Induction Of Antigen-specific Antibody Responses Research Articles

Lipid-based vaccine nanoparticles for induction of humoral immune responses against HIV-1 and SARS-CoV-2

The current health crisis of corona virus disease 2019 (COVID-19) highlights the urgent need for vaccine systems that can generate potent and protective immune responses. Protein vaccines are safe, but conventional approaches for protein-based vaccines often fail to elicit potent and long-lasting immune responses. Nanoparticle vaccines designed to co-deliver protein antigens and adjuvants can promote their delivery to antigen-presenting cells and improve immunogenicity. However, it remains challenging to develop vaccine nanoparticles that can preserve and present conformational epitopes of protein antigens for induction of neutralizing antibody responses. Here, we have designed a new lipid-based nanoparticle vaccine platform (NVP) that presents viral proteins (HIV-1 and SARS-CoV-2 antigens) in a conformational manner for induction of antigen-specific antibody responses. We show that NVP was readily taken up by dendritic cells (DCs) and promoted DC maturation and antigen presentation. NVP loaded with BG505.SOSIP.664 (SOSIP) or SARS-CoV-2 receptor-binding domain (RBD) was readily recognized by neutralizing antibodies, indicating the conformational display of antigens on the surfaces of NVP. Rabbits immunized with SOSIP-NVP elicited strong neutralizing antibody responses against HIV-1. Furthermore, mice immunized with RBD-NVP induced robust and long-lasting antibody responses against RBD from SARS-CoV-2. These results suggest that NVP is a promising platform technology for vaccination against infectious pathogens.

Rational design of adjuvants for subunit vaccines: The format of cationic adjuvants affects the induction of antigen-specific antibody responses

A range of cationic delivery systems have been investigated as vaccine adjuvants, though few direct comparisons exist. To investigate the impact of the delivery platform, we prepared four cationic systems (emulsions, liposomes, polymeric nanoparticles and solid lipid nanoparticles) all containing equal concentrations of the cationic lipid dimethyldioctadecylammonium bromide in combination with the Neisseria adhesin A variant 3 subunit antigen. The formulations were physicochemically characterized and their ability to associate with cells and promote antigen processing (based on degradation of DQ-OVA, a substrate for proteases which upon hydrolysis is fluorescent) was compared in vitro and their vaccine efficacy (antigen-specific antibody responses and IFN-γ production) and biodistribution (antigen and adjuvant) were evaluated in vivo. Due to their cationic nature, all delivery systems gave high antigen loading (> 85%) with liposomes, lipid nanoparticles and emulsions being <200 nm, whilst polymeric nanoparticles were larger (~350 nm). In vitro, the particulate systems tended to promote cell uptake and antigen processing, whilst emulsions were less effective. Similarly, whilst the particulate delivery systems induced a depot (of both delivery system and antigen) at the injection site, the cationic emulsions did not. However, out of the systems tested the cationic emulsions induced the highest antibody responses. These results demonstrate that while cationic lipids can have strong adjuvant activity, their formulation platform influences their immunogenicity.

Recombinant Ehrlichia P29 protein, but not P13 protein, induces a protective immune response in a mouse model of ehrlichiosis (P4280)

Abstract Ehrlichioses are emerging tick-borne bacterial diseases of humans and animals. The diseases are caused by obligately intracelluar bacteria belonging to the genus Ehrlichia. Currently, no vaccine is available against any ehrlichial diseases. Several immunoreactive proteins of ehrlichiae identified using immune sera from human patients and animals that include the major outer membrane proteins, ankyrin-repeat proteins and tandem repeat proteins (TRPs). In the present study, we evaluated E. muris P13 and P29 proteins, which are orthologs of E. chaffeensis TRP32 and TRP47, respectively, as subunit vaccines in a mouse model of ehrlichiosis. Immunization of mice with recombinant P29, but not P13, induced significant protection against a challenge infection. The protection induced by recombinant P29 was associated with the induction of a strong IgG antibody response. In contrast to development of IgG antibodies to P13 in all E. muris-infected mice, fewer animals infected with E. muris had IgG antibodies to P29. We hypothesize that polyclonal activation of B cells by CD4+ Th1 cells and subsequent development of hypergamaglobluinemia during persistent E. muris infection impairs formation of antibodies to antigens, such as P29, with low B cell precursor frequencies. In conclusion, our study indicated that Ehrlichia P29, but not P13, induces protective immune response, and induction of antigen-specific antibody responses impaired during persistent ehrlichial infections.

