Co-delivery of a CD4 T cell helper epitope via covalent liposome attachment with a surface-arrayed B cell target antigen fosters higher affinity antibody responses

Abstract

Liposomal vaccines incorporating adjuvant and CD4 T cell helper peptides enhance antibody responses against weakly immunogenic B cell epitopes such as found in the membrane proximal external region (MPER) of the HIV-1 gp41 subunit. While the inclusion of exogenous helper peptides in vaccine formulations facilitates stronger and more durable antibody responses, the helper peptide incorporation strategy per se may influence the overall magnitude and quality of B cell target antigen immunogenicity. Both variability in individual peptide encapsulation as well as the potential for liposome surface-associated helper peptides to misdirect the humoral response are potential parameters impacting outcome. In this study, we used MPER/liposome vaccines as a model system to examine how the mode of the potent LACK T helper peptide formulation modulates antibody responses against the MPER antigen. We directly compared liposome surface-arrayed palmitoyl LACK (pLACK) versus soluble LACK (sLACK) encapsulated in the liposomes and free in solution. Independent of LACK formulation methods, dendritic cell activation and LACK presentation were equivalent in vivo. The frequency of MPER-specific GC B cells promoted by sLACK was higher than that stimulated by pLACK formulation, a finding associated with a significantly greater frequency of LACK-specific GC B cells induced by pLACK. While there were no significant differences in the quantity of MPER-specific serological responses, the MPER-specific antibody titer trended higher with sLACK formulated vaccines at the lower dose of LACK. However, pLACK generated relatively greater MPER-specific antibody affinities than those induced by sLACK-formulated vaccines. Overall, the results suggest that liposomal surface-associated LACK enhances immunogenicity of LACK through better engagement of LACK-specific B cells. Of note, this is not detrimental to the induction of MPER-specific immune responses; rather, the elicitation of higher affinity anti-MPER antibodies benefits from augmented help delivered via covalent linkage of the pLACK CD4 T cell epitope in conjunction with MPER/liposome presentation.

Incorporation of a Novel CD4+ Helper Epitope Identified from Aquifex aeolicus Enhances Humoral Responses Induced by DNA and Protein Vaccinations

“…Additional CD4+ helper epitopes have also been mapped and explored. For example, a recent study reported that co-delivery of MPER antigen with a Leishmania major -derived HLA I-Ad helper CD4+ T cell epitope (LACK) in liposomes can improve induced anti-MPER antibody responses ( Elbahnasawy et al., 2018 ).…”

“…As such, robust germinal center B cell responses are dependent on presentation of MHC II-restricted epitope, derived from the antigen, by GCB to Tfh cells. However, different epitopes have varying affinity for binding to MHC-II receptors depending on the hosts' haplotype such that peptide vaccines as well as smaller protein domains may not intrinsically contain a potent CD4+ helper epitope to drive germinal center responses ( Elbahnasawy et al., 2018 ; Falugi et al., 2001 ; Pichichero, 2013 ). Such is the rationale for conjugating peptide and carbohydrate vaccines to protein carriers, like Keyhole limpet hemocyanin (KLH) ( Ragupathi et al., 2002 ), tetanus toxin ( Diethelm-Okita et al., 2000 ), or hepatitis B-surface antigen (HbsAg) ( Collins et al., 2017 ).…”

Novel approaches for the design, delivery and administration of vaccine technologies

“…The location of antigen in liposomes influences the type of immune responses generated towards the vaccine. Incorporation of CD4 T cell helper epitopes can aid in generating a stronger antibody response to a B cell target antigen [33,72], and complete spatial segregation of the two antigens by the liposomal bilayer minimizes the immune responses focus on the T cell epitope (Fig. Incorporation of CD4 T cell helper epitopes can aid in generating a stronger antibody response to a B cell target antigen [33,72], and complete spatial segregation of the two antigens by the liposomal bilayer minimizes the immune responses focus on the T cell epitope (Fig.…”

“…T cell responses are induced by both encapsulated and surface-conjugated antigens, while B cell responses are exclusively induced by surface-conjugated antigen [67]. Incorporation of CD4 T cell helper epitopes can aid in generating a stronger antibody response to a B cell target antigen [33,72], and complete spatial segregation of the two antigens by the liposomal bilayer minimizes the immune responses focus on the T cell epitope ( Fig. 1) [33].…”

VelcroVax: a ‘bolt-on’ vaccine platform technology improves antibody titres against a viral glycoprotein in mice

“…Poorly immunogenic haptens displayed on nanoparticles are more effectively recognised by dendritic cells (DCs). In addition, nanoparticle size (30-100 nm) can influence T helper bias and T helper epitopes from protein-based nanoparticles can contribute to anti-hapten immunity, thus humoral responses generated are likely to be higher affinity and more diverse [22][23][24][25][26] .…”