Immune responses of systemic and mucosal lymphoid organs to Pnu-Imune vaccine as a function of age and the efficacy of monophosphoryl lipid A as an adjuvant

B cell-expressed CD1d promotes MPL/TDCM lipid emulsion adjuvant effects in polysaccharide vaccines

T cell-independent type 2 antigens (TI-2 Ags), such as pneumococcal polysaccharides, elicit weak immunoglobulin G (IgG) responses and are refractive to boosting. Overcoming this challenge is critical for improving vaccines. Previously, we demonstrated a lipid-based adjuvant composed of monophosphoryl lipid A, synthetic cord factor, and squalene significantly boosts primary and secondary IgM and IgG production against polysaccharide Ags. Herein, we show beta-2 microglobulin, but not MHC class II, is essential for adjuvant-induced increases in polysaccharide-specific IgG levels. Furthermore, we demonstrate CD1d expression is essential for optimal adjuvant-induced increases in IgG, but is not required for IgG responses to TI-2 Ags administered without adjuvant, with the exception of the bacterial cell wall polysaccharide component, phosphorylcholine. Adoptive transfer of splenic and peritoneal cells from VHB1-8 transgenic mice into CD1d-/- mice revealed adjuvant-induced increases in NP-Ficoll-specific IgG production by CD1d+/+ transgenic B cells, but not recipient B cells, suggesting B cell-expressed CD1d is critical for adjuvant-induced effects on TI-2 antibody responses. Consistent with this, bone marrow chimera mice with selective CD1d deficiency in B cells demonstrated B cell-expressed CD1d was dispensable for iNKT cell development and maintenance but was required for adjuvant-induced increases in protective levels of polysaccharide- and phosphorylcholine-specific IgG. Notably, both iNKT cells and CD1d crosslinking significantly increased IgG production by B cells coactivated with TI-2 Ag and adjuvant, suggesting iNKT-induced CD1d signaling may promote increased IgG production. In summary, our study reveals B cell-dependent CD1d expression is critical for effectiveness of a potent lipid-based adjuvant in augmenting polysaccharide- and phosphorylcholine-specific IgG responses.

Type I IFN Receptor Signaling on B Cells Promotes Antibody Responses to Polysaccharide Antigens

We previously reported monophosphoryl lipid A (MPL) and synthetic cord factor trehalose-6,6'-dicorynomycolate (TDCM) significantly increase Ab responses to T cell-independent type 2 Ags (TI-2 Ags) in a manner dependent on B cell-intrinsic TLR4 expression, as well as MyD88 and TRIF proteins. Given the capacity of MPL to drive type I IFN production, we aimed to investigate the extent to which type I IFN receptor (IFNAR) signaling was required for TI-2 responses and adjuvant effects. Using Ifnar1-/- mice and IFNAR1 Ab blockade, we found that IFNAR signaling is required for optimal early B cell activation, expansion, and Ab responses to nonadjuvanted TI-2 Ags, including the pneumococcal vaccine. Further study demonstrated that B cell-intrinsic type I IFN signaling on B cells was essential for normal TI-2 Ab responses. In particular, TI-2 Ag-specific B-1b cell activation and expansion were significantly impaired in Ifnar1-/- mice; moreover, IFNAR1 Ab blockade similarly reduced activation, expansion, and differentiation of IFNAR1-sufficient B-1b cells in Ifnar1-/- recipient mice, indicating that B-1b cell-expressed IFNAR supports TI-2 Ab responses. Consistent with these findings, type I IFN significantly increased the survival of TI-2 Ag-activated B-1b cells ex vivo and promoted plasmablast differentiation. Nonetheless, MPL/TDCM adjuvant effects, which were largely carried out through innate B cells (B-1b and splenic CD23- B cells), were independent of type I IFN signaling. In summary, our study highlights an important role for B-1b cell-expressed IFNAR in promoting responses to nonadjuvanted TI-2 Ags, but it nonetheless demonstrates that adjuvants which support innate B cell responses may bypass this requirement.

