The use of bone marrow and peripheral blood stem cell transplantation in the treatment of cancer
Authors: F. R. Appelbaum
Journal: CA A Cancer Journal for Clinicians (1996)

Bone marrow or peripheral blood stem cell transplantation is used in the treatment of cancer for two reasons. First, transplantation permits exploitation of the steep dose-response relationship seen in some tumors by allowing administration of doses of systemic chemotherapy and radiotherapy that without transplantation would cause unacceptably severe or lethal myelosuppression. Second, transplantation of allogeneic marrow confers an antitumor effect, separate from the effects of chemoradiotherapy. The first successful bone marrow transplants in humans were performed in the late 1960s. This year, it is estimated that over 15,000 patients will undergo the procedure worldwide (Fig. 1). The first suggestion that bone marrow transplantation might be possible occurred in 1949 when Jacobson et al1 made the observation that mice could survive otherwise lethal total body irradiation if the spleen was protected by lead foil. A similar radioprotective effect was seen if bone marrow from one mouse was given intravenously to a radiated recipient of the same strain.2 By the mid-1950s, several laboratories had shown, using cytogenetic markers, that the radioprotective effect of bone marrow transplantation was due to the replacement of the damaged hematopoietic system of the host with healthy cells of donor origin.3 The potential clinical implications of these studies were noted, and in 1959, the first attempts to treat leukemia using high-dose chemoradiotherapy followed by syngeneic marrow transplantation were initiated by Dr. E. Donnell Thomas.4 Initial attempts to apply transplantation outside the setting of identical twins were unsuccessful because of lack of understanding of the human histocompatibility system. In the late 1950s and early 1960s, human leukocyte antigens (HLA) and their importance in histocompatibility were first recognized. By the mid-1960s, it was demonstrated in an outbred species (the dog) that matching at the major histocompatibility complex allowed for successful allogeneic marrow transplantation.5 The work of Dr. Thomas and fellow investigators led to the first successful allogeneic transplants for leukemia in the late 1960s6 and the gradual acceptance of this therapy during the 1970s.7 Autologous marrow transplantation was first successfully employed to cure patients with lymphoma in the late 1970s8 and became widespread in the 1980s. Today, the annual number of autologous transplants surpasses that of allogeneic transplantation. In 1990, a Nobel prize in medicine was awarded to E. Donnell Thomas for his contributions to this field (Table 1). Estimated number of allogeneic and autologous marrow transplants performed worldwide by year. Data from the Statistical Center of the International Bone Marrow Transplant Registry and the Autologous Blood and Marrow Transplant Registry. Several features of human bone marrow make the transplant procedure feasible. The first is the remarkable regenerative capacity of marrow. In mice it has been demonstrated that the transfer of a single hematopoietic stem cell can result in complete and sustained hematopoietic reconstitution of a lethally irradiated recipient.9 While human bone marrow has never been put to this test, transplantation of considerably less than 10 percent of a donor's total body marrow regularly results in complete and sustained replacement of a patient's entire hematopoietic system. After the transplant, donor marrow cells normally produce all of the patient's red cells, platelets, granulocytes, and T lymphocytes and B lymphocytes as well as the patient's pulmonary alveolar macrophages, Kupffer's cells of the liver, osteoblasts, Langerhans' cells of the skin, and microglial cells of the brain. A second feature of marrow which makes transplantation practical is that after intravenous infusion, marrow cells have the capacity to home to the marrow space. The mechanisms by which this happens are not entirely understood, but a remarkably high percentage of primitive hematopoietic cells appear to end up in the marrow, in some murine studies as many as 50 percent.10 Current studies suggest that early hematopoietic cells are retained in the marrow because marrow endothelial cells express members of a family of cell adhesion molecules termed "selectins," which bind to carbohydrate-based ligands on early hematopoietic cells.11 An additional characteristic of marrow stem cells that has made autologous transplantation feasible is their ability to survive cryopreservation with little, if any, damage. Using relatively simple techniques of freezing and thawing, cryopreserved autologous marrow is virtually as effective as fresh marrow in providing protection after otherwise lethal total body irradiation.12 Cryopreserved autologous marrow is virtually as effective as fresh marrow in providing protection after total