[The Characteristics of T Lymphocyte Reconstitution after Haploid Hematopoietic Stem Cell Transplantation in SAA and Its Relationship with aGVHD].

OBJECTIVE: To investigate the recovery characteristics of T cell subsets in patients with severe aplastic anemia (SAA) who received haploid hematopoietic stem cell transplantation(HSCT) and its relationship with acute graft-versus-host disease(aGVHD). METHODS: The clinical data of 29 SAA patients who received haploid hematopoietic stem cell transplantation in the department of hematology, Shanxi Bethune Hospital from June 2018 to January 2022 were retrospectively analyzed. The absolute counts of CD3+T, CD4+T, CD8+T lymphocytes and the ratio of CD4+T/CD8+T lymphocytes in all patients before transplantation, 14, 21, 30, 60, 90 and 120 days after transplantation were analyzed. The proportion of T lymphocytes was compared in the non-aGVHD group, the grade Ⅰ-Ⅱ aGVHD group and the grade III-IV aGVHD group. RESULTS: The counts of all T cells in 27 patients were far below the normal level at 14 and 21 days after transplantation, but there was obvious heterogeneity. There was a certain relationship between T cell immune reconstitution and conditioning regimen, age, and immunosuppressive treatment before transplantation. CD3+T cells showed a steady upward trend at 30, 60, 90, and 120 days after transplantation, and returned to the normal levels at 120 days after transplantation; faster recovery of CD4+T cells was closely related to aGVHD, which was at 30, 60, 90, 120 days after transplantation showed a slow upward trend, and which was still far below the normal level of 120 days after transplantation. CD8+T cell counts began to recover at 14 and 21 days after transplantation, and the recovery was earlier than the CD4+T cells, and its recovery speed was rapid 30 and 60 days after transptantation, which showed an upward trend and exceeded the normal levels 90 days after transplantation. Since CD8+ T cells reconstituted quickly, while the CD4+ T cells reconstitution was slowly, which made the long-term CD4+T/CD8+T cell ratio after transplantation was inverted . Compared with the non-aGVHD group, the absolute counts of CD3+T, CD4+T, and CD8+T cells in the aGVHD group were significantly higher than those in the non-aGVHD group at each time period after transplantation. In the aGVHD group, grade Ⅲ-Ⅳ aGVHD occurred more frequently in the early post-transplantation period (within 14-21 days), the grade Ⅰ-Ⅱ aGVHD group mostly occurred within 30-90 days after transplantation, and CD3+T, CD4+T, CD8+T cell counts in the grade Ⅲ-Ⅳ aGVHD group were significantly higher than those in the grade Ⅰ-Ⅱ aGVHD group; and the greater the proportion of CD4+T, the more severe the degree of aGVHD. CONCLUSION: The speed of T cell immune reconstitution after SAA haploid transplantation is different, which is related to the conditioning regimen, age, and immunosuppressive therapy before transplantation. The rapid recovery of CD4+ T cells is closely related to the occurrence of aGVHD.