**2. Indications for hematopoietic stem cell transplantation (HSCT) in pediatrics**

There are two types of HSCT: autologous and allogeneic. Autologous HSCT consists of removal, storage and reinfusion of patients own hematopoietic stem cells as a way to restore the patient's depleted bone marrow after high dose myeloablative therapy (figure 2). Allogeneic HSCT consists of transferring both immature and mature blood cells to a patient from the bone marrow, peripheral blood or umbilical cord blood of a sibling, relative or an unrelated donor (figure 2) as a way to restore the patients bone marrow with a new immune system after a conditioning regimen (non-myeloablative or myeloablative chemotherapy). The success of an allo-HSCT is limited by the toxicity associated with the conditioning regimens, graft versus host disease (GVHD) and the development of opportunistic infections. New concepts and interventions over the last two decades have resulted in reduction of the morbidity and mortality associated with allo-HSCT. These include the utilization of reduced intensity regimens, more effective GVHD prophylaxis, new sources of progenitor hematopoietic stem cells, donor lymphocyte infusions and better prophylaxis and treatment for infectious diseases.

The decision to transplant or not to transplant should be determined on individual basis and several factors should be considered including the disease status, age, prior treatments and responses, donor availability and evolving alternative therapies.

Fig. 2. Major Key Steps of HSCT.

#### **2.1 Leukemias**

348 Advances in Hematopoietic Stem Cell Research

Immunodeficiency with hyper IgM Leukocyte adhesion deficiency

X-linked lymphoproliferative disease

Familial hemophagocytic lymphohistiocytosis Selected types of mucopolysaccharidoses, Selected types of peroxisomal and lysosomal

Selected types of life-threatening autoimmune disorders resistant to conventional treatments

Chronic granulomatosis disease Glanzmann thromboasthenia Bernard-Soulier syndrome

Omenn syndrome

Kostmann syndrome

disorders

Abbreviations: ALL= acute lymphoblastic leukemia; AML= acute myeloblastic leukemia; CML= chronic myeloid leukemia; CR1, 2, 3= first, second and third complete remission;

**2. Indications for hematopoietic stem cell transplantation (HSCT) in** 

bStage IV neuroblastoma, renal cell carcinoma, very high risk Ewing sarcoma. Table 1. Main Indications to allogeneic hematopoietic SCT in childhood

aPatients at high risk of recurrence (that is, t (9; 22) or t (4; 11); T-ALL with poor prednisone response,

There are two types of HSCT: autologous and allogeneic. Autologous HSCT consists of removal, storage and reinfusion of patients own hematopoietic stem cells as a way to restore the patient's depleted bone marrow after high dose myeloablative therapy (figure 2). Allogeneic HSCT consists of transferring both immature and mature blood cells to a patient from the bone marrow, peripheral blood or umbilical cord blood of a sibling, relative or an unrelated donor (figure 2) as a way to restore the patients bone marrow with a new immune system after a conditioning regimen (non-myeloablative or myeloablative chemotherapy). The success of an allo-HSCT is limited by the toxicity associated with the conditioning regimens, graft versus host disease (GVHD) and the development of opportunistic infections. New concepts and interventions over the last two decades have resulted in reduction of the morbidity and mortality associated with allo-HSCT. These include the utilization of reduced intensity regimens, more effective GVHD prophylaxis, new sources of progenitor hematopoietic stem cells, donor lymphocyte infusions and better prophylaxis

The decision to transplant or not to transplant should be determined on individual basis and several factors should be considered including the disease status, age, prior treatments and

responses, donor availability and evolving alternative therapies.

Chediak-Higashi syndrome

ALL In CR 1a In CR 2

CML

SCID

**pediatrics** 

& congenital) Thalassemia major Sickle cell disease

 In CR 3 or further AML in CR I or further

Myelodysplastic syndromes

Selected types of solid tumorsb

Infantile malignant osteopetrosis

SCID= severe combined immunodeficiency.

high levels of minimal residual disease).

and treatment for infectious diseases.

