The study of H. pylori putative candidate factors for single- and multi-component vaccine development

Helicobacter pylori has grown to colonize inside the stomach of nearly half of the world’s population, turning into the most prevalent infections in the universe. Medical care failures noticeably confirm the need for a vaccine to hinder or deal with H. pylori. This review is planned to discuss the most known factors as a vaccine candidate, including single (AhpC, BG, CagA, KatA, Fla, Hsp, HWC, Lpp, LPS, NAP, OMP, OMV, SOD, Tpx, Urease, VacA) and multi-component vaccines. Many promising results in the field of single and multivalent vaccine can be seen, but there is no satisfactory outcome and neither a prophylactic nor a therapeutic vaccine to treat or eradicate the infection in human has been acquired. Hence, selecting suitable antigen is an important factor as an appropriate adjuvant. Taken all together, the development of efficient anti-H. pylori vaccines relies on the fully understanding of the interactions between H. pylori and its host immune system. Therefore, more work should be done on epitope mapping, analysis of molecular structure, and determination of the antigen determinant region as well due to design a vaccine, preferably a multi-component vaccine to elicit specific CD4 T-cell responses that are required for H. pylori vaccine efficacy.     

The effect of stable macromolecular complexes of ionic polyphosphazene on HIV Gag antigen and on activation of human dendritic cells and presentation to T-cells

Neonates and infants are susceptible to infection due to distinct immune responses in early life. Therefore, development of vaccine formulation and delivery systems capable of activating human newborn leukocytes is of global health importance. Poly[di(carboxylatophenoxy)phosphazene] (PCPP) belongs to a family of ionic synthetic polyphosphazene polyelectrolyte compounds that can form non-covalent interactions with protein antigens and demonstrate adjuvant activity in animals and in human clinical trials. However, little is known about their ability to activate human immune cells. In this study, we characterized the effects of PCPP alone or in combination with a model antigen (recombinant HIV-Gag (Gag)), on the maturation, activation and antigen presentation by human adult and newborn dendritic cells (DCs) in vitro. PCPP treatment induced DC activation as assessed by upregulation of co-stimulatory molecules and cytokine production. Studies benchmarking PCPP to Alum, the most commonly used vaccine adjuvant, demonstrated that both triggered cell death and release of danger signals in adult and newborn DCs. When complexed with Gag antigen, PCPP maintained its immunostimulatory characteristics while permitting internalization and presentation of Gag by DCs to HIV-Gag-specific CD4⁺ T cell clones. The PCPP vaccine formulation outlined here has intrinsic adjuvant activity, can facilitate effective delivery of antigen to DCs, and may be advantageous for induction of beneficial T cell-mediated immunity. Moreover, polyphosphazenes can further reduce cost of vaccine production and distribution through their dose-sparing and antigen-stabilizing properties, thus potentially eliminating the need for cold chain distribution.     

Robust immune response elicited by a novel and unique Mycobacterium tuberculosis protein using an optimized DNA/protein heterologous prime/boost protocol

An efficacious tuberculosis (TB) vaccine will probably need to induce both CD4 and CD8 T‐cell responses specific to a protective Mycobacterium tuberculosis antigen(s). To achieve this broad cellular immune response we tested a heterologous DNA/protein combination vaccine strategy. We used a purified recombinant protein preparation of a unique M. tuberculosis antigen (rMT1721) found in the urine of TB patients, an optimized plasmid DNA expressing this protein (DNA‐MT1721), and a Toll‐like receptor 4 agonist adjuvant. We found that priming mice with DNA‐MT1721 and subsequently boosting with rMT1721 elicited high titres of specific IgG1 and IgG2a antibodies as well as high magnitude and polyfunctional CD4⁺ T‐cell responses. However, no detectable CD8⁺ T‐cell response was observed using this regimen of immunization. In contrast, both CD4⁺ and CD8⁺ T‐cell responses were detected after a prime/boost vaccination regimen using rMT1721 as the priming antigen and DNA‐MT1721 as the boosting immunogen. These findings support the exploration of heterologous DNA/protein immunization strategies in vaccine development against TB and possibly other infectious diseases.     

