Plasma Cell Contamination in Autografts Determined by Dual Quantification Before Cryopreservation and After Thawing Predicts Transplant Outcomes in Multiple Myeloma: A Prospective, Proof-of-Concept Study

Abstract

Objective: Plasma cell contamination in freshly collected autografts has been rigorously investigated as a marker to identify patients at a high risk of progression after autologous stem cell transplantation (ASCT), with conflicting results. The association between the plasma cell content in thawed autografts and clinical outcomes is yet to be studied.

Methods: This was a prospective cohort study; viable plasma cell content in autografts was quantified by flow cytometry both before cryopreservation and after thawing to evaluate its correlation with transplant outcomes. Multiple myeloma patients undergoing their first ASCT were enrolled. Patients were stratified into a low- or high-plasma cell contamination group with a predefined 2:1 ratio based on combined data from both time-point measurements. The primary endpoint was progression-free survival (PFS) based on plasma cell contamination of autografts.

Results: Forty-nine patients were included in this primary analysis with a median follow-up of 36 months. The median age was 57, and key baseline features were evenly distributed between the 2 groups. High-plasma cell contamination group had a significantly increased risk of progression or death after ASCT (3-year PFS: 31.3% vs. 74.7%, hazard ratios (HR)= 6.36, P < .0001), independent of International Staging System (ISS), response state, age, and genetic features on multivariate analysis (HR = 8.9, P < .0001). The predefined stratification based on data from both time-point cell counts outperformed correlations based on single time-point measurements for predicting PFS. Twenty-eight of 49 patients were found to have more than a 50% reduction in plasma cell/stem cell ratio in the autograft after thawing. These 28 cases had a significantly lower risk of progression or death after ASCT compared to the remaining 21 cases (HR = 0.38, P = .042).

Conclusion: This is the first study to evaluate post-thaw autograft plasma cell content as a risk factor for ASCT failures. Findings support its clinical relevance and encourage further studies to incorporate this potential marker into predictive models.

Cite this article as: Yılmaz U, Elverdi T, Bayar M, et al. Plasma cell contamination in autografts determined by dual quantification before cryopreservation and after thawing predicts transplant outcomes in multiple myeloma: A prospective, proof-of-concept study. Cerrahpaşa Med J. 2026, 50, 0090, doi: 10.5152/cjm.2026.25090