Autologous Transplantation: Basic Concepts and Controversies

General Procedure for Autologous TransplantationControversiesPotential Complications of High-Dose ChemotherapyResults of Autologous TransplantationHealth-Care ImplicationsFuture DirectionsReferences

High-dose chemotherapy (HDCT) with autologous stem-cell is effective against a wide range of malignant diseases. This approach is increasingly used for treating hematologic malignancies and selected solid tumors. Since 1990, the number of autologous transplantations has exceeded the number of allogeneic transplantations.

In this section, we review the general procedure of autologous transplantation and its role in the treatment of cancer. Our objectives are to understand the basic concept of autologous transplantation and to build a knowledge to enable an understanding of its future progression.

Autologous transplantation allows patients to receive a high dose of myelosuppressive chemotherapy, followed by infusion of their own hematopoietic cells, to restore marrow function. The hematopoietic cells contain stem cells that proliferate and differentiate into mature blood lineage, such as leukocytes, platelets, and erythrocytes [1]. Stem cells can be collected from bone marrow or peripheral blood.

General Procedure for Autologous Transplantation

The general approach to autologous transplantation for malignancies involves the following steps.

Assessment of Patients

Transplantation physicians determine whether patients are appropriate candidates for autologous transplantation by performing a complete history, physical examination, laboratory studies, and staging workup of the neoplastic disease. If a patient is a suitable candidate for autologous transplantation, further tests are performed to evaluate the function of systemic organs, such as the lungs, heart, kidneys, and liver.

Induction Chemotherapy

Standard-dose combination chemotherapy can be given before autologous transplantation to reduce the tumor burden. The long-term outcome of transplantation is better in patients who have a minimum volume of disease that responds to standard-dose chemotherapy.

Stem-Cell Collection

Patients undergo stem-cell collection, cryopreservation, and storage of bone marrow or peripheral-blood progenitor (PBP) cells (blood stem cells and peripheral-blood stem cells). Bone marrow is collected from the posterior superior iliac crests by multiple aspirations while the patient is anesthetized. Marrow collection should occur at a time when the marrow is normally cellular and does not contain malignant cells. With current techniques, marrow cryopreservation can be reliably performed, and the stored cells can remain viable for more than 5 years [2-4]. PBP cells are collected by apheresis, usually by using a large-bore vascular catheter in the subclavian vein. Leukapheresis is repeated by using continuous-flow cell separation [5,6]. To collect an adequate cell dose for transplantation, 8 to 12 daily leukaphereses are required. Circulating progenitor cells are mobilized to a higher level during the recovery phase following cytoreduction and treatment with granulocyte-macrophage colony-stimulating factor (GM-CSF, sargramostim [Leukine]) or granulocyte colony-stimulating factor (G-CSF, filgrastim [Neupogen])[7,8].

High-Dose Chemotherapy and/or Radiotherapy (Preparative Regimens)

The dose of antineoplastic agents or radiation that can be administered clinically is limited by its toxic effects to normal tissues [9]. Bone marrow suppression is the dose-limiting toxicity for most chemotherapeutic agents. The doses of radiation and many drugs can be substantially escalated to more effective levels if followed by transplantation of normal hematopoietic cells, thus rescuing the patient from severe and prolonged myelosuppression. For dose-intensive therapy to be successful, the neoplasm must exhibit a dose-dependent response to chemotherapy and/or irradiation so that one (or possibly several) course of intensive combined-modality treatment can eradicate the malignant cells. Candidate neoplastic diseases are listed in Table 1. The intensity of chemotherapy required varies according to the aggressiveness of the disease, with the need to weigh the benefit-to-risk ratio. The actual preparative regimen involves chemotherapeutic drugs alone or combined with radiotherapy. After the preparative regimens are administered, intense supportive care is required to deal with complications related to prolonged neutropenia and the toxic effects of the preparative regimens.

Reinfusion of Collected Stem Cells

The marrow cells or PBP cells are infused intravenously after completion of the preparative regimens. The cells circulate transiently, and sufficient numbers of stem cells home to the marrow and restore hematopoiesis. Autologous transplantation requires a minimum of approximately 10 million to 50 million nucleated marrow cells/kg body weight or 500,000 CD34-positive cells/kg to achieve engraftment [10]. Peripheral blood counts are profoundly suppressed as a result of the effects of the conditioning treatment but generally recover within 3 to 4 weeks with marrow transplantation and within 2 to 3 weeks with PBP cell transplantation.

Administration of Colony-Stimulating Factors

Patients generally receive G-CSF, GM-CSF, or other cytokines to accelerate marrow recovery. G-CSF or GM-CSF administration is continued until the absolute neutrophil count is greater than 1,000/mm³.