body irradiation. An identical twin, when available, is the best possible donor. With syngeneic marrow, there are fewer complications than with allogeneic marrow transplantation, and unlike autologous marrow, marrow from a healthy identical twin cannot be contaminated with tumor cells. Syngenicity is easily established by DNA typing using restriction fragment length polymorphisms. Allogeneic marrow transplantation can be performed using HLA-identical sibling donors, other HLA-matched or HLA-mismatched family members, or HLA-matched unrelated donors. The best results occur with sibling donors who are identical with the patient for HLA class I and class II determinants. The genes encoding HLA are located on chromosome 6 and are codominantly expressed so that the probability of HLA-identity between any two siblings is 25 percent. Given the average family size in the United States, the chance of having an HLA-matched sibling is about 35 percent. The formula for calculating the chance that a patient has an HLA-identical sibling is 1-(0.75)n where n equals the number of siblings. HLA class I antigens (usually referred to as HLA-A and HLA-B) are defined using alloantisera in microcytotoxicity assays. HLA class II antigens are encoded by genes located within the HLA-D region and are termed DP, DQ, and DR. DQ and DR antigens can be identified by alloantisera, but identification of Dp requires cellular techniques, such as mixed lymphocyte culture reactions or more current molecular techniques such as sequence-specific oligonucleotide probe hybridization. While the best results with allogeneic transplantation have been achieved using HLA-identical sibling donors, transplants using family member donors identical with the patient for one haplotype but mismatched for a single locus on the other (A, B, or D) result in nearly equal survival, albeit with a higher incidence of graft-versus-host disease (GVHD).13,14 The results of transplants using family member donors mismatched for two or more loci are considerably worse with more GVHD, more graft rejection, and decreased survival.13,14 Following initial reports that transplantation could be successfully performed using an HLA-matched unrelated donor, there has been a rapid increase in this activity.15,16 Currently, more than 1.3 million normal individuals have volunteered to serve as marrow donors in the United States alone, making the odds of finding an A, B, and D matched unrelated donor about 50 percent.17 On average, it takes about four months from the time a search is initiated to identify a donor and initiate a transplant. Analysis of the first several hundred patients transplanted from unrelated donors suggests that GVHD is more common and long-term cure rates are slightly lower than with the use of matched family members.18,19 Autologous transplantation involves removing and usually cryopreserving a patient's own marrow and reinfusing that marrow to reestablish hematopoietic function after the administration of high-dose chemotherapy or chemoradiotherapy. Deciding the type of transplantation to recommend for any individual patient is complex. Autologous transplantation has the advantage of avoiding GVHD and associated complications but has the disadvantage of potentially containing viable tumor cells and lacking a graft-versus-tumor effect. Because autologous marrow may contain viable tumor cells, numerous strategies have been developed to reduce the number of tumor cells in autologous marrow. Removal of tumor cells (negative selection) using antibodies together with complement, toxins, or immunomagnetic beads is very efficient, removing three to four logs of tumor cells from marrow.20,21 In vitro treatment of marrow with chemotherapy has been studied, as has removal of tumor cells using short-term in vitro culturing of marrow cells.22–24 Techniques involving positive selection of normal hematopoietic stem cells to separate them from tumor cells are also being tested.25 Although gene marking studies have definitively demonstrated that tumor cells in marrow can contribute to relapse,26 it has not been established whether the techniques mentioned above can prevent this outcome. It is also not firmly established how these techniques affect normal marrow function. Several retrospective analyses suggest that purging might be effective in acute myeloid leukemia (AML) and B-cell non-Hodgkin's lymphoma, but prospective, controlled studies have not been performed.21,27 For several decades, it has been recognized that hematopoietic stem cells circulate in the peripheral blood, albeit in very low numbers. Initial studies in animal models demonstrated that at least 10 times more mononuclear cells were needed to rescue animals from lethal total body irradiation if collected from peripheral blood as compared with marrow.28,29 predictably, initial attempts to use peripheral blood stem cells as a source of hematopoietic grafts were complicated by the large number of phereses required (often seven or more) and