CD4 and neoplasm: At the 3-hour imaging time point, CD4-derived PET signals could be clearly distinguished visually (Fig. 1E) and quantification revealed ~3.6-fold higher uptake in the spleen, ~3.5-fold higher uptake in tumor-draining lymph nodes, and ~1.8-fold higher uptake in PyMT tumors in hCD4-KI mice than in WT mice (Fig. 1, F and G, and fig.