T-cell responses to survivin in cancer patients undergoing radiation therapy

Abstract

Purpose: The goal of this study was to determine if radiation therapy (RT) of human cancer enhances or diminishes tumor-specific T-cell reactivity. This is important if immunotherapy is to be harnessed to improve the outcome of cancer radiotherapy.

Experimental design: Lymphocytes were isolated from colorectal cancer (CRC) patients before, during, and after presurgical chemoradiotherapy. Similar samples were taken from prostate cancer patients receiving standard RT. The level of CD8(+) T cells capable of binding tetramers for the tumor-associated antigen survivin, which is overexpressed in both cancer types, was enumerated in HLA-A*0201 patient samples. CD4(+), CD25(high), Foxp3(+) cells were also enumerated to evaluate therapy-induced changes in T(regulatory) cells. For CRC patients, most of whom were enrolled in a clinical trial, pathologic response data were available, as well as biopsy and resection specimens, which were stained for cytoplasmic and intranuclear survivin.

Results: Survivin-specific CD8(+) T lymphocytes were detected in the peripheral blood of CRC and prostate cancer patients and increased after therapy in some, but not all, patients. Increases were more common in CRC patients whose tumor was downstaged after chemoradiotherapy. Biopsy specimens from this cohort generally had higher nuclear to cytoplasmic survivin expression. T(regulatory) cells generally increased in the circulation following therapy but only in CRC patients.

Conclusion: This study indicates that RT may increase the likelihood of some cancer patients responding to immunotherapy and lays a basis for future investigations aimed at combining radiation and immunotherapy.

Fig. 1

A, levels of circulating survivin-reactive CD8⁺ T cells for individual CRC (left) and prostate cancer (right) patients before, during, and after treatment. Solid lines, overall upward trend; dashed lines, downward trend. B, ratios of CD4⁺ to CD8⁺ increase in patients before, during, and after treatment. Box and whisker diagrams summarize individual CD4⁺ to CD8⁺ T-cell ratios in cancer patients and in five healthy controls.^▪, P = 0.008.

Fig. 2

The frequencies of circulating T_regulatory cells in CRC and prostate cancer patients were generally less than those observed in eight healthy volunteers and seemed to rise toward completion of CRT in CRC patients but not after RT in prostate cancer patients. Data are the % of CD4⁺ cells that are CD25^high and Foxp3⁺ presented as box and whisker diagram (A) and as time course for individual patients (B), with solid lines indicating an upward trend (*, P = 0.039), dashed lines do not.

Fig. 3

The tumor antigen survivin was highly expressed in CRC patient specimens, whereas it remained mostly undetectable in normal colon tissue. Survivin seemed to be primarily located in the cytoplasm but occasionally nuclear staining was evident. Magnification, ×800.

Fig. 4

The expression of survivin in CRC tissue sections (21 biopsies, 10 resections), Responders (T downstaging) had higher nuclear survivin levels at biopsy and less at resection. Cytoplasmic survivin levels also were lower in resection specimens from responders. A, box and whisker diagram showing data as median percent tumor staining positive for cytoplasmic (left) and nuclear (right) survivin. Biopsies of patients who responded to preoperative CRT had higher ratios of nuclear to cytoplasmic survivin (B), express more survivin (C), and have more promising changes in circulating survivin-specific C08⁺ T cells than biopsies from nonresponders (D). Solid lines indicate an upward trend; dashed lines do not.