Restaging of the Neoplastic Diseases

Response to the treatment is assessed after full recovery of the bone marrow.

Controversies

The major controversies surrounding autologous transplantation are listed in Table 2.

Autologous vs Allogeneic Transplantation

Autologous transplantation is less likely to produce major side effects than is allogeneic transplantation (Table 3) because the infused cells are not subject to rejection and do not mediate graft-vs-host disease (GVHD) (see "Allogeneic Transplantation"). There is also no immune-mediated graft-vs-tumor effect from the donated cells. Therefore, the most frequent cause of treatment failure is recurrence of the underlying malignancy.

Blood-Progenitor Cells Derived From Bone Marrow vs Peripheral Blood

Transplantation of a relatively small number of stem cells can reconstitute hematopoiesis and immunity in appropriately prepared recipients (Table 4). PBP cells offer an alternative source of hematopoietic cells for transplantation. They are an effective approach for patients who cannot undergo marrow harvest, such as patients who have undergone pelvic radiotherapy. PBP cells are also a potential source for patients with marrow and malignant cell involvement, although it remains to be determined whether the level of contaminating malignant cells is low in the peripheral blood [11]. Transplantation of large numbers of PBP cells results in more rapid recovery of platelets than does marrow transplantation [7,8]. A major area of research involves the development of systems for ex vivo expansion of hematopoietic progenitors from either peripheral blood or marrow [12,13].

Optimal Dose-Intensive Preparation Regimen

The most frequent cause of failure in autologous transplantation is recurrence of underlying malignant disease; this is due to either inadequate systemic cytoreduction or reinfusion of tumor contaminated marrow or PBP cells. Various approaches have been used to improve the efficacy of HDCT and/or radiotherapy. They include increasing the total delivered dosage of chemotherapeutic agents or radiation, using novel chemotherapeutic agents, and using sequential HDCT. However, although increasing the total dosage may result in increased tumor response, more toxic effects may result without improvement in survival. Different agents have been applied, but a clear-cut difference has not been seen among commonly used preparative regimens. There is interest in selecting high-dose regimens with a decreased potential for regimen-related toxicity. Multiple cycles of HDCT may improve the overall tumor response rate [14,15]. At the University of Texas M.D. Anderson Cancer Center, this approach has recently been applied to metastatic breast cancer (four cycles of HDCT with cyclophosphamide [Cytoxan, Neosar], carboplatin [Paraplatin], and paclitaxel [Taxol] with PBP cell support).

Integration of Autologous Transplantation With Posttransplantation Therapy

Relapse of malignancy is the major problem following autologous transplantation. Posttransplantation therapies using biologic therapies to eradicate minimal residual tumor are currently being studied. In allogeneic transplantation, a lower recurrence of leukemia has been seen among patients with acute and chronic GVHD. It is believed that this antitumor effect is mediated by T-cells. Rarely, a GVHD-like syndrome is seen in patients who have undergone autologous transplantation. Cyclosporine (Sandimmune) may induce this GVHD [16]. Gamma interferon (IFN-gamma, Actimmune), which upregulates major histocompatibility complex II expression, enhances this effect and is under evaluation in breast cancer [17]. Interleukin-2 after autologous transplantation in patients with acute leukemia is being evaluated. Also under investigation is alpha interferon (IFN-alfa) after transplantation in patients with lymphoma and Hodgkin's disease [18,19].

Role of Purging

A major concern with autologous transplantation is the possibility that the marrow or the PBP cells may be contaminated by malignant cells at the time of collection. Tumor can be detected by immunohistochemical staining and molecular assays. However, the clinical significance of a positive finding is unknown. A number of investigators are evaluating techniques to detect occult involvement by tumor and approaches to deplete selectively occult malignant cells from the normal marrow cells prior to cryopreservation by ex vivo treatment with antitumor monoclonal antibodies [20], antibody-toxin conjugates [21], chemotherapy [22,23], or physical techniques [24,25]. An alternative method is to select positive hematopoietic stem cells. CD34-positive cells represent less than 1% of the marrow but encompass progenitors capable of reconstituting hematopoiesis [26]. Recently, highly enriched CD34-positive cells have been selected for autologous marrow or blood stem-cell transplantation, resulting in rapid hematologic recovery [27]. The Thy-1 antigen has recently been proposed as a more restricted marker for hematopoietic stem cells [28].

Potential Complications of High-Dose Chemotherapy

In autologous transplantation, the major toxic effects are associated with dose escalation of chemotherapy and radiotherapy [29]. The most common effects are infections from granulocytopenia and systemic reactions from the conditioning regimen (Table 5). Fatal complications generally occur in 10% of patients undergoing autologous transplantation. This rate is lower than that seen with allogeneic transplantation because of the rareness of graft failure and GVHD and because of a more complete immune reconstitution.

