Extended Data Fig. 4: mPET for developing immunoPET detection of T-cell exhaustion.

Mice bearing HKP1 lung tumours were monitored for terminal and progenitor T-cell exhaustion using antibodies against CD39 or Ly108 during disease progression. BLI of lung tumour burden was measured prior to injection, with representative CT slice in thoracic cavity showing potential branch occlusions (bright spots off alveolar bifurcation). Ly108, a marker of effector T cells, decreased with disease burden whereas CD39, a marker of severely exhausted T cells, increased, according to flow-cytometry data. mPET imaging with [⁸⁹Zr]Zr-DFO-CD39 and [¹²⁴I]I-Ly108 at day 7 and day 14 with three levels of tumour burden. At day 7 no discernible difference between low, medium or high tumour burden in mice is seen with either [⁸⁹Zr]Zr-DFO-CD39 or [¹²⁴I]I-Ly108. By day 14, BLI shows an appreciable increase in tumour burden in all mice, with tumour occlusions seen on CT. By mPET there was a general increase in [⁸⁹Zr]Zr-DFO-CD39 and [¹²⁴I]I-Ly108 uptake in the lungs compared to the day-7 group. Less lung uptake was visible with [¹²⁴I]I-Ly108, with increasing tumour burden in the day-14 imaged mice. mPET again could separate two radiotracers in vivo and could be used with further radiotracer engineering to define T-cell exhaustion. N = 3 mice imaged per week (n = 6 total cohort), with each mouse receiving simultaneously [⁸⁹Zr]Zr-DFO-CD39 and [¹²⁴I]I-Ly108 by intravenous injection 48 hours prior to mPET. %IA/CC represents percent injected activity per cubic centimetre.