Experiences with haploidentical stem cell transplantation in children with acute lymphoblastic leukemia

Depletion of CD45RA+ T cells: Advantages and disadvantages of different purification methods

BACKGROUND

Recently, new advances were made regarding the depletion of CD45RA⁺ naïve T cells from haploidentical grafts as they are suspected to be the most alloreactive.

METHODS

Within this project we investigated CD45RA-depletion from G-CSF mobilized PBSC by two different purification strategies according to GMP, specifically direct depletion of CD45RA⁺ cells (one-step approach), or CD34-positive selection followed by CD45RA-depletion (two-step approach).

RESULTS

With log -3.9 and - 3.8 the depletion quality of CD45RA⁺ T cells was equally for both approaches together with a close to complete CD19⁺ B cell depletion. However, due to a high expression of CD45RA the majority of NK cells were lost within both CD45RA depletion strategies. Stem cell recovery after one-step CD45RA-depletion was at median 52.0% (range: 49.7-67.2%), which was comparable to previously published recovery data received from direct CD34 positive selection. Memory T cell recovery including CD4⁺ and CD8⁺ memory T cell subsets was statistically not differing between both purification approaches. The recovery of CD4⁺ and CD8⁺ T cells was as well similar, but overall a higher amount of cytotoxic than T-helper cells were lost as indicated by an increase of the CD4/CD8 ratio.

CONCLUSIONS

CD45RA-depletion from G-CSF mobilized PBSC is feasible as one- and two-step approach and results in sufficient reduction of CD45RA⁺ T cells as well as B cells, but also to a co-depletion of NK cells. However, by gaining two independent cell products, the two-step approach enables the highest clinical flexibility in regard to individual graft composition with precise dosage of stem cells and T cells.

Correlation of rabbit antithymocyte globulin serum levels and clinical outcomes in children who received hematopoietic stem cell transplantation from an alternative donor

We analyzed the correlation between rabbit ATG (rATG) serum levels and clinical outcomes in 37 children who received rATG at a total dose of 10 or 15 mg/kg during HSCT conditioning from an alternative donor. Fourteen patients had advanced malignant diseases, 13 had severe AA, and 10 had inherited disorders. Complete engraftment was achieved in all patients, and no rejection occurred. The cumulative incidence of grades II-IV acute GVHD and extensive chronic GVHD was 27% (95% CI, 12.5-39.6%) and 8.1% (95% CI, 0-23.1%), respectively. Multivariate analysis identified lower rATG levels at week 4 as an independent risk factor in the development of grades II-IV acute GVHD (p = 0.037). Serious infections were not observed in any patient following HSCT. No correlation was found between EBV reactivation and rATG levels at week 2 and week 4 after HSCT. Furthermore, no correlation was found between relapse and rATG levels two and four wk post-transplantation. The probability of five-yr OS among patients was 70.3% (95% CI, 59.8-79.2%). Our results suggest that targeted rATG administration may protect patients from severe acute GVHD without increasing the risk of EBV reactivation or relapse.

Haploidentical stem cell transplantation for children with high-risk leukemia

BACKGROUND

The Chilean population is ethnically diverse, and more than 50% of children referred for hematopoietic stem cell transplantation (HSCT) lack a suitable donor.

PROCEDURE

To expand the donor pool, we assessed the feasibility, tolerance, and efficacy of using a haploidentical (HI) donor and a reduced-intensity conditioning regimen for high-risk pediatric leukemia. This study was facilitated by technology transfer from St. Jude Children's Research Hospital over the 2 preceding years.

RESULTS

Between March 2006 and April 2009, 10 patients (median age, 9.8 years) received T cell-depleted grafts at Calvo Mackenna Hospital in Santiago. Median cell doses were CD34+: 7.45 × 10(6)/kg (range, 4.00-20.20 × 10(6)/kg); CD3+: 0.88 × 10(5)/kg (0.11-1.35 × 10(5)/kg); and CD56+: 71.30 × 10(6)/kg (31.50-131.80 × 10(6)/kg). Nine patients experienced complete engraftment; six of the nine remain alive and clinically well 13-50 months post-HSCT. Three patients died after bone marrow relapse, while only one died of transplant-related causes. Virus reactivation was the main post-transplant complication: 5/10 had positive CMV PCR but none had CMV disease. One patient developed acute GvHD > grade II and only one had chronic GvHD.

CONCLUSIONS

HI-HSCT is feasible in our setting, offers a rational treatment option, and expands the donor pool significantly for children with high-risk leukemia in a developing country. This information is especially relevant to other ethnically diverse populations that are poorly represented in international donor registries.

