Lynn Slobbe

A DNA prime-live vaccine boost strategy in mice can augment IFN-γ responses to mycobacterial antigens but does not increase the protective efficacy of two attenuated strains of Mycobacterium bovis against bovine tuberculosis

The Mycobacterium bovis bacille Calmette–Guérin (BCG) vaccine has variable efficacy for both human and bovine tuberculosis. There is a need for improved vaccines or vaccine strategies for control of these diseases. A recently developed prime‐boost strategy was investigated for vaccination against M. bovis infection in mice. BALB/c and C57BL/6 mice were primed with a DNA vaccine, expressing two mycobacterial antigens, ESAT‐6 and antigen 85 A and boosted with attenuated M. bovis strains, BCG or WAg520, a newly attenuated strain, prior to aerosol challenge. Before challenge, the antigen‐specific production of interferon‐γ (IFN‐γ) was evaluated by ELISPOT and antibody responses were measured. The prime‐boost stimulated an increase in the numbers of IFN‐γ producing cells compared with DNA or live vaccination alone, but this varied according to the attenuated vaccine strain, time of challenge and the strain of mouse used. Animals vaccinated with DNA alone generated the strongest antibody response to mycobacterial antigens, which was predominantly IgG1. BCG and WAg520 alone generally gave a 1–2 log10 reduction in bacterial load in lungs or spleen, compared to non‐vaccinated or plasmid DNA only control groups. The prime‐boost regimen was not more effective than BCG or WAg520 alone. These observations demonstrate the comparable efficacy of BCG and WAg520 in a mouse model of bovine tuberculosis. However, priming with the DNA vaccine and boosting with an attenuated M. bovis vaccine enhanced IFN‐γ immune responses compared to vaccinating with an attenuated M. bovis vaccine alone, but did not increase protection against a virulent M. bovis infection.

A Gene Expression Signature of Invasive Potential in Metastatic Melanoma Cells

Background We are investigating the molecular basis of melanoma by defining genomic characteristics that correlate with tumour phenotype in a novel panel of metastatic melanoma cell lines. The aim of this study is to identify new prognostic markers and therapeutic targets that might aid clinical cancer diagnosis and management. Principal Findings Global transcript profiling identified a signature featuring decreased expression of developmental and lineage specification genes including MITF, EDNRB, DCT, and TYR, and increased expression of genes involved in interaction with the extracellular environment, such as PLAUR, VCAN, and HIF1a. Migration assays showed that the gene signature correlated with the invasive potential of the cell lines, and external validation by using publicly available data indicated that tumours with the invasive gene signature were less melanocytic and may be more aggressive. The invasion signature could be detected in both primary and metastatic tumours suggesting that gene expression conferring increased invasive potential in melanoma may occur independently of tumour stage. Conclusions Our data supports the hypothesis that differential developmental gene expression may drive invasive potential in metastatic melanoma, and that melanoma heterogeneity may be explained by the differing capacity of melanoma cells to both withstand decreased expression of lineage specification genes and to respond to the tumour microenvironment. The invasion signature may provide new possibilities for predicting which primary tumours are more likely to metastasize, and which metastatic tumours might show a more aggressive clinical course.

Manipulation of immune responses to Mycobacterium bovis by vaccination with IL-2- and IL-18-secreting recombinant bacillus Calmette Guerin.

Bacillus Calmette Guerin (BCG) has been reported to show variable efficacy as a vaccine against tuberculosis. We demonstrated that the secretion of biologically active IL‐2 (rBCG/IL‐2), but not IL‐18 (rBCG/IL‐18), by BCG improves its ability to induce and maintain a strong type 1 immune response in BALB/c mice. rBCG/IL‐2 induced significantly higher Ag‐specific proliferative responses, high IFN‐γ production and serum titres of IgG2a 16 weeks after vaccination. This immune profile was correlated to an increased rate of clearance of non‐pathogenic mycobacteria (live BCG delivered intranasally). Surprisingly, however, this strong type 1 immune profile induced no greater protective immunity against aerosol challenge with virulent Mycobacterium bovis than that induced by normal BCG (nBCG). By comparison, vaccination with rBCG/IL‐18 was found to induce significantly less IFN‐γ production in splenic lymphocytes than nBCG. This impaired induction of IFN‐γ was correlated to a significantly lower protective efficacy against M. bovis challenge, as compared to nBCG. The data suggest that manipulation of the immune response to tuberculosis and tuberculosis vaccines will require a more complete understanding of the factors that are important in generating a protective immune response.

