Sexually transmitted infections (STIs) are commonly reported among HIV-1 infected patients. The increasing prevalence of the most common STI, Chlamydia trachomatis (CT), among HIV-1 infected people suggests a role in HIV-1 infectivity. However, the mechanisms modulating the enhancement of HIV-1 infectivity during HIV-1/STIs coinfection remain elusive. The stimulation of CD4 T cells during CT infection may modulate the expression of specific genes, which in turn enhance the susceptibility and infectivity of CT-specific CD4 T cells to HIV-1 infection. After three days of CT stimulation of PBMCs followed by 3 days of HIV-1 infection, we observed a significant increase in HIV-1 p24 levels among clinically diagnosed C. trachomatis-infected patients as compared to cells from healthy donors. Similarly, ex vivo CT antigen-stimulated PBMCs from healthy donors showed enhanced susceptibility to HIV-1 as compared to unstimulated PBMCs. CT-specific CD4 T cells also harbour more HIV-1 copy numbers as compared to healthy unstimulated CD4 T cells. RNA-seq data revealed the upregulation of CCR chemokine receptors and cytokines in CD4 T cells from CT-stimulated CD4 T cells infected with HIV-1. Overall design: PBMCs from healthy blood donors were extracted and stimulated with Chlamydia trachomatis (CT) for three days followed by infection with 50ng/ml of HIV-1 p24 for three days. CD4+ T cells were isolated using the EasySep Human CD4+ T cells isolation kit (Stemcell Technologies, Canada) according to the manufacturer’s instruction followed by RNA extraction. Total RNAs from CT-HIV-1, HIV-1 only, and negative controls were used for RNA-seq at the Beijing Genome Institute (China).