JAK1/2 Inhibition Suppresses T Cell Proliferation and Inflammatory Cytokine Production In An Allogeneic Setting and Ameliorates Graft-Versus-Host Disease (GvHD) In a Murine GvHD Model

Graft-versus-host-disease (GvHD) constitutes a severe complication of allogeneic hematopoietic stem cell transplantation (allo-HSCT). In GvHD, tissue damage is mediated by pro-inflammatory cytokines. Cytokine responses are mediated by activated Janus kinases (JAKs). We hypothesized that JAK1/2 inhibition might reduce T effector cell responses and inflammatory cytokine production in an allogeneic system, thereby ameliorating GvHD. We established an allogeneic (major mismatch) cell culture system using naive BALB/c CD4⁺ CD62L^high T cells that were co-cultured with C57BL/6 (B6) bone marrow derived dendritic cells (DC). JAK 1/2 signaling was specifically blocked using the small molecule inhibitor Ruxolitinib (INCB018424). By using a ³H Thymidine proliferation assay, we found that Ruxolitinib was able to inhibit the proliferation of allogeneic CD4⁺ effector T cells. In our intracellular cytokine staining experiments Ruxolitinib was able to impair the differentiation of naïve T cells into IFN-gamma and IL17A-producing T effector cells. Both cytokines – IFN-gamma and IL-17A – have been linked to aggravated courses of GvHD severity.

In vivo administration of Ruxolitinib signficantly reduced lethal GvHD after allo-HSCT in a murine major mismatch model. BALB/c recipient mice were irradiated and received C57BL/6 (B6) T cell depleted bone marrow along with CD4+ and CD8+ T cells. Animals that were treated with an oral gavage of Ruxolitinib twice daily displayed significantly lower serum levels of IFN-gamma, TNF-alpha, IL-10 and IL-12p70, lower histological and clinical GvHD scores and improved overall survival compared to the control group.

By using luciferase-positive (luc+) CD4+ and CD8+ T cells, we were able to visualize and quantify T cell migration after GvHD induction. The recipient mice received luc+ T cells along with conventional T cell depleted bone marrow. We were able to detect the luc+ T cell signal with a bioluminescence imaging system. At day 9 after allogeneic bone marrow transplantation, migration of donor T cells to GvHD target sites was significantly reduced in Ruxolitinib treated mice compared to control mice.

In summary, our data demonstrate that suppression of inflammatory cytokine responses by JAK1/2 inhibitors modulates T effector cell responses in an allogeneic setting and improves survival in a murine major mismatch GvHD model. These observations suggest that JAK1/2 inhibition might be used for the treatment of GvHD following allo-HSCT.