The PD-1 Regulatory Axis Inhibits T Cell-Independent B Cell Memory Generation and Reactivation

The inability of T cell-independent type 2 (TI-2) Ags to induce recall responses is a poorly understood facet of humoral immunity, yet critically important for improving vaccines. Using normal and V_HB1-8 transgenic mice, we demonstrate that B cell-intrinsic PD-1 expression negatively regulates TI-2 memory B cell (B_mem) generation and reactivation in part through interacting with PDL1 and PDL2 on non-Ag-specific cells. We also identified a significant role for PDL2 expression on B_mems in inhibiting reactivation and Ab production, thereby revealing a novel self-regulatory mechanism exists for TI-2 B_mems This regulation impacts responses to clinically relevant vaccines, because PD-1 deficiency was associated with significantly increased Ab boosting to the pneumococcal vaccine after both vaccination and infection. Notably, we found a B cell-activating adjuvant enabled even greater boosting of protective pneumococcal polysaccharide-specific IgG responses when PD-1 inhibition was relieved. This work highlights unique self-regulation by TI-2 B_mems and reveals new opportunities for significantly improving TI-2 Ag-based vaccine responses.

An Adjuvant That Increases Protective Antibody Responses to Polysaccharide Antigens and Enables Recall Responses

Protection against encapsulated bacteria can be elicited using polysaccharide vaccines. These antigens often behave as T-cell-independent type 2 antigens (TI-2 Ags). However, TI-2 Ags, including pneumococcal polysaccharides, often elicit weak immunoglobulin G (IgG) responses and are refractive to boosting. Conjugate vaccines have not completely overcome this challenge and hence, alternative strategies are required to enhance polysaccharide vaccine responses. Herein, we describe an adjuvant consisting of a Toll-like receptor and C-type lectin receptor agonist pairing that significantly increases primary immunoglobulin M and IgG responses to TI-2 Ags as well as enables significant boosting when coadministered with polysaccharide vaccines. Consistent with this, the adjuvant significantly increased the generation of both TI-2 memory B cells and long-lived antibody secreting cells. Adjuvant effects were highly dependent on B-cell-intrinsic MyD88, but not Trif expression. Importantly, coadministration of the adjuvant with the Pneumovax vaccine significantly increased the protective efficacy of vaccination in a lethal challenge mouse model of pneumococcal respiratory infection. Collectively, these data provide evidence that B-cell-directed adjuvants have promise in significantly improving the quality and quantity of serologic and B-cell memory responses to clinically relevant polysaccharide vaccines.

Strong dose response after immunotherapy with PQ grass using conjunctival provocation testing

Background

Pollinex Quattro Grass (PQ Grass) is an effective, well-tolerated, short pre-seasonal subcutaneous immunotherapy to treat seasonal allergic rhinoconjunctivitis (SAR) due to grass pollen. In this Phase II study, 4 cumulative doses of PQ Grass and placebo were evaluated to determine its optimal cumulative dose.

Methods

Patients with grass pollen-induced SAR were randomised to either a cumulative dose of PQ Grass (5100, 14400, 27600 and 35600 SU) or placebo, administered as 6 weekly subcutaneous injections over 31-41 days (EudraCT number 2017-000333-31). Standardized conjunctival provocation tests (CPT) using grass pollen allergen extract were performed at screening, baseline and post-treatment to determine the total symptom score (TSS) assessed approximately 4 weeks after dosing. Three models were pre-defined (Emax, logistic, and linear in log-dose model) to evaluate a dose response relationship.

Results

In total, 95.5% of the 447 randomized patients received all 6 injections. A highly statistically significant (p < 0.0001), monotonic dose response was observed for all three pre-specified models. All treatment groups showed a statistically significant decrease from baseline in TSS compared to placebo, with the largest decrease observed after 27600 SU (p < 0.0001). The full course of 6 injections was completed by 95.5% of patients. Treatment-emergent adverse events were similar across PQ Grass groups, and mostly mild and transient in nature.

Conclusions

PQ Grass demonstrated a strong curvilinear dose response in TSS following CPT without compromising its safety profile.

