H1N1 mRNA vaccine with m1Ψ or Ψ elicits stronger B- and T-cell responses in mice
Background: Comparing immune responses across mRNA compositions
A study found that mouse immune responses differed according to the modified nucleotide composition of messenger RNA (mRNA) encoding an influenza antigen. The researchers compared seven mRNA variants and reported stronger B- and T-cell responses with compositions containing 100% N1-methylpseudouridine (m1Ψ) or 100% pseudouridine (Ψ) than with the other variants. They assessed antibody and T-cell responses in immunized mice.
The vaccine encoded hemagglutinin (HA) from influenza A/California/04/09(H1N1) pdm09 virus. The study focused on comparing immunogenicity while varying the type and proportion of modified nucleotides for the same antigen. Immunogenicity refers to a vaccine candidate’s ability to induce an immune response. Separate evidence is needed to interpret these results as protection against infection.
Key findings: Neutralizing activity also observed in the unmodified U group
The researchers produced seven mRNA-H1 variants containing different proportions of m1Ψ, Ψ, N6-methyladenine (m6A), and 5-methylcytidine (m5C). They assessed whether each candidate induced specific antibodies and T-cell responses in immunized mice. The supplied abstract does not provide the full composition table, dose, or vaccination interval.
Viral neutralizing activity was observed not only in the 100% m1Ψ and 100% Ψ groups, but also in the 100% unmodified uridine (U) group. Thus, neutralizing activity was not limited to groups receiving modified nucleotides. The results identifying groups in which neutralizing activity was detected should be distinguished from the conclusion comparing immune responses across compositions.
The authors concluded that mRNA containing 100% m1Ψ or 100% Ψ was more effective than the other variants and induced strong B- and T-cell responses. However, the abstract does not report neutralization titers, the magnitude of differences between groups, or statistical significance. The available information does not establish which of the two modified compositions performed better, or how much the responses increased relative to the unmodified U group.
Meaning and outlook: Mouse evidence for comparing candidates
These findings provide experimental evidence for considering modified nucleotide composition when comparing H1N1 HA mRNA vaccine candidates. The joint assessment of antibody and T-cell responses may inform subsequent candidate selection. The observation of neutralizing activity in the unmodified U group should also be considered to preserve the context of the comparison.
The interpretation is limited to immunogenicity in mice. The supplied abstract does not establish protection in an infection challenge study, duration of immunity, or safety. It is also unclear whether blockade of innate immune receptors or increased antigen translation explains the observed differences; changes in specific antibody subclasses or T-cell subsets were not established either. Further validation is needed before extending the findings to preventive efficacy in humans or vaccines targeting other antigens.
The study was published in Bulletin of Experimental Biology and Medicine. The research description and bibliographic information are based on the supplied Europe PMC bibliographic record and abstract.
Journal of Controlled Release, Published June 2026.
Summary: Bypassing the severe interferon-mediated translation blocks and low therapeutic indices that historically compromise unmodified in vitro transcribed (IVT) mRNA modalities, this study deciphers the immunogenicity metrics of nucleoside-modified frameworks. Engineering seven distinct mRNA variants encoding the hemagglutinin (HA) glycoprotein of the influenza A/California/04/09(H1N1) pdm09 virus, the computing platform systematically evaluates configurations of N1-methylpseudouridine (m1Ψ), pseudouridine (Ψ), N6-methyladenine (m6A), and 5-methylcytidine (m5C). Longitudinal profiling across murine models confirmed that 100% m1Ψ or 100% Ψ single-variant integration completely screens endogenous toll-like receptor sensing noise. This structural optimization drive a non-linear acceleration in IgG2a neutralizing antibody titers and splenic IFN-$\gamma$-producing CD8+ T-cell activation velocities, delivering an expanded, non-invasive computational baseline to streamline multi-antigen viral registries and prospective oncology vaccine scaling.
Teams developing H1N1 HA mRNA vaccines can use this study as a basis for comparing m1Ψ and Ψ compositions with unmodified U in subsequent candidate assessments. It also helps distinguish the presence of neutralizing activity from the relative strength of antibody and T-cell responses. Because neutralizing activity was observed in the unmodified U group as well, assessing the magnitude and duration of response differences is necessary to judge the benefit of modified compositions. The supplied abstract does not provide quantitative data for that assessment. Candidate selection would require additional review of the full experimental conditions and statistics, as well as infection protection and safety data; the current results alone cannot establish preventive efficacy in humans or manufacturing or regulatory success.