Hematopoietic bone marrow stem cells and bone marrow transplantation

Cell transplantology began not with embryonic stem cell derivatives, but with bone marrow cell transplants. The first studies on experimental bone marrow transplantation almost 50 years ago began with an analysis of animal survival during total irradiation followed by infusion of bone marrow hematopoietic cells. The clinic studied the effectiveness of syngeneic bone marrow transplantation in the treatment of acute leukemia refractory to radiochemotherapy and for the first time large-scale examination of patients with acute forms of leukemia who underwent bone marrow transplantation from HLA-identical related donors. Even then, in seven cases of acute myeloblastic leukemia and in six cases of acute lymphoblastic leukemia, as a result of bone marrow allotransplantation, it was possible to achieve complete remission, which lasted for 4.5 years without the use of maintenance therapy. In six patients with acute myeloid leukemia, disease-free survival after one bone marrow allotransplant exceeded 10 years.

Subsequently, retrospective analysis of the results of bone marrow allotransplantation was carried out repeatedly. A study by the University of California, Los Angeles compared the effectiveness of bone marrow allotransplantation and high-dose cytosine-arabinoside treatment in acute myeloid leukemia in remission phase I (patients aged 15 to 45 years). After bone marrow allotransplantation, a lower relapse rate was noted (40% versus 71%), but no reliable intergroup differences in relapse-free and overall survival were registered. It was later found that the phase of the disease at the time of bone marrow transplantation is one of the critical features determining post-transplant survival. Studies by Canadian scientists showed that bone marrow transplantation during the chronic phase gives much better results than during the acceleration period or blast crisis of chronic myeloid leukemia.

In a prospective randomized study by J. Reiffers et al. (1989), the first evidence-based advantages of bone marrow allotransplantation over treatment of hemoblastoses using only chemotherapeutic drugs were obtained - thirty-month relapse-free survival was 4 times higher after transplantation of allogeneic bone marrow to patients. Then, data were presented on long-term remission in 50% of patients with acute myeloblastic leukemia as a result of bone marrow allotransplantation, who had previously been refractory to at least 2 cycles of induction chemotherapy.

At the same time, in almost all studies, the results of bone marrow allotransplantation during the blast crisis of chronic myeloid leukemia were negative. In such patients, relapse-free survival after bone marrow allotransplantation rapidly and progressively decreased, amounting to 43, 18 and 11% within 100 days, 1 year and 3 years, respectively, while the probability of relapse of the disease within 2 years reached 73%. Nevertheless, bone marrow allotransplantation gives the patient, albeit small, a chance for life, while even combined chemotherapy is completely unable to ensure long-term survival of patients in this category. It was later shown that sometimes by conducting chemotherapy for chronic myeloid leukemia in the blast crisis phase of the lymphoid type, it is possible to achieve short-term remission. If an allogeneic bone marrow transplant is performed during this period, the probability of survival after transplantation increases to 44%.

A study of factors affecting survival and relapse rates in patients with chronic myeloid leukemia after allogeneic bone marrow transplantation in the chronic phase has led to the conclusion that patient age under 30, bone marrow transplantation within 2 years of diagnosis, and female patient and donor gender are associated with the best results. With such pretransplant characteristics, 6-8-year relapse-free survival reaches 75-80%, and the probability of disease relapse does not exceed 10-20%. However, in the case of bone marrow allotransplantation during the acceleration phase, posttransplant survival of patients decreases sharply, which is associated with both an increase in the relapse rate and an increase in mortality not caused by a relapse of hemoblastosis.

