In immunocompetent mice bearing syngeneic EMT6 tumours, a combination of ICI antibodies used to block PD-1 and stimulate ICOS resulted in the detection by the murine equivalent of 89Zr-crefmirlimab of a significant increase in intratumoral CD8 T cells 11 days after commencement of ICI therapy. Here, CD8A is linked to neoplasm.