Assessment of the efficacy of purging by using gene marked autologous marrow transplantation for children with AML in first complete remission

History and Development of Autologous Stem Cell Transplantation for Acute Myeloid Leukemia

This review describes the development of cryopreservation, the birth of autologous stem cell transplantation (ASCT) and its past and present use to consolidate adult patients with acute myelogenous leukemia (AML). It summarizes the first autografts in patients in relapse, the experience of autografting in complete remission (CR), using bone marrow unpurged or purged in vitro with cyclophosphamide-derivatives, and the important shift to peripheral blood stem cells. The review also discusses the results of recent studies in favor of the use of ASCT to consolidate good- and intermediate-risk patients who reach CR with no detectable minimal residual disease, and those which support the inclusion of maintenance therapy post autograft with hypomethylating agents, anti-BCL-2, and, possibly, in the future, anti AML chimeric antigen receptor-T cells. Carefully applied to well-selected patients, ASCT may regain interest, because of its simplicity, its reduced toxicity, lower non-relapse mortality and better quality of life.

The continuing contribution of gene marking to cell and gene therapy

Gene-marking studies were the first gene-transfer protocols approved for human use. Their intent was not directly therapeutic but rather to track the behavior and fate of cells in vivo, and to use this information to improve treatment protocols. For more than fifteen years, gene-marking studies using retroviral vectors have provided invaluable information about the biology of human hematopoietic cells and T lymphocytes, and have helped guide cell therapies intended to treat malignant disease. Although the safety record of marking studies has been impeccable, the development of leukemia by immunodeficient children treated with retroviral vectors cast a pall over the entire field and essentially brought the era of pure gene-marking studies to an abrupt end. Paradoxically, the impetus these events gave to studying retroviral integration sites in host cell DNA emphasized the additional information that marker studies could provide about the behavior of cells at the clonal level. As confidence has slowly returned, marker studies have reappeared, usually as components of gene therapy protocols in which a marker gene or sequence is incorporated to allow the modified cells to be tracked or imaged in vivo. Hence, gene marking continues to have much to offer in terms of our understanding of the behavior, fate, and safety of gene-modified cells in vivo.

Melphalan-mobilized blood stem cell components contain minimal clonotypic myeloma cell contamination

Optimal methods of stem cell mobilization in multiple myeloma are undefined, and contaminating clonotypic cells could contribute to disease recurrence. A phase 2 trial of intravenous melphalan (60 mg/m2) and granulocyte colony-stimulating factor (G-CSF) (10 microg/kg/d) for mobilization was performed. To enhance reliability, contamination was assessed with 2 sensitive methods, immunoglobulin light and heavy chain variable region patient-specific limiting-dilution polymerase chain reaction (PCR). We evaluated 29 stem cell components (SCCs) from 15 patients; for 9 SCCs, only VL PCR was used because of light chain disease or technical problems with VH primers. For 20 SCCs, VL and VH PCR results were highly correlated (r2 = 0.93, P <.01), with 35% (7 of 20) having identical estimates. VH PCR gave significantly higher estimates for 8-and VL PCR for 5-SCCs, supporting the utility of using 2 methods. Estimated clonotypic contamination per SCC was 0.0009% (range, 0%-0.1%) or 0.5 x 10(4) clonotypic cells per kilogram (range, 0-41.2 x 10(4)/kg), and contamination correlated with CD34+ cells collected (r2 = 0.42, P <.01). Melphalan-mobilized SCCs contain minimal clonotypic contamination.

The effect of graft purging with 4-hydroperoxycyclophosphamide in autologous bone marrow transplantation for acute myelogenous leukemia

BACKGROUND

Autologous bone marrow transplantation is an important therapy for patients with acute myelogenous leukemia (AML). However, leukemia in the graft may contribute to posttransplant relapse. Treatment of the graft with 4-hydroperoxycyclophosphamide (4HC) is sometimes used to decrease numbers of infused leukemia cells (4HC purging). No large controlled trials evaluating efficacy and toxicity of 4HC purging are reported.

METHODS

We studied 294 patients reported to the Autologous Blood and Marrow Registry receiving either a 4HC-purged (n = 211) or unpurged (n = 83) autograft for AML in first (n = 209) or second (n = 85) remission. Analyses were restricted to patients transplanted less than 6 months after achieving remission. Using Cox proportional hazards regression, we compared time to treatment failure (death or relapse, inverse of leukemia-free survival) after 4HC-purged vs unpurged transplants while controlling for important prognostic factors.

RESULTS

Median duration of posttransplant neutropenia was 40 (range, 10-200) days after 4HC-purged transplants and 29 (9-97) days after unpurged transplants (p < 0.01). Transplant-related mortality was similar in the two groups. In multivariate analysis, patients receiving 4HC-purged transplants had lower risks of treatment failure than those receiving unpurged transplants (relative risk, 0.69, p = 0.12 in the first posttransplant year; relative risk, 0.28, p < 0.0001 thereafter). Adjusted three-year probabilities of leukemia-free survival (95% confidence interval) were 56% (47-64%) and 31% (18-45%) after 4HC-purged and unpurged transplants in first remission, respectively. Corresponding probabilities in second remission were 39% (25-53%) and 10% (1-29%).

