PEGylated and CD47-conjugated nanoellipsoidal artificial antigen-presenting cells minimize phagocytosis and augment anti-tumor T-cell responses.

PURPOSE

Antigen-presenting cells (APCs) are powerful tools to expand antigen-specific T cells ex vivo and in vivo for tumor immunotherapy, but suffer from time-consuming generation and biosafety concerns raised by live cells. Alternatively, the cell-free artificial antigen-presenting cells (aAPCs) have been rapidly developed. Nanoscale aAPCs are recently proposed owing to their superior biodistribution and reduced embolism than conventional cell-sized aAPCs, but pose the challenges: easier cellular uptake and smaller contact surface area with T cells than the cell-sized counterparts. This study aimed to fabricate a new "stealth" nano-aAPCs with microscale contact surface area to minimize cellular uptake and activate antigen-specific T cells by combination uses of ellipsoidal stretch, PEGylation, and self-marker CD47-Fc conjugation.

METHODS

The spherical polylactic-co-glycolic acid nanoparticles were fabricated using a double-emulsion method, and then stretched twofold using film-stretching procedure followed by PEGylation and co-coupling with CD47-Fc, H-2K/TRP2-Ig dimers, and anti-CD28. The resulting PEGylated and CD47-conjugated nanoellipsoidal aAPCs (EaAPC) were co-cultured with macrophages or spleen lymphocytes and also infused into melanoma-bearing mice. The in vitro and in vivo effects were evaluated and compared with the nanospherical aAPCs (SaAPC), nanoellipsoidal aAPCs (EaAPC), or PEGylated nanoellipsoidal aAPC (EaAPC).

RESULTS

EaAPC markedly reduced cellular uptake in vitro and in vivo, as compared with EaAPC, EaAPC, SaAPC, and Blank-NPs and expanded naïve TRP2-specific CD8 T cells in the co-cultures with spleen lymphocytes. After three infusions, the EaAPC showed much stronger effects on facilitating TRP2-specific CD8 T-cell proliferation, local infiltration, and tumor necrosis in the melanoma-bearing mice and on inhibiting tumor growth than the control aAPCs.

CONCLUSION

The superimposed or synergistic effects of ellipsoidal stretch, PEGylation, and CD47-Fc conjugation minimized cellular uptake of nano-aAPCs and enhanced their functionality to expand antigen-specific T cells and inhibit tumor growth, thus suggesting a more valuable strategy to design "stealth" nanoscale aAPCs suitable for tumor active immunotherapy.