A phase I study of autologous bone marrow transplantation with stem cell gene marking in multiple myeloma

[Contribution of antineoplastic biotherapy in the treatment of leukemia in children]

Improvements in the chemotherapeutic and transplant regimens have had a significant impact in improving survival rates for pediatric leukemia. However, there are still major problems to address including what options are available for patients with chemoresistant disease and what strategies are available to avoid toxicity associated with highly cytotoxic treatment regimens. Gene and immunotherapy protocols hold great promise. Using gene transfer of a marker gene, a number of biologic issues in the therapy of leukemia have been addressed. For example, by gene marking autologous bone marrow grafts it has been possible to demonstrate that infused marrow contributes to relapse in acute and chronic myeloid leukemias. In the allogeneic transplant setting, genetically modified T-cells have proven valuable for the prophylaxis and treatment of viral diseases and may have an important role in preventing or treating disease relapse. Gene transfer is also being used to modify tumor function, enhance immunogenicity, and confer drug-resistance to normal hematopoietic stem cells. With the continued scientific advancements in this field, gene therapy will almost certainly have a major impact on the treatment of pediatric leukemia in the future.

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.

Low level of gene transfer to and engraftment of murine bone marrow cells from long-term bone marrow cultures

OBJECTIVE

We wanted to determine whether the long-term bone marrow culture (LTBMC) transduction system would lead to efficient gene transfer and engraftment of murine repopulating hematopoietic stem cells (HSC), particularly in nonablated recipients.

MATERIALS AND METHODS

Congenic mouse strains expressing Ly 5.1 or Ly 5.2 and the GP+E86 cell line producing the MGirL22Y vector carrying the gene for enhanced GFP were used. Murine LTBMCs were established and demi-depopulated on days 7 and 14 with addition of vector supernatant on days 8 and 15.

RESULTS

Cell recovery on day 21 was 21.3%+/-3.8% of input cells and CFU-C recovery was 9.7+/-3.4% as compared with CFU-C of input cells. In vitro transduction efficiency determined by CFU-C expressing GFP was 22.2%+/-1.6%. In irradiated (950 cGy) mice transplanted with 2x10(6) LTBMC cells, 94% of nucleated cells in the blood at week 16 were of donor origin. However, GFP was only detected at low level in a few animals at week 4 and not later. Analysis of bone marrow from these mice at week 20 did not show any GFP expression and semiquantitative PCR revealed a transgene level of <1%. When 3.5-20.8x10(6) LTBMC cells (corresponding to 20-100x10(6) fresh cells) were transplanted to nonablated recipients, no engraftment or GFP expression were detected. Competitive repopulation experiments showed that the long-term repopulation ability (LTRA) of the LTMC cells was only 7% of fresh cells.

CONCLUSION

These results indicate that LTBMC transduction of murine cells leads to low-level transduction of progenitors, no gene transfer to repopulating stem cells, and reduction in LTRA in ablated and nonablated recipients.

Engraftment of gene-marked hematopoietic progenitors in myeloma patients after transplant of autologous long-term marrow cultures

We conducted a phase I hematopoietic stem cell (HSC) gene-marking trial in patients undergoing autologous blood or marrow stem cell transplant for the treatment of multiple myeloma. Between 500 and 1000 ml of bone marrow was harvested from each of 14 myeloma patients and 1 syngeneic donor. A mean of 3.3x10(9) cells per patient were plated in 20 to 50 long-term marrow culture (LTMC) flasks and maintained for 3 weeks. LTMCs were exposed on days 8 and 15 to clinical-grade neo(r)-containing retrovirus supernatant (G1Na). A mean of 8.23x10(8) day-21 LTMC cells containing 5.2x10(4) gene-marked granulocyte-macrophage progenitor cells (CFU-GM) were infused along with an unmanipulated peripheral blood stem cell graft into each patient after myeloablative therapy. Proviral DNA was detected in 71% of 68 tested blood and bone marrow samples and 150 of 2936 (5.1%) CFU-GM derived from patient bone marrow samples after transplant. The proportion of proviral DNA-positive CFU-GM declined from a mean of 9.8% at 3 months to a mean of 2.3% at 24 months postinfusion. Southern blots of 26 marrow and blood samples were negative. Semiquantitative PCR analysis indicated that gene transfer was achieved in 0.01-1% of total bone marrow and blood mononuclear cells (MNCs). Proviral DNA was also observed in EBV-transformed B lymphocytes, in CD34+ -enriched bone marrow cells, and in CFUs derived from the latter progenitors. Gene-modified cells were detected by PCR in peripheral blood and bone marrow for 24 months after infusion of LTMC cells. Sensitivity and specificity of the PCR assays were independently validated in four laboratories. Our data confirm that HSCs may be successfully transduced in stromal based culture systems. The major obstacle to therapeutic application of this approach remains the overall low level of genetically modified cells among the total hematopoietic cell pool in vivo.