CONCLUSION

Grafts purged with 4HC are associated with higher leukemia-free survival after autologous bone marrow transplants for AML.

Antibody-directed, effector cell-mediated tumor destruction

Preclinical and clinical development of antitumor strategies using mAbs are showing antitumor efficacy in animal models and in some clinical settings. Preclinical models suggest that mAb treatment would be most effective when provided in the minimal residual disease setting and can involve mAbs in a variety of roles. In murine models, the combination of mAbs with recombinant cytokines, such as IL-2, IL-12, or GM-CSF, can augment the immunologic effect of the mAbs by activating effector cell functions. Efficacy appears to be greatest when the mAb can recruit the effector cells of the host's immune system into helping in the mediation of the antitumor effect. Clinical testing of these concepts is under way.

Gene transfer and the treatment of haematological malignancy

Gene therapy offers an additional therapeutic modality for treating haematological malignancy. Because gene therapies could be truly specific for the malignancy, they should ultimately prove both safe and effective. We have far to go before this full potential is realized, but gene transfer strategies are already showing therapeutic promise. Gene transfer may be used to correct the genetic defect in the tumour, to render it more susceptible to conventional therapies, or the normal host cells more resistant, to induce or amplify an antitumour immune response, or simply as a means of tracking the tumour or cells used for treatment. This article describes examples of each approach and discusses future prospects for the field.

Gene-Marking studies of hematopoietic cells

Gene-marking studies were the first approved clinical protocols introducing exogenous genetic material into human cells. Such studies were never intended to provide direct therapeutic benefit. Instead, they were expected to provide information about normal cell biology and disease pathogenesis that could not be obtained in any other way. However, the information gained from such studies has had a significant impact on disease management. Gene-marking studies have provided valuable insights into the biology of the human stem cell, factors that influence the efficiency of gene transfer, mechanisms of relapse after stem cell transplantation, and the pharmacodynamics of adoptive cellular immunotherapy. With continuing advances in gene-marking technology, the value of the information provided by these studies increases, thereby ensuring their continued relevance to the field of gene transfer.

Allogeneic bone marrow transplantation in children failing prior autologous bone marrow transplantation

Twenty-three children with de novo acute myelogenous leukemia (AML) (n = 20), secondary AML (n = 1), or non-Hodgkin's lymphoma (NHL) (n = 2) underwent allogeneic bone marrow transplantation (alloBMT) for graft failure (n = 1) or recurrent malignancy (n = 22) between February 1992 and August 1999 following autologous BMT (ABMT). Induction chemotherapy was given to 14 patients and nine patients went directly to alloBMT. Five received marrow from matched siblings, 14 from matched unrelated donors and four from mismatched family members. Conditioning regimens included cyclophosphamide, cytarabine, and total body irradiation. Nine patients are alive disease-free between 627 and 2433 days (1.7-6.7 years) post BMT resulting in a 4-year DFS of 39%. Eight patients relapsed at a median of 206 days (range, 35-669 days) post alloBMT and all eventually died. Eight patients (two of whom also relapsed) died of RRT. Although RRT and relapse remain significant problems, a significant percentage of pediatric patients failing ABMT may be cured with alloBMT.

Retroviral transfer of the glucocerebrosidase gene into CD34+ cells from patients with Gaucher disease: in vivo detection of transduced cells without myeloablation

Retroviral gene transfer of the glucocerebrosidase gene to hematopoietic progenitor and stem cells has shown promising results in animal models and corrected the enzyme deficiency in cells from Gaucher patients in vitro. Therefore, a clinical protocol was initiated to explore the safety and feasibility of retroviral transduction of peripheral blood (PB) or bone marrow (BM) CD34+ cells with the G1Gc vector. This vector uses the viral LTR promoter to express the human glucocerebrosidase cDNA. Three adult patients have been entered with follow-up of 6-15 months. Target cells were G-CSF-mobilized and CD34-enriched PB cells or CD34-enriched steady state BM cells, and were transduced ex vivo for 72 hr. Patient 1 had PB cells transduced in the presence of autologous stromal marrow cells. Patient 2 had PB cells transduced in the presence of autologous stroma, IL-3, IL-6, and SCF. Patient 3 had BM cells transduced in the presence of autologous stroma, IL-3, IL-6, and SCF. At the end of transduction, the cells were collected and infused immediately without any preparative treatment of the patients. The transduction efficiency of the CD34+ cells at the end of transduction was approximately 1, 10, and 1 for patients 1, 2, and 3, respectively, as estimated by semiquantitative PCR on bulk samples and PCR analysis of individual hematopoietic colonies. Gene marking in vivo was demonstrated in patients 2 and 3. Patient 2 had vector-positive PB granulocytes and mononuclear bone marrow cells at 1 month postinfusion and positive PB mononuclear cells at 2 and 3 months postinfusion. Patient 3 had a positive BM sample at 1 month postinfusion but was negative thereafter. These results indicate that gene-marked cells can engraft and persist for at least 3 months postinfusion, even without myeloablation. However, the level of corrected cells (<0.02%) is too low to result in any clinical benefit, and glucocerebrosidase enzyme activity did not increase in any patient following infusion of transduced cells. Modifications of vector systems and transduction conditions, along with partial myeloablation to allow higher levels of engraftment, may be necessary to achieve beneficial levels of correction in patients with Gaucher disease.

