Jansen, J.; Vlaming, K. E.; Helgers, L. C.; Schumacher, E.; Kaptein, T. M.; Sanders, R. W.; de Bree, G. J.; Geijtenbeek, T. B. H.; Kootstra, N. A.

Monophosphoryl lipid A (MPLA) and the saponin-MPLA nanoparticle adjuvant (SMNP) are known immunostimulants used as adjuvants in vaccines to boost immunity. These adjuvants are under investigation for use in prophylactic and therapeutic HIV-1 vaccines. However, their effects in ART-treated people with HIV-1 (PWH) remain unclear, as chronic immune activation may reduce responses and potentially reactivate latent virus reservoirs. Here we observed that both adjuvants, MPLA and SMNP, triggered TLR4-dependent cytokine production in monocyte-derived dendritic cells (DCs), but SMNP elicited a stronger response than MPLA based on costimulatory receptor expression and cytokine production. Cytokines produced by adjuvant stimulated dendritic cells were able to induce HIV-1 transcription in a J-Lat cell model. Notably, SMNP, but not MPLA, also induced a cytokine response in PBMC from PWH, albeit lower as compared to in healthy donor PBMC. Importantly, SMNP substantially reduced the size of the inducible HIV-1 reservoir in PWHex vivowithout bystander cytotoxicity. The effect on the viral reservoir was likely caused by the cytokine production induced by SMNP, as supernatants from SMNP stimulated DCs showed a similar viral reservoir reduction. Our findings demonstrate that TLR4-targeted adjuvants, especially SMNP, can effectively induce immune activation, supporting their potential use in therapeutic vaccination. However, as reservoir reduction was observed ex vivo, further evaluation is warranted to ensure safe use of such adjuvants in PWH.