Prevention of Inflammation-Driven Colon Carcinogenesis in Human MUC1 Transgenic Mice by Vaccination with MUC1 DNA and Dendritic Cells

The preventive efficacy of MUC1-specific DNA immunization on inflammation-driven colon carcinogenesis in human MUC1 transgenic (MUC1.Tg) mice was investigated. Mice were vaccinated with MUC1 DNA mixed with autologous bone-marrow-derived dendritic cells (BMDCs), and then colonic tumors were induced by azoxymethane (AOM) injection and oral administration of dextran sulfate sodium (DSS). Two types of tumors, squamous metaplasia and tubular adenoma, were observed. Both expressed high levels of MUC1 as indicated by the binding of anti-MUC1 antibodies with different specificities, whereas MUC1 expression was not detected in normal colonic mucosa. When mice were immunized with MUC1 DNA + BMDCs, tumor incidence, tumor number, and tumor size were significantly reduced. In contrast, vaccination with MUC1 DNA alone or BMDCs alone was ineffective in reducing tumor burden. Inflammation caused by DSS was not suppressed by the MUC1 DNA + BMDCs vaccination. Furthermore, MUC1 protein expression levels, as judged by anti-MUC1 antibody binding in tumors grown after vaccination, did not significantly differ from the control. In conclusion, an inflammation-driven carcinogenesis model was established in MUC1.Tg mice, closely resembling human colon carcinogenesis. In this model, vaccination with MUC1 DNA + BMDCs was effective in overriding MUC1 tolerance and reducing the tumor burden by a mechanism not affecting the level of colonic inflammation.

COVID-19: Clinical status of vaccine development to date

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2)-induced COVID-19 is a complicated disease. Clinicians are continuously facing difficulties to treat infected patients using the principle of repurposing of drugs as no specific drugs are available to treat COVID-19. To minimize the severity and mortality, global vaccination is the only hope as a potential preventive measure. After a year-long global research and clinical struggle, 165 vaccine candidates have been developed and some are currently still in the pipeline. A total of 28 candidate vaccines have been approved for use and the remainder are in different phases of clinical trials. In this comprehensive report, the authors aim to demonstrate, classify and provide up-to-date clinical trial status of all the vaccines discovered to date and specifically focus on the approved candidates. Finally, the authors specifically focused on the vaccination of different types of medically distinct populations.

Fish DNA vaccine against infectious hematopoietic necrosis virus: efficacy of various routes of immunisation

The DNA vaccine, pIHNVw-G, contains the gene for the glycoprotein (G) of the rhabdovirus infectious hematopoietic necrosis virus (IHNV), a major pathogen of salmon and trout. The relative efficacy of various routes of immunisation with pIHNVw-G was evaluated using 1.8 g rainbow trout fry vaccinated via intramuscular injection, scarification of the skin, intraperitoneal injection, intrabuccal administration, cutaneous particle bombardment using a gene gun, or immersion in water containing DNA vaccine-coated beads. Twenty-seven days after vaccination neutralising antibody titres were determined, and 2 days later groups of vaccinated and control unvaccinated fish were subjected to an IHNV immersion challenge. Results of the virus challenge showed that the intramuscular injection and the gene gun immunisation induced protective immunity in fry, while intraperitoneal injection provided partial protection. Neutralising antibodies were not detected in sera of vaccinated fish regardless of the route of immunisation used, suggesting that cell mediated immunity may be at least partially responsible for the observed protection.

A Long-Term Memory Obtained by Genetic Immunization Results in Full Protection from a Mammary Adenocarcinoma Expressing an EBV Gene

We have tested the capability of a plasmid DNA (pDNA) expressing the EBV nuclear Ag-4 (EBNA-4) to evoke a T cell response-associated protective immune response against a tumor expressing this gene. We have found that ACA mice immunized with EBNA-4-expressing plasmid were partially protected against syngeneic mammary carcinoma line (S6C) expressing EBNA-4 (S6C-E4). This protection was enhanced by coimmunizing mice with EBNA-4- and GM-CSF-expressing plasmids, and a full protection was achieved by coimmunizing mice with EBNA-4- and IFN-γ-expressing plasmids. Furthermore, mice that have rejected the EBNA-4-positive tumor were also resistant against a subsequent challenge with the original nontransfected tumor line. We then checked for the ability of pDNA immunization to provide a protective long-term memory response. We indeed found that even after 3 mo from the last immunization, full protection was obtained by this method, as compared with full tumor outgrowth in the control-immunized group. These findings support the concept that a nonviral, pDNA-based vaccination strategy is useful to fully protect from the outgrowth of tumors expressing this EBV gene.

