CD8A and neoplasm: To image antigen-specific CD8+ CTLs with high resolution in the tumour microenvironment, we performed three-plex 3D volumetric LSM-SIM imaging on day 5 (48 h post i.v. injection of ErNP–aCD8 and QD–OVA–tetramer probes on day 3) post vaccination by pErNP–OVA–CpG B. While the pErNP vaccine signal in the tumour was weak by this time after the first vaccination, both ErNP–aCD8 (red colour in Fig. 5b) and QD–OVA–tetramer (green colour in Fig. 5b) signals were strong.