A recombinant lentiviral vector expression system comprises a first vector
that comprises a nucleic acid sequence of at least part of the Equine
Infectious Anemia Virus (EIAV) genome. The vector contains at least one
defect in at least one gene encoding an EIAV structural protein, but is
preferably a gaglpol expression vector. The expression system further
comprises a second vector, also comprising a nucleic acid sequence of at
least part of the Equine Infectious Anemia Virus (EIAV) genome, and
additionally containing a multiple cloning site wherein a heterologous
gene may be inserted. The expression system also comprises a third vector
which expresses a viral envelope protein. The first and third vectors are
packaging signal-defective. When the expression system is transfected into
a lentivirus-permissive cell, replication-defective EIAV particles may be
produced, which particles are useful in delivering heterologous genes to a
broad range of both dividing and non-dividing cells.