{"entity":{"id":"idea-cd8-pet-io","kind":"idea","name":"CD8 PET to stop or switch immunotherapy early","aka":[],"tldr":"Scan for T cells inside the tumour a few weeks after starting immunotherapy. If they have not arrived, change course.","summary":"Scan for T cells inside the tumour a few weeks after starting immunotherapy, and change course if they have not arrived. Tracers such as 89Zr-crefmirlimab, a CD8 minibody, and 18F-AraG image T-cell infiltration and activation, and an early increase has tracked response in phase 2 studies. Response to checkpoint blockade requires T-cell infiltration, CT changes lag by months and pseudoprogression confounds RECIST, so an absent CD8 PET signal at week 4 could identify non-responders early. The test is a prospective trial in NSCLC or melanoma with week-4 CD8 PET, randomising PET non-responders to continue or switch. At early-clinical maturity it addresses the bottleneck No one can predict who responds to immunotherapy.","asOf":"2026-09-04","links":[{"label":"Farwell et al., CD8-targeted PET imaging of tumour-infiltrating T cells in patients with cancer: a phase 1 first-in-human study of 89Zr-Df-IAB22M2C (Journal of Nuclear Medicine 2021)","url":"https://doi.org/10.2967/jnumed.121.262485"}],"tags":[],"related":["f-18","zr-89"],"indications":[],"sections":[],"technologies":["immuno-pet"],"targets":[],"drugs":[],"companies":[],"institutions":[],"pathways":[],"terms":[],"trials":[],"people":[],"bottlenecks":[],"keyPapers":[],"journals":[],"dependsOn":[],"notes":[],"hypothesis":"Absence of CD8 PET increase at week 4 identifies non-responders with >85% specificity, enabling early switch to alternative therapy.","rationale":"Response to checkpoint blockade requires T-cell infiltration; CT changes lag by months; pseudoprogression confounds RECIST.","test":"Run a prospective trial in NSCLC or melanoma with week-4 CD8 PET; randomise PET-non-responders to continue vs switch.","maturity":"early-clinical"},"route":"/ideas/idea-cd8-pet-io/","neighbours":{"isotope":[{"id":"f-18","kind":"isotope","name":"Fluorine-18","route":"/isotopes/f-18/"},{"id":"zr-89","kind":"isotope","name":"Zirconium-89","route":"/isotopes/zr-89/"}],"technology":[{"id":"immuno-pet","kind":"technology","name":"Immuno-PET","route":"/technologies/immuno-pet/"}]}}