Impact of Natural Killer Cell-Associated Factors on Acute Leukemia Outcomes after Haploidentical Hematopoietic Stem Cell Transplantation with αß T Cell Depletion in a Pediatric Cohort.

The technique of αß T cell depletion (αßTCD) is a well-established method of hematopoietic stem cell transplantation (HSCT) for children with acute leukemia owing to the low rates of graft-versus-host disease and nonrelapse mortality (NRM). The graft-versus-leukemia effect is generally ascribed to natural killer (NK) cells conserved within the graft. It is not known whether NK-related factors affect the outcome of αßTCD HSCT, however. The aim of this retrospective study was to explore the impact of NK alloreactivity (based on donor-recipient killer immunoglobulin-like receptor [KIR] mismatch), graft NK cell dose, and blood NK cell recovery on day +30 post-HSCT on the incidences of leukemia relapse and NRM. The pediatric acute leukemia cohort comprised 295 patients who underwent their first HSCT from a haploidentical donor in complete remission. During post hoc analysis, the total cohort was divided into subcohorts by diagnosis (acute lymphoblastic leukemia [ALL]/acute myeloid leukemia [AML]), NK alloreactivity prediction (KIR match/KIR mismatch), graft NK cell dose (less than versus greater than the median value), and blood NK cell recovery on day +30 post-HSCT (less than versus greater than the median value). We also investigated the influence of serotherapy (antithymocyte globulin [ATG] group) versus abatacept + tocilizumab combination [aba+toci] group) on relapse risk in the context of KIR mismatch. The risks of relapse and NRM were calculated by the cumulative risk method, and groups were compared using the Gray test. Multivariate analysis revealed no apparent impact of predicted NK alloreactivity or any other studied NK cell-related factors for the entire cohort. For patients with AML, a significantly higher relapse risk associated with high NK cell graft content on the background of no predicted KIR mismatch (P = .002) was shown. Multivariate analysis confirmed this finding (P = .018); on the other hand, for the KIR-mismatched patients, there was a trend toward a lower risk of relapse associated with high NK cell dose. The use of ATG was associated with a trend toward reduced relapse risk (P = .074) in the AML patients. There was no significant impact of NK-related factors in the ALL patients. Overall, the evaluated NK-related factors did not show a clear and straightforward correlation with the key outcomes of HSCT in our cohort of children with acute leukemia. In practice, the data support prioritization of KIR-mismatched donors for patients with AML. Importantly, a potential interaction of KIR ligand mismatch and NK cell content in the graft was identified. Indirect evidence suggests that additional cellular constituents of the graft could influence the function of NK cells after HSCT and affect their role as graft-versus-leukemia effectors.

Treosulfan-Based Conditioning Regimen in Haematopoietic Stem Cell Transplantation with TCRαß/CD19 Depletion in Nijmegen Breakage Syndrome.

Nijmegen breakage syndrome (NBS) is a DNA repair disorder characterized by combined immunodeficiency and a high predisposition to malignancies. HSCT appears to cure immunodeficiency, but remains challenging due to limited experience in long-term risks of transplant-associated toxicity and malignancies. Twenty NBS patients received 22 allogeneic HSCTs with TCRαß/CD19+ graft depletion with fludarabine 150 mg/m2, cyclophosphamide 20-40 mg/kg and thymoglobulin 5 mg/kg based conditioning regimens (CRs). Twelve patients additionally received low-dose busulfan 4 mg/kg (Bu group) and 10 patients (including 2 recipients of a second HSCT) treosulfan (Treo group) 30 g/m2. Overall and event-free survival were 0.75 vs 1 (p = 0.16) and 0.47 vs 0.89 (p = 0.1) in the Bu and Treo groups, respectively. In the Bu group, four patients developed graft rejection, and three died: two died of de novo and relapsed lymphomas and one died of adenoviral hepatitis. The four living patients exhibited split chimerism with predominantly recipient myeloid cells and predominantly donor T and B lymphocytes. In Treo group, one patient developed rhabdomyosarcoma. There was no difference in the incidence of GVHD, viral reactivation, or early toxicity between either group. Low-dose Bu-containing CR in NBS leads to increased graft failure and low donor myeloid chimerism. Treo-CR followed by TCRαß/CD19-depleted HSCT demonstrates a low level of early transplant-associated toxicity and enhanced graft function with stable donor chimerism.