Molecular and Serological Examination of the Relationship of Human Herpesvirus 8 to Multiple Myeloma: orf 26 Sequences in Bone Marrow Stroma Are Not Restricted to Myeloma Patients and Other Regions of the Genome Are Not Detected

Human herpesvirus 8 (HHV-8) genomic sequences were recently detected by polymerase chain reaction (PCR) and in situ hybridization in bone marrow stromal cells grown from multiple myeloma (MM) patients, but not in cells from control subjects (Rettig et al, Science 276:1851, 1997). We sought to confirm these observations in our own group of MM patients (n = 30). DNA was extracted from adherent stromal cells grown under varying conditions and assayed for HHV-8 sequence using PCR to amplify the orf 26 (KS330) sequence (Chang et al,Science 266:1865, 1997), as initially reported. Samples from human control subjects (n = 25) were concurrently extracted and analyzed. After 30 cycles of amplification, we did not detect any positive samples. In a more sensitive nested PCR, samples from 18 of 30 (60%) MM patients were positive, at about the limit of detection, but orf 26 sequence was also amplified from 11 of 25 (44%) human control samples. However, PCR amplification from other regions of the viral genome (orf 72 and orf 75) was uniformly negative for all MM and control samples, despite equivalent sensitivity. Additionally, all sera from MM patients were negative for HHV-8 IgG by immunofluorescence. Our data do not support a role of HHV-8 in the etiology of MM but may suggest the presence of a related (KS330-containing) virus in MM patients and in some control subjects.

This is a US government work. There are no restrictions on its use.

Molecular and Serological Examination of the Relationship of Human Herpesvirus 8 to Multiple Myeloma: orf 26 Sequences in Bone Marrow Stroma Are Not Restricted to Myeloma Patients and Other Regions of the Genome Are Not Detected

Human herpesvirus 8 (HHV-8) genomic sequences were recently detected by polymerase chain reaction (PCR) and in situ hybridization in bone marrow stromal cells grown from multiple myeloma (MM) patients, but not in cells from control subjects (Rettig et al, Science 276:1851, 1997). We sought to confirm these observations in our own group of MM patients (n = 30). DNA was extracted from adherent stromal cells grown under varying conditions and assayed for HHV-8 sequence using PCR to amplify the orf 26 (KS330) sequence (Chang et al,Science 266:1865, 1997), as initially reported. Samples from human control subjects (n = 25) were concurrently extracted and analyzed. After 30 cycles of amplification, we did not detect any positive samples. In a more sensitive nested PCR, samples from 18 of 30 (60%) MM patients were positive, at about the limit of detection, but orf 26 sequence was also amplified from 11 of 25 (44%) human control samples. However, PCR amplification from other regions of the viral genome (orf 72 and orf 75) was uniformly negative for all MM and control samples, despite equivalent sensitivity. Additionally, all sera from MM patients were negative for HHV-8 IgG by immunofluorescence. Our data do not support a role of HHV-8 in the etiology of MM but may suggest the presence of a related (KS330-containing) virus in MM patients and in some control subjects.

This is a US government work. There are no restrictions on its use.