Hematologic Toxicity From the Preparative Regimens

HDCT induces profound pancytopenia, lasting approximately 2 to 4 weeks until the stem cells restore hematopoiesis. During the period of granulocytopenia, life-threatening infectious complications may occur. GM-CSF and G-CSF have been shown to accelerate hematopoietic recovery after autologous transplantation [30,31] and to improve hematopoiesis in patients with graft failure [32]. Neither G-CSF nor GM-CSF prevents the nadir of granulocytes, but the granulocytopenic period is shortened by approximately 1 week. Neither factor affects erythrocyte or platelet recovery. Use of these colony-stimulating factors reduces the number of febrile days and shortens the period of hospitalization. Novel growth factors, including interleukin-3, interleukin-6, and interleukin-11, used alone and in combination with other factors to enhance platelet recovery, are being studied [33,34]. Thrombopoietin (c-mpl ligand) has recently been cloned and appears most promising. Clinical trials should begin in 1995 [35,36].

Organ Toxicity From the Preparative Regimens

Preparative regimens may cause severe toxic effects involving the lungs, heart, liver, nervous system, and, rarely, other tissues. Organs affected vary depending on the preparative regimens used. Fatal hepatic veno-occlusive disease occurs in approximately 5% of patients who receive transplants for leukemia [37]. This is more common in older patients, patients with preexisting liver-function abnormalities, patients receiving the most intense conditioning regimens, and patients who have received extensive previous chemotherapy.

Pneumonitis ascribed to the toxicity of the conditioning regimen occurs in 5% to 10% of patients [38]; this is particularly common with carmustine (BiCNU) or alkylating agent-based regimens and in patients who have received transplants following mediastinal radiotherapy [39,40]. This condition is often difficult to distinguish from pneumonitis related to cytomegalovirus or other infections.

Cardiac toxicity is common with high-dose cyclophosphamide regimens, particularly when combined with carmustine or other alkylating agents [41,42].

Central nervous system complications are relatively uncommon, but dementia or leukoencephalopathy may occur [43].

Endocrine complications may develop but generally are not life-threatening. Hypothyroidism commonly occurs as a delayed complication 6 months to 2 years following transplantation [44,45].

Intensive combined-modality therapy typically results in sterility for both men and women, although gonadal endocrine and ejaculation functions usually remain intact [46-48]. Cataracts are a common delayed complication of total-body irradiation (TBI)[49].

Toxic effects to the bladder as a result of high-dose cyclophosphamide chemotherapy is a common problem [50,51]. This is probably mediated by acrolein, a metabolite of 4-hydroxycyclophosphamide that is toxic to transitional epithelium. Hemorrhagic cystitis may develop acutely or as a delayed complication weeks to months later. Concurrent treatment with mesna (Mesnex), a uroprotective agent that binds to acrolein, has been reported to reduce the urinary toxicity of cyclophosphamide in patients with marrow transplants without inhibiting the therapeutic effects of cyclophosphamide.

Posttransplant Immunodeficiency: Recipients of autologous transplants undergo a period of immunodeficiency, but their recovery appears more rapid than after allogeneic transplants, and posttransplant infections are less severe than in allogeneic transplant recipients [52].

Posttransplant Infections: A number of infectious complications may develop while patients are undergoing autologous transplantation [53]. There are high incidences of bacterial and fungal infections during profound and prolonged granulocytopenia. Mucosal herpes simplex infections also are common during this period but seldom disseminate; prophylactic treatment with acyclovir may decrease their incidence [54]. Patients who have received autologous transplants recover immunity more quickly than do patients who have received allogeneic transplants and have a much lower risk of infection after recovery of peripheral-blood counts. Late infections develop in a small fraction of autograft recipients. Pneumocystis carinii infection most frequently occurs in patients with lymphoid malignancies; prophylactic trimethoprim/sulfamethoxazole is indicated. Cytomegalovirus infection may occur in heavily immunocompromised patients.

Secondary Malignancies: HDCT and radiotherapeutic regimens are potentially carcinogenic and may predispose a patient to the development of secondary malignancies. A small number of second malignancies have been reported in long-term survivors of marrow transplantation [55,56]. Several cases of immunoblastic sarcoma arising in donor cells have been reported. Lymphoproliferative disorders related to Epstein-Barr infection may occur [57,58], particularly in heavily immunosuppressed patients receiving intravenous antithymocyte globulin, anti-T-cell antibody therapy, or human leukocyte antigen (HLA)-mismatched or T-cell-depleted transplantation. The incidence of treatment-induced malignancies may increase with further follow-up, particularly for radiation-induced tumors that may have a long latency, such as thyroid carcinoma. Recently, secondary acute leukemia and myelodysplastic syndrome have developed in recipients of autologous transplants [59,60]. It is unclear whether these conditions are related to the transplantation or are the cumulative effect of previous therapy. It is possible that the proliferative stress after HDCT promotes the evolution of leukemia.

