Induction of protective immunity against toxoplasmosis in mice by immunization with Toxoplasma gondii RNA

Toxoplasma gondii enters the mucosal surfaces of the host, and so immunity at these sites is of major interest. Due to the compartmentalization of the immune response, systemic immunization does not induce high levels of immunity at mucosal surfaces. Intranasal immunization has been shown to be very effective in inducing both systemic and mucosal immune responses. Immunization with mRNA can induce both humoral and cell-mediated immune responses, both of which are important in conferring immunity to T. gondii. The efficacy of RNA vaccination by the nasal route with T. gondii RNA was evaluated. We assessed the percentage of cumulative survival after an oral challenge with a lethal dose of T. gondii cysts (40 cysts), and the number of brain cysts following a challenge with a sublethal dose of T. gondii 76 K cysts (15 cysts). Vaccinated mice were found to be significantly better protected than non-immunized mice after a challenge with a lethal dose of cysts; and a challenge with a sublethal dose also resulted in fewer brain cysts than in non-immunized mice. Sera and intestinal secretions of immunized mice recognized T. gondii antigens, suggesting that a specific humoral immune response may occur. Moreover, a specific lymphoproliferative response observed in cervical lymph nodes may confer protection. These preliminary findings suggest that RNA vaccination by a mucosal route could be feasible.

Cutting Edge: Innate Immune System Discriminates between RNA Containing Bacterial versus Eukaryotic Structural Features That Prime for High-Level IL-12 Secretion by Dendritic Cells

RNA derived from bacterial but not eukaryotic sources, when transfected into human monocyte-derived dendritic cell precursors, induces high-level IL-12 secretion in conjunction with dendritic cell maturation stimuli. In vitro-transcribed mRNA that mimics the structure of bacterial mRNA in the lack of a long 3'-poly(A) tail likewise induces IL-12 secretion, but this property is lost upon efficient enzymatic 3'-polyadenylation. Among other tested RNAs, only polyuridylic acid induced IL-12 p70. This RNA response phenomenon appears biologically distinct from the classically defined response to dsRNA. RNA-transfected APC also polarize T cells in an IL-12-dependent manner toward the IFN-gamma(high)IL-5 (low) Th1 phenotype, suggesting a link between the detection of appropriately structured RNA and the skewing of immune responses toward those best suited for controlling intracellular microbes. RNA structured to emulate bacterial patterns constitutes a novel vaccine strategy to engender polarized Th1-type immune responses.

Mouse antibody response to a microsporidian parasite following inoculation with a gene coding for parasite ribosomal RNA

This study found that a plasmid construct encoding the small-subunit ribosomal RNA (SSUrRNA) of the microsporidian Microgemma caulleryi generates a humoral response upon intramuscular inoculation in mice. The plasmid used was pCMV, following preliminary trials indicating efficient beta-galactosidase gene expression in mouse muscle cells transfected with pCMV/beta-Gal. The antibodies produced after inoculation with pCMV/SSUDNA recognized parasite spore antigens and reached maximum levels at 30 days postinoculation, subsequently remaining stable for at least 120 days. Due to the highly conserved sequence of the SSUrDNA in different microsporidian species, these results open up interesting prospects for broad-spectrum vaccination.

Mammalian cell expression of malaria merozoite surface proteins and experimental DNA and RNA immunisation

The gene for a 45 kDa merozoite surface protein (MSA-2) of the human malaria parasite Plasmodium falciparum was PCR amplified and cloned into eukaryotic expression vectors VR1012 and pcDNA3 to yield plasmids P1 and P2, respectively. The coding sequences for two N-terminal fragments of the 185 kDa merozoite surface protein (MSA-1) gene were similarly PCR amplified and cloned into vectors VR1020 and VR1012 to yield plasmids P3 and P4, respectively. The MSA-1 signal peptide sequence, present in P4, was replaced with the human tissue plasminogen activator signal sequence in P3. The four plasmids expressed the cloned genes under the control of the cytomegalovirus promoter and carried 3' bovine growth hormone termination/poly A signals. P1, P3 and P4 also contained the cytomegalovirus intron A enhancer sequence. MSA-1 expression was more readily detected than MSA-2 in Cos cells transfected with P3/P4 and P1/P2 respectively. The MSA-2 gene was also cloned into the phagemid pBluescript IISK+ with and without a 3' poly A tail composed of 35 A residues. MSA-2 was synthesised in HeLa cells infected with a recombinant vaccinia virus carrying T7 RNA polymerase when MSA-2 recombinant pBluescript was transfected into the cells. Inoculation with P1 intramuscularly or intradermally and with P2 intradermally into rabbits led to the production of antibodies to MSA-2 detectable by immunofluorescence and Western blotting. Antibodies were also produced against MSA-1 after intramuscular/intradermal inoculation with P3 and P4. Inoculation of rabbits with MSA-2 mRNA yielded better antibody titres when a poly A tail was present. Antibody levels were maintained for > 9 weeks after the final immunisation. However the immune sera failed to inhibit in vitro parasite growth.