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

The technique of αβ T cell depletion (αβTCD) 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 αβTCD 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.

Targeted Therapy With Venetoclax and Daratumumab as Part of HSCT Preparative Regimen in Children With Chemorefractory Acute Myeloid Leukemia

The long-term outcome of allogeneic hematopoietic stem cell transplantation (HSCT) in chemorefractory acute myeloid leukemia (AML) remains suboptimal because of a high relapse rate. Enhancement of conditioning regimens by the incorporation of targeted anti-leukemia agents is a potential approach to improve the efficacy of HSCT. In a pilot trial and extended access cohort, we evaluated the safety and potential value of adding combinations of venetoclax and daratumumab to a preparative regimen among children with chemorefractory acute myeloid leukemia grafted with αβ T-cell-depleted peripheral blood stem cells. All 20 patients had active disease status of AML at the time of transplantation. The preparative regimen included myeloablative conditioning based on either total body irradiation or treosulfan. A haploidentical related donor was used as a graft source for all patients. Engraftment was not compromised, and no excess toxicity was noted. Minimal residual disease-negative complete remission was achieved in 17 patients (85%). The cumulative incidence of grade II to IV acute graft-versus-host disease (GVHD) was 17%, and the cumulative incidence of chronic GVHD was 7%. At 2 years, nonrelapse mortality was 10%, relapse incidence was 46%, event-free survival was 44%, and overall survival was 65%. Our data show the possibility of safely adding targeted agents to conditioning regimens; however, no evidence of a significant improvement in long-term transplantation outcomes in this cohort of patients was observed.

Control of graft-versus-host disease with rabbit anti-thymocyte globulin, rituximab, and bortezomib in TCRαβ/CD19-depleted graft transplantation for leukemia in children: a single-center retrospective analysis of two GVHD-prophylaxis regimens

Both acute GVHD and chronic GVHD remain the leading cause of morbidity and death after allogeneic HSCT. We conducted a retrospective analysis comparing two GVHD-prophylaxis regimens: 35 patients received "Regimen 1" (horse ATG, tacrolimus, and methotrexate) and 46 "Regimen 2" (rabbit ATG, rituximab, and peritransplant bortezomib). All 81 patients with a median age of 9 (0.6-23) years with ALL (n = 31) or AML (n = 50) in complete remission received TCRαβ/CD19-depleted transplants between May 2012 and October 2016, from 40 HLA-matched unrelated and 41 haploidentical donors. After a median follow-up of 3.9 years, the CI of acute GVHD II-IV was 15% (95% CI: 7-30) in the "Regimen 2" group and 34% (95% CI: -54) in the "Regimen 1" group, P = .05. "Regimen 2" was also more effective in the prevention of chronic GVHD; the CI at 1 year after HSCT was 7% (95% CI: 2-19) vs 31% (95% CI: 19-51), P = .005. The CI of relapse at 3 years adjusted for the GVHD-prophylaxis regimen groups 31% (95% CI: 19-51) for the "Regimen 1" vs 21% (95% CI: 11-37) for the "Regimen 2", P = .3. The retrospective observation suggests that the use of the rATG, rituximab, and bortezomib was associated with significantly lower rate of GVHD without the loss of anti-leukemic activity.

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

We evaluated the outcome of αβ 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 αβ 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 αβ 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.

TCR-alpha/beta and CD19 depletion and treosulfan-based conditioning regimen in unrelated and haploidentical transplantation in children with acute myeloid leukemia

We evaluated the depletion of TCR-alpha/beta cells from the graft of children with high-risk AML, who received transplantation from unrelated (n=20) and haploidentical donors (n=13). The preparative regimen included treosulfan, melphalan, fludarabine and anti-thymocyte globulin. Grafts were PBSC engineered by TCR-alpha/beta and CD19 depletion. The graft contained a median of 9 × 10(6)/kg of CD34+ and 20 × 10(3)/kg of αβ-T cells. Post-transplant immune suppression included tacrolimus till day +30 and Mtx in 21 patients, tacrolimus in 5, Mtx in 2 and no prophylaxis in 5 patients. Sixteen patients received native or TCR-alpha/beta-depleted donor lymphocytes at a median of 47 (40-204) days. Median follow-up is 1.76 years. Primary engraftment was achieved in 33 patients (100%). Cumulative incidence of acute GvHD (aGvHD) grade 2-3 was 39 (26-60)%, half of them had skin-only aGvHD. Cumulative incidence of chronic GvHD was 30(18-50)%. Transplant-related mortality is 10(4-26)%. Event-free survival (EFS) is 60(43-76)% and overall survival (OS) is 67(50-84)% at 2 years. In a subgroup of patients, who received transplantation in CR, EFS is 66(48-84)% and OS-72(53-90)% at 2 years. Our data suggest that TCR-alpha/beta and CD19 depletion is a robust method of graft manipulation, which can be used to engineer grafts for children with AML.