Intradermal vaccination against hepatitis B virus infection in an endemic area (Nigeria), two year results

Summary To determine the efficacy and safety of hepatitis B vaccine (Hevac B) given intradermally, 125 Nigerians (aged 1 year to 45 years), who were negative for hepatitis B virus markers, and randomised into two groups were vaccinated. Group 1 (64 volunteers) was given 3 monthly doses of 2 µg vaccine mixed with adjuvant subcutaneously (Institut Pasteur Production-Hevac B) while group 2 (61 volunteers) received 3 doses of 2 µg non-adjuvated vaccine intradermally given 1 month apart. A month after the third dose 83 per cent of group 1, 71 per cent of group 2 showed positive response by developing antibody to hepatitis B surface antigen. The levels of antibody were significantly higher in group 1 at each stage of the follow-up period, including a month after a booster vaccination was given. The positive response was maintained in almost all the initial responders for the 24 month duration of the study. No significant side effect was documented in any of the participants. The results suggest that population at risk in developing countries could be protected with small doses of vaccine administered intradermally.With 1 Figure     

Characterization and Optimization of the Glucan Particle-Based Vaccine Platform

Glucan particles (GPs) are hollow porous Saccharomyces cerevisiae cell walls that are treated so that they are composed primarily of β-1,3-d-glucans. Our previous studies showed that GPs can serve as an effective vaccine platform. Here, we characterize CD4⁺ T-cell and antibody responses in immunized mice as a function of antigen (ovalbumin) encapsulation, antigen dose, particle numbers, time, immunization schedule, and trapping methods. Although we found that GPs served as an effective adjuvant when admixed with free antigens for IgG1 antibody production, stronger CD4⁺ T-cell and IgG2c antibody responses were stimulated when antigens were encapsulated inside GPs, suggesting that the GP platform acts as both an adjuvant and a delivery system. Vigorous T-cell and antibody responses were stimulated even at submicrogram antigen doses, as long as the number of GPs was kept at 5 × 10⁷ particles per immunization. One prime and one boost were sufficient to elicit robust immune responses. In addition, strong antigen-specific antibody and T-cell responses prevailed up to 20 months following the last immunization, including those of gamma interferon (IFN-γ), interleukin 17A (IL-17A), and dual IFN-γ/IL-17A-secreting CD4⁺ T cells. Finally, robust immune responses were observed using generally recognized as safe (GRAS) materials (alginate and calcium, with or without chitosan) to trap antigens within GPs. Thus, these studies demonstrate that antigens encapsulated into GPs make an effective vaccine platform that combines adjuvanticity and antigen delivery to elicit strong durable immune responses at relatively low antigen doses using translationally relevant formulations.     

Montanide ISA 71 VG is Advantageous to Freund's Adjuvant in Immunization Against S. aureus Infection of Mice

The enormous capacity of Staphylococcus aureus to acquire antibiotic resistance makes it a permanent task to search for and to develop new anti‐infectives. One of the possible approaches is the early active immunization of risk patients and animal stocks to prevent S. aureus infections. Based on a S. aureus proteome screen with S. aureus‐specific human antiserum, we have previously identified several anchorless cell wall proteins to be used as novel vaccine candidates. To develop an efficient anti‐S. aureus vaccine, the supplemented adjuvants Montanide^? ISA 71 VG and ISA 206 were compared to Freund's adjuvant in terms of handling, induction of cytokine profile, triggering antigen‐specific immunoglobulin production of different IgG subclasses and provision of increased survival rates in our S. aureus sepsis mouse model. Immunization with ISA 71 VG in comparison with Freund's adjuvant induced slightly delayed but comparably strong increase of antigen‐specific antibody titres and conferred protective effect against S. aureus challenge. In contrast using ISA 206 as adjuvant, significantly lower IgG titres and consequently, no protective effect against S. aureus infection were observed. Handling and tolerability of the Montanide is superior to Freund's adjuvant. Montanide^? ISA 71 VG can serve as an effective adjuvant replacement for Freund's adjuvant in research with a prospective usage in animal and human vaccines against bacterial pathogens.     

