Bone marrow harvest from minors

BM harvest from sibling donors is the most common method of obtaining hematopoietic progenitor and stem cells. In a survey among European pediatric HSCT centers almost all performed this procedure under general anesthesia of the donor. Only a small minority offer BM collection under local/spinal anesthesia, or use both anesthetic options. BM harvest is commonly achieved by repeated insertion of large bore needles into the posterior iliac crests (generally 50–200 times on both sides). This technique of multiple site needle aspiration is not appropriate for young children as the extent of tissue damage due to the smaller size of their bones, post procedure inflammation, chronic scarring and post-operative discomfort is generally unacceptable. Multiple aspirations from one puncture site by repositioning the harvest needle within the bone, are an alternative and preferable practice to limit the number of bone entry sites.

Special attention has to be given to the circulating blood volume of a pediatric donor, and transfusion of irradiated, ABO-compatible red cells might be indicated during or after the BM collection. A directed donor unit might be procured in advance of the procedure, or, in larger donors, an autologous unit of blood might be donated a few weeks before the procedure. All donors should be placed on iron supplementation a minimum of a few weeks before and 2–3 months after a BM harvest, unless blood is transfused during or shortly after the procedure.

An alternative method is described by Kletzel and colleagues using a semi-automated processing technique to salvage red blood cells from pediatric BM donors to minimize the risk of severe anemia following BM harvest and ABO incompatibility in the recipient. Sixty healthy, HLA-matched, pediatric BM donors with a median age 8.0 years (2–19) were studied. The viability before and after cell processing was 99%, with reduced risk of post-bone marrow harvest anemia, decreased volume infused into the donor, and enriching the mononuclear and CD34+ cell population, without affecting hematopoietic reconstitution.

Another option is the administration of recombinant human erythropoietin (rh-Epo) to normal pediatric BM donors. Martinez and colleagues have evaluated the efficacy of administering rh-Epo to 11 healthy BM donors weighing less than 30 kg. For three weeks before harvesting, the donors received 100 units/kg/day rh-Epo subcutaneously and oral iron supplementation (2.5 mg/kg twice daily). Six children with hematocrit values below the normal ranges for their ages after BM harvesting, received 150 units/kg rh-Epo three times a week for 2 additional weeks and oral iron supplementation at the same dose. No rh-Epo side-effects were observed. Hematocrit values before harvesting increased to between 5.7 and 18.5% (mean 10.6 ± 1.2) above the baseline values ( P = .0001). Hematocrit after harvesting decreased to between 4 and 19.5% (mean, 11.1) below the day 0 pre-harvest values. On day +15 all but one patient had a hematocrit value greater than or equal to baseline value. No patient required transfusion during or after BM harvest. However, as this product is not licensed for this indication and the fact that there is no long term safety data with this approach, we strongly discourage incorporation of this practice in routine marrow harvest from healthy pediatric donors.

Pediatric marrow donor safety data is limited to publications from small single-institution studies. Buckner described the Seattle experience with 128 children less than age 10, and an additional 343 donors between the ages of 10 and 19. As with adults, life threatening complications in donors under the age of 20 undergoing BM harvest were rare (2/507, 0.39%). Sanders described harvests from 23 donors under the age of 2 years. None of these donors experienced major difficulties following the harvest. Three donors had significant medical problems diagnosed during the pre-donation evaluation. All harvests were performed from the posterior iliac crests under general anesthesia. Irradiated blood transfusions were given to 85% of these younger donors during the procedure, due to the large volume of marrow required for older, larger recipients. The volume of marrow obtained ranged from 11.5 to 19.3 mL/kg donor weight and contained from 2.5 to 10.4 × 10(8) nucleated cells/kg donor weight. No fatal complications were reported in a recent analysis of Halter and colleagues in donors below 20 years of age. Three pediatric donors with severe adverse events were reported, two BM (cardiac arrest, pulmonary edema) and one PBPC donor (transfusion related acute lung injury). However, the potential risk of blood transfusion associated side effects (eg, infections, tranfusion related acute lung injury, hemolytic transfusion reactions) have to be considered.

The most frequent side effects of marrow harvest are mild and self-limiting such as fatigue, transient anemia and local pain at the harvest site(s). Risks of general anesthesia are no greater than for any other surgical procedure. The procedure rarely results in long term morbidities or life-threatening complications. However, it is important that the team responsible for information, pre-harvest physical examination, donor clearance, general anesthesia and BM collection is experienced in all of the necessary procedures.

