Intravenous injection of interferon-gamma inhibits the proliferation of Listeria monocytogenes in the liver but not in the spleen and peritoneal cavity.

In the present study the effects of intravenous administration of recombinant interferon-gamma (IFN-gamma) on both the proliferation of Listeria monocytogenes in the liver and spleen of mice and the listericidal activity of their peritoneal macrophages were investigated. A single intravenous injection of 1 x 10(6) U or three injections of 2 x 10(5) U recombinant IFN-gamma (rIFN-gamma) induced optimal activation of resident and exudate peritoneal macrophages, as judged by their ability to inhibit the intracellular proliferation of Toxoplasma gondii and their enhanced release of H2O2 and NO2-. The rate of intracellular killing of L. monocytogenes by the rIFN-gamma-activated resident and exudate macrophages was not higher than that by resident macrophages. Addition of 10 ng lipopolysaccharides (LPS) to the rIFN-gamma also did not enhance the bactericidal activity of the activated peritoneal macrophages. The decrease in the number of L. monocytogenes in the peritoneal cavity of mice that had received an i.p. injection of 1 x 10(4) U rIFN-gamma was similar to that in control mice. Intravenous administration of 1 x 10(5) rIFN-gamma activated cells in the liver, as indicated by the increased expression of Ia antigen, and reduced the rate of proliferation of L. monocytogenes in the liver relative to that in control mice when 0.1 LD50 or 1 LD50 L. monocytogenes were injected. However, when 10 LD50 L. monocytogenes were administered there was no effect on their proliferation. The number of L. monocytogenes found initially in the spleen of rIFN-gamma-treated mice was 20-30% of that in the spleen of control mice, but the rate of proliferation of L. monocytogenes was not reduced. These divergent results for the proliferation of L. monocytogenes in the liver, spleen and peritoneal cavity indicate that cells other than macrophages and/or as yet unknown local factors play an important role in the listericidal activity.     

A prime-boost immunisation regimen using DNA followed by recombinant modified vaccinia virus Ankara induces strong cellular immune responses against the Plasmodium falciparum TRAP antigen in chimpanzees

Two chimpanzees were vaccinated intramuscularly against malaria using plasmid DNA expressing the pre-erythrocytic antigens thrombospondin related adhesion protein (PfTRAP) and liver stage specific antigen-1 (PfLSA-1) of Plasmodium falciparum together with GM-CSF protein. A recombinant modified vaccinia virus Ankara (MVA) expressing PfTRAP was injected intramuscularly 6 weeks later to boost the immune response. This sequence of antigen delivery induced a specific and long-lasting T cell and antibody response to PfTRAP as detected by ELISPOT assay and ELISA. Antibody responses were detected after four DNA injections, and were boosted by injection of recombinant MVA expressing PfTRAP. Interferon-gamma secreting antigen-specific T cells were detected in both animals, but only after boosting with recombinant MVA. By screening a panel of PfTRAP-derived peptides, an epitope was identified that was recognized by cytotoxic T lymphocytes in one of the chimpanzees studied. T cells specific for this epitope were present in PBMCs and liver-infiltrating lymphocytes at a frequency of between 1 in 200 and 1 in 500. The high immunogenicity of this prime-boost regimen in chimpanzees supports further assessment of this delivery strategy for the induction of protection against P. falciparum malaria in humans.     

Preclinical evaluation of a chimeric malaria vaccine candidate in Montanide ISA 720: immunogenicity and safety in rhesus macaques

Several malarial antigens are in development as potential vaccine candidates as part of a concerted effort to control the disease, which kills more than one million people per year. Although some antigens have demonstrated an impact against the malaria parasite, Plasmodium falciparum, many researchers hypothesize that a combination of antigens will be required to generate high levels of efficacy against clinical disease. PfCP2.9 is a chimeric protein that includes MSP119 and domain III of AMA1 [AMA1 (111)] of Plasmodium falciparum in a single recombinant molecule. The antigen, formulated in Seppic's ISA 720 adjuvant, is approaching Phase I clinical testing in humans. The purpose of this study was to assess the safety of this vaccine and to explore possible dosage levels for clinical evaluation. Groups of five monkeys each were immunized i.m. with 25 microg, 50 microg, 100 microg and 200 microg of PfCP2.9/ISA 720 in 0.5 mL on days 0 and 112. The mean anti-PfCP2.9 titres to the 50 microg dose group were higher than the other dose groups; however, there was no statistically significant difference between the anti-CP2.9 titres of any of the groups, suggesting that the immune response to PfCP2.9 was saturated at 25 microg. One animal in the 100 microg dose group elicited a higher antibody and IFN-gamma response to PfCP2.9 than the rest of the cohort; this animal developed a small sterile abscess following the second vaccination, which spontaneously resolved within one week. In conclusion: (a) 50 microg is highly immunogenic, appears safe, and is likely to be an appropriate dose for clinical evaluation; and (b) a conservative trial design is warranted to avoid any unexpected reactogenicity with the PfCP2.9/ISA 720 formulation.     

Protection of macaques against Mycobacterium tuberculosis infection by a subunit vaccine based on a fusion protein of antigen 85B and ESAT-6

Various new tuberculosis (TB) vaccine candidates in combination with new delivery systems, including subunit vaccines, are currently being evaluated by a number of laboratories. One vaccine candidate that has shown promising protective capacity in mice and guinea pigs is a fusion of Ag85B and ESAT-6. In this study, we have investigated the efficacy of this Ag85B-ESAT-6 fusion protein vaccine in a non-human primate model for TB. Vaccination of cynomolgus monkeys with the Ag85B-ESAT-6 fusion protein in two different adjuvant (DDA/MPL, AS02A) resulted in a reduction in bacterial number and/or lung pathology in animals challenged with Mycobacterium tuberculosis. Vaccination prevented an increase in C-reactive protein serum levels, general activation of CD4 and CD8 subsets and boosted development of humoral and cellular immune responses to a spectrum of mycobacterial antigens on exposure to M. tuberculosis infection. We show, in two independent experiments, that vaccination of primates with Ag85B-ESAT-6 induces protective immune responses, suggesting that Ag85B-ESAT-6 is a strong candidate for further clinical evaluation. As far as we are aware this is the first report of protection in primates with a subunit vaccine.