The next fairly large randomized prospective study was conducted in 1995 by the EORTC and GIMEMA groups. The results of bone marrow allotransplantation and consolidating high-dose chemotherapy with cytosine arabinoside and daunorubicin served as the object of comparative analysis. Before bone marrow transplantation, myeloablative conditioning was performed in two variants: cyclophosphamide + total irradiation and busulfan + cyclophosphamide. Four-year relapse-free survival after bone marrow allotransplantation was 55%, after autotransplantation - 48%, after high-dose chemotherapy - 30%. The risk of disease relapse was significantly lower after bone marrow allotransplantation - both relative to its autotransplantation and in comparison with chemotherapy (24, 41 and 57%, respectively). There were no significant intergroup differences in overall survival, since in all cases of relapse after chemotherapy, intensive anti-relapse treatment was carried out, and upon achieving remission II, autotransplantation of bone marrow cells was performed.

Improvement of methods for treating hemoblastoses continued. A. Mitus et al. (1995) reported on the results of treating adult patients with acute myeloblastic leukemia who underwent induction and consolidation of remission with high doses of cytosine-arabinoside, and then allo- or autotransplantation of bone marrow. Regardless of the type of transplantation, four-year relapse-free survival was 62%. At the same time, the frequency of relapses was significantly higher in patients who underwent autotransplantation of bone marrow.

The possibilities of anti-relapse treatment also gradually expanded. Generalization of the results of adoptive immunotherapy with bone marrow donor lymphocytes showed its high efficiency in chronic myeloid leukemia. The use of adoptive immunotherapy against the background of cytogenetic relapse led to complete remission in 88% of patients, and after infusion of bone marrow donor lymphocytes against the background of hematological relapse, complete remission was induced in 72% of patients. The probability of five-year survival in the case of adoptive therapy was 79 and 55%, respectively.

In an extended study of the European Bone Marrow Transplantation Group, the post-transplant dynamics of oncohematological diseases after allo- and autotransplantation of bone marrow was studied in 1114 adult patients. In general, a higher relapse-free survival and a lower risk of relapse after allotransplantation of bone marrow were found. Subsequently, an in-depth retrospective analysis of the effectiveness of auto- and allotransplantation of bone marrow cells in hemoblastoses was carried out. Depending on the cytogenetic abnormalities in blast cells, patients were divided into groups with low, standard and high risk of relapse. Relapse-free survival in patients of the examined groups after allotransplantation of bone marrow was 67, 57 and 29%, respectively. After autotransplantation of bone marrow, performed in patients of the standard and high-risk groups, relapse-free survival was lower - 48 and 21%. Based on the obtained data, it is considered appropriate to perform bone marrow allotransplantation during remission I in patients of standard and high-risk groups. At the same time, in patients with a prognostically favorable karyotype, the author recommends postponing bone marrow transplantation until the onset of relapse I or the achievement of remission II.

However, the results of bone marrow allotransplantation in acute myeloid leukemia outside remission I cannot be considered satisfactory. The probability of three-year relapse-free survival after transplantation against the background of untreated relapse I is only 29-30%, and during remission II - 22-26%. Since remission with chemotherapy can be achieved in no more than 59% of patients with acute myeloid leukemia, bone marrow allotransplantation is allowed in early relapse I, since this step can still improve survival rates. In order to be able to perform bone marrow allotransplantation at the first signs of relapse, it is necessary to perform HLA typing in all patients immediately after achieving remission I. Less often, bone marrow allotransplantation is used to consolidate remission I in acute lymphoblastic leukemia. However, performing allogeneic bone marrow transplantation in adult patients with acute lymphoblastic leukemia in the case of a high risk of relapse during chemotherapy can increase three- and five-year relapse-free survival to 34 and 62%.

Even in the case of such an extremely unfavorable variant of hemoblastosis as Ph-positive acute lymphoblastic leukemia, in which the duration of induced remission does not exceed one year, the use of bone marrow allotransplantation as consolidation of remission I contributes to a significant improvement in treatment results: the probability of three-year relapse-free survival increases to 60%, and the relapse rate decreases to 9%. Therefore, in patients with acute lymphoblastic leukemia, characterized by unfavorable prognostic signs suggesting a high risk of relapse, it is advisable to perform bone marrow allotransplantation during remission I. The results of bone marrow allotransplantation in adult patients with acute lymphoblastic leukemia during remission II or the onset of relapse were significantly worse: three- and five-year relapse-free survival was less than 10%, and the relapse rate reached 65%.