Results and factors influencing outcome after fully haploidentical hematopoietic stem cell transplantation in children with very high-risk acute lymphoblastic leukemia: impact of center size: an analysis on behalf of the Acute Leukemia and Pediatric Disease Working Parties of the European Blood and Marrow Transplant group

T cell–depleted haploidentical hematopoietic stem cell transplantation (haploHSCT) is an option to treat children with very high-risk acute lymphoblastic leukemia (ALL) lacking an HLA-identical donor. We analyzed 127 children with ALL who underwent haploHSCT in first (n = 22), second (n = 48), or third (n = 32), complete remission or in relapse (n = 25). The 5-year leukemia-free survival (LFS) was 30%, 34%, 22%, and 0%, respectively. A risk-factor analysis was performed for patients who underwent transplantation in remission (n = 102). Five-year nonrelapse mortality (NRM), relapse incidence (RI), and LFS were 37%, 36%, and 27%, respectively. A trend of improved LFS rate and decreased RI was observed for children given a graft with higher number of CD34+ cells (adjusted P = .09 and P = .07, respectively). In a multivariate analysis, haploHSCT performed in larger centers (performing ≥ 231 allotransplantations in the studied period) was associated with improved LFS rate and decreased RI (adjusted P = .01 and P = .04, respectively), adjusting for different patient-, disease-, and transplant-related factors such as number of previous autotransplantations, cytomegalovirus serology status, type of T-cell depletion, and use of total body irradiation and antithymocyte globulin. In conclusion, higher CD34+ cell dose and better patient selection may improve outcomes of children with ALL who undergo a haploHSCT. Transplant centers initiating programs on haploHSCT for children may collaborate with more experienced centers.

Transplant outcomes in acute leukemia. II

Currently, it is possible to find a hematopoietic stem cell (HSC) donor for virtually all patients with acute leukemia who have an indication to receive an allogeneic hematopoietic stem cell transplant (HSCT) and lack a human leukocyte antigen (HLA)-identical sibling or a well-matched HLA unrelated donor (URD). According to the ethnicity of the patients and the donor registry, approximately 25% to 60% of patients will not find an 8/8 HLA-matched unrelated donor. Other alternative donors, such as HLA-mismatched related donor or unrelated donor umbilical cord blood (UCB), have emerged to solve the lack of a sibling or well-matched URD. In the haploidentical HSCT setting, new techniques of T-cell depletion, new approaches using combinations of immunosuppressive drugs or different conditioning regimens, and developments on immunotherapy have focused attention on this option. Therefore, any physician has to carefully evaluate, for each patient in need of an allograft, all of the possible alternatives in order to choose the best HSC donor, taking into account type of disease to be transplanted, urgency of transplantation, donor characteristics, and center experience. This review evaluates the current status of haploidentical HSCT in acute leukemia, its advantages and remaining limitations compared to other stem cell sources, and how these data may be used in the development of donor selection algorithms.

Cellular immune reconstitution after haploidentical transplantation in children

Delayed immune reconstitution is 1 of the major contributions to the morbidity and mortality after haploidentical transplantation. Patients with a slow recovery of the innate and especially of the adaptive immune system are at high risk for severe and often lethal infections. The reason for delayed immune reconstitution after haploidentical transplantation include the T cell depletion (TCD) of the graft, the thymic dysfunction induced by pretransplant chemotherapies and by the conditioning regimens, and the occurrence of graft-versus-host disease (GVHD) and its treatment. The detailed analysis, understanding, and manipulation of the reconstitution of the cellular immune system will be of utmost importance to overcome the posttransplant immunodefcient status, and should result in a reduced risk of severe and overwhelming infections and hopefully also to a reduced risk of relapse through better immunological control of residual malignant cells.

Indications and donor selections for allogeneic stem cell transplantation in children with hematologic malignancies

Allogeneic stem cell transplantation (SCT) is the only curative approach for many patients with advanced or high-risk leukemia. Advances in supportive care and management of graft-versus-host disease have resulted in improvements in outcomes of related and unrelated donor SCT, creating controversies as to which strategy might be the optimal therapy for individual patients. This article discusses the indications and donor selection strategies for SCT in patients with malignant hematologic disease.

Feasibility and outcome of reduced-intensity conditioning in haploidentical transplantation

Allogeneic stem cell transplantation is for a number of patients with malignant and nonmalignant diseases the only curative approach. For those patients who do not have an HLA-identical-related or -unrelated stem cell donor, a related three-loci mismatch haploidentical stem cell transplantation with T cell-depleted stem cells is a viable option. T cell depletion either by CD34(+) positive selection or by CD3-negative depletion strategies is available and has been investigated. We have shown that reduced-intensity conditioning haploidentical transplantation using mobilized peripheral stem cells negatively depleted from T and B lymphocytes is associated with a rapid immune reconstitution, a low transplant-related mortality rate, and a favorable outcome in patients in remission at the time of transplant. For chemorefractory patients, additional posttransplant cellular and humoral immunotherapeutic strategies are needed for prevention of relapse after transplantation.