A novel SARS-CoV-2 Beta RBD DNA vaccine directly targeted to antigen-presenting cells induces strong humoral and T cell responses.

Throughout the COVID-19 pandemic, several variants of concern (VoC) of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have evolved, affecting the efficacy of the approved COVID-19 vaccines. To address the need for vaccines that induce strong and persistent cross-reactive neutralizing antibodies and T cell responses, we developed a prophylactic SARS-CoV-2 vaccine candidate based on our easily and rapidly adaptable plasmid DNA vaccine platform. The vaccine candidate, referred to here as VB2129, encodes a protein homodimer consisting of the receptor binding domain (RBD) from lineage B.1.351 (Beta) of SARS-CoV-2, a VoC with a severe immune profile, linked to a targeting unit (human LD78ß/CCL3L1) that binds chemokine receptors on antigen-presenting cells (APCs) and a dimerization unit (derived from the hinge and CH3 exons of human IgG3). Immunogenicity studies in mice demonstrated that the APC-targeted vaccine induced strong antibody responses to both homologous Beta RBD and heterologous RBDs derived from Wuhan, Alpha, Gamma, Delta, and Omicron BA.1 variants, as well as cross-neutralizing antibodies against these VoC. Overall, preclinical data justify the exploration of VB2129 as a potential booster vaccine that induces broader antibody- and T cell-based protection against current and future SARS-CoV-2 VoC.

Targeted idiotype-fusion DNA vaccines for human multiple myeloma: preclinical testing.

OBJECTIVES: A homodimeric fusion DNA vaccine targeting idiotype (Id) to antigen-presenting cells (APC) induced robust tumor protection in a mouse model of multiple myeloma (MM). Similar Id vaccine molecules were generated for four patients with MM with three main objectives: (i) do the vaccine molecules induce bona fide anti-Id immune responses in mice? (ii) does targeting of the vaccine molecules to APC enhance immune responses? (iii) can anti-Id antibodies, generated as by-product in vaccinated mice, be used to establish sensitive assays for complete remission (CR) prior to patient vaccination? METHODS: Chimeric vaccine molecules targeting patient Id to mouse major histocompatibility complex (MHC) class II molecules were genetically constructed for four patients with MM. RESULTS: DNA vaccination of mice with chimeric vaccines targeting patient Id to mouse MHC class II molecules elicited antibodies specific for the patient's myeloma protein. Targeting MHC class II greatly enhanced anti-Id responses. Mouse anti-Id antibodies were used to establish myeloma protein-specific enzyme-linked immunosorbent assays (ELISAs) that were between 75 and 1500 times more sensitive than conventional serum protein electrophoresis and immunofixation. CONCLUSIONS: These results pave the way for testing targeted DNA Id vaccines in patients in CR. Id- and patient-specific ELISA could be established affording evaluation of CR depth beyond current serological methods.

Chemokine-idiotype fusion DNA vaccines are potentiated by bivalency and xenogeneic sequences.

V regions of monoclonal Ig express an exquisite B-cell tumor-specific antigen called idiotype (Id). Id is a weak antigen and it is important to improve immunogenicity of Id vaccines. Chemokine receptors are expressed on antigen-presenting cells (APCs) and are promising targets for Id vaccines. Here we compare monomeric and dimeric forms of MIP-1alpha and RANTES that target Id to APCs in a mouse B lymphoma (A20) and a multiple myeloma model (MOPC315). MIP-1alpha was more potent than RANTES. The dimeric proteins were more potent than monomeric equivalents in short-term assays. When delivered in vivo by intramuscular injection of plasmids followed by electroporation, dimeric proteins efficiently primed APCs in draining lymph nodes for activation and proliferation of Id-specific CD4(+) T cells. Good anti-Id antibody responses were obtained, and mice immunized only once were 60% to 80% protected in both tumor models. CD8(+) T cells contributed to the protection. Antibody responses and tumor protection were reduced when the human Ig hinge = C(H)3 dimerization motif was replaced with syngeneic mouse counterparts, indicating that tumor-protective responses were dependent on xenogeneic sequences. The results suggest that bivalency and foreign sequences combine to increase the efficiency of chemokine-Id DNA vaccines.

Induction of central T cell tolerance: recombinant antibodies deliver peptides for deletion of antigen-specific (CD4+)8+ thymocytes.

In order to prevent or ameliorate autoimmune disease, it would be desirable to induce central tolerance to peripheral self-antigens. We have investigated whether recombinant antibodies (Ab) that deliver T cell epitopes to antigen-presenting cells (APC) in the thymus can be used to induce thymocyte deletion. Troybodies are recombinant Ab with V regions specific for APC surface molecules that have T cell epitopes genetically introduced in their C domains. When MHC class II-specific Troybodies with the lambda2(315)T cell epitope were injected into lambda2(315)-specific TCR transgenic mice, a profound deletion of (CD4+)8+ thymocytes was observed. MHC class II-specific Troybodies were 10-100-fold more efficient than non-targeting peptide Ab, and 500-fold more efficient than synthetic peptide at inducing deletion. Similar findings were observed when MHC class II-specific Troybodies with the OVA(323-339) T cell epitope were injected into OVA-specific TCR transgenic mice. Although deletion was transient after a single injection, newborn mice repeatedly injected with MHC class II-specific Troybodies for 4 weeks, had reduced antigen-specific T cells in peripheral lymphoid tissues and reduced T cell responses. These experiments suggest that Troybodies constructed to target specifically thymic APC could be useful tools for induction and maintenance of central T cell tolerance in autoimmune diseases.