by slow engraftment.30 Recently, it has been shown that administration of chemotherapy and/or hematopoietic growth factors leads to a marked rise in the number of hematopoietic progenitors in the peripheral blood, measured either as colony-formed units or as CD34+ cells. This has triggered intensive study of the use of peripheral blood stem cells as a substitute for marrow.31–33 The results have been dramatic. In the autologous setting, with one to three leukaphereses after treatment with granulocyte colony-stimulating factor (G-CSF) or granulocyte-macrophage colony-stimulating factor (GM-CSF), a sufficient number of cells for engraftment can usually be collected. More than 1.3 million individuals in the United States have volunteered to serve as marrow donors. Recovery after engraftment using mobilized peripheral blood stem cells is considerably faster than recovery after using marrow.34,35 Similar results have been demonstrated using G-CSF mobilized cells for syngeneic transplantation, and preliminary results suggest the same can be done in the allogeneic setting.36 Concern about the use of peripheral blood cells for autologous transplants centers around the possibility that contamination with tumor cells is greater than with autologous marrow. For allogeneic transplantation, there is the concern that the amount of T-cell contamination is higher than with marrow. However, given the rapid reliable engraftment that has been demonstrated and the fact that the technique avoids a surgical procedure for the donor, it seems likely that mobilized peripheral blood properly manipulated to remove autologous tumor cells or reduce the number of allogeneic T cells will soon replace marrow as the preferred source of stem cells for use after myeloablative therapy in most circumstances. Following identification of the source of stem cells, the next step in the transplant procedure is the administration of high-dose chemotherapy or radiotherapy or a combination of the two. The goal of the preparative regimen is to eliminate the malignancy and in allogeneic marrow transplantation to sufficiently immunosuppress the patient to allow engraftment. In developing transplant preparative regimens, most investigators have focused on the use of agents that have high activity against the malignancy being treated and also have myelosuppression as their dominant dose-limiting toxicity in the nontransplant setting. Thus, the agents most commonly used are alkylating agents (cyclophosphamide, busulfan, thiotepa, melphalan, carmustine), etoposide, cytarabine, and total body irradiation. The choice of preparative regimen is determined by the particular clinical situation, taking into account the disease under treatment, the age and health of the patient, and the source of marrow. Marrow is usually obtained from the donor's anterior and posterior iliac crests with the donor under spinal or general anesthesia. A total marrow volume of 10 to 15 ml/kg of donor weight is usually obtained with each aspiration site limited to 3 to 5 ml to avoid excessive dilution with peripheral blood. The heparinized marrow is filtered through 0.3-mm and 0.2-mm screens to remove bone spicules and fat. The marrow may require further in vitro treatment to remove unwanted cells, including removing donor red cells to avoid a hematolytic transfusion reaction in the setting of an ABo-incompatible transplant, donor T cells to attempt to avoid GVHD, or tumor cells from autologous marrow as discussed earlier. The risk involved in marrow donation is small. In seattle, for example, there were six serious but nonfatal complications among 1,220 consecutive donations.37 Peripheral blood stem cells are usually collected using continuous flow apheresis techniques from donors previously treated with hematopoietic growth factor alone or after chemotherapy. In seattle, attempts are made to collect a minimum of 5 × 106 CD34+ cells/kg based on studies demonstrating consistent rapid engraftment when this minimum cell dose is met.38 Neutrophil recovery after autologous transplantation for malignant lymphoma. Data on the use of marrow alone or marrow plus granulocyte-macrophage colony-stimulating factor (GM-CSF) from Nemunaitis et al.39 The curve for recovery with granulocyte colony-stimulating factor (G-CSF) mobilized peripheral blood stem cells (PBSC) from Bensinger et al.38 Marrow and peripheral blood stem cell infusions are usually well tolerated although patients sometime develop fever, cough, or mild shortness of breath. Slowing the infusion usually alleviates these symptoms. The rate of engraftment depends on the source of stem cells, the use of hematopoietic growth factor, and the choice of prophylaxis against GVHD. The most rapid engraftment is seen with peripheral blood stem cells, where recovery to granulocyte counts of 100/mm3 usually occurs by day 10 and 500/mm3 by day 12.34 If marrow rather than peripheral blood is used, the granulocyte count usually reaches 100/mm3 by day 16 and 500/mm3 by day 22. This