Co-infusion of mesenchymal stromal cells to prevent GVHD after allogeneic hematopoietic cell transplantation from HLA-mismatched unrelated donors after reduced-intensity conditioning: a double-blind randomized study and literature review

Background: Mesenchymal stromal cells (MSC) have immunomodulatory and hematopoiesis-supporting properties that could potentially benefit hematopoietic stem cell (HSC) engraftment and decrease the incidence and/or severity of graft-versus-host disease (GVHD). Methods: Based on our previous pilot study, we established a multicenter, prospective, randomized, double-blind trial evaluating the efficacy of co-infusing third-party MSC (1.5–3 × 10⁶/kg) versus placebo on the day of HSC transplantation (HCT) to prevent GVHD in recipients of HLA-mismatched unrelated donors after reduced-intensity conditioning. Results: The study planned to include 120 patients to improve 1-year overall survival (OS) from 55 to 77% but was stopped after 9 years for low recruitment (n = 38). One-year OS was 74% in the MSC group and 80% in the placebo group. In multivariate analysis, the incidence of grade II-IV acute GVHD was significantly lower in patients receiving MSC (HR 0.332, 95% CI 0.124–0.890, p = 0.0284). No difference was observed in the incidences of chronic GVHD, infection or relapse, overall or progression-free survival at 1 year or long-term, or hematopoietic and immune reconstitution. Conclusions: Despite premature study closure, the suggested beneficial effect of MSC co-transplantation for the prevention of acute GVHD in HLA-mismatched HCT warrants further investigation.