Evaluation of the adjuvant effect of Salmonella-based Escherichia coli heat-labile toxin B subunits on the efficacy of a live Salmonella-delivered avian pathogenic Escherichia coli vaccine

The present study evaluated the adjuvant effect of live attenuated salmonella organisms expressing the heat-labile toxin of Escherichia coli B subunit (LTB) on the efficacy of an avian pathogenic Escherichia coli (APEC) vaccine. The Asd⁺ (aspartate semialdehyde dehydrogenase) plasmid pMMP906 containing the LTB gene was introduced into a Salmonella enterica Typhimurium strain lacking the lon, cpxR and asd genes to generate the adjuvant strain. Live recombinant Salmonella-delivered APEC vaccine candidates were used for this study. The birds were divided into three groups: group A, non-vaccinated controls; group B, immunized with vaccine candidates only; and group C, immunized with vaccine candidates and the LTB strain. The immune responses were measured and the birds were challenged at 21 days of age with a virulent APEC strain. Group C showed a significant increase in plasma IgG and intestinal IgA levels and a significantly higher lymphocyte proliferation response compared with the other groups. Upon challenge with the virulent APEC strain, group C showed effective protection whereas group B did not. We also attempted to optimize the effective dose of the adjuvant. The birds were immunized with the vaccine candidates together with 1×10⁷ or 1×10⁸ colony-forming units of the LTB strain and were subsequently challenged at 3 weeks of age. The 1×10⁷ colony-forming units of the LTB strain showed a greater adjuvant effect with increased levels of serum IgG, intestinal IgA and a potent lymphocyte proliferation response, and yielded higher protection against challenge. Overall, the LTB strain increased the efficacy of the Salmonella -delivered APEC vaccine, indicating that vaccination for APEC along with the LTB strain appears to increase the efficacy for protection against colibacillosis in broiler chickens.     

Protease‐activated receptor‐2 signalling by tissue factor on dendritic cells suppresses antigen‐specific CD4+ T‐cell priming

The precise function of tissue factor (TF) expressed by dendritic cells (DC) is uncertain. As well as initiating thrombin generation it can signal through protease‐activated receptor 2 (PAR‐2) when complexed with factor VIIa. We investigated the expression and function of TF on mouse bone marrow (BM) ‐derived DC; 20% of BM‐derived DC expressed TF, which did not vary after incubation with lipopolysaccharide (LPS) or dexamethasone (DEX). However, the pro‐coagulant activity of DEX‐treated DC in recalcified plasma was 30‐fold less than LPS‐treated DC. In antigen‐specific and allogeneic T‐cell culture experiments, the TF on DEX‐treated DC provided a signal through PAR‐2, which contributed to the reduced ability of these cells to stimulate CD4⁺ T‐cell proliferation and cytokine production. In vivo, an inhibitory anti‐TF antibody and a PAR‐2 antagonist enhanced antigen‐specific priming in two models where antigen was given without adjuvant, with an effect approximately 50% that seen with LPS, suggesting that a similar mechanism was operational physiologically. These data suggest a novel TF and PAR‐2‐dependent mechanism on DEX‐DC in vitro and unprimed DC in vivo that contributes to the low immunogenicity of these cells. Targeting this pathway has the potential to influence antigen‐specific CD4⁺ T‐cell activation.     

Heat‐Shock Protein gp96 Enhances T Cell Responses and Protective Potential to Bacillus Calmette‐Guérin Vaccine

The commonly used Bacillus Calmette‐Guérin (BCG) vaccine only induces moderate T cell responses and is less effective in protecting against pulmonary tuberculosis (TB) in adults and ageing populations. Thus, developing new TB vaccine candidates is an important strategy against the spread of Mycobacterium tuberculosis. Here, we demonstrated that immunization with heat‐shock protein gp96 as an adjuvant led to a significantly increased CD4⁺ and CD8⁺ T cell response to a BCG vaccine. Secretion of the Th1‐type cytokines was increased by splenocytes from gp96‐immunized mice. In addition, adding gp96 as an adjuvant effectively improved the protection against intravenous challenge with Mycobacterium bovis BCG in mice. Our study reveals the novel property of gp96 in boosting the vaccine‐specific T cell response and its potential use as an adjuvant for BCG vaccines against mycobacterial infection.     