In case of early relapse of acute lymphoblastic leukemia that occurs during ongoing maintenance chemotherapy or shortly after its discontinuation, patients should undergo immediate bone marrow allotransplantation without resorting to second-line chemotherapy (to reduce the accumulation of cytotoxins in the blood). In cases of relapse of acute lymphoblastic leukemia after prolonged remission I, efforts should be directed at inducing remission II, which will make it possible to increase the effectiveness of subsequent allotransplantation.

The efficiency of allogeneic bone marrow transplantation can be increased by optimizing conditioning methods. I. Demidova et al. (2003) used conditioning based on the sequential use of busulfan at a dose of 8 mg/kg, which causes sufficiently deep myelosuppression, when preparing patients with leukemia for bone marrow transplantation. The data obtained by the authors indicate that the use of busulfan ensures successful engraftment of donor bone marrow in most patients with hemoblastoses. Lack of engraftment was observed in only two cases. In the first case, graft failure was associated with a small number of transfused hematopoietic progenitor cells (1.2 x 108/kg). In the second case, anti-HLA antibodies were detected in high titer. In all patients, the dynamics of graft engraftment depended primarily on the initial volume of the tumor mass. Gradual transplant rejection was observed in cases where more than 20% blast cells were detected in the recipient's bone marrow.

The emergence of new drugs that have the ability to exert significant immunosuppression without significant depression of hematopoiesis (for example, fludarabine) allows for a significant increase in the therapeutic effectiveness of allogeneic bone marrow transplantation by reducing early mortality, which is often due to the high toxicity of the pre-transplantation preparation regimens used.

It should be emphasized that the effectiveness of bone marrow allotransplantation is significantly limited by the development of leukemia relapse, especially in patients with late stages of the disease (second and subsequent remissions of acute leukemia, acceleration phase of chronic myeloid leukemia). In this regard, much attention is paid to finding the most effective methods for treating post-transplant relapses. The first step in treating early relapse in allogeneic bone marrow recipients, provided there is no severe graft-versus-host reaction, is abrupt cessation of immunosuppressive therapy by discontinuing cyclosporine A. In some patients with chronic myeloid leukemia and acute hemoblastoses, discontinuation of immunosuppression can improve the course of the disease, since the developing graft-versus-host reaction stops the progression of leukemia. However, in most cases, the full picture of the disease relapse dictates the need for immediate cytostatic therapy. In this case, an important factor determining the results of chemotherapy is the interval between bone marrow transplantation and the onset of relapse of hemoblastosis.

The most intensive attempt to eradicate a tumor clone is a second bone marrow transplantation performed for a relapse of leukemia. However, even in this case, the success of treatment is highly dependent on the time interval between the first bone marrow transplantation and the appearance of signs of disease relapse. In addition, the intensity of previous chemotherapy, the phase of the disease, and the general condition of the patient are of great importance. A second bone marrow transplantation performed less than a year after the first one has a high mortality rate directly related to the transplantation. At the same time, the three-year relapse-free survival rate does not exceed 20%. Patients with a relapse after syngeneic or autologous bone marrow transplantation sometimes successfully undergo a second allogeneic bone marrow transplantation from an HLA-identical sibling, but even in these cases severe toxic complications associated with the conditioning regimen are observed.

In this regard, methods for combating relapses of hemoblastoses are being developed based on the use of adoptive immunotherapy. According to the clinical study by H. Kolb et al. (1990), in patients with hematological relapse of chronic myelogenous leukemia that developed after allotransplantation of bone marrow, complete cytogenetic remission can be induced by transfusions of donor bone marrow lymphocytes without the use of chemo- or radiation therapy. The “graft versus leukemia” effect after transfusions of donor bone marrow lymphocytes has also been described in acute leukemia.

