Interference with Inflammation Induced Endothelial Receptors Prevents Acute Graft-Versus-Host Disease.

Abstract 3559

Poster Board III-496

Acute graft-versus-host disease (GVHD) can be spatio-temporally separated in an initiation phase confined to secondary lymphoid organs (SLO) followed by the GVHD effector phase in the intestinal tract (GIT), liver and skin. Employing non-invasive bioluminescence imaging, fluorescence microscopy and flow cytometry in a murine allogeneic hematopoietic cell transplantation (allo-HCT) model [luciferase⁺ FVB/N (H-2^q) or luciferase⁺ C57Bl/6 (H-2^b) splenocytes plus wild type bone marrow into Balb/c-Rag^−/−cgChain^−/− recipients (H-2^d)] we observed that the proliferation, activation and acquisition of homing receptors by alloreactive T cells occurred in SLO independently whether allogeneic recipients were conditioned (8 Gy) or not conditioned before allo-HCT. However, fewer alloreactive T cells infiltrated target tissues in non-conditioned recipients resulting in significantly delayed GVHD onset as compared to conditioned hosts. We concluded that inflammatory recruitment by GVHD target tissues (GIT, liver and skin) drives the characteristic GVHD organ infiltration.

To explore the signals potentially responsible for recruitment of alloreactive T cells into GVHD target tissues we compared the expression of cytokine induced endothelial adhesion molecules of GVHD target versus non-target tissues of conditioned and non-conditioned allo-HCT recipients.

We found strong endothelial up-regulation of VCAM-1and MAdCAM-1 in target organs of conditioned recipients. As alloreactive effector T cells upregulate homing receptors (a4b7, a4b1, P-lig, E-lig) for vascular endothelial ligands we asked whether interference with these receptor-ligand interactions would prevent GVHD target infiltration. Blocking of either VCAM-1 or MAdCAM-1 alone or VCAM-1 and MAdCAM-1 combined did not reduce the alloreactive T cell infiltration of the target organs. However, when we simultaneously blocked VCAM-1, MAdCAM-1 and CD62P in allo-HCT recipients we could abrogate GVHD target infiltration by alloreactive T cells in the liver, the skin and small intestines (Grade 0), whereas the colon showed clear signs of acute GVHD (Grade 2).

In summary, inflammatory recruitment via endothelial adhesion molecules expressed in GVHD target tissues during the effector phase is essential for GVHD manifestation. Efficient interference of alloreactive T cell homing requires abrogating simultaneously redundant homing receptor-ligand interactions. Application of a combined antibody regimen against VCAM-1, MAdCAM-1 and CD62P appears as a promising strategy to protect from small bowel GVHD. The optimal combination for preventing alloreactive T cell recruitment to the colon still remains to be determined.

Late but selective GVHD intervention through combinatorial short-term blockade of effector T cell trafficking may provide an attractive future clinical application to abrogate GVHD and to enhance the graft-versus-leukemia effect.