Etoposide Combined with FLAG Salvage Therapy Is Effective in Multiple Relapsed/Refractory Acute Myeloid leukemia.

Managing acute myeloid leukemia (AML) is often hampered by repeated failure to achieve complete remission as well as recurrent relapse that causes an emergent need for alternative salvage therapies. The efficacy of most salvage therapies is based on anthracycline combinations. In highly pretreated patients who are not eligible for anthracycline-based protocols therapeutic alternatives are limited. For this particular group we evaluated the efficacy and safety of fludarabine, cytarabine, granulocyte colony-stimulating factor (FLAG) in combination with etoposide (FLAG-Eto) in 36 patients. The complete remission rate (CR) was 25.7% with a median overall survival of 6 months (95% CI 4.5-7.7). The median disease-free survival for CR/CRi/MLFS (CR/CR with incomplete he-matological recovery/morphologic leukemia-free state) patients was 8 months (95% CI 0.6-15.5). The mortality rate on day 30 was 8% and increased on day 60 to 17%. Our results show meaningful anti-leukemic activity of the FLAG-Eto regimen with a moderate toxicity profile in heavily pretreated relapsed/refractory AML patients enabling consolidating allogeneic stem cell transplantation.

Frontline therapy of acute promyelocytic leukemia: Randomized comparison of ATRA and intensified chemotherapy versus ATRA and anthracyclines.

OBJECTIVES: Randomized comparison of two treatment strategies in frontline therapy of acute promyelocytic leukemia (APL): all-trans retinoic acid (ATRA) and double induction intensified by high-dose cytosine arabinoside (HD ara-C) (German AMLCG) and therapy with ATRA and anthracyclines (Spanish PETHEMA, LPA99). PATIENTS AND RESULTS: Eighty of 87 adult patients with genetically confirmed APL of all risk groups were eligible. The outcome of both arms was similar: AMLCG vs PETHEMA: hematological complete remission 87% vs 83%, early death 13% vs 17% (P = .76), overall survival, event-free survival, leukemia-free survival, cumulative incidence of relapse at 6 years 75% vs 78% (P = .92); 75% vs 68% (P = .29); 86% vs 81% (P = .28); and 0% vs 12% (P = .04, no relapse vs four relapses), respectively. The median time to achieve molecular remission (RT-PCR negativity of PML-RARA) was 60 days in both arms (P = .12). The AMLCG regimen was associated with a longer duration of neutropenia (P = .02) and a higher rate of WHO grade ≥3 infections. CONCLUSIONS: The small number of patients limits the reliability of conclusions. With these restrictions, the outcomes of both approaches were similar and show the limitations of ATRA and chemotherapy. The HD ara-C-containing regimen was associated with a lower relapse rate in high-risk APL.

Localized retroperitoneal Castleman's disease: a case report and review of the literature.

INTRODUCTION: Castleman's disease, also known as angiofollicular lymph node hyperplasia, is a rare disease with two known expansion types, unicentric and multicentric, which play a major role in determining therapy. We focus here on the unicentric type, which can be treated and cured by surgery. To date, approximately 1000 cases of Castleman's disease have been reported in the literature. CASE PRESENTATION: A 50-year-old Caucasian woman presented to our Department of Hematology and Internal Oncology with increasing fatigue as her sole symptom. Diagnostic investigations including laboratory studies, ultrasound, computed tomography and magnetic resonance imaging were performed. These revealed an interaortocaval, retroperitoneal tumor mass in her upper abdomen as the only manifestation of the disease. No enlarged lymph nodes were detected. We conducted a laparotomy with radical extirpation of the tumor mass (10×9×5.7cm). Complete tumor resection with clear margins was achieved. A pathological analysis of the resected sample showed atypical lymphoid tissue of small to medium cells with some clearly visible nucleoli, enlarged sinusoidal vessels, pleomorphic calcifications and focally preserved germinal-center-like structures. Histological and immunohistochemical analysis confirmed the diagnosis of Castleman's disease: staining for CD3, CD5, CD10, CD20, CD23, CD79 and Ki-67 was strongly positive in the germinal-center-like structures. Histological findings clearly showed the disease to be the hyaline vascular subtype. Staining for cyclin D1 and CD30 was negative. Expression of CD15 was positive in the enlarged sinusoidal vessels. A supplementary clonality analysis was without pathological findings. Tests for human immunodeficiency virus and human herpes virus 8 were negative and results from a bone marrow biopsy were normal. Our patient recovered well from surgery and was discharged from our hospital. To date, no recurrence of the disease has been detected. CONCLUSION: Castleman's disease is a rare disorder that remains a diagnostic challenge. Radical surgical resection is considered to be the gold standard for treating the unicentric variant of this disease.

