Background:  Without an effective vaccine against HIV infection, topical microbicide development has become a priority. The sulfonated polyanion PRO 2000, a candidate topical microbicide now in phase II/III clinical trials, blocks HIV infection of cervical tissue in vitro and is active against herpes simplex virus (HSV) both in vitro and in a murine model. Dendritic cells (DC) are among the first cell types to contact HIV in the genital tract and facilitate the spread of the virus. Thus, interfering with virus–DC interactions is a desirable characteristic of topical microbicides as long as that does not interfere with the normal function of the DC.

Methods:  Monocyte-derived DC (MDDC) were generated from monocytes in the presence of interleukin-4 (IL-4) and granulocyte-macrophage colony-stimulating factor (GM-CSF). Phytohemagglutinin (PHA) -stimulated CD4⁺ T cells were used in autologous co-cultures with MDDC. Pseudotyped HIVJRFL and HIVBaL were used to assess the effect of PRO 2000 on virus infection and transmission in MDDC-HeLa CD4⁺CCR5⁺/CD4⁺ T cell co-cultures. For transmission experiments, MDDC were exposed to PRO 2000 only during initial incubation with virus. Then cells were washed and co-cultured with HeLa CD4⁺CCR5⁺ or CD4⁺ T cells. HIV infection, binding and binding/internalization were monitored by p24 enzyme-linked immunosorbent assay (ELISA). HIV glycoprotein-mediated cell–cell fusion assay was used to study effect of PRO 2000 on R5 and X4 envelope-mediated fusion. Cell phenotype and endocytic function upon exposure to PRO 2000 was assessed by flow cytometry. Luminex fluorescent bead assay was used to analyze MDDC cytokine profile.

Results:  PRO 2000 effectively blocked single cycle HIVJRFL infection of MDDC-HeLa CD4⁺CCR5⁺ cell co-cultures and HIVBaL infection of MDDC-CD4⁺ T cell co-cultures. Exposure of MDDC to PRO 2000 at the time of incubation with the virus resulted in a dose-dependent decrease in MDDC-mediated infection of target cells. PRO 2000 inhibited HIV capture by MDDC as well as R5 and X4 envelope-mediated fusion. However, exposure to PRO 2000 decreased expression of DC-SIGN on MDDC, inhibited MDDC endocytic function and attenuated the response to lipopolysaccharide (LPS) stimulation at the phenotypic and functional level (cytokine production).

Conclusions:  While efficient block of HIV infection in the highly permissive MDDC T cell environment, and inhibition of MDDC-mediated virus transmission reinforces the potential value of PRO 2000 as a topical microbicide against HIV, the effect of PRO 2000 on immune cell functions in vivo may be difficult to predict and warrants careful evaluation.