Hodgkin and non-Hodgkin lymphoma

Bone marrow failure syndromes (acquired

#### **2.1.1 Acute myeloid leukemia (AML)**

Despite intensive chemotherapy, less than half of all patients with AML will survive in the long term (Creutzin, 2005; Gibson, 2005). Treatment outcome of pediatric AML is not as favorable as in ALL. AML treatment failure is due primarily to disease recurrence, although treatmentrelated mortality remains an important cause of treatment failure. Improvement in AML outcomes have been due primarily to intensification of therapy and improved supportive care guidelines. In AML, treatment intensity is an important determinator of outcome, and many studies have focused on the role of HSCT as post-remission intensification, utilizing both autologous as well as allogeneic HSCT. Allogeneic HSCT may provide a graft versus leukemia effect in pediatric AML. This is supported by a study from Bader et al that showed that preemptive immunotherapy following HSCT in patients with increasing (mixed chimerism) may lead to improved outcome. In another study Neudorf et al reported that children treated with allogeneic-HSCT in the children's cancer group 2891 study who developed acute graft versus host disease (GVHD) had fewer relapses (Bader, 2004; Neudorf et al., 2004).

The American society of bone marrow transplant position statement for the treatment of AML in children indicates that allogeneic HSCT should be recommended in the first complete remission because transplant has better overall survival and leukemia-free survival compared with chemotherapy alone (ASBMT, 2007; Oliansky, 2007). However, the role of allogeneic-HSCT in complete remission one (CR1) is declining because of the better outcome with modern multiagent chemotherapy and better methods of identifying patients that have low risk features at diagnosis and therefore are more likely to be cured with conventional chemotherapy. Recent AML trials (MRC-AML-12 & AML 0531) have shown that prognostic factors like cytogenetic and response to induction therapy are highly predictive of determining patients that are high risk at diagnosis and therefore would benefit from allogeneic-HSCT in CR1, while sparing lower risk patients the potential toxicities associated with an allogeneic-

Hematopoietic Stem Cells Therapeutic Applications 351

dramatically over the past quarter of a century. Currently, over 2500 children in the United States are diagnosed each year with ALL and almost 95% attain a clinical remission after three or four drug induction chemotherapy (Clavell, 1986; Pui, 1998; Reiter, et al., 1994; Rivera, 1993). Over 83% of children with newly diagnosed ALL treated with multi-agent chemotherapy with or without clinical radiotherapy are alive and disease free at 5 years

Despite recent advances in the diagnosis and treatment of childhood ALL, there are several subpopulations of patients that have molecular biological markers or chromosomal abnormalities and biological factors that include poor prednisone response and resistance to initial chemotherapy including persistence minimal residual disease, that makes them very high risk of failing current multi-agent chemotherapy regimens. These very high risk patients require alternative treatment strategies to prevent progression and/or relapse of their disease (Kersey, 1997; Pui,1995). Table 2 defines the very high risk ALL patients.

The indication for HSCT from a match sibling or an unrelated donor for children with ALL in CR1 is limited to the subpopulation of patients that have clinical and biological features that identifies them as very high risk of relapse, as most studies quote an event-free survival (EFS) of less than 50% and a relapse rate of up to 50% (Reiter et al., 1994; Rivera, 1993). Children's oncology group conducted a clinical research study from 1993 to 1996 to investigate the toxicity and efficacy of HSCT in newly diagnosed children with very high risk features of ALL at diagnosis and/or during initial induction chemotherapy and their findings support the current indication of HSCT for very high risk ALL in CR1, especially patients with primary induction failure and Philadelphia chromosome positive ALL

HSCT should also be considered as an option for relapse ALL. The decision to perform an allogeneic matched related or unrelated donor HSCT for patients with relapse ALL depends on many factors which can be considered strong predictors of outcome as suggested from a number of literature reports. Different sites of relapse and the duration of first remission may be the most important factors predicting outcome after a first relapse. Patients with late relapse (over 6 months from therapy withdrawal) may have relatively good outcome with conventional chemotherapy alone (Borgmann et al., 1995; Ritchey, 1999; Uderzo et al., 1990). In contrast, children who relapse (isolated/combined medullary) during therapy or within 30 months of diagnosis seem to benefit more from HSCT than chemotherapy with an eventfree survival rates of 40-50% reported for patients in CR2 who underwent a HSCT

It has been difficult to compare outcomes of patients treated with chemotherapy or HSCT, since patient populations are not necessarily equivalent. Patients with aggressive disease die earlier and may not be included in studies of marrow transplantation, resulting in selection bias (Tichelli et al., 1999). To address this question, matched-pair analyses have been performed for ALL CR2 patients treated with chemotherapy or HSCT (Dreger et al., 1997; Novotny et al., 1998). For patients with early first relapse, HSCT resulted in significantly better EFS rates at 5 years compared with chemotherapy alone (40% vs 17%; p<0.001) (Novotny et al., 1998). Marrow transplantation was associated with a reduced risk of relapse that was not negated by increased treatment related deaths. The difference between chemotherapy and HSCT for patients who experienced a late marrow relapse (45% DFS vs

(Gaynon, 2000; Silverman, 2001; Vilmer, 2000).

