Theragnostic glycol chitosan‐conjugated gold nanoparticles for photoacoustic imaging of regional lymph nodes and delivering tumor antigen to lymph nodes

Lymph node mapping is important in cancer immunotherapy because the morphology of lymph nodes is one of the crucial evaluation criteria of immune responses. We developed new theragnostic glycol‐chitosan‐coated gold nanoparticles (GC‐AuNPs), which highlighted lymph nodes in ultrasound‐guided photoacoustic (US/PA) imaging. Moreover, the ovalbumin epitope was conjugated GC‐AuNPs (OVA‐GC‐AuNPs) for delivering tumor antigen to lymph node resident macrophage. In vitro studies proved the vigorous endocytosis activity of J774A.1 macrophage and consequent strong photoacoustic signals from them. The macrophages also presented a tumor antigen when OVA‐GC‐AuNPs were used for cellular uptake. After the lingual injection of GC‐AuNPs into healthy mice, cervical lymph nodes were visible in a US/PA imaging system with high contrast. Three‐dimensional analysis of lymph nodes revealed that the accumulation of GC‐AuNPs in the lymph node increased as the post‐injection time passed. Histological analysis showed GC‐AuNPs or OVA‐GC‐AuNPs located in subcapsular and medullar sinuses where macrophages are abun-dant. Our new theragnostic GC‐AuNPs present a superior performance in US/PA imaging of lymph nodes without targeting moieties or complex surface modification. Simultaneously, GC‐AuNPs were able to deliver tumor antigens to cause macrophages to present the OVA epitope at targeted lymph nodes, which would be valuable for cancer immunotherapy.