A Fusion Protein of the Hemagglutinin A Antigenic Region of Porphyromonas gingivalis and Maltose-Binding Protein Induces Antibody Responses in the Oral Cavity

Maltose-binding protein (MBP) produced by Escherichia coli acts as an adjuvant when fused to various antigens. In this study, the antigenic region of hemagglutinin A of Porphyromonas gingivalis with a molecular mass of 25 kDa (25k-hagA) was fused to MBP (25k-hagA-MBP) and the efficacy of the resulting fusion protein as a nasal vaccine was assessed. While nasal immunization with 25k-hagA induced no antibody responses, 25k-hagA-MBP elicited high serum IgG, IgA, and secretory IgA anti-25k-hagA antibodies in the saliva. When 25k-hagA-MBP was co-administered with an established mucosal adjuvant, cholera toxin, 25k-hagA-specific serum IgG and salivary IgA antibody responses were not further elevated. Interestingly, 25k-hagA mixed with MBP failed to induce 25k-hagA-specific antibody responses. These findings suggest that MBP must be fused to the target antigen for induction of antigen-specific antibody responses and that nasal administration of 25k-hagA-MBP may be an effective mucosal vaccine for the prevention of P. gingivalis infection.

Salmonella enterica Serovar Typhimurium Vaccine Strains Expressing a Nontoxic Shiga-Like Toxin 2 Derivative Induce Partial Protective Immunity to the Toxin Expressed by Enterohemorrhagic Escherichia coli

Shiga-like toxin 2 (Stx2)-producing enterohemorrhagic Escherichia coli (referred to as EHEC or STEC) strains are the primary etiologic agents of hemolytic-uremic syndrome (HUS), which leads to renal failure and high mortality rates. Expression of Stx2 is the most relevant virulence-associated factor of EHEC strains, and toxin neutralization by antigen-specific serum antibodies represents the main target for both preventive and therapeutic anti-HUS approaches. In the present report, we describe two Salmonella enterica serovar Typhimurium aroA vaccine strains expressing a nontoxic plasmid-encoded derivative of Stx2 (Stx2DeltaAB) containing the complete nontoxic A2 subunit and the receptor binding B subunit. The two S. Typhimurium strains differ in the expression of flagellin, the structural subunit of the flagellar shaft, which exerts strong adjuvant effects. The vaccine strains expressed Stx2DeltaAB, either cell bound or secreted into the extracellular environment, and showed enhanced mouse gut colonization and high plasmid stability under both in vitro and in vivo conditions. Oral immunization of mice with three doses of the S. Typhimurium vaccine strains elicited serum anti-Stx2B (IgG) antibodies that neutralized the toxic effects of the native toxin under in vitro conditions (Vero cells) and conferred partial protection under in vivo conditions. No significant differences with respect to gut colonization or the induction of antigen-specific antibody responses were detected in mice vaccinated with flagellated versus nonflagellated bacterial strains. The present results indicate that expression of Stx2DeltaAB by attenuated S. Typhimurium strains is an alternative vaccine approach for HUS control, but additional improvements in the immunogenicity of Stx2 toxoids are still required.

Transcutaneous Immunization Induces a Higher Antibody Immune Response than Parenteral Immunization

Transcutaneous immunization is a novel strategy of vaccination that utilizes a topical application of antigen to intact skin for induction of immune responses. In this study, we have assessed the potential for application of transcutaneous immunization for development of novel vaccine delivery system. When BALB/c mice were immunized with ovalbumin (OVA) by direct application to shaved skin, OVA-specific serum IgG as well as IgA antibody responses were induced. Interestingly, OVA-specific serum IgG responses were higher than those induced by the intraperitonial immunization. Antigen-specific cell proliferative responses confirmed the antibody titers and showed that significantly higher levels of OVA-specific proliferative responses were induced in the CD4+ T cells from spleen of mice transcutaneously immunized with OVA when compared with levels induced in CD4+ T cells from mice given OVA intraperitonially. Interestingly, while OVA-specific T helper cells from mice immunized intraperitonially produced high IFN-γ with low IL-4 when restimulated with OVA in vitro, transcutaneous immunization resulted in the induction of low IFN-γ with high IL-4 responses. Finally, transcutaneous, but not intraperitonial, immunization with OVA elicited OVA-specific mucosal IgA antibodies in the intestinal tract. These results indicate that transcutaneous immunization may be a better antigen delivery route for induction of antigen-specific antibody responses than parenteral immunization.

