CD4 and cancer: Based on increasing histology-driven evidence from human tumor tissues suggesting CD4+ cells as critical biomarkers to determine therapy efficacy in oncolytic virus 72, CAR T cells 73, and immune checkpoint inhibitor therapy 74-79, 89Zr-CD4-Mb immunoPET holds great promise for clinical translation as a valuable tool for the noninvasive monitoring of CD4+ cells, and the patient-individualized prediction of cancer immunotherapy outcomes.