Background and Aims: Refractory celiac disease type II (RCDII) is characterized by a clonally expanded aberrant cell population in the small intestine. The role of other tissue-resident immune subsets in RCDII is unknown. Here, we characterized CD8 and CD4 T cells in RCDII duodenum at the single-cell level and in situ. Methods: We applied mass cytometry on CD45⁺ duodenal cells derived from intestinal biopsies (n = 23) and blood samples (n = 20) from RCDII patients and controls. Additionally, we analyzed intestinal biopsies from celiac disease (n = 11) and RCDI (n = 2) patients. We performed single-cell RNA-sequencing on CD45⁺ duodenal cells derived from a RCDII patient, immunofluorescence staining for in situ analysis and flow cytometry for phenotyping of RCDII aberrant and CD8 T cells. Results: Compared to healthy controls, we observed that CD27⁺PD-1⁺ memory CD8αβ cells and CD4 T regulatories (Tregs) were more abundant in RCDII duodenum (CD8 ∗∗0.0029; CD4 ∗∗∗0.0001). The CD27⁺PD-1⁺ memory CD8αβ cells expressed the tissue-resident marker CD69, immunoregulatory markers (TIGIT, HAVCR2, TNFRSF9), NKG2A, were enriched for activated pathways and displayed cytotoxic gene signatures (NKG7, PRF1, GZMA). The absence of CD103 accords with their localization in the lamina propria as determined by in situ analysis. The CD25⁺FoxP3⁺CD27⁺CD127^dim/- CD4 Tregs expressed IL1R2 and IL32 and costimulatory molecules (TNFSRS4, ICOS and TNFRSF18) and resided in the lamina propria as well. Flow cytometry confirmed the presence of the inhibitory receptor NKG2A on expanded duodenal CD8 T cells and HLA-E, the ligand for NKG2A, on expanded aberrant cells. Conclusion: RCDII is characterized by the simultaneous presence of an activated CD27⁺PD-1⁺ memory CD8αβ T cell subset and CD4 Tregs, suggesting that checkpoint blockade with anti-NKG2A/PD-1 and/or anticytotoxic T lymphocyte antigen 4 may be an attractive treatment option.

Background & Aims: Refractory celiac disease type II (RCDII) is a rare indolent lymphoma in the small intestine characterized by a clonally expanded intraepithelial intracellular CD3⁺surfaceCD3^-CD7⁺CD56^- aberrant cell population. However, RCDII pathogenesis is ill-defined. Here, we aimed at single-cell characterization of the innate and adaptive immune system in RCDII. Methods: Paired small intestinal and blood samples from 12 RCDII patients and 6 healthy controls were assessed by single-cell mass cytometry with a 39–cell surface marker antibody panel, designed to capture heterogeneity of the innate and adaptive immune system. A second single-cell mass cytometry panel that included transcription factors and immune checkpoints was used for analysis of paired samples from 5 RCDII patients. Single-cell RNA sequencing analysis was performed on duodenal samples from 2 RCDII patients. Finally, we developed a 40-marker imaging mass cytometry antibody panel to evaluate cell–cell interactions in duodenal biopsy specimens of RCDII patients. Results: We provide evidence for intertumoral and intratumoral cell heterogeneity within the duodenal and peripheral aberrant cell population present in RCDII. Phenotypic discrepancy was observed between peripheral and duodenal aberrant cells. In addition, we observed that part of the aberrant cell population proliferated and observed co-localization of aberrant cells with CD163⁺ antigen-presenting cells (APCs) in situ. In addition, we observed phenotypic discrepancy between peripheral and duodenal aberrant cells. Conclusions: Novel high-dimensional single-cell technologies show substantial intertumoral and intratumoral heterogeneity in the aberrant cell population in RCDII. This may underlie variability in refractory disease status between patients and responsiveness to therapy, pointing to the need for personalized therapy in RCDII based on patient-specific immune profiles.