Result of Autologous Transplantation

In this section, we discuss the outcome and current controversies associated with autologous transplantation for various neoplastic diseases (Table 6). The reader is referred to other chapters in this volume on specific diseases for additional discussion of transplantation indications and outcome.

Acute Myelogenous Leukemia

Autologous transplantation has been evaluated for use in patients with acute myelogenous leukemia (AML) who lack an HLA-identical donor [61-63]. Patients undergo collection of marrow or PBP cells while in remission. The major limitation is the likelihood that the remission marrow or PBP cells may be contaminated by small numbers of leukemia cells. The autologous stem cells lack the favorable graft-vs-leukemia effect seen with allograft. For patients receiving autologous transplants while AML is relapsing [64,65], the major problem has been the rapid relapse of leukemia; the median duration of remission has been 3 to 5 months, and less than 10% of patients survive 1 year. Better results have occurred with autologous transplantation in patients in first or second remission [62,66-69]. Relapse of leukemia remains a major problem, but approximately 20% to 40% of patients who receive transplants in second remission achieve a disease-free survival duration of longer than 2 years. These data indicate that this approach may be successful and that relapse of leukemia may not invariably occur. The timing of transplantation is important. The longer the interval from remission to transplantation, the less likely is leukemic contamination.

A number of purging systems have been explored to deplete occult leukemia cells from the harvested marrow or PBP cells in vitro before cryopreservation. Immunologic approaches using anti-AML monoclonal antibodies [70,71], hyperthermia [72], or pharmacologic agents (such as 4-hydroperoxycyclophosphamide or mafosfamide [23,73,74]) have been studied. Although some of the best results are reported in series using purged marrow, no controlled studies have been performed, and the efficacy of purging remains to be determined.

Following autologous transplantation, patients may relapse either from leukemia cells that survive the systemic HDCT or from leukemia cells present in the transplanted marrow. Recent studies in which the autologous marrow was marked in vitro using a retrovirus demonstrated the presence of the marker within leukemia cells after relapse of disease, indicating that malignant cells present in the autologous marrow infusion may contribute to relapse [75].

Poor prognostic factors include secondary leukemia, short interval of initial remission, and cytogenetics. Neither central nervous system involvement nor FAB classification affects the outcome. Development of effective purging techniques is probably necessary. Novel systemic agents to improve antileukemic efficacy, including the use of etoposide in the preparative regimen, are under evaluation. Use of radionuclide-conjugated antimyeloid monoclonal antibodies or bone-seeking radioconjugates can target the malignant cells or marrow and minimize systemic toxic effects [76-78].

Acute Lymphoblastic Leukemia

Autologous transplantation has been evaluated in patients with acute lymphoblastic leukemia (ALL) [79-82]. Unlike the situation in AML, in ALL, a number of monoclonal antibodies to leukemia-associated antigens that are nonreactive with normal hematopoietic progenitors are available [20,83,84]. They include antibodies to the common ALL antigen (CALLA) or T- or B-cell antigens. A number of patients have received autologous transplants using marrow that was treated ex vivo with one or more of these antibodies and complement [79,84-87]. Although each of these antigens is expressed on subpopulations of normal lymphoid cells, the antigens are not present on hematopoietic progenitors. Engraftment and immunologic recovery have consistently occurred. Limitations of this technique include probable antigenic heterogeneity among neoplastic cells. It is unclear whether leukemia stem cells express these cell-surface antigens. Select patients with ALL in second remission have achieved prolonged remissions after receiving intensive chemotherapy, TBI, and autologous marrow transplantation with anti-CALLA antibody and complement-treated marrow [79,86]. These data are difficult to interpret because many of the successful cases reported involved patients who had a relatively good prognosis with conventional treatment (such as patients whose disease relapsed after a long first remission and in whom maintenance therapy was discontinued. Results in patients with average or poor prognostic features have been much less encouraging.

Chronic Myelogenous Leukemia

Allogeneic transplantation is an effective treatment of chronic myelogenous leukemia (CML). However, because many patients lack a histocompatible donor for transplantation, autologous transplantation has been explored as an alternative approach [88]. Autologous transplantation for CML involves collection and cryopreservation of marrow or PBP cells during the chronic phase of the disease. When the disease progresses to the accelerated phase, patients receive intensive chemotherapy alone or in combination with TBI, followed by reinfusion of cryopreserved autologous cells [89,90]. The objective of this approach is to restore the chronic phase. Because Philadelphia-chromosome-positive cells are reinfused, cure is not possible. Some patients have transiently recovered apparently normal hematopoiesis without the Philadelphia chromosome. However, the Philadelphia-chromosome-positive leukemia cells usually become dominant again within a short interval, and the disease recurs.