(Satwani, 2007).

(Kawakami et al.,1990).

HSCT (Ljungman, 2009)**.** Recent analysis by several cooperative groups has now identified relapse risk group parameters based on cytogenetics abnormalities and early response to treatment : Low risk is defined as inversion (16)/t(16;16) or t(8,21). Down syndrome patients are also included in this low risk group; High risk is defined as monosomy 7, monosomy 5,5q deletions, or greater than 15% blasts at the end of induction I but who achieve complete remission after induction II, or high FLT3-ITD alleic ratio; Intermediate risk includes all other patients with no cytogenetic information available. This risk group is used to determine which patients should receive a HSCT in CR1.

Currently, HSCT is not recommended as frontline therapy for low-risk patients with AML in CR1, as they have an overall survival of 60% with conventional chemotherapy and HSCT has not been demonstrated to improve outcome for patients in CR1 **(**Gibson, 2005). HSCT is also not indicated for Myeloid Leukemia of Down Syndrome because HSCT is associated with excess toxicity with or without therapeutic gain (Lange et al., 1998). In addition, HSCT is also not indicated for acute promyelocytic leukemia (APL) due to excellent cure rates with conventional chemotherapy. However, for the few patients with APL who relapse or have persistent minimal residual disease, the prognosis is less favorable and HSCT might be a recommended choice (Oliansky et al., 2007). Allogeneic-HSCT from an HLA-identical sibling is an option for patients defined as intermediate risk. Allogeneic-HSCT from an HLA-identical sibling or an unrelated donor in CR1 is indicated for children with high risk AML including infant AML, therapy-related AML and children with M0 or M7 as it was proven to be more efficient than chemotherapy in some comparative studies with an event free survival ranging from 55 to 72% **(**Gibson, 2005). Regarding the use of haploidentical HSCT for AML, results in children with AML undergoing haploidentical HSCT have shown some effect of natural killer alloreactivity, suggesting that haploidentical HSCT may have a role in early phase very high AML patients (Marks et al., 2006).

HSCT also has an important role in the treatment of relapsed AML because outcome is poor with chemotherapy alone. Marrow transplantation in early first untreated relapse or CR2 results in a two-year EFS rate of 30-40%(Besinger,1995; Schimitz, 1998). Analyzes that attempt to compare outcome based on treatment have shown a survival advantage for patients who receive marrow transplants compared with chemotherapy alone, particularly for patients with longer first remission (Besinger, 1996).Therefore, allogeneic-HSCT from an unrelated or related donor is indicated in children with relapse AML in CR2, as it may provide long-term survival, particularly those in first relapse that are in remission.

Autologous HSCT has been used as consolidation in children with AML in CR1 after induction therapy and represents a valid alternative for high-risk children lacking a matched sibling donor. Nevertheless, results of pediatric studies comparing autologous HSCT with chemotherapy are conflicting. The use of peripheral blood stem cells in children with AML given autologous HSCT is infrequent. Further prospective clinical trials are needed to address the pivotal clinical question of whether autologous HSCT is better than chemotherapy or allograft as consolidation treatment for childhood AML in first CR (Miano et al., 2007).

#### **2.1.2 Acute lymphoblastic leukemia (ALL)**

ALL is not a uniform disease, but consists of different subtypes with different clinical prognostic and cytogenetic features. The prognosis of childhood ALL has improved

HSCT (Ljungman, 2009)**.** Recent analysis by several cooperative groups has now identified relapse risk group parameters based on cytogenetics abnormalities and early response to treatment : Low risk is defined as inversion (16)/t(16;16) or t(8,21). Down syndrome patients are also included in this low risk group; High risk is defined as monosomy 7, monosomy 5,5q deletions, or greater than 15% blasts at the end of induction I but who achieve complete remission after induction II, or high FLT3-ITD alleic ratio; Intermediate risk includes all other patients with no cytogenetic information available. This risk group is used to determine which