Myeloprotection by cytidine deaminase gene transfer in antileukemic therapy.

Gene transfer of drug resistance (CTX-R) genes can be used to protect the hematopoietic system from the toxicity of anticancer chemotherapy and this concept recently has been proven by overexpression of a mutant O(6)-methylguaninemethyltransferase in the hematopoietic system of glioblastoma patients treated with temozolomide. Given its protection capacity against such relevant drugs as cytosine arabinoside (ara-C), gemcitabine, decitabine, or azacytidine and the highly hematopoiesis-specific toxicity profile of several of these agents, cytidine deaminase (CDD) represents another interesting candidate CTX-R gene and our group recently has established the myeloprotective capacity of CDD gene transfer in a number of murine transplant studies. Clinically, CDD overexpression appears particularly suited to optimize treatment strategies for acute leukemias and myelodysplasias given the efficacy of ara-C (and to a lesser degree decitabine and azacytidine) in these disease entities. This article will review the current state of the art with regard to CDD gene transfer and point out potential scenarios for a clinical application of this strategy. In addition, risks and potential side effects associated with this approach as well as strategies to overcome these problems will be highlighted.

Overdiagnosis of a typical carcinoid tumor as an adenocarcinoma of the lung: a case report and review of the literature.

BACKGROUND: Overdiagnosis of bronchopulmonary carcinoid tumors together with overtreatment can cause serious postoperative consequences for the patient. We report of a patient with a typical bronchopulmonary carcinoid tumor, which was initially misdiagnosed and treated as an adenocarcinoma of the lung. GnrH receptors and the associated Raf-1/MEK/ERK-1/2-pathway are potential targets for analogs in cancer treatment. We suspected a correlation between the lack of tumor growth, application of leuprolide and the Raf-1/MEK/ERK-1/2-pathway. Therefore, we examined GnrH receptor status in the examined specimen. CASE PRESENTATION: In 2010 a 77 year-old male patient was shown to have a tumor mass of about 1.7 cm diameter in the inferior lobe of the left lung. Since 2005, this tumor had hitherto been known and showed no progression in size. The patient suffered from prostate cancer 4 years ago and was treated with TUR-P, radiation therapy and the application of leuprolide. We conducted an explorative thoracotomy with atypical segment resection. The first histological diagnosis was a metastasis of prostate cancer with lymphangiosis carcinomatosa. After several immunohistochemical stainings, the diagnosis was changed to adenocarcinoma of the lung. We conducted a re-thoracotomy with lobectomy and systematic lymphadenectomy 12 days later. The tumor stage was pT1 N0 MX G2 L1 V0 R0. Further immunohistochemical studies were performed. We received the results 15 days after the last operation. The diagnosis was ultimately changed to typical carcinoid tumor without any signs of lymphatic vessel invasion. The patient recovered well from surgery, but still suffers from dyspnea and lack of physical performance. Lung function testing revealed no evidence of impairment. CONCLUSION: The use of several immunohistochemical markers, careful evaluation of hematoxylin-eosin sections and the Ki-67 labelling index are important tools in discriminating between carcinoids and other bronchopulmonary carcinomas. Although we could not detect GnrH-receptors in the examined specimen, there may be individual differences in expression. GnrH receptor profiles in typical and atypical carcinoids should be scrutinized. This could lead to new therapeutical options, since the GnrH receptor has already been described on atypical carcinoids. Clinically tested drugs such as leuprolide could come to use.

