Divergence of Primary Cognate B- and T-Cell Proliferative Responses to Subcutaneous and Intravenous Immunization with Virus-Like Particles

Abstract

A major advantage of virus-like particle (VLP) vaccines against HIV is their structural identity to wild-type viruses, ensuring that antigen-specific B-cells encounter the envelope protein in its natural conformation. For the induction of affinity-matured antibodies, the B-cells must also obtain help from T-cells that are restricted by linear epitopes. Using B- and T-cell transgenic mouse models, we compared the efficacy of modified HIV-VLPs delivered by subcutaneous and intravenous immunization to stimulate primary B- and T-cell proliferative responses in different lymphoid organs. VLPs containing an influenza virus hemagglutinin epitope within the HIV-Gag protein induced comparable primary cognate T-cell proliferative responses in the draining lymph node and the spleen, irrespective of the delivery route. In contrast, after subcutaneous immunization with HIV-Gag VLPs containing hen egg lysozyme (HEL) on their surface, the proliferative response of transgenic HEL-specific B-cells was restricted to the draining lymph nodes, while intravenous VLP immunization primarily induced a B-cell proliferative response in the spleen. In vitro co-culture experiments further revealed that the presentation of VLP-associated surface antigens by dendritic cells to cognate B-cells is inefficient. This is consistent with a direct triggering of the B-cell proliferative response by the VLPs and suggests that HIV VLPs may indeed be suitable to directly promote the expansion of B-cells specific for conformational epitopes that are unique to functionally-active Env spikes on the virion. Further investigations are warranted to explore potential differences in the quality and protective potency of HIV-specific antibody responses induced by the two routes.

Generation of T follicular helper cells in vitro: requirement for B‐cell receptor cross‐linking and cognate B‐ and T‐cell interaction

“…We inserted the coding sequence for the OT2 epitope between the matrix and capsid domains of the codon‐optimized HIV‐gag/pol expression plasmid (Fig. a) as described previously . To further confirm our results obtained with the B cells from SW‐HEL BCR‐transgenic mice we used the B cells from b12 mice, another BCR‐transgenic mouse line expressing the broadly neutralizing antibody b12 that is specific to the HIV‐Env gp120 protein …”

“…In contrast to monovalent proteins, VLPs are superior activators of cognate B‐cell responses. VLPs cross‐link BCRs and contain potential Toll‐like receptor stimuli, which may contribute to their efficient B‐cell activation and differentiation in cell culture and their immunogenicity in vivo . Replacing Env‐OT2‐VLPs with a combination of monomeric HIV‐Env protein and the OT‐2 peptide did not induce the generation of BCL‐6 + CXCR5 + T cells as well (data not shown).…”

“…In contrast to previous attempts, we used VLPs to mimic the natural antigenic stimulation of cognate B cells. Previously, we demonstrated the efficient antigen‐dependent activation and differentiation of naive B cells from SW‐HEL BCR‐transgenic mice with the cognate VLPs . Such HIV‐derived HEL‐VLPs (Table ) carry HEL as a transmembrane protein on the surface of the particles in a repetitive manner to mimic the viral envelope protein .…”

“…Such HIV‐derived HEL‐VLPs (Table ) carry HEL as a transmembrane protein on the surface of the particles in a repetitive manner to mimic the viral envelope protein . As a B‐cell targeting antigen‐delivery system, these HEL‐VLPs are able to provide several unique direct effects on the cognate B cells that cannot be achieved by the monovalent form of the antigen …”

“…The proliferation assay of OT2 CD4 + T cells in co‐culture with DCs was performed as described elsewere . Briefly, CD4 + T cells were labelled with 7·5 μ m CFSE (Vybrant CFDA Cell Tracer kit; Invitrogen, Carlsbad, CA) and co‐cultivated with freshly isolated splenic DCs (from BL6 mice) for 64 hr at 37° in the presence of different VLP preparations in various concentrations, as described above.…”