Time Relationships Between Injection of Antigen and Adjuvant I. Adjuvancy of Bordetella pertussis Given at Various Times Before the Primary Antigenic Stimulus

The adjuvant activity of Bordetella pertussis was investigated, both at the cellular and humoral levels, when the bacterial adjuvant was administered at various times before the primary antigenic stimulus of both 8 × 10⁶ and 4 × 10⁸ sheep erythrocytes. In all experiments, both adjuvant and erythrocyte antigen were given intraperitoneally. Adjuvant activity was measured on the basis of the primary immune response and on the degree of priming for the secondary immune reaction. A maximal effect on the primary immune response was found in mice which had received B. pertussis vaccine simultaneously with the erythrocyte antigen. A significant degree of adjuvancy was also demonstrable when B. pertussis vaccine was administered within a period of 48 hr before antigen. Adjuvant effectiveness was less as the time interval between the injection of antigen and adjuvant increased. The process of priming for the secondary response, however, was found to be equally affected when the adjuvant was given either simultaneously with the antigen or 12, 24, and 48 hr before sheep erythrocytes. On the basis of these and previous findings, it is suggested that adjuvancy of B. pertussis is caused chiefly by additional recruitment of responding cells. It is also suggested that memory-cell production may develop concurrently with, but independently of, the cellular proliferative events which lead to antibody formation during the primary immune response.     

Protective effect of egg-propagated Eimeria tenella (local isolates) gametocytes as vaccine(s) against mixed species of coccidia in chickens

Egg propagated gametocytes of Eimeria tenella (local isolates) were used to prepare the adjuvanted (Amphigen) and nonadjuvanted vaccine(s) and evaluated on the basis of cellular, humoral, and challenge responses. Modified splenic cell migration inhibition test and enzyme-linked immunosorbant assay were used to assess the cellular and humoral responses, respectively. Chicken in groups A, B, C, and D were given adjuvanted vaccine (orally), adjuvanted vaccine (subcutaneously, s/c), nonadjuvanted vaccine (orally), and nonadjuvanted vaccine s/c, respectively. Control groups E, F, G, and H were given adjuvant (orally), adjuvant (s/c), phosphate-buffered saline (PBS) + adjuvant (orally), and PBS + adjuvant (s/c), respectively. On 5 and 15 days post vaccination after boosting, significantly higher (P<0.05) cell-mediated and humoral responses were detected in vaccinated chicken compared to control. No significant effect of adjuvant and vaccination route on the immune responses was found. Maximum percent protection (survivors after challenge) against mixed species of genus Eimeria was observed in group A (71.42%) followed by group C (63.63%), B (59.09%), and group D (54.54). Significantly higher (P<0.05) oocysts per gram (OPG) of droppings was observed in the control groups compared to the vaccinated chickens. Maximum percent reduction in OPG was also recorded in group A (86) followed by group C (84), group B (83), and group D (82). From these results, it was concluded that egg-propagated gametocytes (E. tenella) that gave protection upon challenge may be due to the control of E. tenella. Further studies on its feasibility as commercial vaccine are underway.     

Multiple Antigen Peptide Containing B and T Cell Epitopes of F1 Antigen of Yersinia pestis Showed Enhanced Th1 Immune Response in Murine Model

