Radiation and host retinoic acid signaling promote the induction of gut-homing donor T cells after allogeneic hematopoietic stem cell transplantation.

Intestinal graft-versus-host disease (GVHD) remains a devastating complication after allogeneic hematopoietic stem cell transplantation (HSCT). Although it has been well established that gut-tropic donor T cells expressing integrin α4ß7 are required to cause intestinal damage, the factors that control the induction of this pathogenic T cell population remain to be identified. Retinoic acid (RA) plays an important role in inducing α4ß7 expression on T cells. In this study, we showed that gene expression of retinaldehyde dehydrogenase, the key enzyme involved in RA biosynthesis, is significantly increased in the spleen and mesenteric lymph nodes (MLNs) of irradiated mice. In a C57BL/6-into-B6D2F1 allogeneic HSCT model, irradiation significantly increased the induction of α4ß7+ -donor T cells in mesenteric lymph nodes and spleen. Furthermore, we found that the RA pathway modulates the ability of dendritic cells to imprint gut-homing specificity on alloreactive T cells. We also showed that host dendritic cell RA signaling influences GVHD risk. Our studies identified radiation and recipient RA signaling as 2 primary factors that dictate the magnitude of gut-homing donor T cell induction after allogeneic HSCT. Attenuating radiation-associated inflammation and modulating host RA signaling represent feasible strategies to mitigate intestinal GVHD by reducing gut-seeking pathogenic donor T cells.

The parmodulin NRD-21 is an allosteric inhibitor of PAR1 Gq signaling with improved anti-inflammatory activity and stability.

Novel analogs of the allosteric, biased PAR1 ligand ML161 (parmodulin 2, PM2) were prepared in order to identify potential anti-thrombotic and anti-inflammatory compounds of the parmodulin class with improved properties. Investigations of structure-activity relationships of the western portion of the 1,3-diaminobenzene scaffold were performed using an intracellular calcium mobilization assay with endothelial cells, and several heterocycles were identified that inhibited PAR1 at sub-micromolar concentrations. The oxazole NRD-21 was profiled in additional detail, and it was confirmed to act as a selective, reversible, negative allosteric modulator of PAR1. In addition to inhibiting human platelet aggregation, it showed superior anti-inflammatory activity to ML161 in a qPCR assay measuring the expression of tissue factor in response to the cytokine TNF-alpha in endothelial cells. Additionally, NRD-21 is much more plasma stable than ML161, and is a promising lead compound for the parmodulin class for anti-thrombotic and anti-inflammatory indications.

Effects of Donor Vitamin A Deficiency and Pharmacologic Modulation of Donor T Cell Retinoic Acid Pathway on the Severity of Experimental Graft-versus-Host Disease.

Graft-versus-host disease (GVHD) is the major cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation (HSCT). A combination of genetic and nongenetic factors dictates the incidence and severity of GVHD. Recent studies have identified the potential role of the retinoic acid (RA)/retinoic acid receptor (RAR) pathway in the pathogenesis of GVHD. RA is the active metabolite of vitamin A. Thus, a clinically relevant question is whether HSCT donor and/or recipient vitamin A status affects the development of GVHD. It has been previously reported that recipient vitamin A deficiency is associated with reduced intestinal GVHD and prolonged overall survival after experimental allogeneic HSCT. However, it is still unknown whether donor vitamin A status influences GVHD development. In the current study, we report that chronic vitamin A deficiency changes the composition of T cell compartment of donor mice with a reduction in the percentage of CD4+ T cells. We showed that although vitamin A deficiency does not affect donor T cell alloreactivity on a per cell basis, a decreased proportion of donor CD4+ T cells in marrow graft inoculums leads to reduced incidence and severity of GVHD. Furthermore, our proof of principle studies using a pan-RAR antagonist demonstrated that transient inhibition of donor T cell RAR signaling can reduce T cell alloreactivity and their ability to cause lethal GVHD. Our studies provide preclinical evidence that donor vitamin A deficiency may be a nongenetic factor that can modulate the severity of GVHD and pharmacologic interfering RA/RAR pathway in donor T cells might be a valuable approach for mitigating GVHD after allogeneic HSCT.