Efficient Retroviral-Mediated Gene Transfer to Human Cord Blood Stem Cells With In Vivo Repopulating Potential

Recent studies have shown efficient gene transfer to primitive progenitors in human cord blood (CB) when the cells are incubated in retrovirus-containing supernatants on fibronectin-coated dishes. We have now used this approach to achieve efficient gene transfer to human CB cells with the capacity to regenerate lymphoid and myeloid progeny in nonobese diabetic (NOD)/severe combined immunodeficiency (SCID) mice. CD34+ cell-enriched populations were first cultured for 3 days in serum-free medium containing interleukin-3 (IL-3), IL-6, granulocyte colony-stimulating factor, Flt3-ligand, and Steel factor followed by two 24-hour incubations with a MSCV-NEO virus-containing medium obtained under either serum-free or serum-replete conditions. The presence of serum during the latter 2 days made no consistent difference to the total number of cells, colony-forming cells (CFC), or long-term culture-initiating cells (LTC-IC) recovered at the end of the 5-day culture period, and the cells infected under either condition regenerated similar numbers of human CD34+ (myeloid) CFC and human CD19+ (B lymphoid) cells for up to 20 weeks in NOD/SCID recipients. However, the presence of serum increased the viral titer in the producer cell-conditioned medium and this was correlated with a twofold to threefold higher efficiency of gene transfer to all progenitor types. With the higher titer viral supernatant, 17% ± 3% and 17% ± 8%, G418-resistant in vivo repopulating cells and LTC-IC were obtained. As expected, the proportion of NEO + repopulating cells determined by polymerase chain reaction analysis of in vivo generated CFC was even higher (32% ± 10%). There was no correlation between the frequency of gene transfer to LTC-IC and colony-forming unit–granulocyte-macrophage (CFU-GM), or to NOD/SCID repopulating cells and CFU-GM (r2 = 0.16 and 0.17, respectively), whereas values for LTC-IC and NOD/SCID repopulating cells were highly and significantly correlated (r2 = 0.85). These findings provide further evidence of a close relationship between human LTC-IC and NOD/SCID repopulating cells (assessed using a ≥ 6-week CFC output endpoint) and indicate the predictive value of gene transfer measurements to such LTC-IC for the design of clinical gene therapy protocols.

Efficient Retroviral-Mediated Gene Transfer to Human Cord Blood Stem Cells With In Vivo Repopulating Potential

Recent studies have shown efficient gene transfer to primitive progenitors in human cord blood (CB) when the cells are incubated in retrovirus-containing supernatants on fibronectin-coated dishes. We have now used this approach to achieve efficient gene transfer to human CB cells with the capacity to regenerate lymphoid and myeloid progeny in nonobese diabetic (NOD)/severe combined immunodeficiency (SCID) mice. CD34+ cell-enriched populations were first cultured for 3 days in serum-free medium containing interleukin-3 (IL-3), IL-6, granulocyte colony-stimulating factor, Flt3-ligand, and Steel factor followed by two 24-hour incubations with a MSCV-NEO virus-containing medium obtained under either serum-free or serum-replete conditions. The presence of serum during the latter 2 days made no consistent difference to the total number of cells, colony-forming cells (CFC), or long-term culture-initiating cells (LTC-IC) recovered at the end of the 5-day culture period, and the cells infected under either condition regenerated similar numbers of human CD34+ (myeloid) CFC and human CD19+ (B lymphoid) cells for up to 20 weeks in NOD/SCID recipients. However, the presence of serum increased the viral titer in the producer cell-conditioned medium and this was correlated with a twofold to threefold higher efficiency of gene transfer to all progenitor types. With the higher titer viral supernatant, 17% ± 3% and 17% ± 8%, G418-resistant in vivo repopulating cells and LTC-IC were obtained. As expected, the proportion of NEO + repopulating cells determined by polymerase chain reaction analysis of in vivo generated CFC was even higher (32% ± 10%). There was no correlation between the frequency of gene transfer to LTC-IC and colony-forming unit–granulocyte-macrophage (CFU-GM), or to NOD/SCID repopulating cells and CFU-GM (r2 = 0.16 and 0.17, respectively), whereas values for LTC-IC and NOD/SCID repopulating cells were highly and significantly correlated (r2 = 0.85). These findings provide further evidence of a close relationship between human LTC-IC and NOD/SCID repopulating cells (assessed using a ≥ 6-week CFC output endpoint) and indicate the predictive value of gene transfer measurements to such LTC-IC for the design of clinical gene therapy protocols.

