Monophosphoryl lipid A (MPL) upregulates major histocompatibility complex (MHC) class I expression by increasing interferon-gamma (IFN-gamma)

Comparative analysis of Bacillus subtilis spores and monophosphoryl lipid A as adjuvants of protein-based mycobacterium tuberculosis-based vaccines: partial requirement for interleukin-17a for induction of protective immunity

The development of adjuvants for vaccines has become an important area of research as the number of protein-based vaccines against infectious pathogens increases. Currently, there are a number of adjuvant-based Mycobacterium tuberculosis vaccines in clinical trials that have shown efficacy in animal models. Despite these novel adjuvants, there is still a need to design new and more versatile adjuvants that have minimal adverse side effects but produce robust long-lasting adaptive immune responses. To this end, we hypothesized that Bacillus subtilis spores may provide the appropriate innate signals that are required to generate such vaccine-mediated responses, which would be sufficient to reduce the mycobacterial burden after infection with M. tuberculosis. In addition, we compared the response generated by B. subtilis spores to that generated by monophosphoryl lipid A (MPL), which has been used extensively to test tuberculosis vaccines. The well-characterized, 6-kDa early secretory antigenic target of M. tuberculosis (ESAT-6; Rv3875) was used as a test antigen to determine the T cell activation potential of each adjuvant. Inoculated into mice, B. subtilis spores induced a strong proinflammatory response and Th1 immunity, similar to MPL; however, unlike MPL formulated with dimethyldioctadecylammonium (DDA) bromide, it failed to induce significant levels of interleukin-17A (IL-17A) and was unable to significantly reduce the mycobacterial burden after pulmonary infection with M. tuberculosis. Further analysis of the activity of MPL-DDA suggested that IL-17A was required for protective immunity. Taken together, the data emphasize the requirement for a network of cytokines that are essential for protective immunity.

Particulate vaccines: on the quest for optimal delivery and immune response

Subunit vaccines offer a safer alternative to traditional organism-based vaccines, but their immunogenicity is impaired. This hurdle might be overcome by the use of micro- and nanodelivery systems carrying the antigen(s). This review discusses the rationale for the use of particulate vaccines and provides an overview of antigen-delivery vehicles currently under investigation. It further highlights the cellular uptake, antigen processing and the presentation by antigen-presenting cells because these processes are partially governed by particle characteristics and eventually determine the immunological outcome. Finally, we address the attractive concept of concomitant delivery of antigens and immunopotentiators. The condensed knowledge could be an asset for rationally designing antigen-delivery vehicles to obtain safe and efficacious vaccines.

TGF beta secreted by B16 melanoma antagonizes cancer gene immunotherapy bystander effect

Tumor-targeted delivery of immune stimulatory genes, such as pro-inflammatory cytokines and suicide genes, has shown to cure mouse models of cancer. Total tumor eradication was also found to occur despite subtotal tumor engineering; a phenomenon coined the "bystander effect". The bystander effect in immune competent animals arises mostly from recruitment of a cancer lytic cell-mediated immune response to local and distant tumor cells which escaped gene modification. We have previously described a Granulocyte-Macrophage Colony Stimulating Factor (GM-CSF) and Interleukin 2 (IL2) fusokine (aka GIFT2) which serves as a potent anticancer cytokine and it here served as a means to understand the mechanistic underpinnings to the immune bystander effect in an immune competent model of B16 melanoma. As expected, we observed that GIFT2 secreted by genetically engineered B16 tumor cells induces a bystander effect on non modified B16 cells, when admixed in a 1:1 ratio. However, despite keeping the 1:1 ratio constant, the immune bystander effect was completely lost as the total B16 cell number was increased from 10(4) to 10(6) which correlated with a sharp reduction in the number of tumor-infiltrating NK cells. We found that B16 secrete biologically active TGFbeta which in turn inhibited GIFT2 dependent immune cell proliferation in vitro and downregulated IL-2R beta expression and IFN gamma secretion by NK cells. In vivo blockade of B16 originating TGFbeta significantly improved the immune bystander effect arising from GIFT2. We propose that cancer gene immunotherapy of pre-established tumors will be enhanced by blockade of tumor-derived TGFbeta.

The TLR4 agonist, monophosphoryl lipid A, attenuates the cytokine storm associated with respiratory syncytial virus vaccine-enhanced disease

Formalin-inactivated respiratory syncytial virus vaccine (FI-RSV) induces a poorly understood immunopathological response that leads to disease enhancement upon RSV infection of vaccinees. In the cotton rat model, inclusion of monophosphoryl lipid A (MPL) in the FI-RSV formulation was found to mitigate the lung pathology associated with vaccine-enhanced disease. Here we report that the protective effect of MPL on FI-RSV vaccine-enhanced disease is associated with a dramatic reduction in levels of Th1- and Th2-type cytokines and chemokines normally elicited in response to RSV challenge. Our data illustrate the complexity of proinflammatory response elicited by FI-RSV vaccination and RSV infection and the potential importance of MPL in modifying this response.

Antitumour effect of OM-174 and Cyclophosphamide on murine B16 melanoma in different experimental conditions

We report that OM-174, a purified water soluble diphosphorylated and triacetylated lipid A derived from E. coli, is able to reduce tumour progression and to prolong the survival of mice in the B16 melanoma experimental model. At the doses employed in our study OM-174 had an antitumour activity comparable to that of a single high dose of CY. More striking effects were achieved by means of the combination of the two agents in a protocol consisting of a single administration of CY (200 mg/kg) followed by five injections of OM-174 (1 mg/kg). Immunological studies of treated and control mice revealed that the antitumour activity of OM-174, alone or in combination with CY, is mediated by the stimulation of natural killer (NK) and cytotoxic T lymphocyte (CTL) responses as well as by a significant increase in the absolute number of NK1.1, CD4 and CD8 positive cells. OM-174 is thus candidate for association with cytostatic drugs in chemo-immunotherapy protocols.

Development of a CTL vaccine for Her-2/neu using peptide-microspheres and adjuvants

With the ultimate goal of developing a therapeutic cancer vaccine, we encapsulated the Her-2/neu peptide p369-377 in poly(lactide-co-glycolide) microspheres. This formulation was found to effectively elicit CD8+ cytotoxic T cell (CTL) responses in an HLA-A*0201 transgenic mouse model. In contrast, immunization with either peptide alone or peptide formulated in incomplete Freund's adjuvant (IFA) failed to elicit such CTL responses. Responses induced by the peptide-microsphere formulation were found to peak at approximately 6 weeks post-immunization, and were enhanced by delivering increased doses of peptide and with repeated administrations over time. Co-administration of the peptide-microspheres with adjuvants, including granulocyte-macrophage colony stimulating factor, MPL adjuvant and select synthetic Toll-Like Receptor 4 ligands, the aminoalkyl glucosaminide-4 phosphates, significantly augmented CTL responses. These studies provide important guidance for the design of human clinical trials of microsphere vaccines in terms of optimal peptide-microsphere formulation, vaccination regimen, vaccine dose, and adjuvant selection.