Development of a high-titer retrovirus producer cell line and strategies for retrovirus-mediated gene transfer into rhesus monkey hematopoietic stem cells

Transfection of promyelocytic leukemia in retrovirus vector inhibits growth of human bladder cancer cells

AIM

To construct a recombinant retrovirus vector carrying human promyelocytic leukemia (PML) cDNA and identify its expression and biology role in bladder cancer UM-UC-2 cells for future gene therapy.

METHODS

PML full-length cDNA was inserted into the EcoR I and BamH I site of pLXSN vector containing the long terminal repeat (LTR) promoter. The vector was identified by restriction enzyme digestion and then transfected into PA317 packaging cell line by calcium phosphate coprecipitation. PML cDNA was detected by polymerase chain reaction (PCR) and the protein was identified by laser confocal microscopy and Western blot in bladder cancer cells, respectively. The morphology was observed by inverted phase contrast microscope, and MTT assay determined growth curve of the bladder cancer cells.

RESULTS

Restriction enzyme digestion proved that a 2.1 kb PML cDNA was inserted into the pLXSN vector. PCR assay demonstrated that 304 bp fragments were found in UM-UC-2/pLPMLSN transfects. Laser confocal microscopy showed speck dots fluorescence in the UM-UC-2/pLPMLSN nucleus. A 90 kD specific brand was found by Western blot. MTT assay demonstrated the UM-UC-2/pLPMLSN bladder cancer growth inhibition.

CONCLUSION

The retrovirus pLPMLSN vector was successfully constructed and could generate high effective expression of human PML in bladder cancer cell UM-UC-2, suggesting that PML recombinant retrovirus have potential utility in the gene therapy for bladder cancer.

Efficient gene transfer in primitive CD34+/CD38lo human bone marrow cells reselected after long-term exposure to GALV-pseudotyped retroviral vector

Successful retroviral gene transfer into human hematopoietic stem cells was demonstrated in preliminary clinical trials at low efficiency. We have shown previously that gene transfer into committed hematopoietic progenitor cells is more efficient using a gibbon ape leukemia virus (GALV)-pseudotyped retroviral vector instead of an amphotropic retroviral vector. Here, we have conducted a systematic study of human hematopoietic progenitor cells after extended transduction with a GALV-pseudotyped retroviral vector. CD34+/CD38lo Cells were transduced for 5 days and reselected according to phenotype after culture and analyzed for cell cycle status, long-term culture-initiating cell (LTC-IC) activity, and gene transfer. Reselection of rare, very primitive progenitor cells was successful. Equal to fresh CD34+/CD38lo cells, >90% of reselected CD34+/CD38lo cells were in G0/G1. CD34+/CD38lo reselection enriched for LTC-IC (10-fold), as compared to freshly isolated CD34+/CD38lo cells with excellent specificity (82.7% of total LTC-IC were recovered in the reselected CD34+/CD38lo population) and recovery (62% of initial LTC-IC number in CD34+/CD38lo cells were recovered in the reselected fraction after transduction). Gene transfer into primitive progenitor cells was efficient with 50.5% G418-resistant LTC-IC colonies and more than 40 copies of vector provirus detectable per 100 nuclei of CD34+/CD38lo cells. To our knowledge, this is the first systematic analysis of phenotype, function, and cell cycle demonstrating retroviral gene transfer into rare, very primitive human hematopoietic progenitor cells. The chosen strategy should be of considerable value for analyzing and improving gene therapy of the hematopoietic system.

Genetic therapy. Past, present, and future

The early stages of genetic therapy present challenges for clinicians and basic scientists. Clinicians must become familiar with new terminology and concepts, and must keep a perspective on the new field in the face of inflated claims and high-profile failures. Basic scientists must continually return to disease models and to patients to determine what are the proper safety issues and relevant efficacy questions for specific diseases and vector systems. And in an era of instant information, all concerned parties must be careful about how progress is communicated to colleagues, patients, and the lay public.

Retroviral vector-mediated transduction of K-ras antisense RNA into human lung cancer cells inhibits expression of the malignant phenotype

A retroviral vector system was developed to transduce a K-ras antisense construct efficiently into human cancer cells. A 2-kb fragment of K-ras gene DNA in antisense orientation was linked to a beta-actin promoter and inserted into retroviral vector LNSX in two different orientations. The constructs were transfected into amphotropic packaging cell line GP+envAm12 followed by alternating transduction between the ecotropic packaging cell line psi-2 and GP+envAm12. Titers up to 9.7 x 10(7) colony-forming units (cfu)/ml were achieved without detectable replication-competent virus. The human large cell lung carcinoma cell line H460a, which has a homozygous codon 61 K-ras mutation, was transduced with an efficiency of 95% after five to seven repeated transductions. DNA polymerase chain reaction (PCR) and genomic DNA Southern blot analysis showed that the retroviral construct was integrated into the genome of H460a cells. K-ras antisense RNA expression was detected in the cells by Northern analysis, slot blot hybridization, and reverse transcriptase-PCR. Translation of the mutated K-ras p21 protein RNA was specifically inhibited, whereas expression of other p21 species was unchanged. Proliferation of H460a cells was suppressed 10-fold following transduction by the antisense construct. Colony formation in soft agarose and tumorigenicity in an orthotopic lung cancer model in nu/nu mice were dramatically reduced in H460a cells expressing antisense K-ras. We conclude that an antisense construct for K-ras can be expressed effectively in a retroviral vector that can efficiently transduce human cancer cells.

Prospects for virus-based gene therapy for cystic fibrosis

Gene therapy for cystic fibrosis (CF) could potentially be accomplished with one of several recombinant virus vectors, including a murine retrovirus (MMuLV), adenovirus, or adeno-associated virus (AAV). All these vectors take advantage of their respective viruses' mechanisms for delivery of viral DNA to cells, evasion of lysosomal degradation, and optimization of the levels and duration of expression of viral (or vector) DNA. Each has its own unique life cycle, however. The differences among these viruses result in certain advantages and disadvantages, such as the requirement of retroviruses for active cell division, and the potential pathogenic effects from expression of certain adenovirus genes present in adenovectors. While no single vector may be optimal for CF gene therapy in humans, new techniques, such as receptor-mediated gene transfer, seek to take advantage of the desirable properties of one or more of the virus-based systems while avoiding certain potential hazards.