rate can be accelerated by four to six days with the use of G-CSF or GM-CSF posttransplant (Fig. 2).39,40 The use of methotrexate after allogeneic transplant delays recovery by an average of four days.41 platelet recovery generally occurs shortly after granulocyte recovery. Following the standard preparative regimen of cyclophosphamide and total body irradiation, nausea, vomiting, and mild skin erythema develop immediately in almost all patients. Occasionally, hemorrhagic cystitis is seen despite bladder irrigation or mesna therapy, and rarely (less than two percent of cases), acute hemorrhagic carditis can develop. Oral mucositis inevitably develops at about five to seven days posttransplant and usually requires narcotic analgesia. Studies at the Fred Hutchinson Cancer Research Center suggest that self-administration of narcotics using a pump provides the greatest patient satisfaction and, surprisingly, uses a lower cumulative dose of narcotics.42 By 10 days posttransplant, most patients have developed complete alopecia and are profoundly granulocytopenic. Veno-occlusive disease of the liver is a serious complication of high-dose chemoradiotherapy that develops in about 10 percent of patients and is characterized by ascites, tender hepatomegaly, and jaundice occurring any time during the first month posttransplant with a peak incidence at day 16.43 predisposing factors include pretransplant hepatitis of whatever cause and the use of more intensive conditioning regimens.44 About 30 percent of patients who develop veno-occlusive disease will die with progressive hepatic failure and, terminally, a hepatorenal syndrome. Although there is no proven effective therapy, preliminary studies suggest that treatment with alprostadil or tissue plasminogen activator may reverse the disease.45,46 Randomized trials are in progress. Most pneumonias occurring post-transplant are infectious in nature, but idiopathic interstitial pneumonia, which is thought to be a direct toxicity of intensive chemoradiotherapy, occurs in five to 10 percent of patients.47 Biopsies reveal some cases to be characterized by diffuse alveolar damage while other have a more clearly interstitial component. Treatment with high-dose steroids is often attempted, but evidence from randomized trials that steroids change the ultimate outcome of this syndrome is lacking.48 Direct complications of chemoradiotherapy seen late after transplantation include decreased growth velocity in children with delay in the development of secondary sex characteristics.49,50 Most postpubertal women will develop ovarian failure, which should be treated, and most men become azospermic.51,52 Cataracts develop in 10 to 20 percent of patients, especially if steroids are required for treatment of chronic GVHD.53 While the above-listed toxicities represent the usual constellation seen after cyclophosphamide and total body irradiation, other preparative regimens may be associated with their own unique problems. Although complete or sustained engraftment usually occurs following transplantation, in some cases marrow function either does not return or, after temporary engraftment, marrow function is lost. Following autologous transplantation, graft failure may be the consequence of marrow damage suffered prior to collection. For example, in one large randomized study, prior exposure of patients to chemotherapeutic drugs that presumably affect hematopoietic stem cells was highly associated with poor marrow function posttransplant.54 Graft failure after autologous transplantation can also result from marrow damage during ex vivo treatment, during storage, or because of exposure of the patient to myelotoxic agents posttransplant. There is some evidence to suggest that viral infections, for example, with cytomegalovirus (CMV) or human herpesvirus 6, may result in poor marrow function.55,56 Following allogeneic transplantation, graft failure may be the result of graft rejection, which is thought to represent an immunologic reaction against the graft by residual host immune cells.57,58 Immunologically mediated graft rejection is more commonly seen in patients who receive less immunosuppressive conditioning regimens, in recipients of T-cell-depleted marrow, or in recipients of HLA-mismatched marrow.59-60 Recently, it has been observed that some patients with GVHD after a period of normal engraftment develop graft failure and that it is impossible to grow marrow stromal cells from such patients, suggesting that a graft-versus-stroma effect may be the cause of poor graft function in some.61 The approach to treatment of graft failure depends on the likely cause. The obvious first step in all patients with poor graft function is to remove all potential myelosuppressive agents. A reasonable second step is to attempt a trial of GM-CSF because published studies suggest that 40 to 50 percent of patients respond.62 Further therapy depends on the evidence for immunologic rejection based on identification of persistent host