Growth factor displayed on the surface of retroviral particles without manipulation of envelope proteins is biologically active and can enhance transduction.
BACKGROUND
The therapeutic potential of retroviruses can be significantly enhanced by display of specific molecules on the retroviral surface. This has been conventionally achieved by the manipulation of retroviral envelope proteins. In this report we have tested whether the natural budding mechanism of the retrovirus could be exploited to incorporate a specific molecule into the retroviral surface.


METHODS
Retroviral packaging cells were engineered to express the membrane-bound form of human stem cell factor (mbSCF). Surface expression of mbSCF on retroviral packaging cells was confirmed by immunofluorescence and flow cytometry. Incorporation of mbSCF into retroviral particles was demonstrated by virus-binding assay and immunomagnetic capture of virus using antibody to SCF. Retroviral supernatants were tested for activity of the incorporated cytokine by proliferation assays on factor-dependent cells. Amphotropic retrovirus displaying surface mbSCF was used to transduce SCF receptor-positive haematopoietic cells.


RESULTS
Retroviruses incorporating surface SCF showed increased levels of binding to cells (MO7e) expressing the SCF receptor, c-kit. mbSCF displayed on the viral surface retained levels of biological activity comparable with those of soluble recombinant growth factor. Transduction of c-kit-positive target cells with viruses displaying mbSCF showed enhanced levels of transduction in comparison with unmodified viruses.


CONCLUSIONS
Expression of the membrane-bound form of human stem cell factor (mbSCF) on the surface of retroviral packaging cells allows its efficient incorporation into retrovirus particles in a biologically active form, opening up the possibility for the use of retroviral display in many therapeutic areas, such as in gene therapy, drug delivery and in the development of novel vaccines.
Department of Haematology, Faculty of Medicine, Imperial College of Science Technology & Medicine, Du Cane Road, London W12 0NN, UK.
Anil
A
Chandrashekran
Myrtle Y
MY
Gordon
David
D
Darling
Farzin
F
Farzaneh
Colin
C
Casimir
D000818:Animals; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D006801:Humans; D051379:Mice; D019009:Proto-Oncogene Proteins c-kit / Q000096:biosynthesis; D012190:Retroviridae / Q000235:genetics / Q000378:metabolism*; D019089:Stem Cell Factor / Q000096:biosynthesis* / Q000235:genetics; D014759:Viral Envelope Proteins / Q000235:genetics / Q000378:metabolism*
D019089:Stem Cell Factor; D014759:Viral Envelope Proteins; D019009:Proto-Oncogene Proteins c-kit