[Effects of immunohistochemical conditions on the results of PD-L1 (22C3) staining].

Objective

To investigate the optimal experimental conditions (including antigen retrieval time, antibody titers and antibody incubation time) for reliable detection of programmed death-ligand 1 (PD-L1) expression using PD-L1 (22C3) antibody concentrate, and to establish a laboratory developed test for PD-L1 detection.

Methods

Using Dako PD-L1 IHC 22C3 pharmDX staining procedure and scoring guidelines as the standard reference (group A), the PD-L1 expression in 25 tissue specimens (including 15 lung cancer tissues, 5 tonsil tissues and 5 placenta tissues) was detected with Flex+/HRP detection kit (EnVision) under 8 different experimental conditions (groups B1 to B8). The staining results were then compared to those in group A.

Results

In group B1, 3 tissue samples showed the percentages of PD-L1 positive tumor cells were similar to those in group A, while the percentages of PD-L1 positive tumor cells were lower than those in group A in the other samples. In group B7, two case showed a positive rate higher than that in group A that was also above the positive cut-off value, and the rest of the samples had a percentage of PD-L1 positive tumor cells slightly higher than that in group A, but still below the positive cut-off value. The staining results of group B8 were the closest to those of group A compared with the other groups. Although the percentages of PD-L1 positive tumor cells in the B2 to B6 groups were decreased in various degrees as compared with group A, they were still concordant with group A's classification (positive vs. negative) and would not change the choice of clinical treatments.

Conclusions

The experimental conditions are associated with detection rate of PD-L1 expression using 22C3 antibody. In the present study, the most-suitable alterative conditions in the PD-L1 detection using 22C3 antibody concentrate are those applied in the group B8 (including antigen retrieval in Dako PT Link tank at 97 ℃, pH 6.0 for 40 min and incubation with 22C3 antibodies (1∶100 dilution) at room temperature for 60 min, incubation with EnVision Flex+Linker at room temperature for 30 min, incubation with EnVision/HRP at room temperature for 30 min and DAB staining for 5 min), which could provide reliable results at minimum costs.