Peripheral Lymphocyte Dynamics in the Immune Microenvironment of Multiple Myeloma During Autologous Stem Cell Transplantation.

Background and objective Autologous stem-cell transplantation (ASCT) remains the standard of care for multiple myeloma (MM), yet it is not curative. Over the past decade, there has been growing interest in immunotherapy-based strategies, highlighting the need for predictive biomarkers to tailor post-ASCT treatment. Characterization of immune status via peripheral lymphocyte immunophenotyping is a critical step in this process. This study aimed to characterize peripheral blood lymphocyte immunophenotypes in MM patients undergoing ASCT at baseline, during stem cell mobilization, and on day +21 post-transplant, and to establish descriptive longitudinal benchmarks that may inform immune monitoring in this clinical setting. Methods We conducted a prospective, single-center study at the Abu Dhabi Stem Cells Center (Abu Dhabi, United Arab Emirates (UAE), enrolling all MM patients undergoing ASCT between July 2020 and February 2024 (n = 28), with no additional exclusion criteria. Peripheral blood samples were collected at three time points: before ASCT, on day +21 post-ASCT, and from the apheresis product. Canonical lymphocyte markers were analyzed by flow cytometry using a single, polychromatic 10-color antibody panel on a Navios EX cytometer. Results Of the 28 MM patients studied, 40.3% were women. The age range was 23 to 64 years. Markedly low baseline B cell counts were observed (6-175 cells/µL). A significant post-transplant decrease in helper T cells, B cells, and the CD4/CD8 ratio was observed at day +21 compared with baseline. The mean total lymphocyte dose infused (0.20 × 10⁹ cells/kg) was below published thresholds; however, the major lymphocyte subsets exceeded recommended cutoff values, suggesting a potentially favorable prognosis. Dose ranges for non-conventional lymphocyte subsets were also determined Conclusions T helper and B cells declined during the peri-transplant period in patients with MM who underwent ASCT, suggesting a lack of association with the autograft dose of homologous populations. This study provides preliminary, descriptive benchmarks for minority immune cell populations, supporting their potential relevance as prognostic biomarkers.