The absence of reliable biomarkers for the prediction of efficient antitumoral immune responses upon cancer immunotherapy and the growing interest in harnessing CD4+ T cells for their antitumoral potential prompted us to embark on in-depth validation of a minibody-based strategy for tracking endogenous CD4+ T-cell dynamics within tumors and lymphatic organs in vivo by whole-body immune positron emission tomography (immunoPET). This evidence concerns the gene CD4 and cancer.