Retroviral vector-modified bone marrow stromal cells secrete biologically active factor IX in vitro and transiently deliver therapeutic levels of human factor IX to the plasma of dogs after reinfusion

Canine bone marrow stromal cells (BMSCs), transduced ex vivo with retroviral vectors, expressed and secreted biologically active human and canine coagulation factor IX (hFIX and cFIX) in vitro, and on autologous reinfusion expressed hFIX into the circulation of normal (nonhemophiliac) dogs. Human FIX, when expressed in vitro by BMSCs of two dogs at 1.22 and 1.39 microg/10(6) cells/24 hr in medium supplemented with vitamin K, respectively, exhibited 28.1 and 27.3% normal biological activity as determined on the basis of a one-stage clotting assay. BMSCs of two additional dogs expressed 1.54 and 4.81 microg of cFIX/10(6) cells/24 hr in vitamin K-supplemented medium and the expressed cFIX possessed 58.4 and 32.9% normal activity, respectively. Between 2.33 and 3.35 x 10(8) transduced BMSCs, expressing 1.22 and 2.61 microg of hFIX/10(6) cells/24 hr or 3.24 and 7.82 microg of cFIX/10(6) cells/24 hr were reintroduced into the four donor dogs by intravenous infusion. Human FIX was detected in plasma for 7 or 12 days after BMSC reinfusion, with peak levels of 85.8 and 233.0 ng/ml observed at 2 days. Canine anti-hFIX antibodies, which were detected as early as 2-4 days after reinfusion of BMSCs expressing hFIX, may have masked potentially longer duration expression in vivo. Peak plasma levels of hFIX represented 2.1 and 5.8% normal human hFIX levels. When adjusted for percent normal one-stage clotting activity determined in vitro, these levels represented 0.6 and 1.6% normal human hFIX activity levels. Thus, we have demonstrated that retroviral vector-modified BMSCs can deliver human therapeutic levels of hFIX to the circulation of dogs.

Gene therapy for leukemia and lymphoma

Gene therapy of malignant diseases can be divided into four basic approaches: gene interference, gene insertion, immunopotentiation, and suicide gene approaches. This article reviews the application of these approaches in the therapy of leukemias and lymphomas.

Gene marking

Gene marking studies were the first gene transfer protocols to enter clinical practice. To date, clinical marking studies have been limited to the hematopoietic stem cell and its progeny. In this setting, they have provided valuable information about stem cell biology, the factors that influence gene transfer efficiency, and the mechanism of relapse in patients receiving stem cell rescue as therapy for malignant disease. Second-generation studies are beginning to provide even more information about a wider variety of clinical and biological issues. Although marker studies have been useful, it is becoming apparent that the indicator genes used up to now have a number of undesirable characteristics. Future applications of marking, in the hematopoietic system and elsewhere, will require the use of marker elements that will not produce any modification of the cells' behavior. Finally, marker studies have proved safe so far, but follow-up of the treated patients continues.

Bone marrow and clinical gene therapy

Remarkable progress has been made in the last 5 years in the use of gene therapy for the treatment of inherited diseases and acquired disorders. This article reviews these applications with particular emphasis on the use of genetically modified hematopoietic cells.

Gene-marking and haemopoietic stem-cell transplantation

Gene transfer has allowed a number of biological issues in haematopoietic stem-cell transplantation to be addressed. Gene-marking studies have shown that residual malignant cells in infused marrow may contribute to relapse in acute myeloid leukaemia, neuroblastoma and chronic myeloid leukaemia. Double gene-marking techniques with distinguishable retroviral vectors are being used to compare purging techniques and the reconstitution of different sources of stem cells. In allogeneic bone-marrow transplantation, gene-marking has demonstrated that adoptively transferred cytotoxic T cells can persist and reconstitute antiviral immunity.

The contribution of marker gene studies to hemopoietic stem cell therapies

Although the transfer of "therapeutic" genes into hemopoietic stem cells (HSC) offers many opportunities to treat a wide range of human disease, the low efficiency of transfer and limited expression of the transferred gene have so far largely prevented any direct beneficial effect from being obtained. However, gene marker studies in which the transferred genes are used simply to track the individual components of the infused HSC have already shown their utility. Genetic marking may be used to identify cells capable of causing relapse after autologous bone marrow transplantation and to distinguish cells in the graft capable of preventing malignant disease. Marking may also be used to analyze the consequences of ex vivo or in vivo manipulations of the HSC which are intended to accelerate engraftment or augment gene transfer efficiencies. Information obtained from these studies should therefore not only improve the outcome of HSC based therapies, but also aid in the introduction of successful gene therapy protocols.