The present invention provides a retroviral or lentiviral vector having a viral envelope which comprises: (i) a mitogenic T-cell activating transmembrane protein which comprises a mitogenic domain and a transmembrane domain; and/or (ii) a cytokine-based T-cell activating transmembrane protein which comprises a cytokine domain and a transmembrane domain, wherein the mitogenic or cytokine-based T-cell activating transmembrane protein is not part of a viral envelope glycoprotein. When cells such as T-cells of Natural Killer cells are transduced by such a viral vector, they are simultaneously activated by the mitogenic T-cell activating transmembrane protein and/or the cytokine-based T-cell activating transmembrane protein.

The present invention relates to a retroviral system for the transfer of non-viral RNA into target cells and more particularly a retroviral particle capable of delivering multiple RNAs. More particularly, it relates to retroviral particles comprising a protein derived from the Gag polyprotein an envelope protein, optionally an integrase and at least two encapsidated non-viral RNAs, the encapsidated non-viral RNAs each comprising an RNA sequence of interest linked to an encapsidation sequence, each encapsidation sequence being recognised by a binding domain introduced into the protein derived from the Gag polyprotein and/or into the integrase.

The invention features lentiviral transfer vectors that include heterologous nucleic acids to be introduced into a cell. The lentiviral transfer vector may be characterized by the following features: (a) including a cytomegalovirus (CMV) promoter; (b) including a polynucleotide encoding a partial gag protein that includes a mutated INS1 inhibitory sequence that reduces restriction of nuclear export of RNA; (c) not including a polynucleotide encoding the INS2, INS3, and INS4 inhibitory sequences of gag; (d) not including an SV40 origin of replication and/or an f1 origin of replication; (e) including a cPPT sequence that contains splice site; (f) including an EF1alpha promoter with intact splice donor and acceptor sites; and (g) including hepatitis B PRE with mutation in start codon of X protein ORF.

The invention encompasses a lentiviral packaging vector comprising a non-subtype B gag-pol sequence, particularly a subtype D gag-pol sequence. The invention further encompasses methods for making and using these vectors. The invention further encompasses lentiviral vector particles comprising HIV-1 non-subtype B Gag and/or Pol proteins.