Growth Hormone (GH) Deficient Mice With GHRH Gene Ablation Are Severely Deficient in Vaccine and Immune Responses Against Streptococcus pneumoniae

The precise impact of the somatotrope axis upon the immune system is still highly debated. We have previously shown that mice with generalized ablation of growth hormone (GH) releasing hormone (GHRH) gene (Ghrh^−/−) have normal thymus and T-cell development, but present a marked spleen atrophy and B-cell lymphopenia. Therefore, in this paper we have investigated vaccinal and anti-infectious responses of Ghrh^−/− mice against S. pneumoniae, a pathogen carrying T-independent antigens. Ghrh^−/− mice were unable to trigger production of specific IgM after vaccination with either native pneumococcal polysaccharides (PPS, PPV23) or protein-PPS conjugate (PCV13). GH supplementation of Ghrh^−/− mice restored IgM response to PPV23 vaccine but not to PCV13 suggesting that GH could exert a specific impact on the spleen marginal zone that is strongly implicated in T-independent response against pneumococcal polysaccharides. As expected, after administration of low dose of S. pneumoniae, wild type (WT) completely cleared bacteria after 24 h. In marked contrast, Ghrh^−/− mice exhibited a dramatic susceptibility to S. pneumoniae infection with a time-dependent increase in lung bacterial load and a lethal bacteraemia already after 24 h. Lungs of infected Ghrh^−/− mice were massively infiltrated by inflammatory macrophages and neutrophils, while lung B cells were markedly decreased. The inflammatory transcripts signature was significantly elevated in Ghrh^−/− mice. In this animal model, the somatotrope GHRH/GH/IGF1 axis plays a vital and unsuspected role in vaccine and immunological defense against S. pneumoniae.

Calculating therapeutic indices and therapeutic advantages for endotoxins and monophosphoryl lipid A: an evaluation of data from the scientific literature

This review article addresses the question of whether or not monophosphoryl lipid A offers a therapeutic advantage over smaller doses of endotoxin. Biological data were collected from a literature review and these were used to calculate therapeutic indices for monophosphoryl lipid A and endotoxin. Subsequent calculations yielded results which showed that, in humans and in other animals, monophosphoryl lipid A did have a therapeutic advantage over smaller doses of endotoxin.

Evaluation of the effect of MPL and delivery route on immunogenicity and protectivity of different formulations of FimH and MrpH from uropathogenic Escherichia coli and Proteus mirabilis in a UTI mouse model

Urinary tract infections (UTIs) caused by Escherichia coli and Proteus mirabilis are an important cause of morbidity and with the high rate of relapse and spread of multi-drug resistant pathogens, pose a significant public health challenge worldwide. Lack of an efficacious commercial vaccine targeting both uropathogens makes development of a combined vaccine highly desirable. In this study the immunogenicity and protective efficacy of different formulations of FimH of UPEC, MrpH of P. mirabilis and their fusion protein (MrpH.FimH) subcutaneously administered with and without Monophosphoryl lipid A (MPL) adjuvant were evaluated. Our data showed that the subcutaneously administered proteins induced both serum and mucosal IgG, which MPL significantly improved developing a mixed Th1 and Th2 immune response. However, the preparations induced a higher systemic and mucosal IgG and IL-2 levels by this route compared to the intranasal. Immunization of mice with MrpH.FimH fusion with MPL or a mixture of FimH, MrpH and MPL conferred the highest protection of the bladder and kidneys when challenged with UPEC and P. mirabilis in a UTI mouse model. Therefore considering these results MrpH.FimH fusion with MPL administered subcutaneously or intranasally could be a promising vaccine candidate for elimination of UTIs caused by UPEC and P. mirabilis.