Despite the growing numbers of pediatric sibling stem cell donors, little information is available on the potential for adverse psychological responses in the pediatric donor population. Wiener and colleagues investigated eight published reports assessing the pediatric sibling donor experience. Studies were generally small (n<44) and cross-sectional. Results suggested a range of psychological distress responses, with greater distress in the pediatric donor than non-donor siblings. They strongly suggest that for these youngsters, psychological distress exists before, during, or after stem cell donation and transplantation, due to disease impact on the family, irrespective of outcome. Recommendations include future longitudinal research on sibling donor psychological status, identification of sibling donors at high risk of disturbed responses, and development of educational and specific interventions for this generally overlooked but invaluable pediatric population. In general, in the case of a pediatric donor, it has been suggested that there may be a benefit to the donor as well as the patient.

Bone marrow harvest from adults

BM harvest from adults is technically the same as with pediatric donors. Minor adverse events, such as transient syncope, headache, and minor local infections occur in 6%–20% of marrow harvests. However, severe adverse events related to harvest are rare (0.1–0.3%) and risk of death is estimated to be ∼1 in 10,000 (0.0001%). Thus, careful donor selection and follow up are required to ensure donor safety.

PBPC collection from G-CSF stimulated pediatric sibling donors

Peripheral blood apheresis is performed following G-CSF administration, and usually takes about 4–6 hours per day. The number of collections depends on the number of stem cells collected with each procedure. Though the PBPC donation procedures in adult and pediatric donors are technically similar, there are medical risks and complications of PBSC collection that are more likely in pediatric donors. These include difficulty with vascular access with possible need for central venous catheter placement, need for anesthesia or sedation, low platelet count, anemia, need for red blood cell or volume priming before apheresis, vasovagal complications, shifts in blood volume with resultant cardiovascular changes, hypocalcemia due to citrate anticoagulant (or iatrogenic hypercalcemia due to supplementation), hypotension, nausea, and vomiting. In the event that enough stem cells cannot be collected by apheresis, a BM harvest may need to be performed in addition to supplement the graft. Another concern is the risk of developing a hematological malignancy in previously healthy individuals who have received hematopoietic growth factors. It is known that siblings of patients with cancer have an increased risk of leukemia and other cancers. It is difficult therefore to assess an additive risk of developing leukemia after short term exposure to G-CSF. However, recent publications do report small numbers of different types of leukemia, predominantly acute myeloid leukemia, after G-CSF administration before PBPC donation.

In spite of limited safety data in pediatric donors, G-CSF-mobilized stem cell or G-CSF primed BM harvest is an accepted practice in many pediatric transplant centers. Data between 1996 and 2003 from more than 50 centers reporting to the Pediatric Blood and Marrow Consortium (PBMTC) has shown an average of 23% of all matched sibling transplants (30–60/y) have used PBPC collection. Results from 3 separate studies in children using PBSCs as a stem-cell source in matched-related donor transplantations have shown a chronic GVHD disease rate of 63% to 75%, That was twice of what is expected in pediatric patients receiving unstimulated BM.

Nine major U.S. centers reported the administration of G-CSF to pediatric donors before a marrow harvest, as part of a PBMTC pilot study on the use of G-CSF primed marrow as a stem cell source in pediatric patients. This trial demonstrated that priming with a dose of G-CSF (5 μg/kg) results in nucleated and CD34 ⁺ cell yields that were comparable with PBSC collections and greater than that achieved in BM collections, while avoiding the high CD3 ⁺ cell collections typical for PBSCs.

As no clear benefit over conventional BM transplantation for a pediatric donor could be demonstrated, and as G-CSF is not licensed for pediatric donors, PBPC-collection and G-CSF stimulation might appropriately be reserved for exceptional use in siblings following multidisciplinary team discussion and ethical committee approval or as part of an ongoing research study.

PBPC collection from G-CSF stimulated adult donors

In a prospective study of 2,408 unrelated adult PBPC donors who donated between 1999–2004 with a median follow up of 49 months, the overall incidence of serious adverse events was 0.6%. The most common side effects were bone pain, headache, fatigue, hypocalcemia and thrombocytopenia. Complete recovery was universal and no long term effects were noted that could be attributed to PBPC harvest. Women and obese donors were at increased risk of adverse events. While no increase in the incidence of malignancies was noted in this cohort, continued long-term follow up of donors is important.

