Electroporation of Dendritic Cells with 4-1BBL Enhances HIV-Specific CD4 and CD8 T-Cell Responses

4-1BB (CD137) is a costimulatory receptor of the tumor necrosis factor superfamily and is upregulated on activated CD4 and CD8 T-cells. Its ligand, 4-1BBL (CD137L) has been reported to be expressed on activated antigen presenting cells, including dendritic cells (DC). 4-1BB signalling was shown to improve antiviral and antitumor T-cell responses in both mice and humans. CD8 T-cell stimulation with antigen presenting cells overexpressing 4-1BBL leads to an improved T-cell function and a reduced sensitivity to apoptosis in HIV-patients.
To determine the effect of 4-1BBL on HIV- specific T-cell responses, we stimulated CD4 and CD8 T-cells obtained from HIV-patients with mature DC (mDC) co-electroporated with Gag or Nef and/or 4-1BBL. After 6 days of stimulation, T-cell proliferation was measured using CFSE dilution. Antigen/4-1BBL electroporated mDC were found to induce more proliferation (± 2-fold increase) compared to mDC electroporated with Antigen only, in both CD4 and CD8 T-cells. Interestingly, mDC electroporated with 4-1BBL in the absence of Antigen were able to enhance T-cell proliferation compared to mock electroporated mDC. After 10 days of stimulation, CD8 T-cells were restimulated with Antigen DC or Antigen/4-1BBL DC. CD8 T-cells primed with Antigen/4-1BBL and restimulated with Antigen/4-1BBL showed a higher percentage of antigen-specific and degranulating cells compared to CD8 T-cells primed and restimulated with DC electroporated with Gag only. Furthermore, we compared T-cell responses after stimulator with mDC co-electroporated with CD70 and GITRL, two other members of the TNFR superfamily. Preliminary data indicate that DC co-electroporated with antigen, 4-1BBL and CD70 can further enhance proliferation of CD4 and CD8 T-cells, and induce a higher cytokine production of CD4 T-cells, compared to T-cells stimulated with Antigen/4-1BBL. Stimulation with Antigen/CD70 did not lead to an increase of T-cell proliferation compared to stimulation with antigen only. No clear effect of costimulation with GITRL was seen in this set-up.
These data suggest that 4-1BBL electroporated mDC are able to enhance both CD4 and CD8 HIV-specific T-cell responses and that these responses can be further enhanced by combining 4-1BBL with CD70.