The thymus-independent immunity conferred by a pneumococcal polysaccharide is mediated by long-lived plasma cells

It was recently shown that bacterial thymus-independent (TI) antigens confer long-lasting immunity and generate memory B lymphocytes. However, reactivation of TI memory B cells is repressed in immunocompetent mice, thus raising the issue of the mechanism whereby TI vaccines confer immune protection. Here, we propose an explanation to this apparent paradox by showing that a Streptococcus pneumoniae capsular polysaccharide (PS) generates long-lived bone marrow (BM) plasma cells which frequency can be increased by CpG oligodeoxynucleotides (ODNs). The adjuvant effect of CpG ODNs on the PS3 Ab response is directly targeted to B cells and does not involve B-1a cells. We also demonstrated that BM plasma cells generated in response to the thymus-dependent (TD) form of the PS vaccine have a higher secretion capacity than those produced after immunization with the CpG-adjuvanted PS vaccine. Finally, we show that the PS-specific BM plasma cell compartment is sufficient to confer full protection of vaccinated mice against S pneumoniae infection. Altogether, our results show that TI antigens like their TD counterparts can generate both the lymphoid and the plasma cell component of B-cell memory. They also provide a framework for the improvement and widespread usage of TI vaccines.

Immunization of aged mice with a pneumococcal conjugate vaccine combined with an unmethylated CpG-containing oligodeoxynucleotide restores defective immunoglobulin G antipolysaccharide responses and specific CD4+-T-cell priming to young adult levels

Polysaccharide (PS)-protein conjugate vaccines, in contrast to purified PS vaccines, recruit CD4+-T-cell help and restore defective PS-specific humoral immunity in the immature host. Surprisingly, in the immunocompromised, aged host, anti-PS responses to conjugate vaccines are typically no better than those elicited by purified PS vaccines. Although aging leads to defects in multiple immune cell types, diminished CD4+-T-cell helper function has recently been shown to play a dominant role. We show that in response to immunization with purified pneumococcal capsular PS serotype 14 (PPS14) in saline, the T-cell-independent immunoglobulin G (IgG) anti-PPS14 response in aged mice was comparable to that in young mice. In contrast, the T-cell-dependent IgG anti-PPS14 response to a soluble conjugate of PPS14 and pneumococcal surface protein A (PspA) (PPS14-PspA) in saline was markedly defective. This was associated with defective priming of PspA-specific CD4+ T cells. In contrast, immunization of aged mice with PPS14-PspA combined with an unmethylated CpG-containing oligodeoxynucleotide (CpG-ODN) restored IgG anti-PPS14 responses to young adult levels, which were substantially higher than those observed using purified PPS14. This was associated with enhanced PspA-specific CD4+-T-cell priming. Similarly, intact Streptococcus pneumoniae capsular type 14, which contains Toll-like receptor (TLR) ligands, also induced substantial, though modestly reduced, T-cell-dependent (TD) IgG ant-PPS14 responses in aged mice. Spleen and peritoneal cells from aged and young adult mice made comparable levels of proinflammatory cytokines in response to CpG-ODN, although cells from aged mice secreted higher levels of interleukin-10. Collectively, these data suggest that inclusion of a TLR ligand, as an adjuvant, with a conjugate vaccine can correct defective TD IgG anti-PS responses in elderly patients by augmenting CD4+-T-cell help.

Defective microarchitecture of the spleen marginal zone and impaired response to a thymus-independent type 2 antigen in mice lacking scavenger receptors MARCO and SR-A

The macrophage scavenger receptor macrophage receptor with a collagenous structure (MARCO) is expressed in mice by the marginal zone macrophages of the spleen and by macrophages of the medullary cords of lymph nodes, as well as the peritoneal macrophages. MARCO is a relative of scavenger receptor A (SR-A), the more widely expressed prototypic member of the scavenger receptor family. In the present study, we found that genetic ablation of MARCO leads to changes in the organization of the splenic marginal zone, and causes a significant reduction in the size of the resident peritoneal macrophage population, possibly due to changes in adhesion and migration capacity. In mice lacking both MARCO and SR-A these effects are even more apparent. During ontogeny, the appearance and organization of the MARCO-expressing cells in the spleen precedes the appearance of other receptors on macrophages in the marginal zone, such as SIGNR1 and Siglec-1. In the absence of MARCO, a clear delay in the organization of the marginal zone was observed. Similar findings were seen when the reappearance of the various subsets from precursors was studied after depleting macrophages from the adult spleen by a liposome treatment. When challenged with a pneumococcal polysaccharide vaccine, a T-independent type 2 Ag for which an intact marginal zone is crucial, the knockout mice exhibited a clearly impaired response. These findings suggest that both MARCO and SR-A, in addition to being important scavenger receptors, could be involved in the positioning and differentiation of macrophages, possibly through interaction with endogenous ligands.

