Sa1758 In Vitro Adalimumab Exposure Decreases RORγT Expressing and RORγT/FoxP3 Double Expressing T-Lymphocytes From Peripheral Blood of Crohn's Disease Patients: A Study of Th17 Plasticity in Response to Anti-TNF

G A A b st ra ct s recognizing E. coli OmpC. Methods: Tetramer-guided epitope mapping (TGEM) in HLADR*1501 subjects consistently identified a single T cell epitope in OmpC for use in tetramerbased assays. Direct ex vivo characterization was performed by staining with PE-labeled tetramers against OmpC and Flu peptides and subsequent enrichment with anti-PE magnetic beads. Cells were stained for surface markers and analyzed by flow cytometry. Frequency of antigen-specific T cells was calculated as the number of post-enrichment tetramer+ cells/ total pre-enrichment CD4+ cells. Results: The frequency of OmpC-specific T cells was 9.1 (+/-2)/million CD4+ T cells (n=26) compared to 13.7 (+/-2)/million Flu-specific T cells (n= 17), p=.18. The majority of both Flu and OmpC-specific T cells expressed a memory T cell phenotype (CD45RA-). There were no regulatory T cells (CD25+CD127-) identified among OmpC or Flu-specific CD4s. A high percentage of OmpC-specific T cells expressed the guthoming marker, a4b7, compared to Flu-specific T cells (44%+/-2 vs. 13.7% +/-2, p<.0001). Expression of the Th17 marker, CD161, was more frequent on OmpC than Flu-specific T cells (38.5 %+/-5 vs. 13% +/-2, p <.0001). While there was some expression of the Th1 marker, CXCR3, on OmpC-specific T cells, this was less than was expressed by Flu-specific T cells (27%+/-4 vs. 50% +/-5, p= .0015). The current study was underpowered to detect differences in frequency or phenotype among OmpC seropositive and seronegative CD subjects and healthy controls. OmpC-specific T cells identified above were isolated for future RNA transcript analyses to reveal qualitative differences in these cells between patients with and without CD. Conclusions: We have identified T cell epitopes for E.coli OmpC in HLADR *1501 subjects and generated MHC class II tetramers that identify OmpC-specific T cells. OmpC-specific T cells have a frequency similar to Flu-specific T cells and bear a distinct phenotype. They are memory T cells with gut-homing integrin a4b7 expression. They lack Treg markers and express mixed Th1 and Th17 markers. These data confirm that healthy humans and CD subjects harbor commensal-specific T cells and suggest that active suppression of T cell responses is lost in subjects with CD.