Research fellow Massachusetts General Hospital, Harvard Medical School, United States
Disclosure(s):
Juliana Barreto de Albuquerque, PhD: No financial relationships to disclose
Introduction/Rationale: Respiratory infections represent a major global health challenge. Different intranasal vaccine strategies can target specific areas of the respiratory tract, which may influence local and systemic immune responses.
Methods: Here, we combined peptide-major histocompatibility complex class I and II (pMHCI and pMHCII) tetramers with flow cytometry and single cell RNA sequencing (scRNAseq) to comprehensively study spike-specific CD8+ and CD4+ T cells following immunization with SARS-CoV2 spike protein. Following intramuscular (IM) priming with spike protein and poly:IC, we compared different boosting strategies - upper respiratory tract (URT), total respiratory tract (TRT), and IM.
Results: At 4 weeks post-boost, the number of spike-specific CD4+ and CD8+ T cells was higher in the lungs of mice receiving TRT boosting compared to URT or IM boosting. We also observed higher frequencies and numbers of CD4+ and CD8+ resident memory T cells (TRM) in the lungs of TRT versus URT or IM groups. In the nasal mucosa (NM), both TRT and URT boosting resulted in higher frequencies of spike-specific CD4+ and CD8+ TRM cells than IM. Notably, TRT was the only boost strategy that induced serum and lung spike-specific IgA. However, despite generating fewer spike-specific T cells and antibodies than TRT, URT boosting still protected mice against viral challenge. Moreover, both spike-specific CD4+ and CD8+ T cells obtained from the NM expressed higher levels of IFN-g, and spike-specific CD8+ T cells in the NM produced higher levels of granzyme B compared to those cells recovered from lung and spleen. Finally, scRNAseq analysis with barcoded tetramers revealed that epitope specificity influenced CD4+ T cell differentiation resulting in epitope-specific T helper cell bias.
Conclusion: In sum, TRT boosting enhanced lung immunity and epitope-driven CD4+ T cell phenotypes offer a promising approach to guide optimized vaccine design.