Evaluation of the Immunotoxicity of Antiretroviral Drugs Using anIn VitroMethod for the Induction and Measurement of a Specific Antibody Response in Human Peripheral Blood Lymphocytes

We studied the effects of the antiretroviral drugs 3’-azido-3’-deoxythymidine (AZT) and 2’,3’-dideoxycytidine (DDC) on the induction of a specific primary antibody response to the antigen SRC and on Pokeweed mitogen-induced polyclonal immunoglobulin (Ig) production in cultures of normal human peripheral blood lymphocytes.The results presented here show that AZT and DDC inhibited both systems in a dose-dependent way. However, inhibition of the antigen-specific antibody response occurred at drug concentrations significantly lower than those effective on the mitogen-driven polyclonal response. This was particularly striking for DDC, which was approximately 100 times more powerful, on a molar basis, on the specific antibody response than on polyclonal Ig production. Thus, in vitro systems for the induction of antigen-specific antibody responses in human lymphocytes may be important, sensitive tools for preclinical studies of the immunotoxicity of antiretroviral drugs.

An HIV p24 Heptapeptide Down-Regulates Antigen-Specific Responses in Vitro Interfering at the Level of the T3-Ti Complex

Ch7 (RGSDIAG), a synthetic heptapeptide derived from a conserved region of HIV p24 (aa 232-238), was previously shown to suppress antigen-induced responses in cultures of normal human peripheral blood lymphocytes (PBL). We show in this paper that Ch7 is the shortest peptide retaining full inhibitory capacity. Further, the peptide inhibited efficiently and in a dose-dependent manner the induction of a specific antibody response to the antigens SRC (sheep red cells) and Candida albicans but did not exert any effect on the induction of immunoglobulin-secreting cells in PWM-stimulated cultures. Finally, Ch7 inhibited anti-CD3-induced lympho-proliferation but did not affect anti-CD2 activation. These results suggest that a conserved epitope of HIV p24 may be able to prevent the induction of antigen-specific antibody responses by interfering with lymphocyte activation via the T3-Ti complex, resulting in the abrogation of immune functions that are defective in HIV-infected individuals.

Induction of antigen-specific antibody responses in primed and unprimed B cells. Functional heterogeneity among Th1 and Th2 T cell clones.

CD4+ T cells have been recently divided into two subsets. The functions of these subsets are thought to be distinct: one subset (Th1) is responsible for delayed type hypersensitivity responses and another (Th2) is primarily responsible for induction of antibody synthesis. To more precisely define the roles of both subsets in humoral immune responses, we examined the ability of a panel of nominal antigen specific Th1 and Th2 clones to induce anti-TNP specific antibody synthesis in TNP-primed or unprimed B cells. Four of nine Th1 clones induced little or no antibody synthesis with TNP-primed B cells. However, five other Th1 clones were very effective at inducing IgG anti-TNP plaque-forming cell (PFC) responses in primed B cells. One of these Th1 clones was analysed in detail and found to also provide helper function for unprimed B cells. Cognate B-T cell interaction was required for induction of both primary and secondary responses with this clone, indicating that a Th1 clone could function as a "classical" Th cell. The seven IL-4 producing Th2 clones examined were also heterogeneous in their ability to induce antibody secretion by TNP-primed B cells. Although four of the Th2 clones induced IgG and IgM anti-TNP PFC responses, two Th2 clones induced only IgM and no IgG antibody, and another clone failed to induce any anti-TNP PFC. All Th2 clones failed to induce any anti-TNP PFC. All Th2 clones produced high levels of IL-4, but "helper" Th2 clones produced significantly greater amounts of IL-5 than "non-helper" Th2 clones. These studies indicate that some IL-2- and some IL-4-producing T cell clones can induce TNP-specific antibody in cell clones can induce TNP-specific antibody in primed and unprimed B cells, and that Th1 and Th2 clones are heterogeneous in their ability to induce Ig synthesis. Therefore, although T cell clones can be classified as Th1 or Th2 types according to patterns of IL-2, IFN-gamma, or IL-4 synthesis, the functional capacity to induce antibody synthesis cannot be predicted solely by their ability to secrete these lymphokines.

Induction of antigen-specific antibody responses by nonspecific T cell-derived helper factors.

Induction of antigen-specific antibody responses by nonspecific T cell-derived helper factors.