Key Points Our data from the mouse model and patients indicate that inflammatory neovascularization during GvHD is targetable via αv integrin. We identify a negative regulation of GvHD-related neovascularization by miR-100.

ARTICLES 31 Graft-Versus-Host DiseaseDespite advances in immunosuppressive regimens, acute graft-versus-host disease remains a frequent complication of allogeneic hematopoietic cell transplantation. Pathogenic donor T cells are dependent on correct attachment of small GTPases to the cell membrane, mediated by farnesyl-or geranylgeranyl residues, which, therefore, constitute potential targets for graft-versus-host disease prophylaxis. A mouse model was used to study the impact of a farnesyl-transferase inhibitor and a geranylgeranyl-transferase inhibitor on acute graft-versus-host disease, anticytomegalovirus T-cell responses and graft-versus-leukemia activity. Treatment of mice undergoing allogeneic hematopoietic cell transplantation with farnesyl-transferase inhibitor and geranylgeranyl-transferase inhibitor reduced the histological severity of graft-versus-host disease and prolonged survival significantly. Mechanistically, farnesyl-transferase inhibitor and geranylgeranyl-transferase inhibitor treatment resulted in reduced alloantigen-driven expansion of CD4 T cells. In vivo treatment led to increased thymic cellularity and polyclonality of the T-cell receptor repertoire by reducing thymic graft-versus-host disease. These effects were absent when squalene production was blocked. The farnesyl-transferase inhibitor and geranylgeranyl-transferase inhibitor did not compromise CD8 function against leukemia cells or reconstitution of T cells that were subsequently responsible for anti-murine cytomegalovirus responses. In summary, we observed an immunomodulatory effect of inhibitors of farnesyl-transferase and geranylgeranyl-transferase on graft-versus-host disease, with enhanced functional immune reconstitution. In the light of the modest toxicity of farnesyl-transferase inhibitors such as tipifarnib in patients and the potent reduction of graft-versus-host disease in mice, farnesyl-transferase and geranylgeranyl-transferase inhibitors could help to reduce graft-versus-host disease significantly without having a negative impact on immune reconstitution. -access paper. doi:10.3324/haematol.2012.065789 Inhibition of protein geranylgeranylation and farnesylation protects against graft-versus-host disease via effects on CD4 effector T cells ©2013 Ferrata Storti Foundation. This is an open

Caveolin-1 (Cav-1) is a key organizer of membrane specializations that coordinate membrane and protein traffic in different cells including T cells. Cav-1 promotes the formation and stability of plasma membrane raft microdomains that serve as platforms for signal transduction and binds a wide array of signal transducers through interactions with its phosphorylated tyrosine 14 or the so-called scaffolding domain. Several of the proteins identified as Cav-1 binding partners have been suggested to play a role in TCR-regulated membrane dynamics and intracellular signaling. Therefore, we aimed to determine the requirement of Cav-1 for T cells during acute graft-versus-host disease (GvHD). We observed upregulation of Cav-1 in the T cells of mice developing acute GvHD which was dependent on both tissue damage and homeostatic signals as investigated in conditioned WT recipients or RAG-/-C gamma chain-/- non-conditioned mice. By using gene targeted mice we found that Cav-1 deficiency of the donor led to improved survival (p=0.02), lower GvHD histopathology scores (p=0.004) and reduced serum levels of IL-6 (p=0.02) while Treg numbers increased when Cav-1 deficient donors were used. Comparative microarray analysis of WT compared to Cav-1 deficient T cells indicated a reduced IL-17A production in Cav-1 T cells exposed to allogeneic dendritic cells. These observations were confirmed on the protein level. In summary we show a role for Cav-1 in T cells during GvHD as an alloantigen driven T cell response. Regarding the mechanism we describe the relevance of Cav-1 for Th-17 lineage commitment of alloreactive T cells during GvHD. Disclosures: No relevant conflicts of interest to declare.

Allogeneic hematopoietic cell transplantation (allo-HCT) is an important treatment option for different hematological malignancies, but also for some nonmalignant hematological disorders such as sickle cell anemia, aplastic anemia or thalassemia(1). In the ladder group the graft-versus-leukemia (GvL) effect mediated by donor T cells is less important and prevention of graft-versus-host disease (GvHD), which occurs in 40-50% of allo-HCT patients, is a major priority. The common gamma chain (CD132) is a cytokine receptor sub-unit that is common to the interleukin (IL) receptors of IL-2, IL-4, IL-7, IL-9, IL-15 and IL-21. Since several of these cytokines were shown to be increased in the serum of patients developing acute GvHD, we reasoned that inhibition of CD132 could have a profound effect on acute GvHD by inhibiting the bioactivity of multiple proinflammatory cytokines. We observed that anti-CD132 treatment reduced GvHD potently with respect to survival, production of TNF, IFN-γ, IL-6, MCP-1 and GvHD histopathology. Protection was only seen when anti-CD132 was applied in a CD8 T cell-dependent GvHD model while no protection was seen when only CD4 T cells were given. Mechanistically, we could show that CD8 T cells isolated from mice treated with anti-CD132 had reduced levels of Granzyme B and that GvHD induced by Perforin-deficient T cells was resistant towards blockade by anti-CD132 treatment. These data indicated a role of the common gamma chain cytokines for the induction of Perforin/Granzyme B in CD8 T cells during GvHD. Compatible with this notion, exposure of CD8 T cells towards IL-2, IL-7, IL-15 and IL-21 alone or in combination induced increased levels of Granzyme B. Based on these findings, we concluded that CD8 T cells that are activated by common gamma chain cytokines during GvHD produce then Granzyme B which can be blocked by anti-CD132 treatment. This therapeutic approach has particular clinical potential for patients undergoing allogeneic transplantation for nonmalignant indications, since graft-versus-tumor activity is not required. Disclosures: No relevant conflicts of interest to declare.