 3. The mechanisms underlying skin graft rejection in rodents are described, emphasising the crucial role of both helper and effector T cells. 4. The pharmacology of clinically-used immunosuppressants, including CsA, FK506, rapamycin and purine or pyrimidine synthesis inhibitors, in rodent models of skin transplantation is reviewed. 5. The effects of other potential immunosuppressants and compounds modulating immune responses are described, including the effects of UV light and involvement of platelet-derived factors, prostaglandins and thromboxanes.