The unresponsiveness of aged mice to polysaccharide antigens is a result of a defect in macrophage function

A reduction in macrophage (MPhi) function with aging makes mice less responsive to bacterial capsular polysaccharides, such as those present in the pneumococcal polysaccharide vaccine, a model of thymus independent (TI) antigen (Ag). Using trinitrophenol (TNP)-lipopolysaccharide (LPS) and TNP-Ficoll, two other well-studied TI Ag, we studied the mechanistic basis of reduced MPhi function in the aged. We show that aged mice are profoundly hyporesponsive to these TI Ag. As a result of a requirement for MPhi, highly purified B cells from young-adult mice do not respond to TI Ag. When purified, young B cells were immunized with TNP-Ficoll, the antibody production from those cultures reconstituted with MPhi from aged mice was significantly lower than that seen with young MPhi. Consequently, this unresponsiveness can be overcome by a mixture of interleukin (IL)-1beta and IL-6. Upon stimulation with LPS, in comparison with young MPhi, aged MPhi secreted reduced amounts of IL-6, tumor necrosis factor alpha, IL-1beta, and IL-12, cytokines necessary for B cells to respond to TI Ag. LPS also induced aged MPhi to produce an excess of IL-10. Neutralization of IL-10 enhanced the production of proinflamatory cytokines by MPhi upon LPS stimulation and also induced Ab production by aged splenocytes. Thus, the inability of aged MPhi to help the B cell response appears to be caused by an excess of IL-10. As aged MPhi have a reduced number of cells expressing Toll-like receptor 4 and CD14, the imbalance in cytokine production might be partly a result of fewer cells expressing key components of the LPS receptor complex.

Safety evaluation of monophosphoryl lipid A (MPL): an immunostimulatory adjuvant

Animal models have shown the potential use of monophosphoryl lipid A (MPL), a detoxified bacterial lipopolysaccharide, as a vaccine adjuvant. Immunostimulatory activity with diverse effects on the cellular elements of the immune system has been demonstrated and a range of vaccines incorporating MPL, including allergy vaccines, are currently under clinical evaluation. A series of preclinical safety investigations was performed to support clinical use of MPL as used in allergy vaccines and comprised cardiovascular/respiratory assessment in dog (up to 100 microg/kg/day); repeat-dose toxicity in rat, rabbit, and dog (up to 2500 and 1200 microg/kg/day in the rat and dog, respectively); reproduction toxicity in rat and rabbit (up to 100 microg/kg/day); and genotoxicity studies. Overall, repeat-dose toxicity studies in the rat and dog showed expected immunostimulatory effects and/or signs of toxicity associated with overstimulation of the immune system (notably increased spleen weight and white blood cell values). Studies in the rabbit with weekly doses of MPL produced no effects. MPL was shown to have no adverse effects on cardiovascular/respiratory function, reproduction, and genotoxicity.

Intranasal immunization with protein-linked phosphorylcholine protects mice against a lethal intranasal challenge with streptococcus pneumoniae

Immunization against phosphorylcholine (PC) linked to a protein protects mice against Streptococcus pneumoniae when used parenterally, and against Salmonella typhimurium when used orally after entrapment in D,L-Lactide-co-Glycolide microspheres. Here, we immunized BALB/c mice intranasally with a serotype 3 S. pneumoniae strain. Immunization was followed by a rise in anti-PC IgA and IgG titers in serum and in pulmonary secretions, but not by any rise in anti ds-DNA antibody nor any glomerular Ig deposition. The survival rates were 91 and 76% in the two groups of mice, respectively. These rates were significantly higher than those in control mice immunized intranasally either with Thyr loaded in microspheres (0%), blank microspheres (22%), free Thyr (17%), and saline (18%). This demonstrates that the mucosal route is effective for vaccination against S. pneumoniae pneumonia with PC linked to a protein carrier. It constitutes another important step forward in the development of the concept that PC can be used as a mucosal immunogen for protection against the different diseases caused by PC-bearing bacteria.

