Relapse of Aplastic Anemia with Majority Donor Chimerism (Donor-Type Aplasia) Occurring Late after Bone Marrow Transplantation

Mixed T-Cell Chimerism Following Hematopoietic Cell Transplantation for Non-Malignant Disorders Is Common, Facilitates Anti-Viral Immunity, and Is Not Associated with Graft Failure in Pediatric Patients

Myeloid chimerism better reflects donor stem cell engraftment than whole-blood chimerism in assessing graft function following allogeneic hematopoietic stem cell transplant (HCT). We describe our experience with 130 patients aged younger than 18 years, treated with allogeneic HCT using bone marrow or PBSC from HLA-matched donors for non-malignant diseases, whose pre-transplant conditioning therapy included alemtuzumab and who were monitored with lineage-specific chimerism after transplant. At 6 years post-transplant, overall survival (OS) was 91.1% and event-free survival (EFS) was 81.5%, with no grade III-IV acute GvHD or chronic GVHD observed. Recipient T-cells did not contribute to graft loss. Mixed T-cell chimerism (MC) did not affect EFS, and there was no connection between T-cell chimerism and myeloid chimerism in patients with MC or graft loss. MC significantly correlated with virus infection; more children with MC were CMV seropositive than those with complete chimerism (CC). Additionally, MC was more common in patients with CMV viramia post-transplant. CD8 T-cell reconstitution was affected by viral reactivation, including CMV, with CD8 T-cell counts higher in the MC group than in the CC group. Mixed T-cell chimerism is due to autologous, virus-specific, predominantly CD8, T-cell expansion, and is protective and not deleterious to the recipient.

Prospects and Potential for Chimerism Analysis after Allogeneic Hematopoietic Stem Cell Transplantation

Chimerism analysis after allogeneic hematopoietic stem cell transplantation serves to confirm engraftment, indicate relapse of hematologic malignancy, and attribute graft failure to either immune rejection or poor graft function. Short tandem repeat PCR (STR-PCR) is the prevailing method, followed by quantitative real-time PCR (qPCR), with detection limits of 1-5% and 0.1%, respectively. Chimerism assays using digital PCR or next-generation sequencing, both of which are more sensitive than STR-PCR, are increasingly used. Stable mixed chimerism is usually not associated with poor outcomes in non-malignant diseases, but recipient chimerism may foretell relapse of hematologic malignancies, so higher detection sensitivity may be beneficial in such cases. Thus, the need for and the type of intervention, e.g., immunosuppression regimen, donor lymphocyte infusion, and/or salvage second transplantation, should be guided by donor chimerism in the context of the feature and/or residual malignant cells of the disease to be treated.

Recent advances in the diagnosis and treatment of pediatric acquired aplastic anemia

Acquired aplastic anemia (AA) in children is a rare bone marrow failure that requires several special considerations for its diagnosis and treatment compared with that in adults. The most common issue is the differential diagnosis with refractory cytopenia of childhood and inherited bone marrow failure syndromes, which is crucial for making decisions on the appropriate treatment for pediatric AA. In addition to detailed morphological evaluation, a comprehensive diagnostic work-up that includes genetic analysis using next-generation sequencing will play an increasingly important role in identifying the underlying etiology of pediatric AA. When discussing treatment strategies for children with acquired AA, the long-term sequelae and level of hematopoietic recovery that affect daily or school life should also be considered, although the overall survival rate has reached 90% after immunosuppressive therapy or hematopoietic cell transplantation (HCT). Recent advances in HCT for pediatric patients with acquired AA have been remarkable, with the successful use of upfront bone marrow transplantation from a matched unrelated donor, unrelated cord blood transplantation or haploidentical HCT as salvage treatment, and fludarabine/melphalan-based conditioning regimens. This review discusses current clinical practices in the diagnosis and treatment of acquired AA in children based on the latest data.

