Effector Site Immune Dynamics in Refractory Chronic Graft-Versus-Host Disease: A Rockstar Trial Companion Study after Belumosudil Treatment.

Introduction Belumosudil (KD025) is an oral selective rho-associated coiled-coil kinase 2 (ROCK2) inhibitor approved for 3rd line therapy of chronic graft-versus-host disease (cGVHD). Prior studies demonstrated reduced peripheral blood IL-17 activity and regulatory T cell recovery after ROCK2 inhibition but did not examine responses directly in cGVHD affected tissues. Here, we report tissue-level cGVHD immune dynamics after 6-months of belumosudil treatment in oral mucosa, salivary glands, and skin. Methods This companion study is an extension of the pivotal ROCKstar study and evaluated belumosudil 200 mg QD or BID in a total of twenty participants with oral cGVHD (aged 21-77 years) who received 2 to 5 prior lines of systemic therapy. The primary goal of this study was to characterize changes in the local immune cellular profile and IL-17 signaling before and after 6 months of treatment with belumosudil. Enrolled subjects with oral cGVHD consented to additional collection of saliva, peripheral blood and biopsy of the skin, oral mucosa and labial salivary glands at baseline and six months after initiating belumosudil or upon discontinuation of belumosudil if earlier. Matched biospecimens were blinded and analyzed for immune cells and analytes. Comparisons used paired tests at alpha 0.05. Results Significant changes were identified in cGVHD affected tissues after belumosudil treatment. Responders to belumosudil based on overall (N=12) or oral-specific (N=10) NIH response criteria after treatment demonstrated a decrease in oral mucosal collagen type III and I, respectively. In parallel, multiplex immunohistochemistry identified immune cells including CD3+ and CD4+ that significantly decreased in frequency in oral mucosa after treatment in all subjects (Table 1). A decrease in IL-17+ cells was noted in both oral mucosa (N=14 evaluable pairs) and salivary glands (N=11 evaluable pairs) from all subjects. Fewer trends were noted in skin (N=14 evaluable pairs), though lower numbers of innate lymphoid cells were identified in all subjects post-treatment. Patients on the QD arm, who received the FDA-approved dose of belumosudil, demonstrated both a decrease in collagen type I and a drop in the number of IL-17+cells in the oral mucosa which was not observed in the BID arm. Multiplex ELISA measured a drop in salivary TGF-beta-1 after treatment. Spectral flow cytometry identified an increase in frequency of CD4+T regulatory cells among PBMCs after belumosudil treatment. Conclusion After 6 months of belumosudil treatment in patients with skin and oral cGVHD, there was a significant dose-dependent and tissue-specific decrease in collagen levels and reduction in IL-17 and TGF-beta-1 cytokine levels, suggesting a ROCK2 inhibition-induced reduction in tissue fibrosis, as marked by collagen content, and inflammation.