Production of protective human antipneumococcal antibodies by transgenic mice with human immunoglobulin loci

Infections with Streptococcus pneumoniae remain a significant cause of morbidity and mortality. To gain insight into structure-function relationships for human antibodies to pneumococcal capsular polysaccharide (PPS), we studied the response of transgenic mice reconstituted with human immunoglobulin loci, XenoMouse, to PPS antigens in a pneumococcal vaccine. Enzyme-linked immunosorbent assays of sera from mice vaccinated with a 23-valent pneumococcal vaccine revealed that they produced serotype-specific human antibodies, with the greatest response being to the PPS of serotype 3 (PPS 3). Molecular sequence analysis of three monoclonal antibodies (MAbs) to PPS 3 generated from lymphoid cells from mice vaccinated with a 23-valent pneumococcal vaccine or a PPS 3-bovine serum albumin conjugate revealed that they all used heavy-chain immunoglobulin genes from the V(H)3 family, two expressed light chain genes from the human Vkappa1 family, and one expressed a mouse lambda light chain. The protective efficacy of the two MAbs was examined in mice. A 10-microgram dose of both, and a 1-microgram dose of one, significantly prolonged survival from a lethal serotype 3 infection in CBA/N mice. Our data show that XenoMouse mice produced protective, serotype-specific human antibodies to PPS 3, and they lend support to the proposal that these animals represent a useful model to study the human antibody response to PPS antigens.

Pneumococcal vaccines: history, current status, and future directions

Streptococcus pneumoniae is the leading cause of community-acquired pneumonia and bacterial meningitis. Although effective antimicrobial drugs have reduced case fatality, the pneumococcus remains a leading global cause of morbidity and mortality. Therefore, prevention of infection by vaccination with the pneumococcal polysaccharide vaccine is recommended for persons at high risk for serious pneumococcal disease, such as the elderly and individuals with certain underlying medical conditions. Pneumococcal polysaccharide vaccines are safe and effective for the prevention of invasive infection among immunocompetent children and adults but are not immunogenic in infants. Conjugation of pneumococcal polysaccharides to a carrier protein improves immune responses among infants, and conjugate vaccines are currently being evaluated in large efficacy trials. The role of pneumococcal conjugate vaccines in adults has not been determined. Pneumococcal vaccines directed against pneumococcal proteins and DNA vaccines that induce anti-pneumococcal antibodies have been evaluated in animal models and may someday provide complementary or alternative methods for preventing pneumococcal infection. Improved utilization of the pneumococcal polysaccharide vaccine and continued development of improved vaccines are essential, and the emergence of drug-resistant strains of S. pneumoniae highlights the importance of preventing pneumococcal infections by vaccination.

Neonatal Murine B Lymphocytes Respond to Polysaccharide Antigens in the Presence of IL-1 and IL-6

Unlike adults, neonates are unable to respond to polysaccharide Ags, making them especially vulnerable to pathogenic encapsulated bacteria. Since the Ab response to polysaccharides in adult mice requires certain cytokines, it was hypothesized that neonatal murine B cells may be competent to respond to such Ags, but may fail to do so due to a deficiency of cytokines. Neonatal splenocyte cultures, which were otherwise unresponsive to trinitrophenyl (TNP)-Ficoll, a haptenated polysaccharide Ag, mounted an adult-like Ab response when supplemented with IL-1. However, IL-1 failed to induce such a response to TNP-Ficoll when purified B cells were used instead. Although IL-6 alone did not induce a response in whole spleen cells or purified B cells from neonates, it synergized with IL-1 in inducing purified neonatal B cells to respond to TNP-Ficoll. The avidity of the cytokine-induced neonatal anti-TNP Abs was comparable to that of Abs made by adult splenocyte cultures. One effect of IL-1 may be at the level of clonal expansion, since it induced neonatal B cells to proliferate in response to anti-IgM, which was further enhanced by IL-6. The spontaneous secretion of IL-1 by neonatal splenocytes was below the detection limit, while adult splenocytes secreted 30.8 ± 5.2 U/ml, which is of the same order of magnitude as what was required to stimulate neonatal B cells to respond to TNP-Ficoll. Thus, the neonatal unresponsiveness to polysaccharide Ags could be due to the inability of a non-B cell population resident in the neonatal spleen to secrete sufficient quantities of IL-1.

