Mojgan Ahmadzadeh

Tumor antigen-specific T cells are found within melanomas, yet tumors continue to grow. Although the tumor microenvironment is thought to influence the suppression of tumor-reactive T cells, the underlying mechanisms for this T-cell dysfunction are not clear. Here, we report that the majority of tumor infiltrating T lymphocytes (TIL), including MART-1/Melan-A melanoma antigen-specific CD8 T cells, predominantly expressed PD-1, in contrast to T cells in normal tissues and peripheral blood T lymphocytes (PBL). PD-1(+) TIL expressed CTLA-4 and Ki-67, markers that were not expressed by PD-1(-) TIL and T cells in the normal tissues and PBL. Moreover, PD-1(+) TIL were primarily HLA-DR(+) and CD127(-), in contrast to PD-1(-) TIL. Effector cytokine production by PD-1(+) TIL was impaired compared with PD-1(-) TIL and PBL. Collectively, the phenotypic and functional characterizations of TIL revealed a significantly higher frequency and level of PD-1 expression on TIL compared with normal tissue T-cell infiltrates and PBL, and PD-1 expression correlated with an exhausted phenotype and impaired effector function. These findings suggest that the tumor microenvironment can lead to up-regulation of PD-1 on tumor-reactive T cells and contribute to impaired antitumor immune responses.

Many tumors express tumor-specific antigens capable of being presented to CD8+ T cells by major histocompatibility complex (MHC) class I molecules. Antigen presentation models predict that the tumor cell itself should present these antigens to T cells. However, when conditions for the priming of tumor-specific responses were examined in mice, no detectable presentation of MHC class I-restricted tumor antigens by the tumor itself was found. Rather, tumor antigens were exclusively presented by host bone marrow-derived cells. Thus, MHC class I-restricted antigens are efficiently transferred in vivo to bone marrow-derived antigen-presenting cells, which suggests that human leukocyte antigen matching may be less critical in the application of tumor vaccines than previously thought.

It is unknown whether the human immune system frequently mounts a T cell response against mutations expressed by common epithelial cancers. Using a next-generation sequencing approach combined with high-throughput immunologic screening, we demonstrated that tumor-infiltrating lymphocytes (TILs) from 9 out of 10 patients with metastatic gastrointestinal cancers contained CD4(+) and/or CD8(+) T cells that recognized one to three neo-epitopes derived from somatic mutations expressed by the patient's own tumor. There were no immunogenic epitopes shared between these patients. However, we identified in one patient a human leukocyte antigen-C*08:02-restricted T cell receptor from CD8(+) TILs that targeted the KRAS(G12D) hotspot driver mutation found in many human cancers. Thus, a high frequency of patients with common gastrointestinal cancers harbor immunogenic mutations that can potentially be exploited for the development of highly personalized immunotherapies.

Interleukin-2 (IL-2) is historically known as a T-cell growth factor. Accumulating evidence from knockout mice suggests that IL-2 is crucial for the homeostasis and function of CD4+ CD25+ regulatory T cells in vivo. However, the impact of administered IL-2 in an immune intact host has not been studied in rodents or humans. Here, we studied the impact of IL-2 administration on the frequency and function of human CD4+ CD25(hi) T cells in immune intact patients with melanoma or renal cancer. We found that the frequency of CD4+ CD25(hi) T cells was significantly increased after IL-2 treatment, and these cells expressed phenotypic markers associated with regulatory T cells. In addition, both transcript and protein levels of Foxp3, a transcription factor exclusively expressed on regulatory T cells, were consistently increased in CD4 T cells following IL-2 treatment. Functional analysis of the increased number of CD4+ CD25(hi) T cells revealed that this population exhibited potent suppressive activity in vitro. Collectively, our results demonstrate that administration of high-dose IL-2 increased the frequency of circulating CD4+ CD25(hi) Foxp3+ regulatory T cells. Our findings suggest that selective inhibition of IL-2-mediated enhancement of regulatory T cells may improve the therapeutic effectiveness of IL-2 administration.

Lymphopenia is a serious consequence of HIV infection and the administration of cancer chemotherapeutic agents. Although growth factors can be administered to patients to increase circulating neutrophils, there is no effective method to stimulate CD8+ lymphocyte production in humans, in vivo. This report is the first to describe the administration of recombinant interleukin-7 to humans and demonstrates the ability of this cytokine to mediate selective increases in CD4+ and CD8+ lymphocytes along with a decrease in the percentage of CD4+ T-regulatory cells. These studies suggest an important role for interleukin-7 in the treatment of patients with lymphopenia.