One of the important criteria after hematopoietic stem cell transplantation (HSCT) is the reconstitution of naive lymphocytes, since they form the cellular repertoire. The number of newly formed lymphocytes after HSCT is determined by flow cytometry, but in some cases this is not always possible. As an alternative to assessing T and B cell neogenesis, determination of the number of TREC and KREC can be used.
The study included 9 patients diagnosed with acute lymphoblastic leukemia aged 10.1 (4.0 to 16.1) yrs after allogeneic HSCT [HLA-matched-related (n = 4), unrelated healthy donors (n = 5)]. Monitoring points were: 30, 45, 60, 100, 180, 245, and 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.
According to the results, T-lymphocyte recovery begins 3.5 months after HSCT. TREC are detected by day 145 and by day 180 TREC is 1.8 × 103 (1.22-2.0 × 103)/106 leukocytes) without a dynamic decline up to a year after transplantation. CD3+ lymphocytes begin to appear after day 30, this picture is due to the fact that in the early post-transplant period the thymus-independent pathway of immune recovery prevails, which is mediated by donor T lymphocytes. KREC are detected from day 60 and by day 100 cross the threshold of normal values (1.8 × 103(1.7-3.1 × 103)/106 leukocytes). By day 245, KREC begins to slowly decrease, which is not a sign of transplant rejection, but indicates an increase in the total number of CD19+ lymphocytes and the effect of dilution of KREC. CD19+ lymphocytes appear by day 60 and reach the norm by day 100, this indicates that the newly formed pool of B lymphocytes mainly consists of naive cells. The recovery of naive T lymphocytes was characterized by slow dynamics up to day 100 (median 26.4%) after HSCT. Then the number of naive cells gradually increased and the recovery dynamics were similar to the recovery of TREC. By day 180 after HSCT, the median quantitative of naive T lymphocytes was 35.0%. There were no statistically significant differences in the dynamics of TREC/KREC recovery between the groups with related and unrelated transplantation.
Quantitative determination of TREC/KREC allows assessment of T and B lymphocyte neogenesis after HSCT without the use of additional research methods such as flow cytometry.
