Matrix Metalloproteinase-9 in Monocytic Myeloid-Derived Suppressor Cells Correlate with Early Infections and Clinical Outcomes in Allogeneic Hematopoietic Stem Cell Transplantation

The recovery of myeloid-derived suppressor cells (MDSCs) and its relevance in clinical acute graft-versus-host disease (GVHD) and post-hematopoietic stem cell transplantation (HSCT) infections remain to be fully characterized. We examined the expansion of circulating monocytic (M-) MDSCs and granulocytic (G-) MDSCs at the time of engraftment in 130 patients undergoing allogeneic HSCT (allo-HSCT). Compared with the G-MDSC group, the high M-MDSC group had a higher infection rate within 100 days, along with worse 1-year cumulative incidence of treatment-related mortality (TRM) and 2-year probability of event-free survival (EFS). The frequency of M-MDSCs was associated with preceding severe mucositis. Transcriptome profiling analysis of 2 isolated MDSC subtype showed significantly greater matrix metalloproteinase-9 (MMP-9) expression in M-MDSCs than in G-MDSCs. M-MDSCs produced abundantly more MMP-9. Importantly, compared with G-MDSCs, M-MDSCs isolated from patients post-HSCT had a greater capacity to suppress T cell responses, and MMP-9 blockade more forcefully inhibited their immunosuppressive effect. MMP-9 levels also were associated with the occurrence of infections and with transplantation outcomes. Based on these findings, we identify M-MDSCs as a major contributor to infections early after allo-HSCT and worse clinical outcomes via MMP-9.