Stem Cell Boost, Mixed Chimerism & DLI: High-Stakes Post-Transplant Choices

Yan Leyfman, MD, looked back at a particular session hosted at the 2026 Tandem Meetings dedicated to navigating different challenges that may emerge following the use of allogeneic hematopoietic stem cell transplantation (allo-HCT). Across this session, he unraveled key takeaways from a collection of case presentations exploring CD34-positive stem cell boosts, mixed chimerism, and donor lymphocyte infusion (DLI).^1-3

Leyfman, a fellow at NewYork-Presbyterian Hospital and a hematologic malignancies board member for the journal ONCOLOGY^®, identified several key themes throughout these sessions:

1. Poor Graft Function vs Graft Failure
   1. Poor graft function and graft failure are not interchangeable.
   2. CD34-selected stem cell boosts may demonstrate potential benefits regarding overall hematologic responses and complete responses.
   3. Although CD34 selection is not universally available, alternative therapies like eltrombopag (Promacta) may represent pragmatic strategies.
2. Mixed Chimerism
   1. Decreasing CD34-positive donor chimerism may predict relapse sooner than morphology in acute myeloid leukemia or myelodysplastic syndrome, and the window for intervention is short.
   2. Early immunosuppression taper, molecular monitoring, and preemptive DLI prior to overt relapse may be viable strategies.
   3. Overall, mixed chimerism does not guarantee a relapse, but it is a warning.
3. Implementing DLI
   1. DLI has distinct prophylactic, preemptive, and therapeutic uses that are biologically and prognostically different.
   2. Graft-versus-host disease (GVHD) remains a prominent toxicity despite use of DLI.
   3. Balancing relapse vs GVHD and control vs toxicity remain challenges in patient care.

Based on the findings presented in the session, Leyfman noted that chimerism was more prognostic in nature than diagnostic, and that early intervention windows may be narrow. Additionally, he stated that preemptive strategies outperform reactive ones, and that GVHD risks must be carefully navigated via dose calibrations. Practice in the field is no longer a question of “did relapse occur,” but rather “when do we intervene before it does?”

References

1. Kharfan-Dabaja M. Case 1: CD34+ stem cell boost. Presented at: 2026 Tandem Meetings; February 4-7, 2026; Salt Lake City, UT.
2. Savani B. Case 2: mixed chimerism after allo-HCT (HR myeloid malignancies). Presented at: 2026 Tandem Meetings; February 4-7, 2026; Salt Lake City, UT.
3. Bejanyan N. Case 3: DLI – rescue or risk? Presented at: 2026 Tandem Meetings; February 4-7, 2026; Salt Lake City, UT.