Background: The main goal for the development of an HIV-1 vaccine remains the induction of protective antibodies. New modes of antigen delivery are warranted to improve the quality of immune responses. We previously showed that targeting of the Langerhans cells (LC) with anti-Langerin mAb fused to HIV-1 Envelope (LC.Env) drives antigen-specific humoral responses, either in mice or using in vitro cultures of human LCs.

Objectives: i) to develop a next generation of anti-LC targeting through the design of 3 Env monochains (LC3.Env3) to mimic natural Env conformation; ii) to test the immunogenicity of new construct in vivo; iii) to assess early Germinal center (GC) formation in draining Lymph nodes (dLN) by Immunofluorescence (IF).

Methods: Mice were immunized intradermaly, twice with 7 mcg of LC3.Env3 or control LC.Env mAb, with no adjuvant. Post-prime (PP) and -boost (PB) Ab (magnitude and affinity) and cellular responses were assessed by Luminex and FACS, respectively. The germinal center (GC) reaction on dLN was monitored by IF at sequential time points.

Results: As compared to LC.Env, LC3.Env3 (i) induced a faster and stronger Env-IgG response (mean titers 22 and 37 fold higher at day 14 and 28, respectively); (ii) improved the avidity of anti-Env IgG (index of 12% and 36%, 14 days PP and 7 days PB, respectively), consistent with a significant expansion of Tfh and GC B cells (GL-7+/Fas+) 7 days PB; and (iii) led to a rapid formation of structured germinal centers in dLN.

Significance: A LC-HIV Env trimer elicit rapid and robust GC formation. Next generation of anti-LC HIV vaccine would help to improve responses to conformational trimer Env immunogen with the aim to elicit neutralizing antibodies.