Yersinia pestis is a facultative bacterium that can survive and proliferate inside host macrophages and cause bubonic, pneumonic and systemic infection. Apart from humoral response, cell‐mediated protection plays a major role in combating the disease. Fraction 1 capsular antigen (F1‐Ag) of Y. pestis has long been exploited as a vaccine candidate. In this study, F1‐multiple antigenic peptide (F1‐MAP or MAP)‐specific cell‐mediated and cytokine responses were studied in murine model. MAP consisting of three B and one T cell epitopes of F1‐antigen with one palmitoyl residue was synthesized using Fmoc chemistry. Mice were immunized with different formulations of MAP in poly DL‐lactide‐co‐glycolide (PLGA) microspheres. F1‐MAP with CpG oligodeoxynucleotide (CpG‐ODN) as an adjuvant showed enhanced in vitro T cell proliferation and Th1 (IL‐2, IFN‐γ and TNF‐α) and Th17 (IL‐17A) cytokine secretion. Similar formulation also showed significantly higher numbers of cytokine (IL‐2, IFN‐γ)‐secreting cells. Moreover, F1‐MAP with CpG formulation showed significantly high (P < 0.001) percentage of CD4⁺ IFN‐γ⁺ cells as compared to CD8⁺ IFN‐γ⁺ cells, and also more (CD4‐ IFN‐γ)⁺ cells secrete perforin and granzyme as compared to (CD8‐ IFN‐γ)⁺ showing Th1 response. Thus, the study highlights the importance of Th1 cytokine and existence of CD4⁺ and CD8⁺ immune response. This study proposes a new perspective for the development of vaccination strategies for Y. pestis that trigger T cell immune response.     

Anti-CD2 (OX34) MoAb treatment of adjuvant arthritic rats: attenuation of established arthritis, selective depletion of CD4+ T cells, and CD2 down-modulation

Anti-CD2 MoAbs have previously been shown to induce tolerance and to block B cell differentiation, T cell and monocyte activation. Since these immune functions are important in joint inflammation, we asked whether administration of the anti-CD2 MoAb OX34 has a beneficial effect on established rat adjuvant arthritis, a model of human rheumatoid arthritis, and how it affects CD2-bearing leucocyte subsets. Female Lewis rats with established adjuvant arthritis received a total of 5 mg OX34 or isotype-matched control MoAb starting on day 15 after adjuvant injection. Weight and arthritis score (AS) were measured in a blinded fashion. Peripheral blood cells were analysed for numbers of leucocyte subsets at various time points. Animals were killed on day 30 and lymphatic organs were processed for immunohistology. Clinically, OX34 treatment led to increased body weight and reduced AS. Although OX34 binds to CD4⁺ and CD8⁺ T cells in a comparable fashion, OX34 treatment reduced CD4⁺ T cells, but not CD8⁺ T cells. Among CD4⁺ T cells CD45RC⁺ (‘naive’) T cells virtually disappeared; CD45RC⁻ (‘recently activated’) T cells were slightly reduced. A reduction of CD4⁺ T cells was also found in the lung, liver, bone marrow, spleen and lymph nodes. Down-modulation of the CD2 molecule by OX34, again, affected CD4⁺ T cells, suggesting a specific signal for CD4⁺ but not CD8⁺ T cells. In conclusion, the anti-CD2 MoAb OX34 attenuates established rat adjuvant arthritis. In spite of similar binding to CD4⁺ and CD8⁺ T cells, OX34 depletes only CD4⁺ T cells and down-modulates the CD2 molecule on these cells. These results suggest a therapeutic benefit from CD2-directed therapy for chronic types of arthritis.     

Intradermal Delivery of Recombinant Vaccinia Virus Vector DIs Induces Gut‐Mucosal Immunity

Antigen‐specific mucosal immunity is generally induced by the stimulation of inductive mucosal sites. In this study, we found that the replication‐deficient vaccinia virus vector, DIs, generates antigen‐specific mucosal immunity and systemic responses. Following intradermal injection of recombinant DIs expressing simian immunodeficiency virus gag (rDIsSIVgag), we observed increased levels of SIV p27‐specific IgA and IgG antibodies in faecal extracts and plasma samples, and antibody‐forming cells in the intestinal mucosa and spleen of C57BL/6 mice. Antibodies against p27 were not detected in nasal washes, saliva, and vaginal washes. The enhanced mucosal and systemic immunity persisted for 1 year of observation. Induction of Gag‐specific IFN‐γ spot‐forming CD8⁺ T cells in the spleen, small intestinal intraepithelial lymphocytes, and submandibular lymph nodes was observed in the intradermally injected mice. Heat‐inactivated rDIsSIVgag rarely induced antigen‐specific humoral and T‐helper immunity. Moreover, rDIsSIVgag was detected in MHC class II IA antigen‐positive (IA⁺) cells at the injection site. Consequently, intradermal delivery of rDIs effectively induces antigen‐specific humoral and cellular immunity in gut‐mucosal tissues of mice. Our data suggest that intradermal injection of an rDIs vaccine may be useful against mucosally transmitted pathogens.     

