Costimulatory biomarker-specific CD28 PET for early prediction of the response to PD-1 blockade in lung cancer.

The costimulatory receptor CD28 is indispensable for regulating T cell effector function, and the absence of co-stimulation is associated with poor immunotherapy response. However, longitudinal molecular imaging studies targeting CD28 as a costimulatory biomarker using positron emission tomography (PET) have not been reported. Here, we developed the co-stimulation-associated radiotracer [89Zr]Zr-DFO-anti-CD28 to enable early prediction of therapeutic response by identifying recovery of T cell responsiveness following programmed cell death protein 1 (PD-1) blockade in lung cancer. [89Zr]Zr-DFO-anti-CD28 demonstrated high specificity for CD28+ tumor-infiltrating lymphocytes (TILs) in vitro and in vivo. By monitoring CD28 expression and its loss within the tumor microenvironment, [89Zr]Zr-DFO-anti-CD28 PET identified responses to anti-PD-1 therapy earlier than changes in tumor volume observed at day 5, and increased radiotracer uptake correlated with more favorable treatment responses. Repeated PET imaging was performed to monitor dynamic changes in CD28+ TILs induced by different immunotherapies at day 14, and [89Zr]Zr-DFO-anti-CD28 PET captured the CD28-dependent restoration of T cell effector function, further supporting its potential for early prediction. Taken together, costimulatory biomarker-specific CD28 PET molecular imaging may enable noninvasive early prediction of responses to multiple immunotherapies and facilitate the application of precision medicine in lung cancer.