Assessment of immune system reconstitution with TREC and KREC measurements in hematopoietic stem cell transplantation in adult multiple myeloma patients

Aim: The aim of this study is to gather information about immune reconstitution through TREC, KREC copy numbers, and lymphocyte and monocyte subset analysis via flow cytometry before and after autologous stem cell transplantation (ASCT). Additionally, the study aims to evaluate the relationships of these measurements with patient, disease, and transplant parameters. Materials and Methods: A total of 18 patients with adult multiple myeloma undergoing ASCT and 20 healthy control subjects between November 2022 and May 2023 were included in the study. Data were obtained from patient records and the electronic hospital archive system. Immunophenotyping with flow cytometry and TREC/KREC analysis through PCR were performed on peripheral blood samples at days 0 and 100. Results: TREC/KREC levels were lower in the ASCT group compared to healthy controls (p<0.01). A significant increase in TREC/KREC measurements from day 0 to day 100 was observed (p=0.001; p=0.002). In the ASCT group, a negative correlation was found between platelet engraftment days and TREC levels at days 0 and 100 (r=-0.513, p=0.035; r=-0.597, p=0.011), and a positive correlation was observed between CD3, CD4, lymphocyte, and TREC/KREC. At month 3, a significant reversal of the CD4/CD8 ratio from 2.1 to 0.4 was noted. No correlation was found between CD19 and KREC, and there were no associations between patient and disease characteristics, transplant complications, pre and posttransplant treatment responses, and TREC/KREC and immunophenotyping. Conclusion: TREC/KREC measurements are suitable and practical methods for assessing immune recovery and thymic function post-ASCT in multiple myeloma patients. The study plans to be further developed with an increased number of patients, frequent measurements, and long-term follow-up to assess the effects on relapse and survival. Keywords: Multiple Myeloma (MM), Autologous Hematopoietic Stem Cell Transplantation (ASCT), immune reconstitution, flow cytometry, TREC, KREC.