Clonal inventory screens uncover monoclonality following serial transplantation of MGMT P140K-transduced stem cells and dose-intense chemotherapy.

Gene transfer of mutant O(6)-methylguanine-DNA-methyltransferase (MGMT(P140K)) into hematopoietic stem cells (HSCs) protects hematopoiesis from alkylating agents and allows efficient in vivo selection of transduced HSCs. However, insertional mutagenesis, high regenerative stress associated with selection, and the genotoxic potential of alkylating drugs represent considerable risk factors for clinical applications of this approach. Therefore, we investigated the long-term effect of MGMT(P140K) gene transfer followed by repetitive, dose-intensive treatment with alkylating agents in a murine serial bone marrow transplant model and assessed clonality of hematopoiesis up to tertiary recipients. The substantial selection pressure resulted in almost completely transduced hematopoiesis in all cohorts. Ligation-mediated PCR and next-generation sequencing identified several repopulating clones carrying vector insertions in distinct genomic regions that were ∼ 9 kb of size (common integration sites). Beside polyclonal reconstitution in the majority of the mice, we also detected monoclonal or oligoclonal repopulation patterns with HSC clones showing vector insertions in the Usp10 or Tubb3 gene. Interestingly, neither Usp10, Tubb3, nor any of the genes located in common integration sites have been linked to clonal expansion in previous preclinical or clinical gene therapy trials. However, a considerable number of these genes are involved in DNA damage response and cell fate decision pathways following cytostatic drug application. Thus, in summary, our study advocates ligation-mediated PCR and next generation sequencing as an effective and reliable method to identify gene products associated with clonal survival in specific experimental settings such as chemoselection using alkylating agents.

Gene therapy of beta(c)-deficient pulmonary alveolar proteinosis (beta(c)-PAP): studies in a murine in vivo model.

Pulmonary alveolar proteinosis (PAP) due to deficiency of the common beta-chain (beta(c)) of the interleukin-3 (IL-3)/IL-5/granulocyte-macrophage colony-stimulating factor (GM-CSF) receptors is a rare monogeneic disease characterized by functional insufficiency of pulmonary macrophages. Hematopoietic stem cell gene therapy for restoring expression of beta(c)-protein in the hematopoietic system may offer a curative approach. Toward this end, we generated a retroviral construct expressing the murine beta(c) (mbeta(c)) gene and conducted investigations in a murine model of beta(c)-deficient PAP. Functional correction of mbeta(c) activity in mbeta(c)(-/-) bone marrow (BM) cells was demonstrated by restoration of in vitro colony formation in response to GM-CSF. In addition, in a murine in vivo model of mbeta(c)-deficient PAP mbeta(c) gene transfer to hematopoietic stem cells not only restored the GM-CSF-sensitivity of hematopoietic progenitor cells but also, within a period of 12 weeks, almost completely reversed the morphologic features of surfactant accumulation. These results were obtained despite modest transduction levels (10-20%) and, in comparison to wild-type mice, clearly reduced beta(c) expression levels were detected in hematopoietic cells. Therefore, our data demonstrating genetic and functional correction of mbeta(c)(-/-) deficiency in vitro as well as in a murine in vivo model of PAP strongly suggest gene therapy as a potential new treatment modality in beta(c)-deficient PAP.

Docetaxel and gemcitabine in the treatment of soft tissue sarcoma - a single-center experience.

