Long-Term Survival, Illness Severity, and Time-to-Treatment Analysis in Dogs with Immune-Mediated Hemolytic Anemia Following Intravenous Allogeneic Mesenchymal Stem Cell Therapy: A Multicohort Follow-Up Study

Steroid-refractory immune-mediated hemolytic anemia (IMHA) in dogs carries high early mortality, and the 15%–30% of cases that fail corticosteroid-based therapy represent a population with few effective options and a narrowing treatment window. In a prior retrospective study, intravenous allogeneic mesenchymal stem cell (MSC) therapy achieved a 76.7% hematological success rate in 43 dogs with steroid-refractory IMHA. The present multicohort follow-up study extends that work by characterizing illness severity, time-to-treatment, and long-term survival across 137 eligible patients from the same database. In Kaplan–Meier analysis of all 137 eligible patients, comprising both the nonsurvivor cohort ( n = 57) and the lifespan registry ( n = 80), median survival was 1,695 days (4.6 years) in the primary cohort and was not reached in the protocol-assessable cohort ( n = 120). Estimated 1-year survival was 56.9% (95% CI: 48.2%–64.7%) and 65.0% (95% CI: 55.7%–72.8%), respectively, and the survival probability stabilized at approximately 52% through 8.1 years of follow-up. Among the 57 nonsurvivors, 51 had sufficient diagnostic data to calculate a Canine Hemolytic Anemia Objective Score (CHAOS) score; two-thirds (66.7%) met the high-risk threshold (CHAOS ≥ 3) at diagnosis. This exceeds the approximately 50% estimated from a published multicenter reference population, indicating that the Safari nonsurvivor cohort was enriched for severely ill dogs at presentation. Median post-treatment survival in nonsurvivors was 8 days (IQR: 3–38), and dogs receiving only one MSC dose had markedly shorter survival than those receiving two or more (median 4 vs. 19 days, P < 0.01), consistent with fulminant disease limiting completion of therapy rather than treatment failure. Diagnosis-to-treatment delay was shorter in survivors than in nonsurvivors (median 13 vs. 25 days), an exploratory finding warranting prospective evaluation. Taken together, these findings suggest that nonsurvival reflects the severity of the underlying disease and that dogs who respond to MSC therapy have potential for durable multiyear remission.