Postdoctoral Fellow National Institutes of Health, Maryland, United States
Disclosure(s):
Charbel A. Basset, MSc, PhD: No financial relationships to disclose
Introduction/Rationale: Ocular graft-versus-host disease severity correlates with inflammation and fibrotic damage in the lacrimal gland (LG). Long-living stem-like progenitor exhausted TCF1+ PD-1+ T cells (Tpex) have been reported to maintain and replenish the reservoir of exhausted-like effector T cells (Texef). In chronic settings, the cumulative cytotoxicity of CD8+ Texef mediates tissue damage. A comprehensive characterization of the phenotypic and transcriptomic profiles of these pathogenic exhausted populations has not yet been reported.
Methods: To this end, we used an established minor MHC-mismatched murine model of sclerodermatous cGVHD (B10.D2 (H-2d) into BALB/c (H-2d), allogeneic (allo) cGVHD) using syngeneic (syn) controls (Balb/c into Balb/c) assessed at 14-, 21-, and 42-days post-transplant. Here, we longitudinally investigated transcriptional changes in exocrine tissue immune population.
Results: Microscopy identified increased lymphocyte infiltration in the lacrimal gland and conjunctiva. Single cell sequencing was performed on lacrimal gland. Datasets were processed using a robust integrative approach based on scVI deep learning architecture. We identified four distinct exhausted T cell subpopulations expanded in allo LG. Exhaustion, cytotoxic and residency scores were highest for these four subsets. Proportional distribution analysis revealed a substantial early increase in 𝑇𝑐𝑓7⁺, 𝑆𝑒𝑙𝑙⁺, 𝐼𝑙7𝑟⁺, 𝑆𝑙𝑎𝑚𝑓6⁺, 𝑃𝑑𝑐𝑑1⁺ CD8+ Tpex cells in the allo group. Importantly, allo lacrimal glands were marked by the expansion of 𝑇𝑐𝑓7⁻ CD8+ Texef cells that were not present in the syn group. Cell-cell communication analyses inferred an interaction between Tfrcʰⁱ acinar cells and exhausted T cells through Ceacam1-Havcr2, signaling shown to drive terminal exhaustion of Texef.
Conclusion: Overall, scRNAseq results evince a major shift in T-cell fate towards a pathogenic exhausted-like phenotype possibly stemming from an early 𝑇𝑐𝑓7⁺ expressing precursor exhausted population in cGVHD-affected LG.
