Molecular imaging of lymphoid organs and immune activation by positron emission tomography with a new [[sup.18]F]-labeled 2'-deoxycytidine analog

Monitoring immune function with molecular imaging could have a considerable impact on the diagnosis and treatment evaluation of immunological disorders and therapeutic immune responses. Positron emission tomography (PET) is a molecular imaging modality with applications in cancer and other diseases. PET studies of immune function have been limited by a lack of specialized probes. We identified [[sup.18]F]FAC (1-(2'-deoxy-2-[[sup.18]F]fluoroarabinofuranosyl) cytosine) by differential screening as a new PET probe for the deoxyribonucleotide salvage pathway. [[sup.18]F]FAC enabled visualization of lymphoid organs and was sensitive to localized immune activation in a mouse model of antitumor immunity. [[sup.18]F]FAC micro-PET also detected early changes in lymphoid mass in systemic autoimmunity and allowed evaluation of immunosuppressive therapy. These data support the use of [[sup.18]F]FAC PET for immune monitoring and suggest a wide range of clinical applications in immune disorders and in certain types of cancer.