P1373: TACKLING IMMUNOLOGICAL FINDINGS AS SURROGATE MARKERS OF HISTOLOGICAL SEVERITY AND RESPONSE TO THERAPY IN ACUTE GASTROINTESTINAL GRAFT-VERSUS-HOST DISEASE. (23rd June 2022) - Sousa-Pimenta, M.; Freitas, J.; Couto, E.; Coelho, P.; Branca, R.; Pinho Vaz, C.; Leite, L.; Campos, A.