Immunogenicity and protective efficacy of a DNA vaccine encoding the fusion protein of mycobacterium heat shock protein 65(Hsp65) with human interleukin‐2 against Mycobacterium tuberculosis in BALB/c mice

Developing a new generation of vaccines is important for preventing tuberculosis (TB). DNA vaccine is one promising candidate. In this study we evaluated the immunogenicity and protective efficacy of the DNA vaccine encoding the fusion protein of Mycobacterium tuberculosis heat shock protein 65 (Hsp65) with human interleukin‐2 (hIL‐2) in BALB/c mice. We showed that the DNA vaccine pcDNA‐Hsp65‐hIL‐2 could induce high levels of antigen‐specific antibody, IFN‐γ, CD4⁺ and CD8⁺ T cell production. When the immunized mice were infected with M. tuberculosis H37Rv, the organ bacterial loads in the DNA immunized group were significantly reduced compared to those of the saline control group, but the ability to reduce bacteria was not better than for BCG. The histopathology in lungs of the DNA vaccine immunized mice was similar to that of BCG immunized mice, which was obviously ameliorated compared to that of the saline control group. Overall, the DNA vaccine could afford protection against M. tuberculosis infection, though the protection efficacy was not as great as that of conventional BCG.     

Canola oilseed- and Escherichia coli- derived hepatitis C virus (HCV) core proteins adjuvanted with oil bodies,induced robust Th1-oriented immune responses in immunized mice

Induction of broad Th1 cellular immune responses and cytokines is crucial characteristics for vaccines against intracellular infections such as hepatitis C virus (HCV). Plants (especially oilseed tissues) and plant-immunomodulators (like oil bodies) offer cost-effective and scalable possibilities for the production of immunologically relevant and safe vaccine antigens and adjuvants, respectively. Herein, we provide data of the murine immunization by transgenic canola oilseed-derived HCV core protein (HCVcp) soluble extract (TSE) and Escherichia coli- derived rHCVcp in combination with Canola oil bodies (oil) compared to that of the Freund’s (FA) adjuvant. Mice immunized by TSE+ oil developed both strong humeral (IgG) and Th1-biased cellular responses, manifested by high levels of IFN-γ and lower IgG1/IgG2a ratio and IL-4 secretion. Results of the intracellular cytokine staining indicated that TSE+ oil immunization in mice triggered both CD4⁺ and CD8⁺ T cells to release IFN-γ, while CD4⁺ cells were mostly triggered when FA was used. Analyses by qRT-PCR indicated that a combination of rHCVcp/TSE with oil body induced high levels of IL-10 cytokines compared to that of the FA adjuvant. These characteristics are important properties for the design of an HCV vaccine candidate and indicate the potential of Canola-derived antigen and oil bodies in addressing these concerns.     

Increased number and function of natural killer cells in human immunodeficiency virus 1‐positive subjects co‐infected with herpes simplex virus 2

