PD-L1 immunohistochemistry staining
We used the FDA approved test PD-L1 IHC 28-8 pharmDx to assess the PD-L1 expression on the bone marrow biopsies. This is a qualitative immunohistochemical assay which uses monoclonal mouse anti-PD-L1 Clone 22C3 intended for use in the detection of PD-L1 protein in formalin-fixed, paraffin-embedded tissues of different cancers such as non-small cell lung cancer and gastric/gastroesophageal junction adenocarcinoma. This test is used to identify patients who may be treated with pembrolizumab.
Bone marrow sections of 4-5 µm were made with tissues mounted on microscope slides then placed in a 58 ± 2 °C oven for 1 hour. The slides were stained with the PD-L1 IHC 22C3 pharmDx reagent and the samples were incubated. Finally, all the slides were numbered and labeled with codes.