Single-cell RNAseq analysis identified significantly altered gene expression in CD4<sup>+</sup> T lymphocytes.<h4>Discussion</h4>The results of our findings suggest that fentanyl promotes HIV replication <i>ex vivo</i>, emphasizing the need for a deeper understanding of opioid-virus interactions to develop better treatment strategies for individuals with HIV and opioid use disorder. This evidence concerns the gene CD4 and opioid use disorder.