Lung-resident SARS-CoV-2 peptide-specific immune responses in perfused 3D human lung explant models

Abstract

Introduction: Multi-specific and long-lasting T-cell immunity has been recognized to indicate long-term protection against pathogens, including the novel coronavirus, SARS-CoV-2, which is the causative agent of the COVID-19 pandemic. Functional significance of peripheral memory T cells in individuals recovered from COVID-19 (COVID-19⁺) is beginning to be appreciated; however, the role of lung tissue-resident memory (lung TRM) T cells in SARS-CoV-2 infection is still being investigated. This is, in part, due to the lack of preclinical tissue models available to follow the convalescence period.

Methods: Here, we utilize a perfused three-dimensional (3D) human lung-tissue model and show pre-existing local T-cell immunity against SARS-CoV-2 proteins in lung tissues.

Results: We report ex vivo maintenance of functional multi-specific IFN-γ-secreting lung TRM T cells in COVID-19⁺ and their induction in lung tissues of vaccinated COVID-19⁺ subjects. Importantly, we identify SARS-CoV-2 peptide-responding memory B cells and IgA⁺ plasma cells in ex vivo cultured lung tissues of COVID-19⁺. Furthermore, lung tissue IgA levels were increased in COVID-19⁺ and responded to peptide stimulation.

Discussion: In our study, we highlight the importance of utilization of human lung-tissue models to understand the local antiviral immune response in the lung to protect against SARS-CoV-2 infection.

Keywords: COVID-19; SARS-CoV-2 infection; human lung-tissue model; local antiviral immune response; perfused lung explant.

FIGURE 1

Ex vivo perfusion culture of the human lung tissue and exposure to SARS-CoV-2 peptides. (A) Ex vivo model setup process. (B) Bioreactor chamber showing ECM volume-containing tissue. (C) Peptide exposure protocol.

FIGURE 2

Local T-cell response to SARS-CoV-2 peptides within lung tissue cores. (A, B, D–F, H, J, and L–Q) Baseline T-cell differences within lung tissue from uninfected (UN) individuals and individuals recovered from COVID-19 (COVID-19⁺). (C, G, I, and K) Correlation between the convalescence period for COVID-19⁺ samples and the percentage of CD4⁺ T cells (C), PD-1⁺ CD8⁺ T cells (G), CD154⁺ CD69⁺ CD8⁺ T cells (J), and HLA-DR⁺ CD38⁺ CD8⁺ T cells (L). (R–Z) Impact of SARS-CoV-2 peptide exposure on T-cell populations in UN and COVID-19⁺ lung tissues (n = 10 UN and n = 8 COVID-19⁺ [mean (center line) ± SEM]). Statistics shown in blue are comparisons between control and peptide-exposed samples within each group (UN and COVID-19⁺). Statistics shown in black are the change in response between UN and COVID-19⁺ for each peptide when compared to the corresponding control.

FIGURE 3

Memory T-cell response to SARS-CoV-2 peptides within the lung. (A, C, E–G, I, K, and L) Baseline differences in memory T cells within lung tissue from uninfected (UN) individuals and individuals recovering from COVID-19 (COVID-19⁺). (B, D, H, J, and M) Correlation between the convalescence period for COVID-19⁺ samples and the percentage of CD4⁺ tissue-resident memory (TRM) T cells (B), CD8⁺ TRM T cells (D), TRM IFN-γ⁺ CD4⁺ T cells (H), TRM IFN-γ⁺ CD8⁺ T cells (J), and effector-memory CD8⁺ T cells (M). (N–U) Impact of SARS-CoV-2 peptide exposure on memory T-cell populations in UN and COVID-19⁺ lung tissues (n = 10 UN and n = 8 COVID-19⁺ [mean (center line) ± SEM]). Statistics shown in blue are comparisons between control and peptide-exposed samples within each group (UN and COVID-19⁺). Statistics shown in black are the change in the response between UN and COVID-19⁺ for each peptide when compared to the corresponding control.

FIGURE 4

Local B-cell response to SARS-CoV-2 peptides within the lung tissues. (A) Baseline differences in B-cell populations within lung tissue from uninfected (UN) individuals and individuals recovering from COVID-19 (COVID-19⁺). (B) Correlation between the convalescence period for COVID-19⁺ samples and the percentage of CD19⁺ B cells. (C–E) Impact of SARS-CoV-2 peptide exposure on B-cell populations in UN and COVID-19⁺ lung tissues. (F) Correlation between the convalescence period for COVID-19⁺ samples and the percentage of plasma cells. (G) Quantification of circulating SARS-CoV-2-specific IgA; opaque symbols indicate positive samples (measurements over threshold). (H). Photomicrographs showing CD138⁺ plasma cells (red) secreting IgA (green) in UN (left) and COVID-19⁺ samples (right) at day 0 (starting tissue). White arrows pointing to CD138⁺ plasma cells secreting IgA, gray dashed arrows pointing to CD138⁺ plasma cells without IgA secretion. (I and J). Correlation table showing correlation among the convalescence period, peptide response, and class-switched memory B populations (I) and the convalescence period, peptide response, and IgA secretion (J) (n = 5–10 UN and n = 6–8 COVID-19⁺ [mean (center line) ± SEM]). Statistics shown in blue are comparisons between control and peptide-stimulated samples within each group (UN and COVID-19⁺). Statistics shown in black are the change in response between UN and COVID-19⁺ for each peptide when compared to the corresponding controls.