Changes of CD68, CD163, and PD-L1 tumor expression during high-dose-rate and pulsed-dose-rate brachytherapy for cervical cancer

Abstract

Purpose: We hypothesized that radiation doses delivered with high-dose-rate (HDR) and pulsed-dose-rate (PDR) brachytherapy in patients with cervical cancer could trigger immune stimulation by modulating immune cells in the tumor microenvironment. The objective was to determine CD68, CD163, and PD-L1 expression in biopsies from patients with cervical cancer and to compare the effects of HDR vs. PDR brachytherapy on the expression of these proteins.

Methods and materials: Nineteen consecutive women (mean age, 55.9 years) with histologically proven cervical cancer scheduled for brachytherapy after standard external beam irradiation therapy combined with platinum-based chemotherapy were included in a prospective study. Core tissue biopsies were obtained before radiochemotherapy (biopsy #1), after completion of radiochemotherapy and before brachytherapy (biopsy #2), and 2 weeks after completion of brachytherapy (biopsy #3). HDR or PDR brachytherapy was delivered according to availability of equipment. CD68, CD163, and PD-L1 immunohistochemical expression was estimated using a quantitative method. Conditional logistic regression models were used to assess the relationship between gene expression and time of biopsy for each brachytherapy technique.

Results: In relation to CD68 and CD163, statistically significant relationships between gene expression and biopsy tissue samples were not found in any of the brachytherapy techniques, although there was trend toward downexpression of CD68 and CD163 in biopsies #2 and #3 in the HDR brachytherapy cohort only. There was a significant increase in PD-L1 expression in biopsy #3 also in the HDR cohort as compared with the PDR cohort.

Conclusions: Decreased CD68 and CD163 expression did not reach statistical significance, but this trend may have clinical translational potential. Overexpression of PD-L1 in tissue biopsies taken at 14 days in the HDR brachytherapy cohort may tentatively suggest that this time period would be an adequate interval for blockade of the PD-1/PD-L1 axis.

Keywords: Biopsy; Brachytherapy; Immunohistochemical.