Mouse CD4 enhancer sequences, the human CD4 promoter, 8.8 kb of HIV sequences, and an SV40 polyadenylation signal was used for the transgene. The enhancer and promoter sequences were used to drive expression in CD4+ T cells and cells of the dendritic/macrophage lineage. The HIV sequence contained the following mutations: stop oligos (a 14-mer sequence introdicing stop codons in all 3 reading frames) in the gag and vif genes, a 22 bp deletion of the pol gene followed by a stop oligo, a deletion of nucleotides 5622-5737 in the vpr gene, a deletion of nucleotides 6062-6180 in the vpu gene, and a G to T nonsense mutation at nucleotide5854 of the tat gene. Northern blot analysis showed high transgene expression in the thymus, moderate expression in lymph nodes, and weak expression in kidneys, lungs, intestines, and liver.