lymphocytes in peripheral blood or marrow of the patient. If persistent host cells are found, the patient should receive further immunosuppression before a second transplant is performed. Regimens now in use are antithymocyte globulin plus cyclophosphamide or high-dose steroids plus an anti-CD3 antibody.63 If no residual host cells are found, sometimes a second marrow infusion without prior immunosuppression can lead to recovery of hematopoiesis.64 The two most commonly used agents to prevent acute GVHD are methotrexate and cyclosporine. GVHD is the result of the reaction of allogeneic T cells transferred with the graft or developing from it with targets of the genetically different host. GVHD developing during the first three months is categorized as acute and is characterized by an erythematous maculopapular skin rash, which unlike many rashes often involves the palms and soles, by persistent anorexia and/or diarrhea, and by liver disease characterized by rises in bilirubin, transaminase, and alkaline phosphatase.65 Skin, liver, and endoscopic intestinal biopsies are the usual methods of establishing a diagnosis. The incidence of acute GVHD increases in older patients and recipients of mismatched marrow and in those unable to receive full doses of the drugs used to prevent GVHD.13,66,67 The two most commonly used agents to prevent acute GVHD are methotrexate and cyclosporine, and they are equally effective when used individually.68 The combination of the two is more effective in preventing acute GVHD than either alone.69,70 Removal of T cells from the allogeneic marrow is also effective in preventing acute GVHD, but in most circumstances has been associated with an increased incidence of graft rejection and leukemic relapse.71,72 Accordingly, the use of partial T-cell depletion (i.e., complete depletion followed by adding back a fraction of the T cells) and the use of interleukin-2 after engraftment of T-cell-depleted marrow are all under study.73,74 once acute GVHD develops, it can be treated with steroids, antithymocyte globulin, and monoclonal antibodies against T cells or their receptors.75–78 GVHD that develops or persists after three months posttransplant is termed chronic GVHD and has features in common with collagen vascular diseases, including a malar rash, sclerodermatous changes, sicca syndrome, arthritis, obliterative bronchiolitis, and, in some cases, bile duct degeneration and cholestasis.79 Chronic GVHD develops in 20 to 40 percent of patients and is seen more often in patients with prior acute GVHD and in older patients.80 prednisone and/or cyclosporine is the usual treatment, and in some cases, azathioprine or thalidomide has been useful.81–83 In most patients, chronic GVHD eventually resolves and immunosuppressive therapy can be withdrawn, but one to three years of treatment may be required. Patients with chronic GVHD on immunosuppression are susceptible to bacterial infections and should receive prophylactic trimethoprim/sulfamethoxazole and/or penicillin. During the first two to three weeks posttransplant, all patients are severely granulocytopenic. Most develop a fever, and in about one third, a positive blood culture is found. Febrile granulocytopenic patients should be treated with broad-spectrum antibiotics, and in many centers antibiotics are initiated once patients become granulocytopenic to prevent septicemia. The prophylactic administration of fluconazole reduces the incidence of Candida albicans infection.84 Patients who remain febrile despite antibiotic and antifungal prophylaxis represent a difficult challenge, and their management is guided by individual aspects of the patient and the institutional experience. At most centers, the addition of amphotericin B is the usual next step.85 Granulocyte transfusions can be effective in treating specific infections, particularly now that donors can be treated with G-CsF prior to donation, greatly increasing the number of granulocytes that can be collected and transfused.86 There is no established role for prophylactic granulocyte transfusions.87 Laminar air flow isolation can reduce the incidence of infection, but has no impact on survival in patients being transplanted as treatment for malignancy.88 With current supportive care, the risk of death due to an infectious cause during the period of granulocytopenia is less than five percent. In the past, CMV infection was frequently seen posttransplant. More recently, it has been shown that primary CMV infection can be prevented in CMV-seronegative patients by the sole use of CMV-seronegative blood products.89 In CMV-seropositive patients, treatment with ganciclovir as soon as virus excretion is evident can diminish the incidence of CMV-associated disease and death, but some patients will develop disease simultaneously with or before excretion is noted.90 Ganciclovir prophylaxis beginning at the time of engraftment can prevent the development of CMV disease in most patients, but ganciclovir causes significant marrow