An in vivo comparison of bacillus Calmette–Guérin (BCG) and cytokine-secreting BCG vaccines

A recombinant bacillus Calmette–Guérin (BCG) vaccine has been developed, which constitutively secretes interleukin (IL)‐2. Groups of deer were immunized with either normal BCG (Pasteur 1173 P2 strain) or recombinant BCG (rBCG/IL‐2) and their immune responses were monitored over 3 months. Animals gained weight over this period and showed no signs of adverse reactions to either vaccine. Lymphocyte transformation responses did not differ significantly between the two groups. No antibody that was specific for BCG was detected in any animal. Intradermal skin‐test responses to BCG antigens showed that the rBCG/IL‐2 induced a smaller delayed‐type hypersensitivity response than the normal BCG. Cytokine transcription was determined by reverse transcription–polymerase chain reaction (RT–PCR). While IL‐2 and interferon‐γ (IFN‐γ) levels did not differ significantly between the two groups, the level of IL‐4 was found to be lower in the group given rBCG/IL‐2. This resulted in a strong interferon‐γ:IL‐4 ratio, suggesting a skewing of the immune response towards a Type 1 response. The rate at which the vaccine was eliminated from the host was the same regardless of whether BCG or rBCG was used. At autopsy (3 months after vaccination) 99·99% of the organisms had been eliminated. The small number of organisms isolated from the draining lymph node of animals given rBCG/IL‐2 were grown in antibiotic‐containing media. They were shown to still contain the shuttle plasmid and to secrete biologically active IL‐2, indicating that the plasmid was stably maintained despite the host’s immune response and in the absence of antibiotic selection.

Environmental Strains of Mycobacterium avium Interfere with Immune Responses Associated with Mycobacterium bovis BCG Vaccination

ABSTRACT Prior exposure of a vaccinee to certain species of environmental mycobacteria can prime the immune system against common mycobacterial antigens, which can in turn reduce the subsequent efficacy of live attenuated mycobacterial vaccines (such as Mycobacterium bovis BCG), in both human and livestock vaccination programs. In this study, two strains of Mycobacterium avium, both isolated from New Zealand livestock, were investigated to determine their growth characteristics and effects on the immune system in murine models. Markedly different effects on the immune system were observed; an IS901-negative strain (WAg 207) induced significant up-regulation of cell surface activation markers (major histocompatibility complex II, CD80, and CD86) on in vitro-derived dendritic cells and induced the release of proinflammatory monokines (interleukin-1β [IL-1β], IL-6, and tumor necrosis factor alpha) in dendritic cell-macrophage cocultures following direct in vitro contact of cells with bacteria. In contrast, an IS901-positive strain (WAg 206) had none of these effects. When mice were exposed to M. avium via oral infection prior to BCG parenteral immunization, both strains were shown to be capable of decreasing subsequent antigen-stimulated gamma interferon secretion by splenic lymphocytes, although this effect was more significant for strain WAg 206. Both strains also induced a mycobacterial antigen-specific serological response in M. avium-sensitized and BCG-immunized mice; this response was greater in WAg 206-sensitized mice, and there was a predominance of immunoglobulin G1 antibody. The down-regulation of IFN-γ responses and the up-regulation of antibody responses are characteristic of a switch to a type 2 immune response. The different results may be linked to the inherent growth characteristics of the two strains, since WAg 206 was shown to grow slowly in murine macrophages in vitro and to cause a persistent systemic infection following infection in vivo, while WAg 207 grew fast and did not persist in mice. The implications of these findings for BCG vaccination protocols are discussed.

Influenza hemagglutinin peptides fused to interferon gamma and encapsulated in liposomes protects mice against influenza infection.

The immunogenicity of a peptide vaccine may be improved by fusing antigen to a cytokine and administering this chimeric protein in a particulate delivery system. We have investigated this using a vaccine comprising an immunodominant T cell epitope and a B cell epitope from influenza haemagglutinin (HATB) fused to interferon gamma and encapsulated in liposomes (HATB/IFN-gamma/lipo). Controls comprised groups receiving HATB/IFN-gamma mixed with liposomes, HATB incorporated in liposomes or heat inactivated PR8 influenza virus (HI PR8). IFN-gamma production in mice treated with HATB/IFN-gamma/lipo was significantly higher than in mice inoculated with either HATB/IFN-gamma mixed with liposomes or HATB incorporated in liposomes but less than HI PR8. Lung viral titres were significantly lower in mice treated with HATB/IFN-gamma/lipo compared with those treated with HATB/IFN-gamma mixed with liposomes. HI PR8-treated mice recorded a nil viral titre. There was no correlation between the level of antibody production and clearance of virus from the lungs. These data suggest that particulate delivery systems may be useful adjuncts to improve immune responses to chimeric proteins and to induce protection against disease.

DNA fusion vaccines incorporating IL-23 or RANTES for use in immunization against influenza.