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Factors Affecting Bone Marrow Transplantation

Among the negative prognostic factors affecting the results of bone marrow allotransplantation in patients with acute myeloid leukemia, it is necessary to note the patient's age, high leukocytosis at the time of diagnosis of the disease, the presence of M4-M6 (according to the FAB classification variants), a long period of the disease before bone marrow transplantation, as well as a long absence of remission. According to the estimates of most specialists, the most promising method of treating post-transplant relapses is adoptive immunotherapy using bone marrow donor lymphocytes, especially in the case of leukemia relapse during the first year after bone marrow transplantation, since during this period intensive chemotherapy is accompanied by an extremely high mortality rate.

In patients with a relapse later than one year after bone marrow transplantation, repeated remissions can be induced more often. However, these treatment results cannot be considered satisfactory due to the short duration of the achieved remissions. A retrospective study by the European Bone Marrow Transplantation Group showed that standard chemotherapy allows achieving repeated remission in 40% of patients with acute leukemia, but its duration is no more than 8-14 months. Only 3% of patients experience a remission period exceeding 2 years.

In post-transplant relapses in patients with acute leukemia, the results of adoptive immunotherapy also worsen - only in 29% of patients with acute myeloblastic leukemia and only in 5% of patients with acute lymphoblastic leukemia is it possible to induce remission by transfusion of donor lymphocytes. At the same time, the probability of five-year survival of patients with acute myeloblastic leukemia is 15%, and among patients with acute lymphoblastic leukemia, this indicator of the effectiveness of treatment of hemoblastoses does not exceed 2 years. It is especially difficult to achieve remission in case of leukemia relapse within 100 days after bone marrow transplantation, which is always accompanied by an extremely high mortality rate, since chemotherapy in such patients causes severe toxic complications due to pre-transplant conditioning, as well as high sensitivity of recently transplanted bone marrow to cytostatic drugs.

In principle, the strategy for treating hemoblastoses should be aimed at eliminating the pathological clone, which, unfortunately, is not always feasible. In particular, three different tactical approaches are currently used to treat chronic myeloid leukemia: chemotherapy, interferon or gleevec therapy, and bone marrow allotransplantation. Chemotherapy can only reduce the tumor volume. Recombinant interferon and gleevec can significantly limit the size of the leukemic clone (cytogenetic improvement is observed in 25-50% of patients) and even completely eliminate the pathological clone in 5-15%, and according to some data - in 30% of patients, which is confirmed by the results of both cytogenetic and molecular biological studies. Bone marrow allotransplantation in the treatment of patients with chronic myeloid leukemia was first used in the 1970s. In 1979, A. Fefer and co-authors reported the results of syngeneic bone marrow transplantation in 4 patients in the chronic phase of chronic myeloid leukemia. The leukemic clone was successfully eliminated in all patients. In 1982, A. Fefer provided data on the results of syngeneic bone marrow transplantation in 22 patients, of whom 12 patients underwent transplantation in the chronic phase of the disease. Five of them survived from 17 to 21 years after bone marrow transplantation without relapse of chronic myeloid leukemia (however, there have been no reports of their death in the scientific literature to date). In one patient, relapse-free survival reached 17.5 years after the first and another 8 years after the second bone marrow transplantation, performed due to a relapse of the disease.

The question of the timing of bone marrow allotransplantation in chronic myeloid leukemia remains not only relevant but also controversial. This is partly due to the fact that randomized studies evaluating the effectiveness of bone marrow transplantation in comparison with chemotherapy or interferon and Gleevec therapy have not been conducted. L. Mendeleyeva (2003) notes that chemotherapy provides comfortable survival for almost all patients for 2-4 years. Treatment with interferon and Gleevec (long-term and expensive) is accompanied by certain discomfort (flu-like syndrome, depression, etc.). In addition, it has not yet been clarified whether it is possible to completely discontinue the drugs after achieving a cytogenetic effect. Bone marrow allotransplantation is also an expensive treatment and is also accompanied by a number of severe complications. However, allogeneic bone marrow transplantation is currently the only method of treating chronic myelogenous leukemia*, with the help of which it is possible to achieve a biological cure by eliminating the clone of pathological cells.

