Next-Generation Mnull RSV Vaccines Show Enhanced Immunogenicity in Mice

10 Apr 20264 min read0 viewsJournal Feed

GIST

We previously demonstrated that vaccination with RSV-Mnull, a prototype single-cycle live vaccine lacking the matrix (M) gene, generated anti-viral serum IgG and memory T cell responses, and reduced challenge virus shedding and pulmonary dysfunction in mice. Here we further characterized the response to RSV-Mnull, and designed and tested second generation Mnull vaccines.

In mice, prime-boost vaccination with RSV-Mnull generated pre-fusion (preF) and attachment protein (G) -specific serum IgG and lung IgA, and protected from lung pathology, showing that a single-cycle live vaccine was effective in this model. In an effort to enhance efficacy for future human application, second generation Mnull vaccines were designed, in which nonstructural protein 1 (NS1), a known interferon (IFN) antagonist, was relocated to reduce expression.

In addition, the G or F genes were moved to the first genome position (RSV-Mnull/G1 and RSV-Mnull/F1 respectively). In vitro, RSV-Mnull/G1 and RSV-Mnull/F1 showed reduced NS1 levels and increased IFN-β induction, whereas IFN-λ levels were not affected.

Viruses with relocated NS1 also displayed enhanced anti-viral state in uninfected cells.

Clinical Editorial

Strategic aims and study design: advancing single-cycle RSV vaccines

In vivo, prime-boost vaccination evaluated serum IgG, lung IgA, and protection from lung pathology following challenge.

The study builds on prior work showing that RSV-Mnull, a single-cycle live vaccine lacking the M gene, elicited antiviral serum IgG and memory T cell responses and reduced challenge virus shedding and pulmonary dysfunction in mice.
The authors designed second-generation Mnull candidates (RSV-Mnull/G1 and RSV-Mnull/F1) with two main modifications: relocating nonstructural protein 1 (NS1), a known IFN antagonist, to reduce its expression, and repositioning G or F genes to the first genome position.
In vitro characterization assessed NS1 levels, IFN-β and IFN-λ induction, and antiviral state in bystander cells.

Immunogenicity profile and mucosal–systemic responses

RSV-Mnull/G1 and RSV-Mnull/F1 each demonstrated reduced NS1 expression and increased IFN-β induction in vitro, with no change in IFN-λ relative to controls.
Relocated NS1-containing constructs displayed an enhanced antiviral state in uninfected cells, suggesting broader innate immune activation.
Serologic findings indicated distinct alterations in antigen-specific antibody landscapes: RSV-Mnull/G1 raised higher anti-G serum IgG, while RSV-Mnull/F1 increased the ratio of anti-preF to anti-G IgG.
RSV-Mnull subjected to single-cycle replication produced lower lung IgA than wild-type RSV; however, NS1 relocation reversed this deficit, yielding early IgA induction and restoring levels to those seen with wild-type RSV.

Impact on humoral quality and antigen targeting

The data imply that genomic positioning of NS1, G, and F influences how G and F antigens are presented or processed, consequently shaping IgG and IgA responses.
All vaccine constructs generated antibodies capable of neutralizing RSV in vitro, indicating preserved functional antibody activity across designs.

Protection against challenge and pathology

All RSV-Mnull–based vaccines conferred protection against a high-dose challenge with wild-type RSV, evidenced by neutralization capacity and attenuation of disease features.
Regarding lung pathology, RSV-Mnull/G1 and RSV-Mnull/F1 did not show clear superiority over the prototype RSV-Mnull in this model, which may reflect model limitations rather than intrinsic failure of the vaccine designs.
Nonetheless, the engineered Mnull variants achieved robust systemic and mucosal antibody responses, with enhanced anti-G or anti-F mucosal humoral components, and protection against pathology despite single-cycle replication.

Context and implications for future development

The findings support the concept that altering genome organization can modulate IFN induction and antigen-specific humoral responses, potentially informing optimization for human use.