INTRODUCTION: Advanced stage/metastatic soft tissue sarcoma (STS) has a poor prognosis especially after failure of the established first-line treatment. In patients with relapsed leiomyosarcoma, however, the combination of gemcitabine (G) and docetaxel (D) recently has emerged as a valuable salvage therapy. PATIENTS AND METHODS: A retrospective analysis of G (900 mg/m2, days 1+8) and D (100 mg/m2, day 8) was performed in 34 patients with STS, and response rate (RR), overall survival (OS), time to progression (TTP), and toxicities were evaluated. RESULTS: Analysis of these 34 patients revealed a RR of 15% with no complete remission (CR) and 5 partial remissions (PR). Of note, 4/5 PR were achieved in patients with leiomyosarcoma. In 13 patients (38%) disease stabilization (SD) could be achieved resulting in a clinical benefit rate (CBR), defined as CR+PR+SD, of 53%. Median OS was 12.5 and TTP was 2.4 months for the whole group and 2.8 months for patients with leiomyosarcoma. A progression- free rate at 3 months of 38% and 45%, respectively, was observed in these 2 groups. Major side effects were 47% hematological and 26% grade 3/4 nonhematological toxicity. CONCLUSION: With regard to the observed CBR further use of GD seems to be warranted even in pretreated patients with STS.

Gene Therapy of ßc-Deficient Pulmonary Alveolar Proteinosis (ßc-PAP): Studies in a Murine in vivo Model.

Pulmonary alveolar proteinosis (PAP) due to deficiency of the common ß-chain (ßc) of the interleukin-3 (IL-3)/IL-5/granulocyte-macrophage colony-stimulating factor (GM-CSF) receptors is a rare monogeneic disease characterized by functional insufficiency of pulmonary macrophages. Hematopoietic stem cell gene therapy for restoring expression of ßc-protein in the hematopoietic system may offer a curative approach. Toward this end, we generated a retroviral construct expressing the murine ßc (mßc) gene and conducted investigations in a murine model of ßc-deficient PAP. Functional correction of mßc activity in mßc-/- bone marrow (BM) cells was demonstrated by restoration of in vitro colony formation in response to GM-CSF. In addition, in a murine in vivo model of mßc-deficient PAP mßc gene transfer to hematopoietic stem cells not only restored the GM-CSF-sensitivity of hematopoietic progenitor cells but also, within a period of 12 weeks, almost completely reversed the morphologic features of surfactant accumulation. These results were obtained despite modest transduction levels (10-20%) and, in comparison to wild-type mice, clearly reduced ßc expression levels were detected in hematopoietic cells. Therefore, our data demonstrating genetic and functional correction of mßc-/- deficiency in vitro as well as in a murine in vivo model of PAP strongly suggest gene therapy as a potential new treatment modality in ßc-deficient PAP.

A novel nonobese diabetic/severe combined immunodeficient xenograft model for chronic lymphocytic leukemia reflects important clinical characteristics of the disease.

We here describe a novel xenograft model of chronic lymphocytic leukemia (CLL) generated by infusion of human primary CLL cells into immunodeficient nonobese/severe combined immunodeficient (NOD/SCID) mice. Combined i.v. and i.p. injection of peripheral blood mononuclear cells (PBMC) from 39 patients with CLL resulted in highly reproducible splenic (37 of 39) and peritoneal (35 of 39) engraftment, which remained stable over a time span of 4 to 8 weeks. By comparison, recovery of leukemic cells from bone marrow (21 of 39) or peripheral blood (8 of 22) was substantially lower. The engraftment pattern of CLL PBMC 4 weeks posttransplant was correlated with clinical disease activity: infusion of PBMC from donors with Binet stage A, lymphocyte doubling time of >12 months, and normal lactate dehydrogenase (LDH) serum levels led to marked engraftment of T cells whereas comparably few tumor cells could be detected. In contrast, NOD/SCID mice receiving PBMC from donors with advanced stage Binet C, lymphocyte doubling time of <12 months, and elevated LDH serum levels exhibited predominant engraftment of tumor cells and comparably low numbers of T cells. These results suggest that this model reflects the heterogeneity and important clinical characteristics of the disease, and thus may serve as a tool for preclinical drug testing and investigation of the pathophysiology of CLL.

Reliable generation of stable high titer producer cell lines for gene therapy.