A major limitation of autologous transplantation for advanced CML is resistance of acute-phase cells to intensive chemoradiotherapy. Although most patients who receive transplants when their disease is in the accelerated phase or in blast crisis achieve a brief second chronic phase, its median duration is only 4 months, and fewer than 30% of patients survive 1 year. This therapy thus must be considered of marginal benefit and cannot be routinely recommended.

A gene-marking study indicated that tumor contamination of the autograft is one of the reasons for the recurrence of disease [91]. Therefore, attempts have been made to prolong the duration of the chronic phase by performing autologous transplantation in patients whose disease is still in the chronic phase using marrow collected in cytogenetic remission or the early chronic phase. Another recent approach is to collect autologous PBP cells when they contain predominantly diploid cells. PBP cells are collected from patients whose disease is in partial or complete cytogenetic remission after interferon or intensive chemotherapy. The cells may be treated in vitro to separate normal cells from leukemia cells by a variety of developmental approaches, including separation on the basis of HLA-DR expression or treatment in long-term culture [92-95]. Because of the likelihood of residual disease after transplantation, enhanced cytotoxic preparative regimens and posttransplantation biologic therapy, such as that with IFN-alfa, to eliminate the minimal residual disease are being studied.

Chronic Lymphocytic Leukemia

Recently, autologous transplantation with monoclonal antibody-purged autologous marrow has been evaluated and has produced complete remissions (CRs) in patients with advanced disease [96]. Allogeneic transplantation was more effective in young patients with an HLA-identical donor. Autologous transplantation requires a large-scale study and long-term follow-up to definitely assess its long-term benefits.

Lymphoma

Autologous transplantation has been extensively studied in patients with non-Hodgkin's lymphoma [97,98]. Most of these patients have been treated for high- and intermediate-grade lymphomas that failed to respond or that relapsed after treatment with standard combination chemotherapy. Patients have received either intensive chemotherapy alone, such as with BEAC (carmustine, etoposide [VePesid], cytarabine, and cyclophosphamide) or a cyclophosphamide plus TBI regimen [98-102]. Results have been highly variable. Most patients achieve CR with this treatment, and approximately one third survive in remission for several years.

The best results have been noted in patients treated in second remission or in patients with relapsed disease that is still responsive to chemotherapy [103]. Recently, encouraging results have been reported in patients receiving autologous transplants in partial remission (PR) after initial induction therapy [104]. Toxic reactions have been a major problem, particularly in patients with heavily pretreated disease and in debilitated patients; severe hepatic, cardiac, and pulmonary reactions may occur. Studies have investigated the use of IFN-a as a posttransplantation therapy [18].

Autologous transplantation in low-grade lymphoma (LGL) has shown encouraging results with high-dose cyclophosphamide plus TBI; 20% to 60% of patients with relapsed LGL survive from 3 to 5 years free of recurrence, depending on prognostic features [101,102,105]. One concern of autologous transplantation for patients with LGL is the propensity of this disease to involve the bone marrow during the course of its natural history and the potential of this disease for late relapse.

Techniques have recently been developed for selectively purging malignant lymphoid cells from normal marrow cells using ex vivo treatment with monoclonal antibodies against lymphoid cell-surface antigens that do not cross-react with normal hematopoietic progenitors. Normal marrow cells can be separated from malignant B-cells by using monoclonal antibody and complement treatment or immunomagnetic beads [106,107]. Many institutions employ ex vivo treatment of the harvested autologous marrow to deplete malignant cells. For clinical marrow harvests, purging techniques generally achieve an approximately 2 to 3 log reduction of malignant cells, and these systems cannot effectively deplete cells from patients with clinically involved marrow. Recently, Gribben et al reported significantly improved disease-free survival in patients receiving autologous transplants that were successfully purged of evidence of residual lymphoma as assessed by bcl-2 gene rearrangement by polymerase chain reaction [106-109]. The efficacy of purging remains to be definitively established, but the elimination of bone-marrow contamination is likely to be increasingly important with the evolution of effective preparative regimens to eradicate systemic disease successfully.