BCG-Related Inflammatory Syndromes in Severe Combined Immunodeficiency After TCRαß+/CD19+ Depleted HSCT.

INTRODUCTION: The live-attenuated BCG vaccine is known to cause disseminated Mycobacterium bovis infection in patients with severe combined immunodeficiency (SCID). However, BCG-related post-hematopoietic stem cell transplantation (HSCT) immune reconstitution inflammatory syndromes, similar to those described in patients with HIV infections, are less-known complications of SCID. PATIENTS AND METHODS: We reported on 22 BCG-vaccinated SCID patients who had received conditioned allogeneic HSCT with TCRαß+/CD19+ graft depletion. All BCG-vaccinated patients received anti-mycobacterial therapy pre- and post-HSCT. Post-transplant immunosuppression consisted of tacrolimus in 10 patients and of 8 mg/kg tocilizumab (d-1, + 14, + 28) and 10 mg/kg abatacept (d-1, + 5, + 14, + 28) in 11 patients. RESULTS: Twelve patients, five of whom had BCG infection prior to HSCT, developed BCG-related inflammatory syndromes (BCG-IS). Five developed early BCG-IS with the median time of manifestation 11 days after HSCT, corresponding with a dramatic increase of CD3+TCRγδ+ in at least two patients. Early BCG-IS was noted in only one out of 11 patients who received tocilizumab/abatacept and 4 out of 11 patients who did not. Seven patients developed late BCG-IS which corresponded to T cell immune recovery; at the time of manifestation (median 4.2 months after HSCT), the median number of CD3+ cells was 0.42 × 109/ and CD3+CD4+ cells 0.27 × 109/l. In all patients, late BCG-IS was controlled with IL-1 or IL-6 inhibitors. CONCLUSION: BCG-vaccinated SCID patients undergoing allogeneic HSCT with TCRαß+/CD19+ graft depletion are at an increased risk of early and late BCG-IS. Anti-inflammatory therapy with IL-1 and IL-6 blockade is efficient in the prevention of early and treatment of late BCG-IS.

αß T Cell-Depleted Haploidentical Hematopoietic Stem Cell Transplantation without Antithymocyte Globulin in Children with Chemorefractory Acute Myelogenous Leukemia.

We evaluated the outcome of αß T cell-depleted haploidentical hematopoietic stem cell transplantation (HSCT) in a cohort of children with chemorefractory acute myelogenous leukemia (AML). Twenty-two patients with either primary refractory (n = 10) or relapsed refractory (n = 12) AML in active disease status received a transplant from haploidentical donors. The preparative regimen included cytoreduction with fludarabine and cytarabine and subsequent myeloablative conditioning with treosulfan and thiotepa. Antithymocyte globulin was substituted with tocilizumab in all patients and also with abatacept in 10 patients. Grafts were peripheral blood stem cells engineered by αß T cell and CD19 depletion. Post-transplantation prophylactic therapy included infusion of donor lymphocytes, composed of a CD45RA-depleted fraction with or without a hypomethylating agent. Complete remission was achieved in 21 patients (95%). The cumulative incidence of grade II-IV acute graft-versus-host disease (GVHD) was 18%, and the cumulative incidence of chronic GVHD was 23%. At 2 years, transplantation-related mortality was 9%, relapse rate was 42%, event-free survival was 49%, and overall survival was 53%. Our data suggest that αß T cell-depleted haploidentical HSCT provides a reasonable chance of long-term survival in a cohort of children with chemorefractory AML and creates a solid basis for further improvement.