Ph.D. Candidate University of Rochester Medical Center, United States
Introduction/Rationale: People living with HIV (PLWH) exhibit increased platelet activation and formation of platelet monocyte complexes (PMCs). in vitro PMC derived dendritic cells (PMDCs) exhibit an immunosuppressive phenotype via decreased antigen uptake and reduced T cell stimulation. TGFβ and β2M have been shown to polarize monocytes to pro-reparative/pro-inflammatory states ,respectively, in a dose dependent manner during vascular events. This study investigates the role of platelet derived TGFβ and β2M in modulating the immunogenicity of PMDCs in PLWH.
Methods: Monocytes and platelets were isolated from PLWH and people without HIV (PWOH). TGFβ and β2M secreted by platelets was quantified by ELISA and monocytes were either treated directly with TGFβ/β2M or co-cultured with collagen activated autologous platelets with or without TGFβ/β2M inhibitors. Monocytes were then differentiated into immature (iDC) and ΨHIV-pulsed mature DCs (mDC). Cellular functions were measured via ELISA and flow cytometry.
Results: Platelets from PLWH secreted higher levels of TGFβ than PWOH with or without activation. High dose TGFβ treated monocytes exhibited decreased functional surface marker expression such as CD84 and CD14 at both monocyte and iDC stages, secretion of proinflammatory TNFα in iDCs, and immunostimulatory CD163 at both iDC and mDC stages when compared to untreated monocytes. Inhibiting TGFβ at the platelet stage reversed these effects. Further, it also reduced the levels of TGFβ intrinsically produced by PMDCs.
Conclusion: These results suggest that platelet-derived TGFβ is a factor in inducing immunosuppressive phenotypes in PMDCs, especially in PLWH as they exhibit increased PMCs and platelet-origin TGFβ, compared to PWOH. Inhibition of platelet-monocyte interactions or suppressing platelet-origin TGFβ may improve endogenous antiviral responses in PLWH. Using platelet-free monocytes can potentially improve the immunogenicity of DC-based vaccine therapies where monocytes serve as a predominant source for autologous DCs.