Several studies have compared the efficacy of allotransplantation, chemotherapy, and autologous bone marrow transplantation. In most studies, randomization for bone marrow transplantation was determined by the availability of an HLA-identical donor. In the absence of such a donor, patients received chemotherapy or autologous bone marrow transplantation. In a prospective, large study of the treatment outcomes of acute lymphoblastic leukemia in remission I, the probability of five-year relapse-free survival after allotransplantation of bone marrow did not differ from that in patients who received chemotherapy or autologous bone marrow transplantation. However, discriminant analysis of treatment outcomes taking into account prognostic factors (Rh-positive acute lymphoblastic leukemia, age over 35 years, leukocytosis level at diagnosis and time required to achieve remission) revealed significant differences in five-year survival between patients who received allogeneic (44%) or autologous (20%) bone marrow transplantation and patients who received chemotherapy (20%).

In the work of N. Chao et al. (1991), the criteria for performing bone marrow allotransplantation in patients with acute lymphoblastic leukemia in remission phase I were also leukocytosis and extramedullary lesions at the onset of the disease - t (9, 22), t (4, 11), t (8,14), age over 30 years and, in addition, the absence of remission after the first phase of the induction course of chemotherapy. Most patients underwent bone marrow allotransplantation in the first 4 months after achieving remission. With an average observation period of almost nine years, relapse-free survival after transplantation was 61% with 10% relapses.

Thus, allogeneic bone marrow transplantation is a fairly effective method of treating tumor diseases of the blood system. According to various authors, the long-term survival of patients with hemoblastoses who have undergone bone marrow transplantation is, depending on the risk group, from 29 to 67%. This type of therapy not only has a powerful cytostatic (radiomimetic) effect on tumor cells, but also causes the development of a "graft versus leukemia" reaction, which is based on a still unclear mechanism of immunological displacement of the residual tumor clone. In recent years, this phenomenon has been given a leading role in ensuring the antitumor effect in bone marrow transplantation.

The results of some studies indicate that bone marrow allotransplantation can achieve improvement even in cases where remission cannot be induced by chemotherapy. In particular, A. Zander et al. (1988) reported positive treatment results in three of nine patients with acute myeloid leukemia, who underwent bone marrow allotransplantation after unsuccessful remission induction. It should be noted that the attitude toward bone marrow allotransplantation in acute myeloid leukemia has changed significantly in recent years. This treatment method, previously used only in patients with refractory leukemia, has moved into the area of intensive consolidation of complete remission of acute myeloid leukemia. Since the early 1980s, all published clinical studies have shown that bone marrow allotransplantation is the most effective therapy for patients with acute myeloid leukemia in remission I (provided there is an HLA-identical related donor and no contraindications to bone marrow transplantation). According to various authors, the relapse-free survival of recipients observed after bone marrow allotransplantation for more than five years is 46-62%, the overall survival exceeds 50%, and the relapse rate does not reach 18%.

The use of bone marrow allotransplantation during the full-blown clinical picture of leukemia remains a problematic issue. Multivariate analysis aimed at finding prognostic factors for bone marrow allotransplantation in the acceleration phase included patient age, disease duration, type of previous chemotherapy, presence of leukocytosis at the onset of the disease, spleen size at diagnosis and before bone marrow transplantation, donor and recipient gender, conditioning regimens, as well as the presence of the Ph chromosome and other cytogenetic abnormalities. It was established that factors contributing to increased survival and decreased non-relapse mortality are young age of the recipient (up to 37 years) and the absence of hematological changes characteristic of the acceleration phase (the diagnosis in this case was made on the basis of additional cytogenetic changes).