Adjuvants influence the quantitative and qualitative immune response in BALB/c mice immunized with respiratory syncytial virus FG subunit vaccine

The ability of monophosphoryl lipid A (MPL), QS-21 and alum to alter the immunologic response to immunization with respiratory syncytial virus a chimeric FG construct (FG) subunit vaccine was examined in BALB/c mice. FG/MPL, FG/alum, and FG/MPL/QS-21 combinations increased non-neutralizing antibody response, while FG/QS-21 did not. FG subunit vaccine with MPL, QS-21, or both had cytokine responses more closely resembling primary infection than FG/alum, with decreased interleukin-4 mRNA levels and increased IgG2a isotype antibody. The lungs of the mice immunized with FG subunit vaccines showed a heightened inflammatory response to respiratory syncytial virus challenge as compared to live virus immunization. Adjuvants can be used to alter the humoral and cellular responses to RSV subunit immunization.

Cellular basis of decreased immune responses to pneumococcal vaccines in aged mice

Previously, model systems were developed in our laboratory to study murine immune responses to the 23-valent pneumococcal polysaccharide vaccine Pnu-Imune, both in vivo and in vitro (M. Garg and B. Subbarao, Infect. Immun. 60:2329-2336, 1992; M. Garg, A. M. Kaplan, and S. Bondada, J. Immunol. 152: 1589-1596, 1994). Using these systems, we found that aged mice did not respond to the vaccine in vivo or in vitro. Cell separation studies showed that the unresponsiveness of the aged spleen cells to the vaccine was not due to an intrinsic B-cell defect or to T-cell-mediated immunosuppression but resulted from an accessory cell deficiency. Irradiated spleen cells from young mice enabled the old mouse spleen cells to respond to the vaccine. Interestingly, irradiated spleen cells from old mice also restored the vaccine responsiveness in old mice but were required in greater numbers than the young mouse spleen cells to induce similar levels of response. The accessory cell was an adherent cell that could be removed by passage through Sephadex G-10 and thus may be a macrophage. Accessory function could also be provided by the cytokine interleukin-1 (IL-1), IL-4, or IL-5 but not IL-2 or IL-6. Thus, one reason for the deficient immune response to pneumococcal vaccine in aged mice is a quantitative defect in adherent accessory cells.

Induction of pneumococcal polysaccharide-specific mucosal immune responses by oral immunization

Liposome and cholera toxin (CT) are considered to be effective antigen delivery vehicles and adjuvants for mucosal vaccines. The effect of these antigen delivery systems on adjuvant responses to mucosally administered pneumococcal polysaccharide (Pnup) was investigated in this study. Both mucosal (e.g. oral) and systemic (i.p.) immunization of mice with purified preparations of Pnup type 23F induced antigen-specific IgM responses in sera. Interestingly, oral immunization of as little as 10 micrograms of Pnup type 23F was sufficient to induce systemic IgM responses. Pnup-specific IgM antibodies peaked by day 7 and no booster responses were evident after a second dose on day 14. In order to examine whether IgG and IgA Pnup-specific immune responses are induced by mucosal immunization, the mucosal adjuvant CT was mixed with Pnup type 23 as an oral vaccine. Co-oral administration of CT and Pnup type 23F resulted in the induction of Pnup-specific faecal IgA antibodies. These results were confirmed by detecting antigen-specific IgA-spot-forming cells in mononuclear cell suspensions prepared from the intestine of immunized mice. These findings suggest that oral immunization with Pnup in the presence of mucosal adjuvants, such as CT, could induce Pnup-specific IgA responses whereas Pnup alone did not. In an attempt to further enhance antigen-specific antibody responses, Pnup type 23F was encapsulated in liposomes and used as mucosal vaccine. However, immunogenicity of Pnup was not improved.

