Minimal Residual Disease Monitoring after Reduced Intensity Conditioning (RIC) Allogeneic Transplantation: May Help To Individualize Post-Transplant Immunotherapeutic Strategies.

We have analyzed the impact of MRD monitoring (detected by flow cytometry) on the outcome of 56 patients undergoing RIC allogeneic SCT. Of them, 67% reached complete remission (CR), 11% partially responded (PR) and 22% progressed or did not respond. MRD assessment after transplant distinguished different risk populations. At day +100, 80% of patients with high MRD levels (>10⁻² leukemia asocciatted immunophenotypical cells, LAIP cells) versus 27% of patients with low MRD (<10⁻⁴) had relapsed. Accordingly, 3 categories could be clearly idenitified in terms of relapse free survival (RFS) at 5 years: 62% of patients with low MRD levels (<10⁻⁴) were event free as compared to only 28% and 20% among patients with intermediate (>10⁻⁴ and <10⁻²) and high MRD (>10⁻²) (p=0.0047). In multivariate analysis, patients’ age > 60 years (HR: 4,005; 95% CI 1.1–14.1, p=0.03), advanced disease status at transplant (HR: 4,087; 95% CI 1.3–12, p=0.01), failure to develop acute (HR: 4,785; 95% CI 1.2–18, p=0.02) and chronic GVHD (HR: 8,166; 95% CI 2.5–26.1, p=<0.001) and MRD levels, ≥10⁻⁴ on day +100 (HR: 5,795; 95% CI 1.7–19.1, p=0.004) adversely influenced RFS. Our study suggests that monitoring of MRD is a useful tool for predicting risk of relapse.