Comparisons of unmanipulated haploidentical donor, unrelated cord blood donor and matched unrelated donor hematopoietic stem cell transplantation in pediatric acquired severe aplastic anemia: a single center study

We retrospectively analyzed the outcomes of 240 pediatric SAA patients who underwent unmanipulated alternative HSCT between September 2012 and November 2020 at our center. The incidence of GF (PGF + SGF) was higher in the UCBD cohort compared to the MUD and HID cohorts [(13.5% ± 6.5%) vs (0%), and (1.6% ± 5.3%), respectively, p = .0001]. The incidence of platelet engraftment within 180 days post-HSCT was lower in the UCBD cohort (82.4% ± 2.3%) compared to the HID group (96.2% ± 1.3%) and the MUD group (97.4% ± 0.5%) (p = .020). the median duration time for platelet engraftment in the UCBD cohort was 29 days, longer than in HID cohort 14 days and the MUD cohort 13 days (p = .005). UCBD cohort had a lower 3-year failure-free survival (FFS) (70.5% ± 8.4%) compared to the HID cohort (81.1% ± 4.3%) and the MUD cohort (92.5% ± 3.1%) (p = .030) and lower 3-year GVHD/relapse free survival (GRFS) (63.3% ± 9.5.4%) compared to the HID cohort (75.5% ± 6.8%) and MUD cohort (87.9% ± 4.5%) (p = .002). UCBD-HSCT had inferior FFS and GRFS compared to an HSCT with an HID or MUD in pediatric patients with acquired SAA. A UCBD-HSCT had a higher GF and lower incidence of platelet engraftment and longer platelet engraftment time.

Unmanipulated haploidentical donor and matched unrelated donor hematopoietic stem cell transplantation in patients with paroxysmal nocturnal hemoglobinuria: a single-center study

We analyzed the outcomes of 32 patients with paroxysmal nocturnal hemoglobinuria (PNH) who underwent either a haploidentical donor (HID) or a matched unrelated donor (MUD) hematopoietic stem cell transplantation (HSCT). Seventeen patients received an HSCT from an HID and 15 patients received an HSCT from an MUD. The median follow-up time of the surviving patients was 36 months (range: 12-96 months). No significant differences were observed in the 3-year overall survival (OS) between the HID and MUD cohorts (74.1%±11.4% vs. 93.3%±6.4%, respectively, p=.222) or in the 3-year failure-free survival (68.8%±11.8% vs. 86.7%±8.8%, respectively, p=.307). Treatment-related mortality occurred in five patients. A univariate analysis of risk factors revealed platelet engraftment failure negatively impacted OS and FFS. We conclude that HID and MUD-HSCT are feasible and can be effective options for those PNH patients with concomitant bone marrow failure, recurrent life-threatening thrombosis, and uncontrollable hemolysis.

Recurrent aplastic anemia with donor-type aplasia: A rare occurrence in the Indian subcontinent

Donor-type aplasia (DTA) is a condition where an individual continues to be aplastic even after a successful engraftment of a hematopoeitic stem cell transplant with a majority of donor type cells in the bone marrow. This entity has been seen with varying frequency around the world, especially in Southeast Asia. However, its incidence in the Indian subcontinent remains fairly low. Here is a case of a 17-year-old child with DTA who had a 89% population of donor cells after a successful transplant and presented with recurrent severe aplastic anemia later. The patient eventually succumbed to his condition before a second transplant could be performed. The awareness about the seriousness of this relatively rare condition, therefore, needs to be emphasized.

Donor-Host Lineage-Specific Chimerism Monitoring and Analysis in Pediatric Patients Following Allogeneic Stem Cell Transplantation: Influence of Pretransplantation Variables and Correlation with Post-Transplantation Outcomes

