Vaccination with an ovalbumin/interleukin-4 fusion DNA efficiently induces Th2 cell-mediated immune responses in an ovalbumin-specific manner

Targeting HIV-1 envelope glycoprotein trimers to B cells by using APRIL improves antibody responses

An HIV-1 vaccine remains elusive, in part because various factors limit the quantity and quality of the antibodies raised against the viral envelope glycoprotein complex (Env). We hypothesized that targeting Env vaccines directly to B cells, by fusing them to molecules that bind and activate these cells, would improve Env-specific antibody responses. Therefore, we fused trimeric Env gp140 to A PRoliferation-Inducing Ligand (APRIL), B-cell Activating Factor (BAFF), and CD40 Ligand (CD40L). The Env-APRIL, Env-BAFF, and Env-CD40L gp140 trimers all enhanced the expression of activation-induced cytidine deaminase (AID), the enzyme responsible for inducing somatic hypermutation, antibody affinity maturation, and antibody class switching. They also triggered IgM, IgG, and IgA secretion from human B cells in vitro. The Env-APRIL trimers induced higher anti-Env antibody responses in rabbits, including neutralizing antibodies against tier 1 viruses. The enhanced Env-specific responses were not associated with a general increase in total plasma antibody concentrations, indicating that the effect of APRIL was specific for Env. All the rabbit sera raised against gp140 trimers, irrespective of the presence of CD40L, BAFF, or APRIL, recognized trimeric Env efficiently, whereas sera raised against gp120 monomers did not. The levels of trimer-binding and virus-neutralizing antibodies were strongly correlated, suggesting that gp140 trimers are superior to gp120 monomers as immunogens. Targeting and activating B cells with a trimeric HIV-1 Env-APRIL fusion protein may therefore improve the induction of humoral immunity against HIV-1.

Approaches to enhance the efficacy of DNA vaccines

DNA vaccines consist of antigen-encoding bacterial plasmids that are capable of inducing antigen-specific immune responses upon inoculation into a host. This method of immunization is advantageous in terms of simplicity, adaptability, and cost of vaccine production. However, the entry of DNA vaccines and expression of antigen are subjected to physical and biochemical barriers imposed by the host. In small animals such as mice, the host-imposed impediments have not prevented DNA vaccines from inducing long-lasting, protective humoral, and cellular immune responses. In contrast, these barriers appear to be more difficult to overcome in large animals and humans. The focus of this article is to summarize the limitations of DNA vaccines and to provide a comprehensive review on the different strategies developed to enhance the efficacy of DNA vaccines. Several of these strategies, such as altering codon bias of the encoded gene, changing the cellular localization of the expressed antigen, and optimizing delivery and formulation of the plasmid, have led to improvements in DNA vaccine efficacy in large animals. However, solutions for increasing the amount of plasmid that eventually enters the nucleus and is available for transcription of the transgene still need to be found. The overall conclusions from these studies suggest that, provided these critical improvements are made, DNA vaccines may find important clinical and practical applications in the field of vaccination.

Effects of Inula Britannica on the production of antibodies and cytokines and on T cell differentiation in C57BL/6 mice immunized by ovalbumin

In this study, we investigated the effects of Inula Britannica on the production of antibodies against ovalbumin, and the differentiation of T cells, in C57BL/6 mice. The oral administration of Inula Britannica suppressed IL-4 and IL-6 production in lymphocytes collected from an inguinal lymph node in the immunized leg. On the other hand, the intraperitoneal administration of Inula Britannica suppressed IgG1 production, the ratio of IFN-gamma+IL-4-/IFN-gamma-IL-4+ cells and cytokine production of IL-6. It was presumed that the effects of Inula Britannica on the production of antibodies were induced by regulation of the balance of Th1 and Th2. Further, IL-4 and IL-6 production by lymphocytes collected from an inguinal lymph node in the immunized leg were suppressed, and therefore production of antibodies was suppressed.

IL-2 linked to a peptide from influenza hemagglutinin enhances T cell activation by affecting the antigen-presentation function of bone marrow-derived dendritic cells

Chimeric proteins containing antigen linked to cytokines have shown some promise as vaccine candidates but little is known of their mechanism of action, particularly at the level of the antigen-presenting cell. We have investigated this using a chimeric protein in which an immunodominant T cell epitope from influenza hemagglutinin peptide (HA), recognized in the context of I-E(d), was fused to IL-2. Immature murine dendritic cells (DC) derived from bone marrow (BMDC) were used to present the chimeric protein to a T cell hybridoma with TCR specific for the HA peptide (A5 cell line). HA-IL-2 was found to induce significantly higher T cell activation than HA alone. Although the inclusion of IL-2 and HA separately did increase the response of A5 cells compared to HA alone, they were not as effective as the HA-IL-2 chimeric protein. When an antibody known to block IL-2 receptor alpha chain (CD25) was included, A5 activation was reduced, suggesting a role for the receptor in this process. Expression of CD25 on A5 cells was low during activation, implying that the effect was mediated by CD25(+) BMDC. Antigen uptake and processing of HA-IL-2 by BMDC was required since fixing BMDC, prior to antigen exposure, greatly reduced their ability to activate A5 cells. The function of CD25 on DC is currently unknown. Our results suggest this receptor may play a role in antigen uptake and subsequent T cell activation by receptor-mediated endocytosis of antigen attached to IL-2. This finding that may have implications for the development of a new generation of vaccines.

Genetic adjuvants for DNA vaccines

The relatively low efficacy of DNA vaccines in inducing immune responses, especially in large animal species and humans, has impaired their practical use. Despite considerable effort expended on improving DNA vaccine delivery, only minute amounts of Ag are available for immune induction following DNA vaccination. Two complementary strategies have been used to improve and modulate the immune response induced by DNA vaccines: (i) supplementing DNA vaccines with plasmids encoding cytokines and (ii) targeting the Ag encoded by DNA vaccine through genetically fusing the Ag to molecules binding cell surface receptors. This paper reviews recent progress in these two areas and possible mechanisms responsible for the observed effects.

Effects of Astragali root and Hedysari root on the murine B and T cell differentiation

It has traditionally been known in Asian countries that the Astragali and Hedysari roots have similar beneficial effects. They have been applied in clinical practice for immunological diseases, we investigated their effects on specific antibody production, B cells and T cells in BALB/c mice immunized with ovalbumin (OVA). Both the Astragali and Hedysari roots reduced the production of IgG2a in the primary response to OVA. Hedysari root reduced the production of IgG2a in the secondary response. Both reduced the production of IgM, suppressed IL-6 production in spleen cells. It was presumed that the suppression of IgG2a production was induced by the suppression of IL-6, which is an antibody production inducer. It was found that the Hedysari root increased the B cells and activated them, and the Astragali root also tended to increase them. In addition, Hedysari root decreased the proportions of IFN-gamma-producing cells in splenic CD4(+) T lymphocytes. It was shown that the Astragali and Hedysari roots could act as a growth factor of B cells by increasing the proportion of the total B cells and activated B cells. In conclusion, both the Astragali and Hedysari roots showed the same actions, but the latter was more effective.