Background:
Developing an effective HIV-1 vaccine is contingent on generating protective antibodies (Abs). Novel antigen delivery methods are needed to enhance immune responses. One promising approach involves directing antigens to dendritic cells (DC) through fused monoclonal antibodies (mAbs) to amplify both cellular and humoral responses. Previous studies have shown success in targeting skin Langerhans cells (LC) with anti-Langerin mAbs fused to HIV-1 Envelope (LC.Env), inducing antigen-specific humoral responses in mice and human LC:T/B co-cultures. In this study, we aimed to refine LC targeting by designing three Env monochains instead of 2 (LC3.Env3) mimicking natural Env conformation. We aim to investigate whether these new trimeric Env constructs could stimulate germinal center (GC) and Tfh cell reactions, ultimately leading to the production of Env-binding IgG and HIV neutralizing antibodies (NeutAb) in vivo.
Methods:
B6 mice were intradermally immunized with LC3.Env3 or control LC.Env mAb (5 mcg of Env antigen) at day (D) 0 and D21, without adjuvant. Antibody (magnitude and affinity) and cellular responses were assessed post-prime (PP) and post-boost (PB) using Luminex and FACS, respectively. GC/Tfh reactions in draining lymph nodes (dLN) were monitored through immunofluorescence at various times. Additionally, rabbits were subcutaneously immunized with 50 mcg LC3.Env3 without adjuvants, and serum NeutAb levels were evaluated.
Results:
Compared to LC.Env, LC3.Env3: (i) elicited a rapid and potent Env-IgG response, with mean titers measuring 22- and 37-fold higher at D14 PP and D7 PB, respectively. (ii) enhanced the avidity of anti-Env IgG, resulting in an index increase of 12% and 36% at D14 PP and D7 PB, respectively. This was accompanied by a marked expansion of Tfh and GC B cells (GL-7+/Fas+) at D7 PB. (iii) swiftly induced the formation of structured germinal centers in dLN, indicative of a robust immune response. Significant Tier-1 NeutAb induction was observed in rabbits immunized with LC3.Env3.
Conclusions:
This study underscores that HIV Env antigen can be adeptly targeted to LC as a trimer, intensifying both the magnitude and quality of humoral responses without using any adjuvant and after only two shots. In addition, the strategy of targeting SOSIP-like trimeric Env to LC holds substantial promise for eliciting broadly neutralizing antibodies (bNAb) against HIV and will require an optimization of the vaccination regimen.