Procurement, processing, cryopreservation and banking

Cord blood, known to be rich in hematopoietic stem cells and typically discarded with the placenta at birth, can be collected without physical risk to the mother or baby. It can be collected from the delivered placenta ( ex uter o) or during the third stage of labor ( in utero ). Many public cord blood banks employ dedicated staff to perform ex utero collections away from the delivery room so that the privacy of the family is preserved and obstetricians are not distracted from their usual practices. Alternatively, obstetricians or midwives perform in utero collections while waiting for the placenta to deliver. In either case, after sterile preparation, the umbilical vein is punctured with a 17-gauge needle attached to a sterile, closed system collection bag containing citrate phosphate dextrose anticoagulant, which is positioned lower than the placenta. Blood flows from the placenta through the cord, by gravity into the bag over approximately 9–10 minutes. Experienced collectors harvest an average of 110 mL from a single placenta. The cord blood unit is labeled and subsequently sent to the bank for processing, testing, cryopreservation, and storage.

There are two types of cord blood banks, public and private. Public cord blood banks store cord blood units donated voluntarily by women after delivering normal term babies. The mother and family give written consent for donation, agree to donor screening and give up all rights to the cord blood which, if qualified, is listed on an unrelated donor registry. Unrelated transplant programs use cord blood units from public banks for transplantation of patients lacking other suitable donors. The costs of the donation, procurement, testing, storage and distribution are borne by the public cord blood bank.

Private banks, which are for-profit entities, store “directed donations” collected by obstetricians from babies born into families who save the cord blood for the use of that family. They may intend to use the cord blood for the baby itself for future use in treating degenerative diseases (autologous donation), although indications for this are unproven, or for another family member in need of future transplantation (eg, genetic or malignant diseases of the blood, immune system or inborn errors of metabolism). Families have to pay private banks for this service. Despite aggressive marketing by some private banks, evidence that such future use will be efficacious in currently lacking. Another misleading pitch by some banks to parents is that autologous cord blood could be used if the child developed leukemia in the future. However, childhood leukemia is very uncommon and most such children can be cured with conventional chemotherapy alone and in those who fail this approach, allogeneic transplantation is the treatment of choice. The fact that leukemic cells can be seen in autologous cord blood of children presenting with leukemia from 1–11 years of age is another reason to advise against the use of autologous cord blood to treat pediatric patients with malignancies.

Acute lymphoid leukemia (ALL)

More than 70% of pediatric patients with ALL are cured with chemotherapy alone. Certain characteristics predict a very poor response to chemotherapy, such as the presence of Philadelphia chromosome (Ph+), hypodiploidy, infant leukemia with MLL gene rearrangement and slow response to chemotherapy (>28 days to achieve CR1). Transplant is indicated in such patients in first complete remission (CR1) to decrease the risk of relapse and improve leukemia free survival (LFS). Arico and colleagues pooled data on 326 patients with Ph+ ALL from multiple institutions and concluded that matched sibling BMT was superior to chemotherapy and other types of transplantation with 5-yr LFS of 65% with transplant versus. 25% with chemotherapy ( P <.001) and a decreased risk of relapse with transplant (RR 0.3, P <.001). Only few studies have directly compared outcomes of transplant versus chemotherapy in CR1, reflecting the challenges of conducting clinical trials in this population. Balduzzi and colleagues showed in a prospective multicenter trial that allogeneic HSCT from HLA matched sibling donors was superior to chemotherapy alone in children with very high risk ALL in CR1. Furthermore, the BFM-Study group showed a superiority of allogeneic HSCT compared with chemotherapy alone in high-risk childhood T-cell ALL. A minority of studies have failed to show a survival benefit from transplant in CR1.

For patients with ALL who relapse and achieve a second or subsequent remission (CR2 or beyond), LFS after matched sibling transplant ranges from 35%–65% for ALL in CR2 and 20%–30% for patients in CR3 or beyond. For children with relapsed ALL it has been shown that MRD HSCT improves survival compared with chemotherapy alone. The length of first remission is prognostic in patients with relapsed ALL. The most comprehensive data comes from retrospective registry analysis by Eapen and colleagues, who compared 188 pediatric patients receiving chemotherapy on POG studies with 186 patients undergoing matched sibling BMT. Patients with short CR1 (<36 months after diagnosis) had a significant decrease in relapse risk (RR 0.49, P <.001) with TBI containing regimens as compared with chemotherapy alone. Also noted was the fact that transplant did not provide benefit over chemotherapy for patients with a longer CR1 (≥36 months). In contrast, Gaynon and colleagues found no benefit for MRD transplant in ALL patients with early relapse. In general, patients with isolated extramedullary relapse respond well to chemotherapy alone, and transplant is not indicated, the notable exception being CNS relapse very close (<18 months) to diagnosis.

