Lymphocyte homeostasis and the antitumor immune response

Immune responses to cancer: are they potential biomarkers of prognosis?

Recent technical improvements in evaluations of immune cells in situ and immune monitoring of patients with cancer have provided a wealth of new data confirming that immune cells play a key role in human cancer progression. This, in turn, has revived the expectation that immune endpoints might serve as reliable biomarkers of outcome or response to therapy in cancer. The recent successes in linking the T-cell signature in human colorectal carcinoma (CRC) with prognosis have provided a strong motive for searching for additional immune biomarkers that could serve as intermediate endpoints of response to therapy and outcome in human cancers. A number of potentially promising immune biomarkers have emerged, but most remain to be validated. Among them, the B-cell signature, as exemplified by expression of the immunoglobulin G kappa chain (IGKC) in tumor-infiltrating lymphocytes (TIL), has been validated as a biomarker of response to adjuvant therapy and better survival in patients with breast carcinoma and several other types of human solid tumors. Additional immune endpoints are being currently tested as potentially promising biomarkers in cancer. In view of currently growing use of immune cancer therapies, the search for immune biomarkers of prognosis are critically important for identifying patients who would benefit the most from adjuvant immunotherapy.

Immune responses to malignancies

Immune responses to tumor-associated antigens (TAs) are often detectable in tumor-bearing hosts, but they fail to eliminate malignant cells or prevent the development of metastases. Patients with cancer generate robust immune responses to infectious agents (bacteria and viruses) perceived as a "danger signal" but only ineffective weak responses to TAs, which are considered as "self." This fundamental difference in responses to self versus nonself is further magnified by the ability of tumors to subvert the host immune system. Tumors induce dysfunction and apoptosis in CD8(+) antitumor effector cells and promote expansion of regulatory T cells, myeloid-derived suppressor cells, or both, which downregulate antitumor immunity, allowing tumors to escape from the host immune system. The tumor escape is mediated by several distinct molecular mechanisms. Recent insights into these mechanisms encourage expectations that a more effective control of tumor-induced immune dysfunction will be developed in the near future. Novel strategies for immunotherapy of cancer are aimed at the protection and survival of antitumor effector cells and also of central memory T cells in the tumor microenvironment.

Human circulating CD4+CD25highFoxp3+ regulatory T cells kill autologous CD8+ but not CD4+ responder cells by Fas-mediated apoptosis

Mechanisms utilized by human regulatory T cells (Treg) for elimination of effector cells may vary. We investigated the possibility that the mechanism of Treg suppression depends on Fas/FasL-mediated apoptosis of responder cells (RC). CD4(+)CD25(high)Foxp3(+) Treg and autologous CD4(+)CD25(-) and CD8(+)CD25(-) subsets of RC were isolated from blood of 25 cancer patients and 15 normal controls and cocultured in the presence of OKT3 and IL-2 (150 or 1000 IU/ml). Suppression of RC proliferation was measured in CFSE assays. RC and Treg apoptosis was monitored by 7-aminoactinomycin D staining in flow-based cytotoxicity assays. Treg from all subjects expressed CD95(+), but only Treg from cancer patients expressed CD95L. These Treg, when activated via TCR plus IL-2, up-regulated CD95 and CD95L expression (p < 0.001) and suppressed CD8(+) RC proliferation (p < 0.001) by inducing Fas-mediated apoptosis. However, Treg cocultured with CD4(+) RC suppressed proliferation independently of Fas/FasL. In cocultures, Treg were found to be resistant to apoptosis in the presence of 1000 IU/ml IL-2, but at lower IL-2 concentrations (150 IU/ml) they became susceptible to RC-induced death. Thus, Treg and RC can reciprocally regulate Treg survival, depending on IL-2 concentrations present in cocultures. This divergent IL-2-dependent resistance or sensitivity of Treg and RC to apoptosis is amplified in patients with cancer.

Alterations in the T-Cell Receptor Variable β Gene–Restricted Profile of CD8+ T Lymphocytes in the Peripheral Circulation of Patients with Squamous Cell Carcinoma of the Head and Neck

PURPOSE

Apoptosis of activated CD8(+) T cells is often seen in tumor-infiltrating lymphocytes and circulating peripheral blood mononuclear cells (PBMC) in patients with squamous cell carcinoma of the head and neck (SCCHN). We investigated whether T-cell receptor (TCR) variable beta chain (Vbeta)-restricted T cells were more sensitive to apoptosis than non-TCR Vbeta-restricted T cells.

EXPERIMENTAL DESIGN

Flow cytometry analysis with anti-TCR Vbeta antibodies was used to define expansions and contractions of Vbeta-restricted T cells in patients with SCCHN relative to normal donors. This staining was combined with Annexin V binding to indicate early T-cell apoptosis.

RESULTS

The TCR Vbeta profiles of CD3(+) T cells in tumor-infiltrating lymphocytes and PBMCs of patients with SCCHN were altered relative to controls, with one to five expansions and numerous contractions of TCR Vbeta-restricted T cells detected. These types of alterations were significantly greater in CD8(+) than CD4(+) T cells. Enhanced Annexin V binding to CD8(+) T cells was evident in PBMCs obtained from all patients, with 3 of 13 showing preferential targeting for apoptosis of TCR Vbeta-restricted T cells.

CONCLUSIONS

TCR Vbeta profiles of CD8(+) T cells were altered in patients with SCCHN relative to normal controls. This may reflect increased apoptosis of expanded or contracted CD8(+) T cells, which define the TCR Vbeta profile of antigen-responsive T-cell populations in patients with cancer.