Preclinical Efficacy of a Trivalent Human FcγRI-Targeted Adjuvant-Free Subunit Mucosal Vaccine against Pulmonary Pneumococcal Infection

Abstract

Lack of safe and effective mucosal adjuvants has severely hampered the development of mucosal subunit vaccines. In this regard, we have previously shown that immunogenicity of vaccine antigens can be improved by targeting the antigens to the antigen-presenting cells. Specifically, groups of mice immunized intranasally with a fusion protein (Bivalent-FP) containing a fragment of pneumococcal-surface-protein-A (PspA) as antigen and a single-chain bivalent antibody raised against the anti-human Fc-gamma-receptor-I (hFcγRI) elicited protective immunity to pulmonary Streptococcus pneumoniae infection. In order to further enhance the immunogenicity, an additional hFcγRI-binding moiety of the single chain antibody was incorporated. The modified vaccine (Trivalent-FP) induced significantly improved protection against lethal pulmonary S. pneumoniae challenge compared to Bivalent-FP. In addition, the modified vaccine exhibited over 85% protection with only two immunizations. Trivalent-FP also induced S. pneumoniae-specific systemic and mucosal antibodies. Moreover, Trivalent-FP also induced IL-17-and IL-22-producing CD4 + T cells. Furthermore, it was found that the hFcγRI facilitated uptake and presentation of Trivalent-FP. In addition, Trivalent-FP also induced IL-1α, MIP-1α, and TNF-α; modulated recruitment of dendritic cells and macrophages; and induced CD80/86 and MHC-II expression on antigen presenting cells.With over 90 known serotypes, Streptococcus pneumoniae remains the leading cause of community acquired pneumoniae. In addition, younger and immunocompromised populations are more vulnerable to infection. Furthermore, S. pneumoniae causes over 1 million deaths per year in children aged less than 5 years [10]. To date, two polysaccharide-based subunit vaccines are available to combat select serotypes. However, use of these 13 and 23 serotype vaccines cause serotype replacement in the vaccinated population [11]. This results in a surge of non-vaccine serotypes within the vaccinated population. Thus, new approaches to pneumococcal vaccines are required, which can generate protection over multiple serotypes. The pneumococcal surface protein A (PspA) has been known to induce cross-serotype protection against S. pneumoniae [12]. Thus, not only is S. pneumoniae a significant global health problem, it also expresses a well-defined protective protein antigen, making it a particularly suitable model to test and optimize our mucosal subunit vaccine platform.Previously we have shown that targeting vaccine antigens to antigen-presenting cells (APCs) eliminates the need for adjuvants.By genetically fusing a bivalent single-chain variable fragment-based antibody (Bivalent anti-human-Fc-gamma-receptor-I (FcγRI)), which specifically recognizes human-FcγRI, to a pneumococcal antigen (PspA), a fusion protein named Bivalent-FP was obtained ( Figure 1A). Bivalent-FP induces systemic and mucosal antibodies and protection against pulmonary S. pneumoniae infection by intranasal immunization. However, this vaccine requires at least three i...

SARS-CoV-2: Immunity, Challenges with Current Vaccines, and a Novel Perspective on Mucosal Vaccines

“…In addition, we also observed Th17 and Th22 responses in the mouse lungs following IN immunization (Figure 4). The immunized mice were protected against lethal pneumococcal pneumonia [219]. We also observed that IN immunization induced significantly higher IgG and IgA responses in the BAL compared to IM immunization (unpublished data).…”

“…In two separate studies, the hFcγRI-targeting approach was evaluated in a mouse model of pneumococcal pneumonia [218,219]. In both studies, APC targeting was realized with a monoclonal Ab that binds to hFcγRI (α-hFcγRI) [220].…”

Diverse Mechanisms of Protective Anti-Pneumococcal Antibodies

“…Another study demonstrated that by fusing a humanized single-chain antibody component (in which the variable domain binds to FcgRI) to PspA, protection could be achieved in the absence of adjuvant (Bitsaktsis et al, 2012). This vaccine could be enhanced further by adding an additional FcgRI binding moiety to the vaccine mentioned above (Kumar et al, 2020). PspA vaccines have advanced to human clinical trials and demonstrated safety and robust antibody responses (Briles et al, 2000b;Nabors et al, 2000;Frey et al, 2013), however, concerns exist about using full length PspA due to its sequence homology with human cardiac myosin (Ginsburg et al, 2012).…”

Bimodal Targeting of Human Leukocytes by Fc- and CpG-Decorated Polymersomes to Tune Immune Induction

“…Among all identified receptors, targeting FcRs, which recognize the Fc fragment of immunoglobulins, is a well-studied and promising approach to improve the potency of vaccine formulations. − Multiple studies provided evidence that parenteral immunization of mice with Fc-fusion protein antigens resulted in enhanced cellular and humoral immune responses compared to immunization with antigens lacking the Fc domain. − In the context of nanoparticles, decoration with Fc fragments has also been shown to improve particle internalization by murine macrophages. , Moreover, FcR targeting enhances transcytosis and is, therefore, especially of interest for mucosal applications. − …”