Non invasive visualization of tumor infiltrating lymphocytes in patients with metastatic melanoma undergoing immune checkpoint inhibitor therapy: a pilot study
Early in the course of immunotherapy there is frequently a transient enlargement of tumor masses (pseudo progression) due to tumor infiltration by TILs. Current clinical imaging modalities are not able to distinguished pseudo progression from true tumor progression. Thus, patients often remain on treatment 4 8 weeks longer to confirm disease progression. Nuclear medicine offers the possibility to image immune cells and potentially discriminate pseudo progression and progression. We conducted a pilot study in patients with metastatic melanoma receiving ipilimumab (IPI) or pembrolizumab (PEMBRO) to assess safety and feasibility of SPECT/CT imaging with 99mTc interleukin 2 (99mTc HYNIC IL2) to detect TILs and distinguish between true progression from pseudo progression. Scans were performed prior to and after 12w treatment. After labelling,99mTc HYNIC IL2 was purified and diluted in 10 mL of 5% glucose with 0.1% human serum albumin. Of the 5 patients (2 treated with IPI and 3 with PEMBRO) enrolled, two failed to complete the second scan as they discontinued IPI due grade 3 colitis (1 patient) or patient refusal after developing multiple toxicities attributed to IPI (1 patient) Following the first scan, one patient reported to have a grade 1 pruritus with grade 1 pain. No other toxicities attributed to the radiopharmaceutical infusion were reported. Metastatic lesions could be visualized by 99mTc IL2 imaging and there was positive correlation between size and 99mTc HYNIC IL2 uptake, both before and after 12 weeks of therapy. The results of this pilot study demonstrate the safety and feasibility of 99mTc IL2 imaging and has led to a number of hypotheses to be tested in future studies.
Oncotarget