OBJECTIVE: Retroviral vectors represent one of the most robust technologies for in vivo expression of heterologous gene sequences and are still the most commonly used vectors in clinical gene therapy trials. The production of high titer retroviral preparations, however, can be a problematic procedure for certain constructs. METHODS: GALV- or RD114-pseudotyped retroviral particles carrying selectable fluorescence markers or drug resistance genes, such as the green fluorescent protein (GFP) or the O(6)-methylguanine-DNA-methyltransferase (MGMT) mutants, were used to stably transduce Phoenix-(FNX-)eco cells. Thereafter, a polyclonal population of producer cells was generated by enriching cells with high marker gene expression. In addition, single producer clones were selected by limiting dilution. RESULTS: Retroviral titers were increased 1-2 logs by enriching for a polyclonal population of producer cells, and selection of single producer clones allowed another 1- to 2-log increase in titers. Using this method, reproducibly high titer viral preparations allowing efficient transduction of hematopoietic stem cells were generated. CONCLUSION: A reliable and time-effective method to generate stable high titer producer cells based on the FNX-cell line for problematic retroviral vector constructs is described.

Gene transfer of cytidine deaminase protects myelopoiesis from cytidine analogs in an in vivo murine transplant model.

Hematopoietic stem cell gene transfer of the drug-resistance gene cytidine deaminase (CDD) protecting cells from the cytotoxic cytidine analogs cytarabine and gemcitabine was investigated in a murine transplant model. Following transplantation of CDD-transduced cells and cytarabine application (500 mg/kg; days 1-4; intraperitoneally) significant myeloprotection was demonstrated with nadir counts of peripheral blood granulocytes and thrombocytes of 2.9 +/- 0.6/nL versus 0.7 +/- 0.1/nL (P < .001) and 509 +/- 147/nL versus 80 +/- 9/nL (P = .008), respectively (CDD versus control). Protection also was observed from otherwise lethal gemcitabine treatment (250 mg/kg; days 1-3). Stable levels of gene-marked cells in primary and secondary recipients were demonstrated for up to 9 months, and whereas CDD overexpression clearly reduced B- and T-lymphocyte numbers, no major toxicity was observed in the myeloid compartment. Despite the profound myeloprotective properties, however, CDD overexpression did not allow for pharmacologic enrichment of transduced hematopoiesis in our model. Thus, in summary, our data establish CDD as a drug-resistance gene highly suitable for myeloprotective purposes, which, given the lack of selection observed in our hands, might best be used in combination with selectable drug-resistance genes such as MGMT (P140K) or MDR1.

Recurrent high-grade leiomyosarcoma with heterologous osteosarcomatous differentiation.

Leiomyosarcomas (LM) of the soft tissue comprise approximately 5-10% of all soft tissue sarcomas. Besides the classic LM, several distinctly uncommon features of the cellular and growth patterns of LM have been described. The term "dedifferentiated LM" has rarely been used in the literature to describe soft tissue LM containing areas of undifferentiated, pleomorphic appearance or detectable heterologous differentiation. We report on a case of high-grade LM with almost entire transition to an osteosarcoma, which was classified as recurrent high-grade LM with heterologous osteosarcomatous differentiation. The identification of areas with osteosarcomatous dedifferentiation in soft tissue sarcomas can be of clinical importance because of a possible change in oncologic treatment strategies.

Serum free light chain analysis and urine immunofixation electrophoresis in patients with multiple myeloma.

PURPOSE: Retrospective studies have shown that immunoassays measuring free light chains (FLC) in serum are useful for diagnosis and monitoring of multiple myeloma. This study prospectively evaluates the use of FLC assays and, for the first time, investigates the relationship between serum FLC concentrations and the presence and detectability of Bence Jones (BJ) proteins in the urine. PATIENTS AND METHODS: Three hundred seventy-eight paired samples of serum and urine were tested from 82 patients during the course of their disease. The sensitivities of serum FLC analysis and urine immunofixation electrophoresis (IFE) in detecting monoclonal FLC were compared. Serum FLC concentrations required for producing BJ proteins detected by IFE were determined. RESULTS: Abnormal FLC were present in 54% of serum samples compared with 25% by urine tests. In abnormal serum samples for kappa or lambda, the sensitivity of IFE to detect the respective BJ proteins in urine were 51% and 35% and the median serum FLC concentrations required to produce detectable BJ proteins were 113 and 278 mg/L. Renal excretions of monoclonal FLC increased with serum concentrations, but excretions significantly decreased at high serum concentrations combined with renal dysfunction. CONCLUSION: Serum FLC assays are significantly more sensitive for detecting monoclonal FLC than urine IFE analysis. They also have the advantage of FLC quantification and are more reliable for monitoring disease course and response to treatment.

