The genetic sequence of the glycoprotein (FeLV-env gene), a portion of the reverse transcriptase (FeLV-pol gene) and the complete nucleoprotein (FeLV-gag gene) from the feline leukemia virus were inserted into the genomic DNA of a plaque purified isolate of the parent canarypox strain ALVAC.

The transfer of the target genes into ALVAC is done by co-transfecting chicken embryonic fibroblast cells with (i) the expression cassette plasmid into which the target genes (FeLV-env, -gag and -pol) and the promoter had been transferred by the calcium phosphate method and (ii) the rescue canarypox virus (ALVAC strain), causing homologous recombination in the cytoplasm and thus transferring the target gene into ALVAC.

Note: The disease "feline leukemia" is cased by a virus (the "feline leukemia virus", FeLV). FeLV is usually transmitted between infected cats when the transfer of saliva or nasal secretions is involved. If not defeated by the animal’s immune system, the virus can be lethal. Despite the its name, the disease is not a form of cancer. The name stems from the fact that the first disease associated with the virus was a form of leukemia, and by the time it was discovered that the virus was the causal agent, the misleading name was already being used by pet owners.