Monitoring of Immune Recovery After Hematopoietic Stem Cell Transplantation in Patients with Aplastic Anemia by Quantitative Determination of TREC and KREC

Background and Aims Analysis of T- and B-lymphocyte recovery after hematopoietic stem cell transplantation (HSCT) is important for assessing the positive dynamics of treatment. Flow cytometry is informative enough to monitor immune recovery in the post-transplant period. However, the determination of the number of TREC and KREC can be used to assess T and B cell neogenesis. Methods We describe 15 patients with aplastic anemia after allogeneic HSCT (HLA-matched-related [n = 8], transplantation from unrelated healthy donors [n = 7]). The age of patients was 15.0 (1.9-17.0) yrs. Monitoring points were 30, 45, 60, 100, 180, 245, 365 days after HSCT. Reconstitution of T and B lymphocytes was assessed based on the results of flow cytometry. Quantitative of TREC and KREC was performed using the multiplex RQ-PCR. Results KREC are detected by day 45 and reach the threshold of normal values by day 100. By day 245, the number of KREC begins to slowly decrease, which is not a sign of transplant rejection, but indicates an increase in the total number of CD19+ cells and the effect of dilution of KREC-positive lymphocytes. T-lymphocyte recovery begins later. TREC are determined by day 145 and by day 180 the median of TREC-positive lymphocytes is 800 copies per 1 × 106 lymphocytes without a dynamic decline up to a year after transplantation. In turn, according to immunophenotyping data, CD3+ begins to appear after day 30, which indicates that the number of activated T lymphocytes then decreases and the number of naive ones increases. This picture is due to the peripheral expansion of T lymphocytes, which predominate in the donor transplant, and the beginning of the production of the recipient's own cells. CD19+ lymphocytes appear by day 60 and reach the norm by day 100, which indicates that the newly formed pool of B lymphocytes mainly consists of naive cells. No statistical differences were found between the groups with related and unrelated HSCT in the dynamics of TREC reconstitution. For KREC, significant differences in the increase in quantity are observed by day 100 (p < 0.05). Conclusions Quantitative determination of TREC and KREC allows assessment of T and B cell neogenesis without the use of additional research methods such as flow cytometry. This method can be used as a predictor of reconstitution of T and B cell function.