Multiple myeloma: VI International Workshop, June 14-18, 1997, Boston, Massachusetts, USA

The VI International Workshop on Multiple Myeloma was organised by Professor Kenneth C Anderson, Dana Farber Cancer Institute, and held on June 14-18, 1997, in Boston, MA, USA. More than 500 participants from all over the world joined this workshop. Several subjects were introduced and one of the most exciting items of news was the identification of Kaposi's sarcoma-associated herpes virus in the bone marrow stromal cells of patients with MM. The aim of this overview is to give a glimpse of the subjects discussed and the statements made.

Retroviral Gene Transduction of Adult Peripheral Blood or Marrow-Derived CD34+ Cells for Six Hours Without Growth Factors or on Autologous Stroma Does Not Improve Marking Efficiency Assessed In Vivo

Our previous work in patients undergoing autologous transplant for multiple myeloma (MM) or breast cancer (BC) has shown that retroviral transduction of adult CD34+ cells for 72 hours in the presence of interleukin-3 (IL-3), IL-6, and stem cell factor (SCF ) resulted in .01% to 1% long-term marking of peripheral blood and marrow cells (Blood 85:3948, 1995). In this study we compare these previous studies to transduction with no added growth factors, previously shown to result in higher levels of marking in children (Lancet 342:1134, 1993) or transduction in the presence of an autologous stromal layer. Peripheral blood (PB) mononuclear cells were collected via apheresis after high-dose cyclophosphamide and granulocyte colony-stimulating factor. Bone marrow (BM) was also harvested in all patients. One third of both BM and PB collections were enriched for CD34+ cells and transduced with one of two marking vectors containing the neomycin-resistance gene to distinguish cells originating from BM and PB posttransplantation. Cells from 3 MM and 2 BC patients were transduced without growth factors for 6 hours and cells from 2 MM and 2 BC patients were transduced in the presence of autologous marrow stroma. Immediately posttransduction, the percentage of Neo-resistant PB and BM progenitors (colony-forming units) were: 0% to 19% in the 6-hour no growth factor group and 0% to 36% in the autologous stroma group. After conditioning therapy, both transduced and untransduced PB and BM fractions were infused into the patients. Semi-quantitative nested DNA polymerase chain reaction was performed on total, mononuclear, and granulocyte fractions of PB and BM at 1, 3, 6, 9, 12, and 18 months. Poor marking has been observed in both groups, with no consistently positive patients. These results compare unfavorably with our prior experience using growth factors during transduction. Further optimization of transduction conditions and vectors needs to be developed to improve transduction efficiency of adult human repopulating hematopoietic cells.

Human somatic cell gene therapy

The prelude to successful human somatic gene therapy, i.e. the efficient transfer and expression of a variety of human genes into target cells, has already been accomplished in several systems. Safe methods have been devised to do this using non-viral and viral vectors. Potentially therapeutic genes have been transferred into many accessible cell types, including hematopoietic cells, hepatocytes and cancer cells, in several different approaches to ex vivo gene therapy. Successful in vivo gene therapy requires improvements in tissue-targeting and new vector design, which are already being sought. Gene-transfer protocols have been approved for human use in inherited diseases, cancer and acquired disorders. Although the results of these trials to date have been somewhat disappointing, human somatic cell gene therapy promises to be an effective addition to the arsenal of approaches to the therapy of many human diseases in the 21st century if not sooner.