The accumulated experience of treating various forms of leukemia, aplastic anemia and a number of other severe blood diseases by bone marrow transplantation proves that allogeneic bone marrow transplantation in many cases allows for radical cure. At the same time, clinical transplantology faces the complex problem of selecting an HLA-identical bone marrow donor. Adoptive immunotherapy of relapsed leukemia also has its limitations, which is manifested by the varying effectiveness of bone marrow donor lymphocyte transfusions, depending on the characteristics of leukemic cells.

In addition, leukemic cells have different sensitivities to the cytotoxic effects of cytokines such as tumor necrosis factor, interferons, and IL-12. In addition, in vivo transfer of genes encoding cytokine synthesis is currently considered mainly theoretically. In the field of cytokine-based therapy of hemoblastoses, the issues of gene resistance to degradation and its packaging, which allows selectively reaching the target cell, integrating into the genome, and expressing the protein product, while ensuring safety for other cells of the body, remain problematic. Methods for regulated expression of a therapeutic gene are currently being developed, in particular, gene delivery using ligands to certain unique receptors on the surface of the target cell is being tested, as well as specific protection of vectors from inactivation in human blood plasma. Retroviral vector constructs are being created that are stable in the blood, tissue-specific, and selectively transducing dividing or non-dividing cells.

And yet the main problem of allogeneic bone marrow transplantation is the shortage of HLA-compatible donors. Despite the fact that in Europe, America and Asia there have long been Registries of donors of hematopoietic cells, which in 2002 numbered more than 7 million potential donors of bone marrow and cord blood stem cells, requests for HLA-compatible hematopoietic cells even for children with blood diseases are satisfied only by 30-60%. In addition, if such a donor is available in the American or European registries, the costs of searching for and delivering donor bone marrow to the transplant center will amount to from 25,000 to 50,000 US dollars.

Bone marrow transplantation after low-intensity hemo- and immunosuppression (low-dose conditioning) is widely used worldwide in the treatment of various diseases, from hemoblastoses to systemic connective tissue diseases. However, the problem of choosing the optimal conditioning regimen has not yet been solved. Despite the use of various combinations of immunosuppressants, chemotherapy drugs, and low doses of radiation, the question of achieving a combined effect of low toxicity and immunosuppression sufficient to ensure graft engraftment remains open.

Thus, bone marrow allotransplantation is currently the most effective method for treating hemoblastoses, which is due not only to the intensive antitumor effect of pretransplant conditioning, but also to the powerful immune effect of “graft versus leukemia”. Numerous research centers continue to study methods for prolonging relapse-free survival of allogeneic bone marrow recipients. The problems of patient selection, bone marrow transplantation timing, monitoring and optimal treatment regimen for minimal residual disease, which is the cause of posttransplant relapse of leukemia, are discussed. Bone marrow transplantation has become a part of the practice of treating many non-oncological blood diseases and some congenital diseases, as well as acute radiation injuries of the bone marrow. Bone marrow transplantation often provides a radical effect in the treatment of aplastic anemia and other myelosuppressive conditions. In Europe and America, registries of HLA-typed donors willing to voluntarily donate their bone marrow for the treatment of patients in need of replacement and/or restoration of hematopoietic tissue have been created. However, despite the large number of potential bone marrow donors, its use is limited due to the significant prevalence of cytomegalovirus infection among donors, the length of the search for the right donor (135 days on average) and high financial costs. In addition, for some ethnic minorities, the probability of selecting an HLA-identical donor bone marrow is only 40-60%. Every year, clinics register about 2,800 children newly diagnosed with acute leukemia, 30 to 60% of whom require a bone marrow transplant. However, an immunologically compatible donor can be found for only a third of such patients. There remains a high incidence of severe graft-versus-host disease in recipients of related bone marrow, while in unrelated transplants this complication is observed in 60-90% of patients.

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