Graft versus host disease (GvHD), which is the primary complication of allogeneic bone marrow transplantation, can alter the intestinal barrier targeted by activated donor T-cells. Chemical inhibition of the stress protein HSP90 was demonstrated in vitro to inhibit T-cell activation and to modulate endoplasmic reticulum (ER) stress to which intestinal cells are highly susceptible. Since the HSP90 inhibitor 17-allylamino-demethoxygeldanamycin (17AAG) is developed in clinics, we explored here its ability to control intestinal acute GvHD in vivo in two mouse GvHD models (C57BL/6BALB/c and FVB/NLgr5-eGFP), ex vivo in intestine organoids and in vitro in intestinal epithelial cultures. We show that 17AAG decreases GvHD-associated mortality without impairing graft versus leukemia effect. While 17AAG effect in T-cell activation is just moderate at the dose used in vivo, we observe a striking intestinal integrity protection. At the intestine level, the drug promotes the splicing of the transcription factor X-box binding protein 1 (XBP1), which is a key component of the ER stress. This effect is associated with a decrease in intestinal damage and an increase in Lgr5(+) stem cells, Paneth cells and defensins production. The importance of XBP1 splicing control is further confirmed in cultured cells and organoids of primary intestinal epithelium where XBP1 is either shRNA depleted or inhibited with toyocamycin. In conclusion, 17AAG has a protective effect on the epithelial intestinal barrier in mouse models of acute GvHD. This compound deserves to be tested in the therapeutic control of acute GvHD.

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Glycoprotein 96 (Gp96)-peptide complexes are highly investigated for vaccines preparation, particularly in cancer therapy. Gp96, formerly called tumor rejection antigen (TRA)-1, is able to elicit an immune response that can protect mice against tumors, when the mice share the same haplotype than those bearing the tumors from which Gp96 was purified. Secreted Gp96-peptide complexes act as danger signals thereby stimulating the innate immunity regardless of the chaperoned peptides. In contrast, the tumor rejection antigen role of Gp96-peptide complexes is held by the chaperoned peptides in a dose-dependent manner. The purification step is crucial both for insuring the quality and the quantity of Gp96-peptide complexes. To this aim, different methods have been described but they are often suboptimal for the quantification of these complexes. In this review, we discuss a hot topic: the use of the chaperone Gp96 for vaccination purposes in cancer, and also detail the current methods for quantifying Gp96-peptide preparations.