Intranasal unadjuvanted PspA spikes lung-resident memory immunity after parenteral pneumococcal vaccination

Intramuscular (IM) prime-boost vaccination with outer membrane vesicle (OMV)-delivered pneumococcal surface protein A (OMV-PspA) formulated with alum is safe but it compromises protection against respiratory Streptococcus pneumoniae (Spn) infections. To enhance pulmonary immunity, we employ a "prime-spike" strategy: IM OMV-PspA/alum prime-boost followed by an intranasal booster with adjuvant-free PspA. The immunization regimen demonstrates a favorable safety profile in mice and provided robust, nearly complete protection against Spn D39 (serotype 2) and A66.1 (serotype 3) strains during both primary infection and influenza-induced secondary infection. The induced PspA-specific antibodies exhibit potent opsonophagocytic killing of clinical isolates. Moreover, the strategy significantly increases lung-resident memory B cells, antibody-secreting cells (ASCs), tissue-resident memory T cells, and their respective interferon-γ-, tumor necrosis factor-α-, interleukin (IL)-17A-, and IL-4-producing cells. These findings strongly support the prime-spike approach as a promising strategy against both primary and secondary respiratory pneumococcal disease.