The incorporation of RANTES or IL-23 into DNA vaccines may improve their immunogenicity by the recruitment and activation of dendritic cells. This may also select for a TH1 response counteracting the TH2 response which can predominate when a DNA vaccine is delivered by gene gun. We have immunized mice with various DNA constructs encoding APR/8/34 influenza virus hemagglutinin (HA), either fused to or separate from, IL-23 or RANTES using a gene gun. Those immunized with IL-23/HA fusion constructs and challenged with influenza 27 weeks post-vaccination, tended to have cleared more virus than those vaccinated with HA DNA. Mice immunized with the RANTES/HA fusion construct produced a mixed TH1/TH2 response whereas in HA-vaccinated mice, a TH2 response predominated. Immunization with a plasmid in which HA and RANTES were under the control of separate promoters, failed to generate a mixed TH1/TH2 response suggesting that enhanced antigen uptake via RANTES receptors may contribute to the mixed immune response generated to the fusion construct. Overall these findings provide further evidence that Type 1 cytokines or chemokines, fused to antigen in a DNA vaccine, can influence the nature and the longevity of the immune response and ultimately, its protective capacity.

A prolonged immune response to antigen delivered in poly ( ∈ -caprolactone) microparticles

A single dose vaccine formulation which induces both humoral and cell‐mediated immune responses over a prolonged period would provide a potent weapon against infectious disease. We have used a water‐in‐oil‐in‐oil, solvent evaporation method for generating poly ∊‐caprolactone microparticles and tested their ability to induce an immune response against the model antigen ovalbumin. We hypothesized that the initial release of antigen from the surface of the poly ∊‐caprolactone microparticles would act as the priming dose and that the delayed release over the following months, due to diffusion from or break‐down of the microparticles, would act as a boost to the immune response. Ovalbumin encapsulated in the poly ∊‐caprolactone microparticles was able to induce both antibody and cell‐mediated immune responses. However our results suggest that the spontaneous release had little effect on the immune response. Despite this the response was maintained for at least 8 months following a single immunization. Both humoral and cell‐mediated immune responses were induced in mice. This simple method of vaccine formulation offers a cost‐efficient way to deliver antigen in a single dose to the immune system.

MITF and PAX3 Play Distinct Roles in Melanoma Cell Migration; Outline of a "Genetic Switch" Theory Involving MITF and PAX3 in Proliferative and Invasive Phenotypes of Melanoma.

Melanoma is a very aggressive neoplasm with a propensity to undergo progression and invasion early in its evolution. The molecular pathways underpinning invasion in melanoma are now just beginning to be elucidated, but a clear understanding of the transition from non-invasive to invasive melanoma cells remains elusive. Microphthalmia-associated transcription factor (MITF), is thought to be a central player in melanoma biology, and it controls many aspects of the phenotypic expression of the melanocytic lineage. However, recently the paired box transcription factor PAX3 was shown to transcriptionally activate POU3F2/BRN2, leading to direct repression of MITF expression. Here we present a theory to explain melanoma phenotype switching and discuss the predictions that this theory makes. One prediction is that independent and opposing roles for MITF and PAX3 in melanoma would be expected, and we present empirical evidence supporting this: in melanoma tissues PAX3 expression occurs independently of MITF, and PAX3 does not play a key role in melanoma cell proliferation. Furthermore, we show that knockdown of PAX3 inhibits cell migration in a group of “lower MITF” melanoma cell lines, while knockdown of MITF promotes cell migration in a complementary “higher MITF” group of melanoma cell lines. Moreover, the morphological effects of knocking down PAX3 versus MITF in melanoma cells were found to differ. While these data support the notion of independent roles for MITF and PAX3, additional experiments are required to provide robust examination of the proposed genetic switch theory. Only upon clear delineation of the mechanisms associated with progression and invasion of melanoma cells will successful treatments for invasive melanoma be developed.

PAX3 knockdown in metastatic melanoma cell lines does not reduce MITF expression.

PAX3 and MITF are important transcriptional activators in the melanocyte lineage and PAX3 is thought to control MITF expression during normal melanocyte differentiation. However, it is not clear whether this is still true in melanoma and whether the effects of knockdown of PAX3 on the inhibition of melanoma growth or survival are by its regulation of MITF. By western blot and quantitative real-time reverse transcription-PCR, we investigated the relationship between PAX3 and MITF expression in 27 metastatic melanoma and one immortalized melanocyte cell lines. All lines were found to express both PAX3 and MITF proteins but levels varied by 15 fold and more than 100 fold, respectively. The expression of PAX3 protein was correlated with that of MITF (r=0.75; P<0.001) but the expression of PAX3 protein and MITF mRNA was not. Immunofluorescence microscopy showed that individual cells expressed widely differing relative amounts of PAX3 and MITF protein. By MTT cell proliferation and flow cytometry assays, both MITF and PAX3 proteins seemed to be functional, as knockdown with siRNA led to reduced proliferation and induction of apoptosis. However, knockdown of PAX3 with small interfering RNA did not decrease MITF expression and vice versa. In one cell line (NZM15), silencing of PAX3 induced terminal differentiation whereas silencing of MITF induced expression of FOXD3, a repressor of melanogenesis. The results suggest that the melanoma lines used in this study show considerable phenotypic variation of expression of these two transcriptional activators and reflect a deregulation of the developmental process operating in the genesis of the melanocyte lineage, and that they probably function independently to enhance the survival of melanoma cells.