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Abstract
Background
Pembrolizumab is an antibody designed against programmed cell-death protein-1 (PD-1), which is expressed on the surface of activated T cells. Tumor cells can upregulate PD-L1, which binds to PD-1 and mediates T cell anergy. By antagonizing the PD-1/PD-L1 binding, pembrolizumab can enhance T cell killing in multiple tumor types. RT can be immunostimulatory, therefore, combination therapy may yield enhanced efficacy. Here, we evaluated the immune biomarkers related to a patient who failed combined treatment with radiation and pembrolizumab.
Methods
Phase I clinical trial (
Results
The patient was randomized to fractionated radiation 20 Gy in 5 fractions to an anterior chest wall metastasis. Following RT he received 5 cycles of pembrolizumab. He was found to have disease progression at radiated chest wall lesion as well as non-radiated metastatic sites on subsequent image studies. Flow cytometry analysis of his peripheral lymphocyte substance revealed no change in CD8+ cells from baseline (25%) compared to post-radiation (24%) and post-pembrolizumab (24%). CD4+ cells at baseline, post-RT and post-pembrolizumab were 43%, 42% and 35%. Flow cytometry of peripheral blood post-pembrolizumab revealed high level of PD-1 expression on CD8 cells, with low level expression of PD-1 on CD4 cells. RT-PCR on biopsies taken pre-RT and post-RT revealed no T lymphocyte transcripts.
Conclusions
We present a patient with metastatic clear cell RCC who experienced rapid disease progression following combination treatment. The patient failed to demonstrate expansion of CD8 lymphocytes, the CD4 cells failed to express PD-1 marker and the tumor biopsy before and after RT failed to demonstrate the presence of T lymphocytes. We hypothesize that the lack of tumor infiltrating lymphocytes may play a role in treatment failure. Alternatively, we hypothesize that the tumor microenvironment is heterogeneous with known non-redundant immune checkpoints, which may have contributed to treatment failure. Currently, we are exploring alternative mechanisms of resistance to pembrolizumab by analyzing immunocheckpoints such as Ox-40, CTLA-4, CD73, Tim3, and Lag3.
Trial registration
ClinicalTrials.gov identifier
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