Hodgkin's Disease

Nearly 30% of patients with Hodgkin's disease fail to achieve a durable CR. Autologous transplantation can produce durable remissions in selected patients with Hodgkin's disease that is chemotherapy sensitive [110-112]. Patients with systemic relapse after receiving combination chemotherapeutic regimens, such as MOPP (mechlorethamine [Mustargen], vincristine [Oncovin], procarbazine [Matulane], and prednisone) and ABVD (doxorubicin [Adriamycin, Rubex], bleomycin [Blenoxane], vinblastine, and dacarbazine), with a first-remission duration of longer than 12 months can be retreated with another round of standard-dose chemotherapy and can achieve a CR rate of more than 90%, although most of these patients ultimately relapse [113]. However, when patients have relapsing disease within 1 year, salvage chemotherapy with MOPP, ABVD, or comparable regimens produces a CR rate of only 29% to 50% and a disease-free survival rate of less than 20% at 5 years [114,115]. Favorable prognostic features include first remission for more than 1 year, good performance status, involvement of a limited number of nodal sites, absence of visceral disease, and absence of B symptoms. For patients in second systemic relapse, long-term disease-free survival with conventional chemotherapy is rare. For patients with recurrent Hodgkin's disease, treatment with HDCT or chemotherapy plus TBI with autologous transplantation results in a CR rate of more than 50% to 80% and a disease-free survival rate of 20% to 60% at 3 to 5 years [106,116-120]. Although no controlled trials have been reported, results in patients with initial remissions of less than 1 year appear superior to those reported with standard-dose salvage chemotherapy.

Controversy remains regarding the selection of patients for autologous transplantation [121] and the definition of the most effective preparative regimen. Initial studies used cyclophosphamide in combination with TBI [122-124]. TBI is not an ideal treatment of Hodgkin's disease; it is not possible to administer whole-body doses greater than 15 Gy in humans, and radiation doses exceeding 40 Gy are necessary to control active sites of Hodgkin's disease when local radiotherapy is used. In addition, patients with Hodgkin's disease frequently receive mediastinal radiotherapy as part of their initial treatment; these patients have a high rate of radiation pneumonitis if they are later treated with TBI. HDCT regimens have been better tolerated. The most commonly used preparative regimens involve therapy with CBV (cyclophosphamide, carmustine, and etoposide) [118,125]. The doses used have varied widely from institution to institution: 4.5 to 6.0 g/m² cyclophosphamide, 300 to 600 mg/m² carmustine, and 1,200 to 2,400 mg/m² etoposide. With increasing dose, there is an increased rate of extramedullary toxic effects, and treatment-related death rates have ranged from 5% to more than 20%. It is unclear whether the higher-dose regimens result in superior long-term disease-free survival. Other regimens, such as etoposide plus melphalan (Alekeran) [127] and CBV plus cisplatin (Platinol) [128] have been studied, but there is no evidence that any of them is superior to CBV therapy.

Prognostic factors for response and survival after autologous transplantation include age, performance status, disease stage at transplantation, number of extranodal disease sites, number of previous treatment regimens, and response to previous chemo- and radiotherapy. These prognostic factors are similar to those for patients receiving salvage chemotherapy. Patients with all favorable prognostic features have a disease-free survival rate of more than 70% at 4 years, compared with approximately 20% in patients with adverse prognostic factors [118].

Patient selection and disease-related factors have such a major impact on response and survival rates that it is difficult to compare treatment regimens among institutions or in different subsets of patients in which prognostic features vary or are not well defined. It is also difficult to compare autologous transplantation with salvage chemotherapy because of differences in patient eligibility and selection, time censoring, and prognostic factors. The optimal roles and the interaction of salvage chemotherapy and autologous transplantation are uncertain. Some institutions have performed autologous transplantation as the first treatment of relapsed disease. Others have instituted several courses of a salvage chemotherapy program, such as DHAP with collection of autologous marrow between courses and institution of dose-intensive therapy with autologous transplantation after achieving maximal cytoreduction with the salvage regimen. This latter approach has the advantages of providing treatment immediately after relapse, collecting the marrow between courses, and using the HDCT at the time of minimal tumor burden.

Studies are in progress involving radioimmunoconjugates that localize within the tumor and selectively irradiate the malignancy with minimal systemic toxic effects [129,130], such as yttrium-90-labeled antiferritin antibodies. High-dose treatment with radioimmunoconjugates often causes severe myelosuppression, which requires autologous marrow or PBP cell infusion for hematologic recovery. Lower doses could potentially be given before or after HDCT as a means of producing additional cytoreduction. PBP cell collection is an effective approach in patients who cannot undergo marrow harvest, such as patients who have received pelvic irradiation or who have extensive bone involvement. It remains to be determined whether the level of contaminating malignant cells is lower in the peripheral blood than in the marrow of these patients; nonetheless, successful transplantation using PBP cells has been reported in patients with marrow involvement [131].