Effective DNA Vaccination Against Listeriosis by Prime/Boost Inoculation with the Gene Gun

Protective immunity against Listeria monocytogenes strongly depends on CD8+ T lymphocytes, and both IFN-γ secretion and target cell killing are considered relevant to protection. We analyzed whether we could induce a protective type 1 immune response by DNA vaccination with the gene gun using plasmids encoding for two immunodominant listerial Ags, listeriolysin and p60. To induce a Th1 response, we 1) coprecipitated a plasmid encoding for GM-CSF, 2) employed a prime/boost vaccination schedule with a 45-day interval, and 3) coinjected oligodeoxynucleotides (ODN) containing immunostimulatory CpG motifs. DNA immunization of BALB/c mice with plasmids encoding for listeriolysin (pChly) and p60 (pCiap) efficiently induced MHC class I-restricted, Ag-specific CD8+ T cells that produced IFN-γ. Coinjection of CpG-ODN significantly increased the frequency of specific IFN-γ-secreting T cells. Although pChly induced specific CD8+ T cells expressing CTL activity, it failed to stimulate CD4+ T cells. Only pCiap induced significant CD4+ T cell and humoral responses, which were predominantly of Th2 type. Vaccination with either plasmid induced protective immunity against listerial challenge, and coinjection of CpG ODN improved vaccine efficacy in some situations. This study demonstrates the feasibility of gene gun administration of plasmid DNA for inducing immunity against an intracellular pathogen for which protection primarily depends on type 1 CD8+ T cells.

Activation of CD4 T Cells by Somatic Transgenesis Induces Generalized Immunity of Uncommitted T Cells and Immunologic Memory

Cellular immune responses were analyzed in vivo after a single intraspleen inoculation of DNA coding for a 12-residue Th cell determinant associated with a 12-residue B cell epitope, a process termed somatic transgene immunization. We show that CD4 T cells are readily activated and produce IL-2, IFN-γ and IL-4, characteristics of an uncommitted phenotype. Linked recognition of the two epitopes coded in the same transgene promoted IgM-IgG1 switch and enhanced the total Ab response but had no effect on IgG2a Abs. Although originating in the spleen, T cell responsiveness was found to spread immediately and with similar characteristics to all lymph nodes in the body. A single inoculation was also effective in establishing long term immunologic memory as determined by limiting dilution analysis, with memory T cells displaying a cytokine profile different from that of primary effector T cells. These studies provide evidence that by initiating immunity directly in secondary lymphoid organs, an immune response is generated with characteristics that differ from those using vaccines of conventional DNA or protein in adjuvant administered in peripheral sites. Somatic transgene immunization can therefore be used to probe T cell responsiveness in vivo and represents a tool to further understanding of the nature of the adaptive immune response.

Dose Dependence of CTL Precursor Frequency Induced by a DNA Vaccine and Correlation with Protective Immunity Against Influenza Virus Challenge

Intramuscular injection of BALB/c mice with a DNA plasmid encoding nucleoprotein (NP) from influenza virus A/PR/8/34 (H1N1) provides cross-strain protection against lethal challenge with influenza virus A/HK/68 (H3N2). CTL specific for the H-2Kd-restricted epitope NP147–155 are present in these mice and are thought to play a role in the protection. To assess the effectiveness of NP DNA immunization in comparison with influenza virus infection in the induction of CTL responses, we monitored the frequency of CTL precursors (CTLp) in mice following i.m. injection with NP DNA or intranasal infection with influenza virus and showed that the CTLp frequency in NP DNA-immunized mice can reach levels found in mice that had been infected with influenza virus. We also measured the CTLp frequency, anti-NP Ab titers, and T cell proliferative responses in mice that were injected with titrated dosages of NP DNA and documented a correlation of the CTLp frequency and the Ab titers, but not proliferative responses, with the injection dose. Furthermore, we observed a positive correlation between the frequency of NP147–155 epitope-specific CTLp and the extent of protective immunity against cross-strain influenza challenge induced by NP DNA injection. Collectively, these results and our early observations from adoptive transfer experiments of in vitro activated lymphocytes from NP DNA-immunized mice suggest a protective function of NP-specific CTLp in mice against cross-strain influenza virus challenge.

