Kinetics of Intratumoral Immune Cell Activation During Chemoradiation for Cervical Cancer

Purpose

Radiation therapy has direct cytotoxic effects on tumor-infiltrating lymphocytes, but it also has immune stimulatory effects that increase immune cell infiltration. The dynamics of these competing effects on immune cells at the site of the tumor are poorly characterized during chemoradiation treatment (CRT) because of the difficulty of obtaining consecutive tumor biopsies. We used a minimally invasive cervical cytobrushing method to analyze the kinetics of intratumoral immune cell changes in patients with cervical cancer during CRT.

Methods and Materials

Cervical brushings were obtained from 20 patients with cervical cancer at baseline and during fractionated radiation therapy and cisplatin (weeks 1, 3, and 5). Matching peripheral blood mononuclear cells were obtained from 9 patients at the same time points. Cells were analyzed using multispectral flow cytometry to identify T cell and myeloid cell subsets and their activation status. Changes in immune cell subsets throughout treatment were calculated using matched-pair analysis with Wilcoxon rank sum test.

Results

We observed a significant decline in CD3+ total T cells, as well as CD8+ and CD4+ T-cell subsets in the first week of treatment from baseline, followed by variable expansion at weeks 3 and 5. This coincided with higher levels of proliferating CD8+ T cells expressing Ki67 at week 3 of treatment. The percentages of activated CD8+ T cells expressing CD69 continuously increased over the course of treatment, whereas the percentage of activated CD11c+CD11b– dendritic cells was highest during the first week. Many of these changes were not observed in the blood.

Conclusions

Our results identified immune dynamic changes during CRT, indicating that CRT may be immune activating at the site of the tumor. This study also suggests the importance of sequential analyses of the local tumor microenvironment in addition to peripheral blood.

Introduction

Cervical cancer is among the most common malignancies among female patients worldwide, with an annual incidence of more than 500,000 women and an annual death rate of more than 250,000 women. (1) Locally advanced cervical cancer can be treated effectively with chemoradiation therapy (CRT) over a 7-week course of treatment requiring daily external beam radiation followed by brachytherapy (2); however, the rate of response to treatment is highly variable. 3, 4 Rapid responders to CRT are more likely to remain free of disease in the long term, but the mechanisms that underlie this heterogeneity in response rates are not well understood. Historically, radiation therapy (RT) was considered to have immunosuppressive effects; lymphocytes are one of the most radiosensitive cell types, (5) and peripheral lymphocyte counts generally decrease through the course of pelvic radiation. (6) More recently, radiation has been shown to uncover tumor antigens through tumor cell death, which enhances antigen presentation and induces antitumor T-cell responses. (7) Furthermore, radiation increases the release of damage associated molecular patterns, which attract and activate cells of the innate and adaptive immune system. (8)

Because of the challenges of obtaining frequent biopsies during RT, studies of immune activation are based on animal models using hypofractionated regimens, clinical studies with evaluation of tumors at very limited time points, or a focus on peripheral immune responses. As a result, the kinetics of intratumoral immune activation during RT are poorly understood. To discern the sequential changes within the cervix tumor microenvironment during CRT, we adapted the cytobrush methodology, demonstrated to be a reliable and minimally invasive technique to characterize immune cells within the female genital tract of HIV-positive patients in a multicenter clinical trial. (9) We recently reported the utility of this methodology for monitoring CD4 T cells at multiple mucosal tissues after intranasal vaccination in rhesus macaques. (10) By using this minimally invasive method, we characterized the immune infiltrate with multispectral flow cytometry at baseline and at weeks 1, 3, and 5 of CRT. Because T-cell infiltration has been associated with better prognosis in patients with cervical cancer and myeloid cells are known to modulate this infiltration, we focused our analysis on these populations. (11)