# Immunodominance is a poor predictor of vaccine-induced T follicular helper cell quality

## TL;DR

The study shows that not all CD4+ T cell epitopes provide equal help for strong antibody responses, challenging assumptions about immunodominance in vaccine design.

## Contribution

The study reveals that immunodominance is not a reliable indicator of CD4+ T cell help quality for B cells in vaccine contexts.

## Key findings

- Priming of naïve CD4+ T cells is efficient, but immunodominance does not predict quality of B cell help.
- A single MHC class II epitope can drive robust germinal center responses and high IgG titers.
- Multimerizing antigens on nanoparticles can unlock subdominant CD4+ T cell responses to support antibody production.

## Abstract

Rational engineering of vaccine immunogens to focus B cell responses on potently neutralising epitopes is a promising approach to improve the potency, breadth and durability of viral vaccines. Such strategies, however, can compromise vaccine immunogenicity through the unintended exclusion of CD4+ T cell epitopes, which are critical for the development of T follicular helper (TFH) cells and to support high affinity antibody production.

Using a prototypic influenza haemagglutinin (HA) stem immunogen lacking effective CD4+ T cell help in C57BL/6 mice, we interrogated the minimal requirements for T cell help needed to drive serological responses to vaccination.

We find that priming of naïve CD4+ T cells is markedly efficient, however the immunodominance of a given CD4+ T cell epitope is not predictive of the propensity to provide high quality help to antigen-specific B cells. In the context of soluble antigens, provision of a single MHC class II epitope is sufficient to drive robust germinal centre responses and serum IgG titres. However not all CD4+ epitopes provide equivalent levels of B cell help, despite priming comparable numbers of antigen-specific CD4+ T cells. Finally, we show multimerizing and arraying antigens on nanoparticle scaffolds unlocks highly subdominant, near-undetectable CD4+ T cell helper responses to support a T-dependent antibody response.

Our findings emphasise the importance of CD4+ T cell help for programming robust and durable humoural immunity, and provide crucial insights to guide the rational incorporation of favourable T cell epitopes into vaccines.

The study was funded by the 10.13039/501100000925NHMRC.