Currently, HSCT is not recommended as frontline therapy for low-risk patients with AML in CR1, as they have an overall survival of 60% with conventional chemotherapy and HSCT has not been demonstrated to improve outcome for patients in CR1 **(**Gibson, 2005). HSCT is also not indicated for Myeloid Leukemia of Down Syndrome because HSCT is associated with excess toxicity with or without therapeutic gain (Lange et al., 1998). In addition, HSCT is also not indicated for acute promyelocytic leukemia (APL) due to excellent cure rates with conventional chemotherapy. However, for the few patients with APL who relapse or have persistent minimal residual disease, the prognosis is less favorable and HSCT might be a recommended choice (Oliansky et al., 2007). Allogeneic-HSCT from an HLA-identical sibling is an option for patients defined as intermediate risk. Allogeneic-HSCT from an HLA-identical sibling or an unrelated donor in CR1 is indicated for children with high risk AML including infant AML, therapy-related AML and children with M0 or M7 as it was proven to be more efficient than chemotherapy in some comparative studies with an event free survival ranging from 55 to 72% **(**Gibson, 2005). Regarding the use of haploidentical HSCT for AML, results in children with AML undergoing haploidentical HSCT have shown some effect of natural killer alloreactivity, suggesting that haploidentical HSCT may have a

HSCT also has an important role in the treatment of relapsed AML because outcome is poor with chemotherapy alone. Marrow transplantation in early first untreated relapse or CR2 results in a two-year EFS rate of 30-40%(Besinger,1995; Schimitz, 1998). Analyzes that attempt to compare outcome based on treatment have shown a survival advantage for patients who receive marrow transplants compared with chemotherapy alone, particularly for patients with longer first remission (Besinger, 1996).Therefore, allogeneic-HSCT from an unrelated or related donor is indicated in children with relapse AML in CR2, as it may

Autologous HSCT has been used as consolidation in children with AML in CR1 after induction therapy and represents a valid alternative for high-risk children lacking a matched sibling donor. Nevertheless, results of pediatric studies comparing autologous HSCT with chemotherapy are conflicting. The use of peripheral blood stem cells in children with AML given autologous HSCT is infrequent. Further prospective clinical trials are needed to address the pivotal clinical question of whether autologous HSCT is better than chemotherapy or

ALL is not a uniform disease, but consists of different subtypes with different clinical prognostic and cytogenetic features. The prognosis of childhood ALL has improved

provide long-term survival, particularly those in first relapse that are in remission.

allograft as consolidation treatment for childhood AML in first CR (Miano et al., 2007).

patients should receive a HSCT in CR1.

role in early phase very high AML patients (Marks et al., 2006).

**2.1.2 Acute lymphoblastic leukemia (ALL)** 

dramatically over the past quarter of a century. Currently, over 2500 children in the United States are diagnosed each year with ALL and almost 95% attain a clinical remission after three or four drug induction chemotherapy (Clavell, 1986; Pui, 1998; Reiter, et al., 1994; Rivera, 1993). Over 83% of children with newly diagnosed ALL treated with multi-agent chemotherapy with or without clinical radiotherapy are alive and disease free at 5 years (Gaynon, 2000; Silverman, 2001; Vilmer, 2000).

Despite recent advances in the diagnosis and treatment of childhood ALL, there are several subpopulations of patients that have molecular biological markers or chromosomal abnormalities and biological factors that include poor prednisone response and resistance to initial chemotherapy including persistence minimal residual disease, that makes them very high risk of failing current multi-agent chemotherapy regimens. These very high risk patients require alternative treatment strategies to prevent progression and/or relapse of their disease (Kersey, 1997; Pui,1995). Table 2 defines the very high risk ALL patients.

The indication for HSCT from a match sibling or an unrelated donor for children with ALL in CR1 is limited to the subpopulation of patients that have clinical and biological features that identifies them as very high risk of relapse, as most studies quote an event-free survival (EFS) of less than 50% and a relapse rate of up to 50% (Reiter et al., 1994; Rivera, 1993). Children's oncology group conducted a clinical research study from 1993 to 1996 to investigate the toxicity and efficacy of HSCT in newly diagnosed children with very high risk features of ALL at diagnosis and/or during initial induction chemotherapy and their findings support the current indication of HSCT for very high risk ALL in CR1, especially patients with primary induction failure and Philadelphia chromosome positive ALL (Satwani, 2007).

