Modulation of germinal center and antibody dynamics via ipsilateral versus contralateral immunization against SARS-CoV-2

Human clinical trials have reported immunological outcomes can differ between ipsilateral (same side) and contralateral (alternate sides) prime-boost vaccination. However, our mechanistic understanding of how keeping or shifting the anatomical sites of immunization impacts the resultant germinal centers (GCs) and antibody responses is limited. Here, we use an adjuvanted SARS-CoV-2 spike vaccine to dissect GC dynamics in draining lymph nodes and serological outcomes following ipsilateral or contralateral prime-boost vaccination in C57BL/6 mice. Contralateral vaccination elicited independent GCs at distinct lymph nodes, where robust secondary GCs only appeared upon secondary distal vaccination, while ongoing GCs from the primary site were not boosted. In contrast, ipsilateral vaccination resulted in sustained GC activity. Ipsilateral vaccination accelerated the development of antibody titers against ancestral (wild-type [WT]), Beta, and BA.1 but were later comparable between ipsilateral and contralateral groups in terms of magnitude, durability, and neutralization capacity beyond 28 d. Using a heterologous SARS-CoV-2 WT/BA.1 spike prime-boost model, cross-reactive GC responses were generated against WT and BA.1 spike, with analogous serological and GC dynamics to our homologous model. Within the cross-reactive GC B cells, differential recognition of WT and BA.1 antigens was observed and were further compartmentalized in primary or secondary GCs, depending on ipsilateral or contralateral regimes. Collectively, maintaining a common prime-boost site augments the kinetics of memory B cell recall and transiently drive higher antibody titers, but longer-term serological outcomes are unaffected by the anatomical localization of immunization.