Accumulation of CD4⁺ T cells in the colon of CsA-treated mice following myeloablative conditioning and bone marrow transplantation

Syngeneic graft vs. host disease (SGVHD) was first described as a graft vs. host disease-like syndrome that developed in rats following syngeneic bone marrow transplantation (BMT) and cyclosporin A (CsA) treatment. SGVHD can be induced by reconstitution of lethally irradiated mice with syngeneic bone marrow cells followed by 21 days of treatment with the immunosuppressive agent CsA. Clinical symptoms of the disease appear 2-3 wk following cessation of CsA therapy, and disease-associated inflammation occurs primarily in the colon and liver. CD4⁺ T cells have been shown to play an important role in the inflammatory response observed in the gut of SGVHD mice. Time-course studies revealed a significant increase in migration of CD4⁺ T cells into the colon during CsA therapy, as well as significantly elevated mRNA levels of TNF-α, proinflammatory chemokines, and cell adhesion molecules in colonic tissue of CsA-treated animals compared with BMT controls, as early as day 14 post-BMT. Homing studies revealed a greater migration of labeled CD4⁺ T cells into the gut of CsAtreated mice at day 21 post-BMT than control animals via CsAinduced upregulation of mucosal addressin cell adhesion molecule. This study demonstrates that, during the 21 days of immunosuppressive therapy, functional mechanisms are in place that result in increased homing of CD4⁺ T effector cells to colons of CsA-treated mice.