Delayed hematopoietic and immune reconstitution after allogeneic stem cell transplantation in children with aplastic anemia and mixed chimerism

Summary

Introduction

Allogeneic hematopoietic stem cell transplantation (alloHSCT) is an effective curative option for patients with aplastic anemia (АА). Chimerism monitoring provides information on donor cell engraftment after alloHSCT. Whereas stable mixed chimerism (MC) is considered a favorable outcome in rare graft-versus-host disease (GvHD) development, there is no information about differences in cell reconstitution according to the chimerism level. The aim of our study was to compare hematopoietic and immune reconstitution in AA patients with MC and full donor chimerism (FDC) developing after alloHSCT.

Patients and methods

The study included 16 HSCT with reduced intensity conditioning (RIC) performed in patients of 1 to 19 years old (a median of 11 y.o.) with AA (11, severe AA; 2, Fanconi anemia; 2, Diamond–Blackfan anemia; 1, with сongenital type II amegakaryocytic thrombocytopenia). On days +30, +45, +60, +80, +100, +140, +180, +245, +365 after alloHSCT, a standard immunologic assay was performed, and chimerism was determined by PCR of STR markers in peripheral blood and/or bone marrow. If chimerism level was 97-100%, the result was confirmed by Real-time PCR of InDel polymorphisms as more sensitive method.

Results

During the first year after alloHSCT, 9 patients had FDC (98- 100%) and 7 had MC (5-98%). FDC was associated with earlier engraftment in all cell lineages and earlier independence on red cell (р=0.013) and platelet (р=0.014) transfusions compared to MC. BM patients with FDC had more myelokaryocytes [the effect size (ES) was 84.6(21.1-148.1)*109 /L; p=0.011], and erythroid cells [ES, 35.8 (10.1-61.5)*109 /L; р=0.008] on day+30, more megakaryocytes [ES, 0.03 (0.002- 0.057) *109 /L; р=0.037] on day+365.
Over the first year, patients with FDC had higher average leukocyte levels [ES 2.5(1.4-3.7)*109 /L; p=0.004], neutrophils [ES 1.73(1.0-2.4)*109 /L; p=0.0001], monocytes (ES 0.15(0.05-0.24)*109 /L; p=0.007) in peripheral blood. The leukocyte counts achieved normal levels on day+30 in DC group, and on day +365 in MC group, whereas lymphocytes returned to normal values on day+245 and on day+365, accordingly.
The FDC group had higher lymphocyte levels [on day+245 ES 1.1(0.5-1.7)*109 /L; p=0.0009; on day+375 ES 0.97(0.4- 1.6)*109 /L; р=0.0012], B-lymphocyte levels [on day+245, ES was 0.27(0.11-0.42)*109 /L; p=0.0011; on day+375, ES 0.25(0.11-0.38)*109 /L; р=0.0003], T lymphocyte level [on day+245, ES was 1.2(0.5-1.8)*109 /L; p=0.0008; on day+375 ES 0.6(0.03-1.1)*109 /L; р=0.04], CD8+T-lymphocyte level [on day+245, ES 1(0.5-1.4)*109 /L; p=0.0001; on day+375 ES 0.5(0.1-0.8)*109 /L; р=0.017]. There was no difference in CD4+T, NK and NKT cell reconstitution.
In contrast, the levels of activated T cells (CD3+HLA-DR+) were higher in MC group on day+45 [ES 0.31(0.04- 0.59)*109 /L; p=0.03], then decreased in MC group, being higher in FDC group on day+245 [ES 0.56(0.2-0.9)*109 /L; p=0.0023]. An increase of activated T-cells in FDC group occurred gradually and activated T-cells achieved normal levels on day+60. In MC group, activated T-cells had normal levels from day+30 till day+365, however, there was a rapid increase in amount of the activated T-lymphocytes at day+45 compared to day+30 (p=0.031), followed by a decrease on day+80. Moreover, we observed a long persistence of MC in T-cell subpopulation, while other cell lineages retained FDC. Residual host T-cells in MC could be activated by donor alloantigenes after HSCT that, probably, leading to delayed hematopoietic and immune reconstitution.

Conclusion

MC after alloHSCT in patients with AA was associated with delayed hematopoietic and immune recovery and long transfusion dependence. Keywords Chimerism, aplastic anemia, allogeneic hematopoietic stem cell transplantation, hematopoietic and immune reconstitution, children.