Host-vector system which can be used in gene therapy

Process for expressing a transgene for gene therapy which consists in using the following steps:

• a) construction of a host-vector system obtained by transfection, into a eukaryotic host cell, on the one hand, of a pseudo-retroviral sequence in which the env gene is deleted totally and replaced with the transgene, especially at the level of the ATG of the said env gene and, on the other hand, a nucleic acid sequence containing, in its structure, a sequence encoding an envelope protein under the control of a promoter, where appropriate combined with the transgene and flanked at its 3′ end by a polyadenylation sequence,
• b) bringing the said system into contact with the cells in which the tranagene has to be expressed,
• c) where appropriate, again transferring, into the target cells, the abovementioned sequence containing the env gene.

Use, in the manufacture of a medicinal product for gene therapy, of a host-vector system obtained by the following successive steps:

• a) simultaneous transfection, into a eukaryotic host cell, on the one hand, of a pseudo-retroviral sequence in which the env gene is deleted totally and replaced with the transgene and, on the other hand, a nucleic acid sequence containing, in its structure, a sequence encoding an envelope protein under the control of a promoter, where appropriate, combined with the transgene and flanked at its 3′ end by a polyadenylation sequence, and, where appropriate, combined at its 3′ end with a homologous sequence of the defective recombinant retrovirus used in the host-vector system of a gene encoding a retroviral protein,
• b) bringing the said system into contact with the cells in which the transgene has to be expressed,
• c) where appropriate, again transferring, into the target cells, the abovementioned sequence containing the env gene.

Medicinal product which can be used in gene therapy, characterized in that it contains, as active ingredient, vehicles containing a recombinant retroviral sequence substituted, at the level of the env. gene, by a transgene of interest, and outside the region for regulating the expression of the retroviral sequences, especially outside the LTRs, a sequence carrying an env. gene in dependence on a promoter.

Recombinant viral vector containing a transgene of interest, which can be used in gene therapy, characterized in that:

• a gene essential for the constitution of infectious viral particles is substituted by a transgene of interest,
• this essential gene is present on the same vector, or a different vector, but is no longer in dependence on the viral promoters and,
• the product of this gene acts in trans and makes it possible to reconstitute defective viral particles.