Factors affecting bone marrow transplantation
Among the negative prognostic factors affecting the results of bone marrow allotransplantation in patients with acute myeloblastic leukemia, the age of the patient, high leukocytosis at the time of diagnosis, the presence of M4-M6 (according to the FAB classification), a long period of the disease before bone marrow transplantation, as well as a prolonged absence of remission. According to the estimates of the majority of specialists, the most promising method for the treatment of posttransplantation relapses is adoptive immunotherapy with the use of bone marrow donor lymphocytes, especially in the case of relapse of leukemia within the first year after bone marrow transplantation, since intensive chemotherapy is accompanied by extremely high lethality during these periods.
In patients with relapse that occurred later than a year after bone marrow transplantation, repeated remissions can be induced more often. However, these results of treatment can not be considered satisfactory due to the short-term achieved remissions. A retrospective study of the European bone marrow transplantation group showed that standard chemotherapy allows to achieve a remission in 40% of patients with acute leukemia, but the duration is not more than 8-14 months. In all, 3% of patients have a remission period of more than 2 years.
In posttransplant recurrences, the results of adoptive immunotherapy worsen in patients with acute leukemia - only in 29% of patients with acute myeloblastic leukemia and only 5% of patients with acute lymphoblastic leukemia manage to induce remission by transfusion of donor lymphocytes. 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 hemoblastosis treatment does not exceed 2 years. It is particularly difficult to achieve remission in the case of relapse of leukemia within 100 days after bone marrow transplantation, which is always accompanied by extremely high lethality, since chemotherapy in such patients causes severe toxic complications due to pre-transplantation 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 myelogenous leukemia: chemotherapy, interferon or glivec therapy, and bone marrow allotransplantation. Chemotherapy can only reduce the volume of the tumor. Recombinant interferon and glyvek can significantly limit the size of the leukemia clone (cytogenetic improvement is observed in 25-50% of patients) and even completely eliminate 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. Allotransplantation of the bone marrow in the treatment of patients with chronic myelogenous leukemia was first applied in the 70s of the XX century. In 1979, A. Fefer and co-authors reported on the results of syngeneic bone marrow transplantation in 4 patients in the chronic phase of chronic myelogenous leukemia. The leukemia 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 which in 12 patients transplantation was performed in the chronic phase of the disease. Five of them lived after bone marrow transplantation without recurrence of chronic myelogenous leukemia from 17 years to 21 years (with no reports of death in the scientific literature to date). In one patient, disease-free survival reached 17.5 years after the first and 8 years after the second, performed for the relapse of the disease, bone marrow transplantation.
The question of the timing of bone marrow allotransplantation in chronic myelogenous leukemia remains to this day not only relevant but also controversial. This is partly due to the fact that randomized studies to evaluate the effectiveness of bone marrow transplantation in comparison with chemotherapy or therapy with interferon and glivec was not carried out. L. Mendeleeva (2003) notes that chemotherapy provides a comfortable survival rate for almost all patients within 2-4 years. Treatment with interferon and glyvek (long and costly), accompanied by a certain discomfort (flu-like syndrome, depression, etc.). In addition, until now it has not been determined whether complete cancellation of the drugs is possible after the cytogenetic effect has been achieved. Allograft bone marrow is also expensive treatment, and is also accompanied by a number of serious complications. However, the transplantation of allogeneic bone marrow is the only method for treating chronic myelogenous leukemia, * with which one can achieve biological cure by eliminating a clone of pathological cells.
In some studies, a comparative analysis of the efficiency of bone marrow allotransplantation, chemotherapy and autologous bone marrow transplantation was performed. In most studies, randomization for bone marrow transplantation was determined by the presence of an HLA-identical donor. In the absence of such patients, chemotherapy or bone marrow autotransplantation was performed. In a prospective extensive study of the results of treatment of acute lymphoblastic leukemia in the phase of remission I, the probability of a five-year disease-free survival after bone marrow allotransplantation did not differ from those in patients receiving chemotherapy or autologous bone marrow transplant. However, a discriminant analysis of the results of treatment with regard to prognostic factors (Rh-positive acute lymphoblastic leukemia, age over 35 years, the level of leukocytosis in the diagnosis and the time taken to achieve remission) revealed significant differences in the five-year survival in patients receiving allogeneic (44% ) or autologous (20%) bone marrow, and patients undergoing chemotherapy (20%).
In the work of N. Chao and co-authors (1991), the criteria for carrying out bone marrow allotransplantation in patients with acute lymphoblastic leukemia in phase I of remission were also leukocytosis and extra-oesophageal lesions in the onset of the disease - t (9, 22), t (4, 11 ), t (8,14), age over 30 years and, in addition, no remission after the first phase of the induction course of chemotherapy. Most patients had bone marrow allotransplantation in the first 4 months after remission was achieved. At almost nine years of average follow-up, disease-free survival after transplantation was 61% at 10% relapse.
Thus, allogeneic bone marrow transplantation is a rather effective method of treating tumor diseases of the blood system. According to different authors, the long-term survival of patients with hemoblastosis, who underwent bone marrow transplantation, is 29 to 67% depending on the risk group. Therapy of this kind not only exerts a powerful cytostatic (radiomimetic) effect on tumor cells, but also causes the development of the "graft versus leukemia" reaction, which is based, for the time being, on the not very clear mechanism of immunological displacement of the residual tumor clone. In recent years, this phenomenon has been given a leading role in providing an antitumor effect in bone marrow transplantation.