The impact of donor-host chimerism in post-hematopoietic stem cell transplantation (HSCT) outcomes is poorly understood. We were interested in studying whether pre-HSCT variables influenced lineage-specific donor-host chimerism and how lineage-specific chimerism impacts post-HSCT outcomes. Our main objective was to study pre-HSCT variables as predictors of lineage-specific donor-host chimerism patterns and to better characterize the relationship between post-HSCT lineage-specific chimerism and adverse outcomes, including graft failure and disease relapse. We conducted a retrospective data analysis of all patients who underwent allogeneic HSCT at the Pediatric Transplantation and Cellular Therapy service at Memorial Sloan Kettering Cancer Center between January 2010 and June 2015 and had at least 2 measurements of split-lineage chimerism. The trend of lineage-specific donor-host chimerism post-HSCT and the impact of age, disease, graft type, and pretransplantation conditioning regimen on chimerism at 3 months and 12 months post-HSCT were studied. The Wilcoxon signed-rank test, Mann-Whitney-Wilcoxon test, and Cox proportional hazard models were used for statistical analyses. A total of 137 patients were included (median age, 11.3 years). Most patients had a hematologic malignancy (n = 95), and fewer had a nonmalignant disorder (n = 27) or primary immune deficiency (n = 15). Myeloablative conditioning regimens (n = 126) followed by T cell-depleted (TCD) peripheral blood stem cell or bone marrow grafts (n = 101) were most commonly used. Mixed chimerism (MC) of total peripheral blood leukocytes (PBLs) did not predict loss of donor chimerism in all lineages and when stable was not associated with graft failure or rejection in this analyses. Split chimerism with complete donor chimerism (CC) of myeloid, B, and natural killer cells, but not T cells, occurred early post-HSCT, but full donor T cell chimerism was achieved at 12 months post-HSCT by most patients. MC within the T cell lineage was the major contributor to PBL MC, with lower median donor T cell chimerism at 3 months than at 12 months (91%) post-HSCT (51% versus 91%; P < .0001). Predictors of MC at 3 and 12 months were (1) age <3 years (P = .01 for PBLs and P = .003 for myeloid lineage); (2) nonmalignant disorder (P = .007 for PBLs); and (3) the use of reduced-intensity conditioning regimens. TCD grafts produced lower donor T cell chimerism at 3 months post-HSCT compared with unmodified grafts (P < .0001), where T cell lineage CC was achieved early post-HSCT. The donor T cell chimerism was similar at 12 months in the 2 types of grafts. Umbilical cord blood grafts had CC in all lineages at all time points post-HSCT. Loss of donor B cell chimerism was associated with increased risk of relapse in hematologic malignancies (hazard ratio, 1.33; P = .05). Age, underlying disease, conditioning regimen, and graft manipulation can impact post-HSCT donor-host chimerism and be predictors for early MC. MC in total PBLs and T cells was not related to graft failure or disease relapse. Whole-blood PBL chimerism analysis is not sufficient to assess the significance of post-HSCT donor-host status; rather, lineage-specific chimerism, particularly for myeloid, T, and B cells, should be analyzed to guide interventions and inform outcomes.

Conditioning regimen for allogeneic bone marrow transplantation in children with acquired bone marrow failure: fludarabine/melphalan vs. fludarabine/cyclophosphamide

Fludarabine/cyclophosphamide-based conditioning regimens are standard in bone marrow transplantation (BMT) for acquired bone marrow failure in children, however, graft failure may occur. Using the data from a nationwide transplantation registry, we compared the outcomes of children aged <16 years with acquired aplastic anemia and refractory cytopenia of childhood who underwent allogeneic BMT with either fludarabine/melphalan (n = 71) or fludarabine/cyclophosphamide (n = 296) between 2000 and 2016. The fludarabine/melphalan regimen provided excellent outcomes, with 3-year overall survival and failure-free survival rates of 98% and 97%, respectively. The 83% 3-year failure-free survival in the fludarabine/cyclophosphamide group was significantly inferior (P = 0.002), whereas the overall survival did not differ between the two groups. Late graft failure was the most common cause of treatment failure in the fludarabine/cyclophosphamide group, which experienced a significantly higher incidence of late graft failure than the fludarabine/melphalan group (11% vs. 3%; P = 0.035). Multivariate analyses showed that the fludarabine/melphalan regimen was associated with a better failure-free survival (hazard ratio [HR] 0.12; P = 0.005) and lower risk of late graft failure (HR 0.16; P = 0.037). Fludarabine/melphalan-based conditioning regimen can be a promising option for children with acquired bone marrow failure receiving BMT.