Lymphatic networks enable diversification of B cell responses to vaccines

Keywords

● Vaccination

● Humoral immunity

● Lymphatic networks

Main Findings

The lymphatic chain downstream of a vaccination site exposes multiple interconnected draining lymph nodes (dLNs) to spatial gradients of antigen and inflammation. Whether these gradients shape B cell and humoral immunity, and whether this can be modulated by the design of vaccine was unclear. The authors of this preprint previously reported that such spatial gradients differentially program innate and T cell responses. In this preprint, they planned to extent this framework to the programs that modulate B cells following vaccination.

Using footpad immunization in C57Bl/6 animals with ovalbumin ((OVA)/Nitrophenol (NP)-OVA and LPS adsorbed in alum), they combine antigen tetramer staining with Immunoglobulin Heavy chain (IgH) B cell receptor (BCR) sequencing, and high-parameter confocal and intravital imaging. They find that dLNs of distinct distances and antigen-gradients each independently prime antigen-specific B cells that are functionally specialized. For example:

· Proximal dLNs favour antibody-secreting cells (ASCs) of great clonal diversity in germinal centers (GC); dLNs positioned at distal locations in turn impose a more stringent early GC B cell selection, with delayed Tfh differentiation constraining distal GC priming.

· Proximal dLNs remodel a capillary-rich medullary niche that retains largely sessile ASCs driving early humoral responses, promoted by interleukin(IL)-6.

· The localized gradient of inflammation further drives divergent isotype class switch recombination (CSR): neutralizing IgG2b predominates in proximal dLNs while, IgG1 distally. This regional specialization relied on the concentration of LPS that reached a lymph node. The availability of IL-4 in more distal dLN played an important role in the CSR of ASCs.

· These programs are tunable: redirecting LPS to the distal dLN enhances IgG2b switching, larger injection volumes and glycosylated protein nanoparticles selectively boost distal GCs, and ipsilateral-distal boosting enhances distal B cell memory recall.

In summary, the authors present data supporting that spatial gradients of antigen and inflammation along the draining lymphatic chain contribute distinct humoral outputs at each dLN that can be tuned through vaccine delivery and design.

Limitations

● Model translatability: The authors extend their initial OVA footpad immunization findings to an alternative antigen-adjuvant platform (malaria antigen nanoparticle vaccine and oil-in-emulsion adjuvant) and alter primary immunization site to the tail base, strengthening the generalizability of the spatial B cell program. However, it falls short in establishing whether this paradigm operates in clinically relevant immunization routes and formulations. Would the spatial programming of GC output and gradients of antigen and inflammatory stimuli differ in standard immunization settings for humans, where afferent lymphatic drainage and node positioning differ from the mouse? Perhaps clinically approved TLR agonists used in vaccine formulations (e.g., CpG oligonucleotides) would similarly bolster ASC production and IgG2b isotype switching when compared to LPS. Moreover, would bypassing the LPS gradient and triggering a proximal vaccine response in a distal dLN have a beneficial effect on the protection of a vaccinated animal?

● Lack of functional or protective endpoint: The authors demonstrate important distinctions in GC selection stringency and avidity between proximal and distal dLN responses, but did not link this to antibody function, both in terms of affinity and durable protection. Does high-avidity selection in distal dLNs translate to more potent or broadly neutralizing serum antibodies, and do the tuneable aspects of vaccine design identified by the authors ultimately improve protection against infection?

● Mechanism of ASC retention: The authors provide elegant, orthogonal evidence for ASC sessility in the proximal dLN medullary niche but fall short of establishing mechanism. Does the medullary capillary niche actively retain ASCs through specific molecular signals, and does it also support their long-term survival in the dLN? Would a retention signal act distinctively on IgG2 but not on IgG1 ASC?

● T cell spatial programming as a potential upstream driver of humoral responses: The authors elegantly establish that antigen and inflammation gradients drive a spatial B cell program, in part shaped by delayed Tfh differentiation distally, strengthening the case that lymph node position instructs humoral output. However, it falls short in determining how much of this program is shaped by the spatially distinct effector and memory-precursor T cell fates that their group previously showed arise from those same gradients (Conlon et al., J Exp Med 2025). How does the effector T cell bias in proximal dLN shape the cytokine environment and modulate antigen persistence through interactions with antigen-bearing cells? In a recall response, do Tfh in distal dLN have a greater propensity to persist as memory cells, given their previous work showing a memory precursor bias in distal dLNs, that better support secondary GC responses?

Significance/Novelty

The authors’ work gives an impetus to study immunization not just as a single lymph node unit, but as a network of lymph nodes that mount independent, qualitatively distinct B cell responses that differ in ASC and GC output, repertoire breadth, isotype, GC selection stringency, and recall.

The authors identified several practical and cost-effective methods to re-program spatially encoded immunization outcomes, by modulating injection volume, nanoparticle glycosylation, adjuvant targeting, and boost site. Each option can selectively tune distal node responses without disturbing proximal ones, suggesting that the spatial architecture of the humoral response can be rationally optimized for specific clinical goals, whether that is early protective titers, high-affinity neutralizing antibody, or durable memory.

Credit

Reviewed by Ash Hagerman (University of Toronto, Department of Immunology) as part of a cross-institutional journal club between the Icahn School of Medicine at Mount Sinai, the University of Oxford, the Karolinska Institute and the University of Toronto.

The author declares no conflict of interests in relation to their involvement in the review.