Janus Kinase-2 Inhibition Induces Durable Tolerance to Alloantigen by Dendritic Cell-Stimulated Human T Cells, Yet Preserves Immunity to Recall Antigen

Abstract

1903 Janus kinase 2 (JAK2) conveys signals from receptor binding by several inflammatory cytokines, including IL-6, IL-12, and IL-23, via phosphorylation of signal transducer and activator of transcription 3 (STAT3). These cytokines promote the development and expansion of T helper 1 (Th1) cells, which use IL-12, and Th17 cells, which use IL-6 and IL-23. Th1 and Th17 cells can in turn induce alloreactive end organ damage in GvHD. JAK2 is therefore a principle gatekeeper of alloreactivity and inflammation, and it represents an attractive target to control GvHD. We demonstrate that TG101348, a synthetic small molecule, highly selective JAK2 inhibitor, when present during initial and secondary encounters between human T cells and allogeneic monocyte-derived dendritic cells (moDCs), induces durable, profound, and specific T cell tolerance on reexposure to the same alloantigens. TG101348 ablates IL-6/JAK2-mediated phosphorylation of STAT3 in T cells (24% v 0%, P<0.05, n=5) but has no off-target effects on IL-2 or IL-15/JAK3/pSTAT5-dependent signaling, which would interfere with Tregs and other effector T cell responses. JAK2 inhibition preserves Treg numbers and thereby enhances the ratio of CD4+ Tregs to CD8+CD25+ effector T cells in favor of Tregs (Treg:Effector 1:2 vs 1:1, P<0.05, n=5). JAK2 inhibition also reduces the production of IL-6 (255 vs 157 pg/ml, P<0.05, n=5) and TNF-alpha (50 vs 15 pg/ml, P<0.05, n=4) in allogeneic MLRs, impairing the activation of central and effector memory T cells as well as the expansion of responder Th1 (24% vs 14%, P<0.05, n=4) and Th17 (2% vs 1%, P<0.05, n=4). T cells, stimulated by moDCs in the presence of TG101348, demonstrate a marked reduction in proliferative capacity upon reexposure to fresh allogeneic moDCs from the original stimulating party, even in the absence of the JAK2 inhibitor during the secondary MLR (P<0.05, n=4). Responses to stimulation de novo by influenza matrix peptide (fluMP), a pathogenic nominal antigen, remain intact (P=NS, n=4). Conversely, TG101348 also inhibits secondary MLR responses by T cells, which have already been sensitized to alloantigens in a primary MLR without the JAK2 inhibitor (P<0.05, n=4). The durable tolerance against full HLA disparities in each of these settings provides preclinical data in vitro that JAK2 represents a relevant biologic target for preventing or treating graft-versus-host disease (GvHD), or even solid organ allograft rejection, without broader immune impairment. Disclosures: No relevant conflicts of interest to declare.

Advances in understanding the pathogenesis of graft‐versus‐host disease

“…IL6, IL 23) to STAT proteins. Inhibition of JAK2 with small molecules in vitro , when administered early after HCT, promotes tolerance between human T cells and DCs and increases Treg to T effector ratios in vivo (Betts et al , ). The relative contribution of various JAK proteins is unknown, but combined blockade of JAK1/2 with ruxolitinib reduced GVHD mortality in mice (Spoerl et al , ).…”

Peritransplantation Ruxolitinib Prevents Acute Graft-versus-Host Disease in Patients with Myelofibrosis Undergoing Allogenic Stem Cell Transplantation

“…There is preclinical and clinical evidence that JAK signaling plays a major role in GVHD, suggesting a potential role of JAK inhibition in the prevention and treatment of GVHD [10]. Here we report on 12 patients with advanced myelofibrosis who were treated with ruxolitinib and scheduled for ASCT as curative treatment.…”

Selecting patients with primary myelofibrosis for stem cell transplant using clinical, mutational, and transplant‐specific profiles

“…There is preclinical and clinical evidence that JAK signaling plays a major role in graft‐versus‐host disease (GVHD), suggesting a potential role of JAK inhibition in the prevention and treatment of GVHD . A small report on 12 patients with advanced myelofibrosis who were treated with ruxolitinib and scheduled for allo‐HCT as curative treatment investigated the impact on GVHD prevention when ruxolitinib (5 mg twice daily) was not stopped at the time of conditioning and was continued throughout the peritransplantation period until stable engraftment occurred .…”