The results of some studies indicate that with the use of bone marrow allotransplantation, it is possible to achieve improvement even in cases when chemotherapy can not be induced to remission. In particular, A Zander and co-authors (1988) report positive results of treatment in three of the nine patients with acute myeloblastic leukemia, whose bone marrow allotransplantation was performed after ineffective remission induction. It should be noted that in recent years the attitude towards bone marrow allotransplantation in acute myeloblastic leukemia has changed significantly. This method of treatment, previously used only in patients with refractory leukemia, moved to the area of intensive consolidation of complete remission of acute myeloblastic leukemia. Since the beginning of the 1980s, all published clinical studies have indicated that bone marrow allotransplantation is the most effective therapy for patients with acute myeloblastic leukemia in remission I (provided there is an HLA-identical related donor and no contraindications to bone marrow transplantation). According to different authors, the recurrence-free survival of recipients after bone marrow allografting for more than five years is 46-62%, the overall survival rate exceeds 50%, and the relapse rate does not reach 18%.
A problematic issue remains the use of bone marrow allotransplantation in the period of a detailed clinical picture of leukemia. Multifactor analysis aimed at the search for predictors of bone marrow allotransplantation in the accelerating phase included the age of patients, the duration of the disease, the nature of previous chemotherapy, the presence of leukocytosis in the onset of the disease, the size of the spleen in diagnosis and before bone marrow transplantation, donor and recipient sex, and the presence of Ph-chromosome and other cytogenetic disorders. It has been established that the factors contributing to the improvement of survival and the reduction of non-relapse-related mortality are the young age of the recipient (up to 37 years) and the absence of hematologic changes characteristic for the acceleration phase (the diagnosis was based on additional cytogenetic changes).
The accumulated experience in the treatment of various forms of leukemia, aplastic anemia and a number of other serious diseases of the blood system through bone marrow transplantation proves that the transplantation of allogeneic bone marrow in many cases allows a radical cure. At the same time, in clinical transplantology there is a complex problem of selecting an HLA-identical bone marrow donor. Adoptive immunotherapy of relapses of leukemias also has its limitations, which is manifested by different efficacy of transfusions of bone marrow donor's lymphocytes, depending on the characteristics of leukemia cells.
In addition, leukemia cells have a different sensitivity to the cytotoxic effects of such cytokines as tumor necrosis factor, interferons and IL-12. In addition, the in vivo transfer of genes coding for the synthesis of cytokines is currently being considered theoretically. In the field of cytokine-genetic therapy of hemoblastoses, the issues of resistance of the gene to degradation, as well as its packaging, allowing 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. Currently, methods for the controlled expression of a therapeutic gene are being developed, in particular, gene delivery by ligands to certain unique receptors on the surface of the target cell is tested, as well as specific protection of vectors from inactivation in human blood plasma. Retroviral vector constructs are created, stable in blood, tissue-specific and selectively transducing dividing or non-dividing cells.
And yet the main problem of allogeneic bone marrow transplantation is the deficiency of HLA-compatible donors. Despite the fact that in Europe, America and Asia there are already a number of hematopoietic donor donors with more than 7 million potential donors of bone marrow and cord blood stem cells for 2002, requests for HLA-compatible hematopoietic cells even for children with diseases of the blood system are met only by 30-60%. In addition, if such a donor is available in the American or European registries, the cost of finding and delivering the donor bone marrow to the transplant center will be between $ 25,000 and $ 50,000.
Bone marrow transplantation after hemo- and immunosuppression of reduced intensity (low-dose conditioning) is widely used throughout the world in the treatment of a variety of diseases, from hemoblastosis to systemic connective tissue diseases. However, the problem of choosing the optimal conditioning mode has not been solved yet. Despite the use of various combinations of immunosuppressants, chemotherapy and small doses of radiation, it remains an open question to achieve the combined effect of low toxicity and immunosuppression sufficient to ensure engraftment of the graft.
Thus, bone marrow allotransplantation is currently the most effective method for treating hemoblastoses, which is due not only to the intense antitumor effect of pre-transplant conditioning, but also to the powerful immune effect of "graft versus leukemia." Numerous research centers continue to study ways of prolonging relapse-free survival of allogeneic bone marrow recipients. The problems of selecting patients, the timing of bone marrow transplantation, monitoring and the optimal treatment regimen for the minimal residual disease, which is the cause of post-transplantation relapse of leukemia, are discussed. Bone marrow transplantation has entered the practice of treating many non-oncological diseases of the blood and some congenital diseases, as well as acute radiation damage to the bone marrow. Bone marrow transplantation often gives a radical effect in the treatment of aplastic anemia and other mielodepressive conditions. In Europe and America, registers of HLA-type donors have been created, willing to voluntarily sacrifice their bone marrow for the treatment of patients who need to replace and / or repair hemopoietic tissue. However, despite the large number of potential bone marrow donors, its use is limited due to the high prevalence of cytomegalovirus infection among donors, the duration of the search for the donor (average 135 days) and large financial costs. In addition, for some ethnic minorities, the probability of selecting an HLA-identical donor bone marrow is only 40-60%. Annually clinics register about 2800 children, who first fell ill with acute leukemia, from 30 to 60% of whom need bone marrow transplantation. However, only one third of these patients can find an immunologically compatible donor. There is still a high incidence of severe "graft-versus-host" reactions in recipients of the bone marrow, and in unrelated transplantation this complication occurs in 60-90% of patients.