CD86 (B7-2) Can Function to Drive MHC-Restricted Antigen-Specific CTL Responses In Vivo

Activation of T cells requires both TCR-specific ligation by direct contact with peptide Ag-MHC complexes and coligation of the B7 family of ligands through CD28/CTLA-4 on the T cell surface. We recently reported that coadministration of CD86 cDNA along with DNA encoding HIV-1 Ags i.m. dramatically increased Ag-specific CTL responses. We investigated whether the bone marrow-derived professional APCs or muscle cells were responsible for the enhancement of CTL responses following CD86 coadministration. Accordingly, we analyzed CTL induction in bone marrow chimeras. These chimeras are capable of generating functional viral-specific CTLs against vaccinia virus and therefore represent a useful model system to study APC/T cell function in vivo. In vaccinated chimeras, we observed that only CD86 + Ag + MHC class I results in 1) detectable CTLs following in vitro restimulation, 2) detectable direct CTLs, 3) enhanced IFN-γ production in an Ag-specific manner, and 4) dramatic tissue invasion of T cells. These results support that CD86 plays a central role in CTL induction in vivo, enabling non-bone marrow-derived cells to prime CTLs, a property previously associated solely with bone marrow-derived APCs.

Induction of CD8+ T Cell Responses to Dominant and Subdominant Epitopes and Protective Immunity to Sendai Virus Infection by DNA Vaccination

While recent studies have demonstrated that DNA vaccination induces potent CD8+ T cell memory in vivo, it is unclear whether this memory is qualitatively and quantitatively comparable with that induced by natural viral infection. In the current studies, we have investigated the induction of CD8+ memory CTL responses to Sendai virus nucleoprotein (NP) in C57BL/6 mice following gene gun vaccination. The data demonstrate that this mode of vaccination induces potent long-lived memory CTL precursors (CTLp) specific for both the dominant (NP324–332/Kb) and the subdominant (NP324–332/Db) epitopes of NP. The frequencies of T cells specific for each of these epitopes in the spleen is about 1:2000 CD8+ T cells, similar to those induced by intranasal infection with Sendai virus. Moreover, the induction of memory CTLp by DNA vaccination is independent of MHC class II molecules or Ab, as is the case for memory CTLp induction by live Sendai virus infection. CTLp specific for both epitopes are capable of migrating to the lung following Sendai virus infection and express potent cytotoxic activity at the site of infection. Consistent with this activity, DNA vaccination with Sendai virus NP induced a substantial degree of Ab-independent protection from a challenge with a lethal dose of Sendai virus. Taken together, these data demonstrate that for the parameters tested, DNA vaccination is indistinguishable from live virus infection in terms of priming functional memory CTLp with broad specificity for both dominant and subdominant T cell epitopes.

Contribution of Cells at the Site of DNA Vaccination to the Generation of Antigen-Specific Immunity and Memory

Gene gun-mediated DNA vaccination stimulates an immune response characterized by the activation of IgG-secreting B cells and IFN-γ-secreting T cells. To monitor the contribution of cells at the site of vaccination to this process, transfected skin was periodically removed and grafted onto naive recipients. Immediate removal of vaccinated skin abrogated the development of an immune response. Low-level IgG production was stimulated when the vaccination site was left in place for ≥5 h, with the strength of this response increasing the longer the site remained intact (for up to 2 wk). Measurable primary T cell responses were observed in animals whose vaccination site remained in place for ≥1 day. Skin grafts transferred 0 to 24 h postvaccination stimulated a primary immune response in naive recipients. Memory B and T cells were generated in animals whose site of vaccination remained intact for 5 to 12 h. Skin transferred within 12 h of vaccination triggered memory B and T cell development in graft recipients, while the removal of skin >12 h postvaccination did not reduce memory in vaccinated mice. These findings suggest that 1) primary immunity is induced by cells that migrate rapidly from the site of immunization, 2) nonmigratory cells influence the magnitude of this primary response, and 3) migratory cells alone are responsible for the induction of immunologic memory.