HSCT should also be considered as an option for relapse ALL. The decision to perform an allogeneic matched related or unrelated donor HSCT for patients with relapse ALL depends on many factors which can be considered strong predictors of outcome as suggested from a number of literature reports. Different sites of relapse and the duration of first remission may be the most important factors predicting outcome after a first relapse. Patients with late relapse (over 6 months from therapy withdrawal) may have relatively good outcome with conventional chemotherapy alone (Borgmann et al., 1995; Ritchey, 1999; Uderzo et al., 1990). In contrast, children who relapse (isolated/combined medullary) during therapy or within 30 months of diagnosis seem to benefit more from HSCT than chemotherapy with an eventfree survival rates of 40-50% reported for patients in CR2 who underwent a HSCT (Kawakami et al.,1990).

It has been difficult to compare outcomes of patients treated with chemotherapy or HSCT, since patient populations are not necessarily equivalent. Patients with aggressive disease die earlier and may not be included in studies of marrow transplantation, resulting in selection bias (Tichelli et al., 1999). To address this question, matched-pair analyses have been performed for ALL CR2 patients treated with chemotherapy or HSCT (Dreger et al., 1997; Novotny et al., 1998). For patients with early first relapse, HSCT resulted in significantly better EFS rates at 5 years compared with chemotherapy alone (40% vs 17%; p<0.001) (Novotny et al., 1998). Marrow transplantation was associated with a reduced risk of relapse that was not negated by increased treatment related deaths. The difference between chemotherapy and HSCT for patients who experienced a late marrow relapse (45% DFS vs

Hematopoietic Stem Cells Therapeutic Applications 353

Dramatic responses to oral imatinib administration were observed in adult patients with CML (Druker et al., 2001; Hughes et al., 2003). However, clinical experience with imatinib in the pediatric population is limited. Several studies have shown that treatment with imatinib has resulted in prolonged molecular response with limited drug toxicity with comparable results with those in adult patients (Millot et al., 2006). Imatinib is now implemented in the primary treatment regimen for children, but the paucity of evidence on its ability to result in permanent cure and the potential complications that may arise from long-term treatment with imatinib have prevented imatinib from superseding HSCT as the primary means of curative treatment in children. The results of allogeneic HSCT in children with CML are similar to those observed in adults; HSCT-related complications such as transplant-related mortality and graft versus host disease remain significant

There is a general consensus for the need for HSCT in patients with imatinib resistance or those with advance-phase (accelerated and blast phase). (Table 3). However, issues such as when to undertake HSCT in chronic-phase CML pediatric patients or how best to treat patients who have relapsed after HSCT are still controversial. When considering HSCT vs imatinib in pediatric CML patients in early chronic phase, one must consider that the objective for treatment of childhood CML is not palliation, but cure. Hence, the possible adverse effects that stem from long-term tyrosine kinase weigh more heavily in the childhood CML population. HSCT still remains an important treatment option especially for younger patients with CML depending on physician and patient preferences. As a result of multiple clinical trials in adults that have documented great results with the use of imatinib in CML in chronic phase (87% of patients treated with imatinib showed complete cytogenetic response at 18 months with 3.3% disease progression) (O'Brian et al., 2003), this results have been applied to children, and imatinib is now also the front-line treatment for

Table 3. Definition of Accelerated Phase and Blast Phase Chronic Myeloid Leukemia (by

challenges.

childhood CML.

Adapted from Swerdlow, 2008; Speck, 1984.

WHO2008 and IBMTR Criteria)

65%) (Chessells et al., 1986; Hoogerbrugge et al., 1995) was evident but not statistically significant.

Another factor to consider when deciding whether HSCT is an option for relapse ALL is the phase of leukemia at the time of transplant because it is also highly predictive for the risk of leukemia relapse and death from non-relapse causes. In particular, patients transplanted in relapse with over 30% circulating blast, have very poor survival following HSCT (Kessinger, 1989). Patients transplanted in remission compared to those in relapse have a two to five fold reduction in risk of relapse (p=0.0001) (36).

In summary the current opinion is that the earlier the relapse the more difficult is to obtain and maintain a second complete remission, so HSCT should be consider as an elective therapeutic option in order to eradicate a resistant disease. Relapse patients who fail to achieve remission prior to transplant have very poor outcome, so HSCT should not be undertaken.

Any one or more of the following: - Cytogenetics


Table 2. Ultra High-Risk Criteria of Childhood ALL in CR1.
