Identification of a potential physiological precursor of aberrant cells in refractory coeliac disease type II

Refractory coeliac disease type II (RCDII) is a severe complication of coeliac disease (CD) characterised by aberrant intraepithelial lymphocytes (IELs) of unknown origin that display an atypical CD3(-)CD7(+)icCD3(+) phenotype. In approximately 40% of patients with RCDII these lymphocytes develop into an invasive lymphoma. In the current study we aimed to identify the physiological counterpart of these cells.

RCDII cell lines were compared with T-cell receptor positive (TCR(+)) IEL (T-IEL) lines by microarray analysis, real-time quantitative PCR and flow cytometry. This information was used to identify cells with an RCDII-associated phenotype in duodenal biopsies from non-refractory individuals by multicolour flow cytometry.

RCDII lines were transcriptionally distinct from T-IEL lines and expressed higher levels of multiple natural killer (NK) cell receptors. In addition to the CD3(-)CD7(+)icCD3(+) phenotype, the RCDII lines were distinguishable from other lymphocyte subsets by the absence of CD56, CD127 and CD34. Cells matching this surface lineage-negative (Lin(-)) CD7(+)CD127(-)CD34(-) phenotype expressed a functional interleukin-15 (IL-15) receptor and constituted a significant proportion of IELs in duodenal specimens of patients without CD, particularly children, and were also found in the thymus. In patients without CD, the Lin(-)CD7(+)CD127(-)CD34(-) subset was one of four subsets within the CD3(-)CD7(+)icCD3(+) population that could be distinguished on the basis of differential expression of CD56 and/or CD127.

Our studies indicate that the CD3(-)CD7(+)icCD3(+) population is heterogeneous and reveal the existence of a Lin(-) subset that is distinct from T, B, NK and lymphoid tissue inducer cells. We speculate that this IL-15 responsive population represents the physiological counterpart of aberrant cells expanded in RCDII and transformed in RCDII-associated lymphoma.