Multiple Myeloma

Recently, autologous transplantation has been studied in patients up to 65 years of age with multiple myeloma [132]. Favorable results also have been reported with PBP cell transplantation [133,134]. Patients most likely to benefit have primary resistant or responding disease with low beta2-microglobulin and lactate dehydrogenase levels treated within 1 year of diagnosis [135].

Pediatric Solid Tumors

Autologous transplantation may be useful in the treatment of several pediatric tumors that are highly sensitive to a number of chemotherapeutic agents and radiation yet have a poor prognosis in patients with advanced disease, such as neuroblastoma and Ewing's sarcoma. Patients with highly advanced or recurrent neuroblastoma have a dismal prognosis with standard treatment [136]. Several studies using high-dose combined-modality therapy and allogeneic or autologous transplantation in such patients are currently in progress [137-139].

Neuroblastoma frequently involves the bone marrow. Monoclonal antibodies to neuroblastoma-related antigens can be used to detect microscopic marrow involvement and to purge metastatic neuroblastoma cells from the marrow prior to cryopreservation [24]. PBP cell transplantation has also been used, although tumor cells may contaminate blood [11]. Gene-marking studies of autologous marrow demonstrate that malignant cells infused in the autotransplant may contribute to relapse [75]. The most encouraging results have been reported with treatment of patients at an earlier point in their disease and with the use of more intensive pretransplant conditioning regimens involving combination chemotherapy plus TBI in addition to either allogeneic or autologous marrow transplantation.

Patients with Ewing's sarcoma are also potential candidates for autologous transplantation. This tumor is responsive to chemotherapy and irradiation and rarely involves the bone marrow. Either high-dose melphalan or cyclophosphamide plus TBI [140] in combination with autologous transplantation can produce a CR in patients with relapsed Ewing's sarcoma, but these responses are usually brief. Intensive chemoradiotherapy with autologous transplantation may be more effective in consolidation treatment as part of first-line therapy [141].

Breast Cancer

Breast cancer now represents the most common disease treated by autologous transplantation. For metastatic hormone-refractory breast cancer treated with standard-dose combination chemotherapy, such as CMF (cyclophosphamide, methotrexate, and fluorouracil or FAC (fluorouracil, doxorubicin, and cyclophosphamide), increasing the dose intensity improves both CR and PR rates and prolongs the interval to disease progression [142]. Standard-dose chemotherapy produces a CR rate of 15% to 25% and an overall response rate of 50% to 70%. The median response duration is typically 8 to 12 months. The median survival duration ranges from 12 to 18 months, and less than 5% of patients remain disease free at 5 years. The most effective HDCT regimens used with autologous transplantation include combinations of alkylating agents and related drugs, including cyclophosphamide, ifosfamide (Ifex), melphalan, thiotepa (Thioplex), carmustine, cisplatin, or carboplatin [143,148].The doses of these agents typically can be increased threefold over standard doses when followed by autologous transplantation.

Studies in patients with chemotherapy-responsive metastatic breast cancer have documented that this approach significantly increases the CR rate to more than 50% and that approximately 20% of patients survive longer than 5 years free of recurrent disease. Recently, to improve the efficacy of HDCT, several treatment courses have been evaluated [149,150]. Favorable prognostic factors in these patients include responsiveness to standard-dose chemotherapy, limited tumor bulk and number of disease sites, absence of liver involvement, and good performance status [146,151]. However, this apparent improved outcome may be due to patient selection bias [152]. Randomized prospective studies comparing standard chemotherapy with HDCT currently are underway.

Because dose-intensive therapy is most effective in patients with a minimal burden of chemotherapy-sensitive tumor cells, the optimal use of this approach may be as adjuvant therapy in patients whose local-regional breast cancer is at high risk for relapse [148,153,154]. HDCT and autologous transplantation have recently been evaluated as adjuvant therapy for patients with “high-risk” stage II or III disease (generally defined as stage II disease with 10 or more positive axillary nodes or stage III disease). Five-year disease-free survival rates with standard adjuvant therapy range from 25% to 57%. In preliminary studies, approximately 70% of these high-risk patients survive free of relapse at 5 years after receiving HDCT and autologous transplantation [148]. It is difficult to compare directly the results of HDCT with standard-dose chemotherapy. Patients referred for HDCT must be young (generally younger than age 60), have good organ function and performance status, and must be clinically stable so they can be transferred to the transplantation center. Patients receiving HDCT are thus highly selected, and controlled clinical studies with either case controls or a randomized control group are necessary for definitive analysis [151,155,156].

