TCR GAMMA CLONALITY ASSESSED BY NGS DOES NOT HELP TO DISTINGUISH EGPA FROM HES

Background: Hypereosinophilia-associated syndromes are a heterogeneous group of diseases characterized by sustained and elevated blood eosinophilia with evidence of eosinophil-induced organ damage. Classically, Eosinophilic Granulomatosis with Polyangiitis (EGPA) and Hypereosinophilic Syndrome (HES) present several overlapping clinical and laboratory features, making it challenging to correctly insert patients in restricted and well-defined categories with specific and more effective therapeutic approaches in daily practice. Therefore, great efforts are ongoing searching for novel biomarkers able to differentiate these two disorders. Aims: To detect T cell receptor gamma (TCRG) clonal rearrangements in EGPA and HES, comparing the frequency of distribution of the V and J region segments in 21 patients afferent to the hematology, rheumatology or pulmonology divisions. Methods: Consecutive patients with a diagnosis of EGPA and HES were enrolled into the study. Inclusion criteria were: documentation of a persistent peripheral eosinophilic count of ≥1.5 x10 9 /L and signs or symptoms of organ involvement. Clinical and laboratory data of the patients were collected. Sequence-based determination of the frequency distribution of TCRG Gene Rearrangements was performed using next-generation sequencing with the Illumina MiSeq (LymphoTrack TRG assay, Invivoscribe). Results: We included 21 patients (9 with EGPA and 12 with HES). Four EGPA patients were MPO-ANCA positive. We detected TCRG clonal rearrangements in 44% patients with EGPA and in 42% patients with HES. No association was observed between TCRG clonal rearrangements and ANCA status in EGPA patients. The following recurrent TCRG gene rearrangements were observed: Vg10JgP1 (5 cases) and Vg4Jg1/2 (4 cases) were observed in both EGPA and HES, whereas Vg9Jg1/2 (2 cases) and Vg10Jg1/2 (2 cases) were observed only in patients with HES. The presence of TCRG rearrangement was not different according to the symptoms (asthma, vasculitis, skin, heart, gut, lung involvement, splenomegaly). IL2, IL5, IL4, eosinophil cationic protein (ECP), absolute eosinophils were measured: IL5 and ECP were higher in the polyclonal than in the clonal cases (9±2.5 vs 1.7±0.9; p=0.021 and 121.8±61.5 vs 39.5±1.5; p=0.07). On the contrary, no difference was observed in the absolute eosinophil count. Finally, the presence/absence of TCRG clonality did not significantly impact on the response to treatment (immunosuppressive or interferon) and on the progression-free survival length. Summary/Conclusions: Conclusions: Even if preliminary, this study reveals a similar T cell receptor gamma repertoire in EGPA and HES, with recurrent rearrangements, thus suggesting a possible antigen-driven inflammatory response underlying hypereosinophilia in both EGPA and HES. Interestingly, this study confirms our previous results showing the TCR delta rearrangement (assessed by qualitative PCR) in 40% of the EGPA patients.