Acute myeloid leukemia (AML)

In AML patients, outcomes after chemotherapy were very poor in the 1970s. As such, patients with available matched sibling donor have traditionally received allogeneic transplant – so called ‘biologic randomization’. The outcomes of several of these studies indicate benefit of allogeneic transplant over chemotherapy in pediatric patients with AML in CR1. Horan and colleagues found that MRD BMT is an effective treatment for pediatric patients with intermediate risk AML in first CR. Woods and colleagues found superiority for BMT from MRD in children and adolescents. In a systematic review and meta-analysis, 6 trials with donor versus. no donor comparisons were analyzed (total number of patients was 1486). The overall result of this meta-analysis showed an advantage for matched sibling transplantation. With increasing intensity of upfront chemotherapy, the gap between outcomes of chemotherapy and HSCT may be narrowing. However, at present, the American Society of Blood and Marrow Transplantation recommends transplant in CR1 for AML patients, if a matched sibling donor is available. In Europe, there is a trend to refrain from HSCT in first remission, reserving this option in case of relapse hoping to avoid early and late sequelae associated with HSCT.

Patients with AML who relapse after chemotherapy can achieve remission after treatment with agents such as mitoxantrone and ARA-C about 70%–75% of the time as reported by the French group. The 5-year overall survival (OS) of these patients after allogeneic HSCT in CR2 was approximately 40%–50%. Thus one-third of relapsed patients could be salvaged with transplant. Early relapse (<12 months after CR1) was predictive of poor outcome.

Peripheral blood progenitor cell transplantation from HLA identical siblings

In recent years there have been PBPC transplantations from MRD in children with acute leukemias. Early outcomes data on the use of PBPC transplantation in pediatric patients suggest rapid engraftment, with comparable relapse risk, but increased incidence of chronic GVHD.

The first comparison between BM and PBPC in children was a single center observation in 16 pediatric patients, where a faster engraftment and a higher incidence of acute GVHD was noted but no difference in OS. The only available multicenter, retrospective analysis comparing PBPC versus BM transplant in patients (age: 8–20 years) with ALL or AML came from the IBMTR and showed a higher mortality after PBPCT. Outcomes of PBPCTs in 143 patients were compared with 630 BM transplants. The patient cohort was not completely comparable as PBPC recipients were older and more likely to have advanced leukemia, more likely to receive growth factors, and higher cell doses, and have undergone HSCT more recently. The PBPC donors tended to be older than BM donors. Donor age was highly correlated with recipient age in both groups: median 18 years (4–36) for PBPC donors and median 14 years (2–37) for BM donors. Hematopoietic recovery was faster after PBPC transplantation. Risks of grade II – IV acute GVHD were similar, but chronic GVHD risk was higher after PBPC transplantation. While the risk of leukemic relapse was similar between the two groups, overall mortality was higher resulting in a 10% decrease in OS in the group receiving PBPCs.

Umbilical cord blood (UCB) transplantation from HLA identical siblings

UCB transplantation (UCBT) from matched related siblings has been performed since 1988, demonstrating acceptable outcomes when sufficient cell dose is infused. Wagner and colleagues reported 44 patients undergoing sibling donor UCBT. Indication for transplant was acute leukemia in 18 of these patients. The majority of patients received a UCB unit that was fully matched or had 1 antigen mismatch. The probability of event-free survival was 46%, Smythe and colleagues reported three transplantations in children with ALL from cryopreserved sibling UCB. Two patients died from relapse, and one was alive 4 years after the procedure. Outcome data comparing HSCT using UCB versus. BM from HLA identical siblings is scant. Rocha and colleagues studied the records of 113 children who received an UCB from a HLA-identical sibling transplanted between 1990 and 1997, and compared them with the records of 2052 children who were transplanted using BM from HLA-identical siblings during the same period. The recipients of UCB were younger than the recipients of BM (median age, 5 years vs 8 years; P <.001), weighed less and were less likely to have received methotrexate for GVHD prophylaxis. Multivariate analysis demonstrated a lower risk of acute GVHD (relative risk, 0.41; P = .001) and chronic GVHD (relative risk, 0.35; P = .02) among recipients of UCB transplants. When compared with recovery after BM transplantation, the likelihood of recovery of the neutrophil count and the platelet count was significantly lower in the first month after UCB transplantation, although overall engraftment rates were similar. Mortality was similar in both groups. Deaths related to infection from any cause and hemorrhage were more common in the UCB group, whereas deaths related to GVHD, interstitial pneumonitis, and organ failure were more common in the BM group The number of relapse related deaths was similar in the two groups. OS was not statistically different between the two groups.