Preclinical assessment of human hematopoietic progenitor cell transduction in long-term marrow cultures

Long-term marrow cultures (LTMCs) were established from 27 human marrows. Hematopoietic cells were subjected to multiple rounds of exposure to retroviral vectors during 3 weeks of culture. Seven different retroviral vectors were evaluated. LTMCs were assessed for viability, replication-competent retrovirus, progenitors capable of proliferating in immune-deficient mice, and gene transfer. The average number of adherent cells and committed granulocyte-macrophage progenitors (CFU-GM) recovered from LTMCs was 28% and 11% of the input totals, respectively. There was no evidence by marker rescue assay or polymerase chain reaction (PCR) of replication-competent virus production during LTMC. No toxicity to cellular proliferation due to the transduction procedure was observed. The adherent layers of LTMCs exposed to retroviral vectors were positive for proviral DNA by PCR and by Southern blot analysis. Fifty-three percent of 1,427 individual CFU-GM from transduced LTMC adherent layers were positive for vector-derived DNA. For neocontaining vectors, the average G418 resistance was 28% of 1,393 LTMC-derived CFU-GM. Forty percent of 187 tissues from 30 immune-deficient mice injected with human LTMC cells were positive for human DNA 4-5 weeks after adoptive transfer. These studies indicate that multiple exposures of human LTMCs to retroviral vectors result in consistent and reproducible LTMC viability and gene transfer into committed progenitors. Our results further support the use of transduced LTMC cells in clinical trials of hematopoietic stem cell gene transfer.

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.

Multiple myeloma, high-dose treatment and autologous stem cell transplantation--current status

High-dose chemo-radiotherapy with autologous stem cell transplantation (ASCT) has introduced the concept of complete remission for multiple myeloma, and can improve survival and life quality for selected groups of myeloma patients. A number of prognostic factors have been identified, where ASCT in early disease, i.e. as part of front-line treatment, seems to be of particular importance for a favourable outcome. Even so, most myeloma patients will not be cured by high-dose therapy, but new strategies such as repeated autografting and post-graft alpha-interferon maintenance treatment seem to add additional advantages with respect to survival and freedom of disease progression. The technical development has enabled efficient in vitro myeloma cell depletion of the autograft as well as highly sensitive detection of minimal residual disease after treatment, but the clinical significance of these issues remains to be determined, and this question is addressed in ongoing gene marking studies. The application of novel therapeutic principles, e.g. gene therapy and immunotherapy, might further ameliorate the outcome for patients with multiple myeloma.

The role of haematopoietic stem cell-supported myeloablative therapy for the management of multiple myeloma

Haematopoietic stem cell-supported myeloablative therapy appears to be a promising treatment modality for MM. It yields increased overall response and CR rates when compared with conventional chemotherapy, and seems to prolong the duration of survival. These conclusions, while encouraging, have mostly been drawn from uncontrolled studies carried out in select groups of patients and, obviously, need to be confirmed in controlled clinical trials. While the results of these studies are still awaited, the wider application of BMT should probably be encouraged. As in other malignancies, the best candidates appear to be those less heavily pre-treated, with chemosensitive disease, low tumour cell mass and other favourable prognostic features, for example low beta 2-microglobulin levels. Under these conditions, the chance of entering CR following BMT, be it autologous or allogeneic, is currently estimated to be of at least 50%, and the long-term probability of survival averages approximately 30%. However, while it appears that a plateau for progression-free survival cannot be ascertained following a single ABMT, reported observations of patients with continued disease-free survivals up to and beyond 10 years after allografting suggest that this latter procedure may be curative. It seems likely therefore that the higher mortality related to allogeneic BMT (which in recent years decreased from 50% to approximately 30% as the results of a better selection of patients and increasing experience in their management) may be offset by more durable control of the disease and cure in a certain proportion of patients. Recurrence of underlying malignant disease remains, however, a major problem and is the most common cause of treatment failure following BMT. For this reason, attempts to improve the impact of transplantation are warranted. Options currently under investigation include the development of more effective conditioning regimens, as applied in double auto-transplant or with targeted therapy using antibody-radionuclide conjugates, as well as post-transplant immunomodulation with either IFN-alpha, interleukin-2 or idiotype vaccines. In addition, many other problems regarding BMT for MM are still unresolved and could be properly addressed only in future clinical trials. The most important of these issues include the choice of the best conditioning regimen and the optimal source of haematopoietic stem cells, the nature of relapse after autografting, the need to purge or not to purge the autologous marrow, the existence of a 'graft-versus-myeloma' effect and its role in prolonging the duration of disease control and, finally, the likelihood of cure, especially for patients with molecularly-defined CR.

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.