Improving the biosafety of cell sorting by adaptation of a cell sorting system to a biosafety cabinet.

BACKGROUND: The jet-in-air cell sorters currently available are not very suitable for sorting potentially biohazardous material under optimal conditions because they do not protect operators and samples as recommended in the guidelines for safe biotechnology. To solve this problem we have adapted a cell sorting system to a special biosafety cabinet that satisfies the requirements for class II cabinets. With aid of this unit, sorting can be performed in conformance with the recommendations for biosafety level 2. METHODS: After integrating a modified fluorescence-activated cell sorter (FACS) Vantage into a special biosafety cabinet, we investigated the influence of the laminar air flow (LAF) inside the cabinet on side stream stability and the analytical precision of the cell sorter. In addition to the routine electronic counting of microparticles, we carried out tests on the containment of aerosols, using T4 bacteriophage as indicators, to demonstrate the efficiency of the biosafety cabinet for sorting experiments performed under biosafety level 2 conditions. RESULTS: The experiments showed that LAF, which is necessary to build up sterile conditions in a biosafety cabinet, does not influence the conditions for side stream stability or the analytical precision of the FACS Vantage cell sorting system. In addition, tests performed to assess aerosol containment during operation of the special biosafety cabinet demonstrated that the cabinet-integrated FACS Vantage unit (CIF) satisfies the conditions for class II cabinets. In the context of gene transfer experiments, the CIF facility was used to sort hematopoietic progenitor cells under biosafety level 2 conditions. CONCLUSIONS: The newly designed biosafety cabinet offers a practical modality for improving biosafety for operators and samples during cell sorting procedures. It can thus also be used for sorting experiments with genetically modified organisms in conformance with current biosafety regulations and guidelines.

Resection of residual disease in patients with metastatic gastrointestinal stromal tumors responding to treatment with imatinib.

Gastrointestinal stromal tumors (GIST) are the most common mesenchymal tumors of the gastrointestinal tract. Long-term survival of patients with metastatic disease has only been observed in patients with completely resected disease. Recently, the tyrosine kinase inhibitor imatinib has been found to yield responses in the majority of patients with metastatic GIST suggesting improved resectability in responding patients. Combined treatment approaches including resective surgery after imatinib treatment in patients with advanced metastatic disease have rarely been explored. We report a series of 90 patients with metastatic GIST in whom treatment with imatinib enabled 12 patients with mostly recurrent and extensive disease to be considered for resection of residual disease. In 11 of these patients, complete resection could be achieved. Viable tumor cells were found in all but one resected specimens suggesting that despite favorable radiological or clinical responses, imatinib is unlikely to induce pathological complete responses. Until more mature data from prospective trials are available, these data suggest that an early aggressive surgical approach should be considered for all patients with metastatic GIST. Further trials investigating a combined surgical and pre/postoperative treatment with imatinib in patients with advanced metastatic GIST are warranted.

Thalidomide in combination with dexamethasone for pretreated patients with multiple myeloma: serum level of soluble interleukin-2 receptor as a predictive factor for response rate and for survival.