Natural killer (NK) cells bridge the interface between innate and adaptive immunity and are implicated in the control of herpes simplex virus 2 (HSV‐2) infection. In subjects infected with human immunodeficiency virus 1 (HIV‐1), the critical impact of the innate immune response on disease progression has recently come into focus. Higher numbers of NK cells are associated with lower HIV‐1 plasma viraemia. Individuals with the compound genotype of killer cell immunoglobulin‐like receptor (KIR) 3DS1 and human leucocyte antigen (HLA)‐Bw4‐80I, or who have alleles of KIR3DL1 that encode proteins highly expressed on the NK cell surface, have a significant delay in disease progression. We studied the effect of HSV‐2 co‐infection in HIV‐1‐infected subjects, and show that HSV‐2 co‐infection results in a pan‐lymphocytosis, with elevated absolute numbers of CD4⁺ and CD8⁺ T cells, and NK cells. The NK cells in HSV‐2 co‐infected subjects functioned more efficiently, with an increase in degranulation after in vitro stimulation. The number of NK cells expressing the activating receptors NKp30 and NKp46, and expressing KIR3DL1 or KIR3DS1, was inversely correlated with HIV‐1 plasma viral load in subjects mono‐infected with HIV‐1, but not in subjects co‐infected with HSV‐2. This suggests that HSV‐2 infection mediates changes within the NK cell population that may affect immunity in HIV‐1 infection.     

The role of antigen-presenting cells and interleukin-12 in the priming of antigen-specific CD4+ T cells by immune stimulating complexes

Immune stimulating complexes (ISCOMs) containing the saponin adjuvant Quil A are vaccine adjuvants that promote a wide range of immune responses in vivo, including delayed-type hypersensitivity (DTH) and the secretion of both T helper 1 (Th1) and Th2 cytokines. However, the antigen-presenting cell (APC) responsible for the induction of these responses has not been characterized. Here we have investigated the role of dendritic cells (DC), macrophages (Mφ) and B cells in the priming of antigen-specific CD4⁺ T cells in vitro by ISCOMs containing ovalbumin (OVA). OVA ISCOMs pulsed bone marrow (BM)-derived DC but not BM Mφ, nor naïve B cells prime resting antigen-specific CD4⁺ T cells, and this response is greatly enhanced if DC are activated with lipopolysaccharide (LPS). Of the APC found in the spleen, only DC had the capacity to prime resting antigen specific CD4⁺ T cells following exposure to OVA ISCOMs in vitro, while Mφ and B cells were ineffective. DC, but not B cells purified from the draining lymph nodes of mice immunized with OVA ISCOMs also primed resting antigen-specific CD4⁺ T cells in vitro, suggesting that DC are also critical in vivo. Using DC and T cells from interleukin (IL)-12 p40^−/− mice, we also identified a crucial role for IL-12 in the priming of optimal CD4⁺ T cell responses by OVA ISCOMs. We suggest that DC are the principal APC responsible for the priming of CD4⁺ T cells by ISCOMs in vivo and that directed targeting of these vectors to DC may enhance their efficancy as vaccine adjuvants.     

Studies of the immunological activities of the outer membrane protein from Escherichia coli

The outer membrane protein (OMP) prepared from Escherichia coli was found to be a potent mitogen for murine B cells and to be capable of inducing polyclonal antibody formation as well as a proliferative response. Spleen cells from nude mice responded equally as well to OMP as those from their normal litter-mates, whereas nylon-wool-purified T cells or thymocytes failed to respond. The proliferative response was dependent on the presence of macrophages. The macrophage dependency of the polyclonal antibody response seemed to be less than that of the proliferation. OMP was mitogenic for lipopolysaccharide (LPS)-resistant C3H/HeJ spleen cells, further indicating that OMP is an unique B-cell mitogen distinct from LPS.

OMP also enhanced the specific antibody response sixty-seven-fold to an optimal dose of sheep red blood cells (SRBC) in vitro. The kinetics of the response, however, was not altered from that of cultures without OMP. The anti-SRBC response of spleen cells from C3H/HeJ mice was also enhanced by the addition of OMP, suggesting that the adjuvant effects were not due to the LPS in the preparation. Antibody responses in vitro to TI-1 antigens, trinitrophenyl-LPS (Boivin) (TNP-LPS^B) and TNP-Brucella abortus, were not enhanced in the presence of OMP. In contrast OMP enhanced the response to TI-2 antigens, TNP-LPS^W (Westphal) and dinitrophenyl-Ficoll and T cells were shown to be required for these augmented antibody responses. Enhancement was not seen in nude mouse spleen cell cultures but was seen when nylon-wool-purified T cells were added to the cultures.