Several prospective, randomized studies are ongoing for patients with high-risk local-regional disease to assess the role of HDCT and autologous transplantation in this setting. Dose-intensive therapies must be integrated with other modalities into the overall treatment of breast cancer. This treatment is most likely to be curative if administered at a time of minimal tumor burden and before the evolution of drug resistance. The ideal timing should be as adjuvant therapy in patients with high-risk local-regional disease in whom alternative therapies are likely to fail and in patients with metastatic disease in CR from standard-dose chemotherapy.

Relapse remains a major problem, and the use of biologic or immunologic therapies for minimal residual breast cancer after autologous transplantation is under evaluation. As previously described, autologous GVHD is induced by cyclosporine and interferon is under evaluation [16,17].

Purged bone marrow with 4-hydroperoxycylcophosphamide [157-159] or CD34-positive selected PBP cells is considered to reduce tumor contamination [160-163]. Controlled trials are needed, however, to demonstrate that purging improves clinical outcome.

Other Solid Tumors

In adults, other chemotherapy-responsive solid tumors, such as ovarian cancer [164], testicular germ-cell carcinomas [165-167], small-cell carcinoma of the lungs [168,169], and melanoma [170], are under study.

Health-Care Implications

There is controversy regarding in which clinical settings HDCT and autologous transplantation should be considered as an experimental procedure [171-174]. In experimental therapy, the risks and benefits are unknown. An established treatment is one in which there is sufficient experience to define the risks and the anticipated benefits; unfortunately, established systemic therapies for most advanced cancers are known to have only limited effectiveness. Many insurance carriers exclude coverage for experimental therapy, and some have denied payment for HDCT and autologous transplantation on this basis. This is inappropriate. Thousands of patients have received this therapeutic approach, and the results are consistent and well documented. For the indications previously discussed, nearly every study has determined that the response rate is improved over that with standard-dose alternatives, and a fraction of patients have achieved a prolonged disease-free survival. It is clear, however, that important questions remain regarding the optimal use and role of this form of therapy. Use of autologous transplantation should be restricted to cancer research centers, and patients should be enrolled in ongoing clinical trials.

The cost of HDCT and autologous marrow or PBP cell transplantation is primarily related to the length of hospitalization for supportive care, blood-product transfusions, and antibiotic treatment of granulocytopenic infections. The typical length of hospitalization is 3 to 4 weeks. There has been a recent effort to transfer a major portion of care to outpatient clinics. Well-organized outpatient infusion centers can administer dose-intensive treatment to clinically stable patients, and with the rapid hematologic recovery induced by growth factors and PBP cells, patients may not routinely require admission.

Future Directions

The collection of marrow or PBP cells offers the potential for ex vivo genetic therapy to improve treatment results. Transfection of genes for drug resistance, such as MDR1, into normal marrow cells may allow better tolerance to subsequent chemotherapy with agents such as doxorubicin, vinca alkaloids, and paclitaxel [175]. Alternative strategies include transfecting cytokine genes into hematopoietic cells or directly into the malignant cells to enhance immune reactivity against the tumor [176,177]. Improvement in the results of autologous transplantation for solid tumors requires the development of more effective treatment regimens that are not excessively toxic to normal tissues. A number of chemotherapeutic agents, including cyclophosphamide, melphalan, busulfan (Myleran), carmustine, lomustine (CCNU), mitomycin (Mutamycin), etoposide, and amsacrine, can be escalated to two to five times their standard dosage in the setting of autologous marrow transplantation. Further phase I and II clinical studies are required to determine the efficacy and nonhematopoietic toxicity of other chemotherapeutic agents in high doses. Candidate drugs should have documented efficacy in standard dosage, should have toxic effects limited primarily to the bone marrow, and should lack substantial nonmarrow toxic effects.

Novel classes of drugs, including anthrapyrazoles, topoisomerase-I inhibitors, and taxanes, have activity against many cancers and may be important components of future high-dose combination chemotherapeutic regimens. Approaches with targeted radiation therapy, such as monoclonal antibody-radionuclide immunoconjugates, are under active evaluation as a means to target radiotherapy to the tumor; this approach results in few systemic toxic effects, other than myelosuppression, which can be ameliorated by autologous marrow or blood stem-cell transplantation.

It may be possible to improve results further using strategies to overcome drug resistance mechanisms, such as the administration of inhibitors to p-glycoprotein or chemoprotectant agents. Kinetic resistance and the presence of poorly vascularized tumor masses are factors that limit the effectiveness of a single course of HDCT. Greater overall dose intensity may be achieved by repeated courses of therapy. The ability to collect large numbers of marrow and peripheral-blood hematopoietic cells allows the administration of two to four courses of treatment [14,15]. Nonhematopoietic toxic effects may be cumulative, and some dose reduction is necessary for multiple-course regimens to achieve optimal cytoreduction with an acceptable level of toxicity.

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