suppression in at least 10 percent of patients.91 Therefore, current studies are evaluating alternative strategies to prevent CMV infection such as monitoring peripheral blood posttransplant for the development of CMV antigenemia and only initiating ganciclovir prophylaxis if and when patients turn positive. Herpes simplex infection, if not prevented, contributes to the severity of early oral mucositis and esophagitis. However, the prophylactic use of acyclovir 250 mg/m2 intravenously every eight hours can prevent herpes simplex reactivation in almost all seropositive patients.92 Pneumocystis carinii used to cause pneumonia in five to 10 percent of patients posttransplant, but now can be prevented in virtually all patients by treatment with oral trimethoprim/sulfamethoxazole for one week pretransplant and then resuming treatment two days per week once engraftment occurs. Dapsone may be useful in preventing infection with P carinii in patients allergic to sulfa drugs. Patients more than three months posttransplant are still at risk for varicella-zoster infections and if they have chronic GVHD for recurrent bacterial infections. Varicella-zoster infection usually presents as localized disease, but it will disseminate in about one third of patients. The case fatality rate of disseminated varicella-zoster infection occurring during the first nine months posttransplant is 33 percent, and thus all patients with varicella-zoster infection occurring during this early time period should be treated with acyclovir to prevent dissemination.93 As noted previously, patients with chronic GVHD receiving immunosuppression should remain on trimethoprim/sulfamethoxazole and/or penicillin to reduce late bacterial infections. Allogeneic marrow transplantation is the only form of therapy able to cure patients with AML who fail induction therapy, curing 15 to 20 percent of such patients.94,95 Thus, all patients aged 55 years or younger with newly diagnosed AML should be HLA typed along with their families soon after diagnosis to enable transplantation for those who fail induction. Allogeneic transplantation can cure about 30 percent of patients in second remission and 35 percent of those in untreated first relapse. These results are superior to those achieved without transplantation and therefore represent situations that are clear indications for the procedure.96–98 The best results with allogeneic transplantation are obtained in patients transplanted in first remission, with a cure rate of 40 to 70 percent reported.99,100 At least 14 prospective comparisons of marrow transplantation for those with HLA-matched siblings versus chemotherapy for those without have been published. In these series, the cure rate with marrow transplantation has ranged from 40 to 64 percent, while that for chemotherapy has ranged from 19 to 24 percent.101–115 However, there have been important advances in both chemotherapy and transplantation since the conduct of most of these studies. Further, it remains untested whether a strategy of transplantation in first remission is superior to the combination of initial chemotherapy followed by transplantation as salvage therapy. Autologous marrow transplantation for patients with AML in first and second remission in several phase II studies has yielded similar results to those achieved with allogeneic transplantation.116–120 In general, relapse rates after autologous transplantation have been substantially higher than for allogeneic transplantation, but the incidence of death from transplant-related complications has been somewhat lower. In the few studies where the two approaches have been compared head-to-head, allogeneic transplantation has shown a small survival advantage.117,121 The largest of these studies, presented only in abstract form, assigned 569 patients with AML in first remission to allogeneic transplantation, autologous transplantation, or continued chemotherapy and found disease-free survival at four years to be 54 percent, 49 percent, and 30 percent, respectively.121 As with AML, allogeneic transplantation for patients with acute lymphocytic leukemia (ALL) who fail induction therapy or develop chemotherapy-resistant disease can cure 15 to 20 percent of patients, and thus these settings represent indications for the procedure.94 The results of transplantation for patients in second remission are better, with cure rates of 30 to 50 percent reported by several groups.122,123 However, further intensive chemotherapy also can cure some patients who suffered initial relapse. This is particularly true for children who relapse more than 18 months after initial induction chemotherapy. A recent study comparing the outcome of allogeneic transplantation in 255 children to that of an equal number of children treated with chemotherapy reported a five-year disease-free survival of 36 percent for transplant patients compared with 16 percent for chemotherapy patients.124 The relative benefit of transplantation compared with chemotherapy w