Biodegradable Nanoparticle Mediated Antigen Delivery to Human Cord Blood Derived Dendritic Cells for Induction of Primary T Cell Responses

Abstract

Dendritic cells (DCs) in the peripheral tissues act as sentinels of the immune system. They detect and capture pathogens entering the body and present their antigens to T cells to trigger responses directed towards elimination of the pathogen. The induction of peripheral tolerance against self and certain foreign antigens is also believed to be mediated through DCs. The outcome of any immune response is largely controlled by the microenvironment of antigen capture, processing and presentation by DCs. The “context” of antigen delivery to DCs will directly influence the microenvironment of antigen presentation and hence the regulation of immune responses. We report here preliminary investigations describing the formulation of a pharmaceutically acceptable, biodegradable, and strategic nanoparticulate delivery system, and its application for efficient antigen loading of DCs to achieve antigen specific T cell activation. “Pathogen-mimicking” nanoparticles capable of interacting with DCs were fabricated by incorporating monophosphoryl lipid A (MPLA; toll-like receptor (TLR) 4 ligand) or CpG ODN (seq #2006; TLR9 ligand) in biodegradable copolymer, poly(_d,_l-lactic-co-glycolic acid) (PLGA). The uptake of PLGA nanoparticles by human umbilical cord blood derived DCs (DCs propagated from CD34₊ progenitors) was conclusively demonstrated by scanning electron microscopy (SEM), fluorescence activated cell sorting (FACS) and confocal laser scanning microscopy (CLSM). Cell phenotype at day 12 of cultures was determined as immature DC using specific cell surface markers, i.e. CD11c_hi (∼90%), MHC-II₊ (∼70%), CD86_low (∼20%), CD83_low (∼5%), CD80₊ (∼40%), CD40₊ (∼40%), and CCR7_low (∼5%). Tetanus toxoid (TT), a model antigen, was encapsulated in nanoparticles along with an immunomodulator, i.e. either MPLA or CpG ODN. DCs pulsed with various antigen formulations were co-cultured with autologous naïve T cells at various cell ratios (DC: T cells were 1:5–20). The DCs pulsed with TT and MPLA together in nanoparticles induced significantly higher T cell proliferation (P<0.05) as compared to when DCs pulsed with TT and MPLA in solution were employed. A similar trend was observed when CpG ODN was used instead of MPLA in the TT nanoparticles. This strategy of antigen delivery to DCs was then tested with a cancer vaccine candidate, a MUC1 lipopeptide. The T cell proliferation observed in the presence of nanoparticulate MUC1 and MPLA pulsed-DCs was much higher than DCs pulsed with soluble antigen (P<0.0005). These results indicate that PLGA nanoparticles mimicking certain features of pathogens are efficient delivery systems for targeting vaccine antigens to DCs and activation of potent T cell responses.

Keywords::

• CD34 stem cells
• Antigen delivery
• immunization
• Primary immune response
• MPLA
• CpG ODN