The aim of this study was to assess the side effects and the efficacy of thalidomide alone or in combination with dexamethasone in relapsed multiple myeloma (MM) and to evaluate possible predictive factors for response rate and survival. Twenty-nine pretreated patients were enrolled, including 13 patients with a relapse after high-dose chemotherapy. The median number of relapses was 3 (range: 1-7). Twenty-two patients received thalidomide in combination with dexamethasone and seven patients thalidomide alone. The dosage of thalidomide was 400 mg/day and the dosage of dexamethasone 20 mg/m2 daily for 4 consecutive days every 3 weeks. Cycles of dexamethasone were given until maximal decline of myeloma protein was achieved, whereas therapy with thalidomide was maintained until disease progression. Responses occurred in 62% of patients, including 5 (17%) complete remissions and 13 (45%) partial remissions. The median event-free survival (EFS) was 7.2 months and the median overall survival (OS) 26.1 months. In multivariate analysis, pretreatment serum levels of soluble interleukin-2 receptor (sIL-2R) were a significant prognostic factor for EFS, and those of beta2-microglobulin (beta2M) and sIL-2R for OS. Serum levels of sIL-2R significantly increased after 3 weeks of treatment in 89% of patients, possibly representing lymphocyte activation induced by thalidomide. Two patients died of septic complications within 3 months after starting treatment with thalidomide and dexamethasone and one patient of herpes encephalitis after 26 months of treatment with thalidomide alone. Also, one case of pneumonia and one case of deep venous thrombosis of the lower limb occurred. Other side effects were somnolence, peripheral neuropathy, and bradycardia occurring in 35, 55, 38 and 55% of patients, respectively. The combination of thalidomide and dexamethasone is an effective therapy in heavily pretreated myeloma patients with a high response rate and acceptable toxicities. A powerful predictive factor both for EFS and OS was the pretreatment serum level of sIL-2R.

Efficient protection from methotrexate toxicity and selection of transduced human hematopoietic cells following gene transfer of dihydrofolate reductase mutants.

OBJECTIVE: While retrovirally mediated gene transfer of dihydrofolate reductase mutants (mutDHFR) has convincingly been demonstrated to confer methotrexate (MTX) resistance to murine hematopoietic cells, clinical application of this technology will require high efficacy in human cells. Therefore, we investigated retroviral constructs expressing various point mutants of human DHFR for their ability to confer MTX resistance to human clonogenic progenitor cells (CFU-C) and to allow for in vitro selection of transduced CFU-C. METHODS: Primary human hematopoietic cells were retrovirally transduced using MMLV- and SFFV/MESV-based vectors expressing DHFR(Ser31), DHFR(Phe22/Ser31), or DHFR(Tyr22/Gly31). MTX resistance of unselected and in vitro-selected CFU-C was determined using MTX-supplemented methylcellulose cultures and gene transfer efficiency was assesed by single-colony PCR analysis. RESULTS: While less than 1% mock-transduced CFU-C survived the presence of > or =5 x 10(-8) M MTX, MMLV- and SFFV/MESV-based vectors expressing DHFR(Ser31) significantly protected CFU-C from MTX at doses ranging from 2.5 to 30 x 10(-8) M. Vectors expressing DHFR(Phe22/Ser31) or DHFR(Tyr22/Gly31) were even more protective and MTX-resistant CFU-C were observed up to 1 x 10(-5) M MTX. Three-day suspension cultures in the presence of 10-20 x 10(-8) M MTX resulted in significant selection of mutDHFR-transduced CFU-C. The percentage of CFU-C resistant to 10 x 10(-8) M MTX increased fourfold to 20-fold and provirus-containing CFU-C increased from 27% to 79-100%. CONCLUSION: Gene transfer of DHFR using suitable retroviral backbones and DHFR mutants significantly increases MTX resistance of human CFU-C and allows efficient in vitro selection of transduced cells using a short-term selection procedure.

Hematoprotection by transfer of drug-resistance genes.

Myelosuppression represents a major side effect of cytotoxic anti-cancer agents. Infection due to granulocytopenia and the risk of bleeding due to thrombocytopenia compromise the potential of curative and palliative chemotherapy. Considering the many chemotherapeutic agents for which drug resistance genes have been described, and the recent improvements in vector and transduction technology, it seems conceivable that drug resistance gene transfer into a patient's autologous hematopoietic stem or progenitor cells will be able to reduce or abolish chemotherapy-induced myelosuppression.