New strategies for using mucosal vaccination to achieve more effective immunization

Future progress in vaccination will be significantly advanced by application of emerging technologies for immunization of mucosal surfaces. It should now be possible to maximize the antigenicity of many vaccines and facilitate their interaction with appropriate lymphoid tissues to induce protective cellular and humoral responses. Mucosal vaccines requiring no more than two doses are achievable with current technologies. Living vaccines have been among the most promising candidates for mucosal vaccination, but with few exceptions their promise is still to be realized. Development of new microencapsulated delivery systems and adjuvants has made non-living vaccines reasonable options for mucosal immunization. To be practical, such vaccines should be developed as combined agent vaccines, possibly deliverable by multiple mucosal routes. Although strategies to be used for specific mucosal vaccines will depend upon a number of factors pertinent to the disease agent, in concept an adjuvant administered with inactivated but maximally antigenic pathogens or their recombinant adhesive subcomponents could prove to be among the more practical mucosal vaccine options for use globally.

Abrogation of suppression of delayed hypersensitivity induced by Candida albicans-derived mannan by treatment with monophosphoryl lipid A

Monophosphoryl lipid A (MLA), derived either from Salmonella minnesota or Salmonella typhimurium, was tested for its ability to alter Candida albicans mannan (MAN)-specific suppression. Since we showed previously that naive mice injected intravenously (i.v.) with MAN developed suppressor T cells capable of down-regulating delayed-type hypersensitivity when transferred to immunized recipients, MLA was tested for its ability to influence suppressor activity in the donors of suppressor cells. T-lymphocyte-enriched suspensions from donor mice treated with MLA, especially that derived from S. typhimurium, 2 or 3 days after the injection of MAN lost the ability to suppress delayed-type hypersensitivity when transferred to immunized mice. Transferable suppressor activity was reduced but not always completely abrogated when donor animals were treated with MLA 1 day following the administration of MAN. In several experiments, S. minnesota MLA also abrogated activity, but it was not effective in other transfer experiments. In a different type of experiment, MLA was given to immunized mice which had been suppressed directly with MAN. Mice were immunized, either by the introduction of C. albicans intragastrically followed by inoculation intradermally (i.d.) or by two i.d. inoculations, and MAN-specific suppressor cells were induced in such animals by the i.v. injection of MAN 1 day before the first or second i.d. inoculation in animals given intragastric plus i.d. inoculations and those given two i.d. inoculations, respectively. MLA was administered to such mice prior to the i.v. injection of MAN, on the same day, or 1 to 4 days thereafter. S. typhimurium MLA, especially when given to mice 2 days following the administration of MAN, caused a partial abrogation of suppressor activity. Overall, however, MLA, at 5 to 100 micrograms, had variable and minimal effects on suppressor activity in immunized mice suppressed by the i.v. administration of MAN. In summary, MLA is clearly capable of abrogating MAN-induced suppression when given to nonimmunized animals in which MAN-specific suppressor cells had been induced, but its efficacy in immunized animals suppressed by the i.v. administration of MAN was marginal.

Reversal of age-associated decline in immune response to Pnu-imune vaccine by supplementation with the steroid hormone dehydroepiandrosterone

Recently, we reported that murine antibody responses to the 23-valent pneumococcal polysaccharide (Pnu-Imune) vaccine declined with age. Here we present data to support the concept that age-associated immune defects are not only due to intrinsic defects in immune cells but are also due to extrinsic factors emanating from the neuroendocrine system. We found that supplementation with dehydroepiandrosterone, a steroid hormone known to be reduced in the aged, corrects the immune deficiency of aged mice and significantly enhanced their splenic immune responses to the Pnu-Imune vaccine.