The objective of the present work was to evaluate the efficacy of a novel antigen carrier using mannosylated gelatin nanoparticles with entrapped inactivated porcine reproductive and respiratory syndrome virus (PRRSV) in inducing T cell mediated immunity in vitro. Gelatin nanoparticles (GNP) were modified with mannose to form mannosylated gelatin nanoparticles (MnGNP), which can efficiently and specifically target monocyte derived dendritic cells (MoDCs). The inactivated PRRSV was encapsulated in the MnGNP and GNP, referred to as MnGNP-PRRSV and GNP-PRRSV, respectively. All these prepared nanometer particles were characterized for size, surface charge, drug encapsulation efficiency, and drug release. The efficacy of MnGNP in targeting MoDCs was investigated, as well as the subsequent MoDCs maturation and T cell mediated cytotoxicity. The developed MnGNP-PRRSV particle was characterized with a nanometric size of 302.67 ± 3.2 nm, surface charge of 23.81 ± 1.26 mV, and PRRSV encapsulation efficiency of 63.2 ± 1.85 %. The maximum uptake of MnGNP in MoDCs in vitro was 15.5 times higher than GNP with a shorter reaction time that peaked 4 h earlier. The uptake of MnGNP-PRRSV induced maturation of MoDCs and significantly enhanced expression of SWC-3a, CD80, CD1, SLA I, SLA II on MoDCs, compared to PRRSV (p < 0.001). The cytokine secretion of IL-1β, IL-6, IL-10, and IL-12 was also increased in MoDCs when treated with MnGNP-PRRSV, compared to PRRSV (p < 0.05). The matured MoDCs triggered T lymphocytes in autologous peripheral blood mononuclear cells (PBMCs) activation, proliferation, and differentiation into effector cytotoxic T lymphocyte, suggesting increased amount of activated T cells after MnGNP-PRRSV treatment. Additionally, the function of T cells to kill PRRSV infected cells was 83.98 ± 2.62 % when triggered by MnGNP-PRRSV, compared to 60 ± 4.7 % in PRRSV group (p < 0.001). These results indicate that MnGNP with entrapped inactivated PRRSV can effectively and specifically target dendritic cells for maturation and activation, and subsequently improve T cell activation, proliferation and function to kill PRRSV infected cells.