We generated transgenic mice in which red, green, yellow, or cyan fluorescent proteins (together termed XFPs) were selectively expressed in neurons. All four XFPs labeled neurons in their entirety, including axons, nerve terminals, dendrites, and dendritic spines. Remarkably, each of 25 independently generated transgenic lines expressed XFP in a unique pattern, even though all incorporated identical regulatory elements (from the thyl gene). For example, all retinal ganglion cells or many cortical neurons were XFP positive in some lines, whereas only a few ganglion cells or only layer 5 cortical pyramids were labeled in others. In some lines, intense labeling of small neuronal subsets provided a Golgi-like vital stain. In double transgenic mice expressing two different XFPs, it was possible to differentially label 3 neuronal subsets in a single animal.

Conventional radiotherapy, in addition to its well-established tumoricidal effects, can also activate the host immune system. Radiation therapy modulates tumour phenotypes, enhances antigen presentation and tumour immunogenicity, increases production of cytokines and alters the tumour microenvironment, enabling destruction of the tumour by the immune system. Investigating the combination of radiotherapy with immunotherapeutic agents, which also promote the host antitumour immune response is, therefore, a logical progression. As the spectrum of clinical use of stereotactic radiotherapy continues to broaden, the question arose as to whether the ablative radiation doses used also stimulate immune responses and, if so, whether we can amplify these effects by combining immunotherapy and stereotactic ablative radiotherapy (SABR). In this Perspectives article, we explore the preclinical and clinical evidence supporting activation of the immune system following SABR. We then examine studies that provide data on the effectiveness of combining these two techniques — immunotherapy and SABR — in an approach that we have termed ‘ISABR.’ Lastly, we provide general guiding principles for the development of future clinical trials to investigate the efficacy of ISABR in the hope of generating further interest in these exciting developments.

Purpose This study was designed to provide the foundation for combining immunotherapy to induce tumor antigen-specific T cells with proton radiation therapy to exploit the activity of those T cells. We have recently defined “immunogenic modulation,” a mechanism distinct from immunogenic cell death, whereby tumor cells surviving photon radiation therapy nonetheless become more susceptible to cytotoxic T lymphocyte (CTL)-mediated lysis. However, to our knowledge, there are no prior studies examining the role of proton radiation on tumor immune sensitivity. Materials and Methods Using cell lines of tumors frequently treated with proton radiation, such as prostate, breast, lung, and chordoma, we examined the effect of proton radiation on the viability and induction of immunogenic modulation in tumor cells by flow cytometric and immunofluorescent analysis of surface phenotype and the functional immune consequences. Results These studies show for the first time that a) proton and photon radiation induced comparable upregulation of surface molecules involved in immune recognition (HLA, ICAM-1, and the tumor-associated antigens CEA and MUC-1), b) proton radiation mediated calreticulin cell-surface expression, increasing sensitivity to cytotoxic T-lymphocyte killing of tumor cells, and c) cancer stem cells (CSCs), which are resistant to the direct cytolytic activity of proton radiation, nonetheless upregulated calreticulin after radiation in a manner similar to non-CSCs. Conclusions These findings offer a rationale for the use of proton radiation in combination with immunotherapy, including for patients who have failed radiation therapy alone or have limited treatment options.

Radiation has long been the standard of care for many types of cancer. It is employed to locally eradicate tumor cells as well as alter tumor stroma with either curative or palliative intent. Radiation-induced cell damage is an immunologically active process in which danger signals are released that stimulate immune cells to phagocytose and present locally released tumor-associated antigens (TAAs). Recent studies have indicated that radiotherapy can also alter the phenotype of cancer cells that remain after treatment. These cells upregulate TAAs as well as markers, including major histocompatibility complex and costimulatory molecules, that make them much more immunostimulatory. As our understanding of the immunomodulatory effects of radiation has improved, interest in combining this type of therapy with immune-based therapies for the treatment of cancer has grown. Therapeutic cancer vaccines have been shown to initiate the dynamic process of host immune system activation, culminating in the recognition of host cancer cells as foreign. The environment created after radiotherapy can be exploited by active therapeutic cancer vaccines in order to achieve further, more robust immune system activation. This review highlights preclinical studies that have examined the alteration of the tumor microenvironment with regard to immunostimulatory molecules following different types of radiotherapy, including external beam radiation, radiolabeled monoclonal antibodies, bone-seeking radionuclides, and brachytherapy. We also emphasize how combination therapy with a cancer vaccine can exploit these changes to achieve improved therapeutic benefit. Lastly, we describe how these laboratory findings are translating into clinical benefit for patients undergoing combined radiotherapy and cancer vaccination.

Purpose: Saccharomyces cerevisiae, a nonpathogenic yeast, has been used previously as a vehicle to elicit immune responses to foreign antigens, and tumor-associated antigens, and has been shown to reduce tumor burden in mice. Studies were designed to determine if vaccination of human carcinoembryonic antigen (CEA)-transgenic (CEA-Tg) mice (where CEA is a selfantigen) with a recombinant S. cerevisiae construct expressing human CEA (yeast-CEA) elicits CEA-specificT-cell responses and antitumor activity. Experimental Design: CEA-Tg mice were vaccinated with yeast-CEA, and CD4 + and CD8 + T-cell responses were assessed after one and multiple administrations or vaccinations at multiple sites per administration. Antitumor activity was determined by tumor growth and overall survival in both pulmonary metastasis and s.c. pancreatic tumor models.Results: These studies demonstrate that recombinant yeast can break tolerance and that (a) yeast-CEA constructs elicit both CEA-specific CD4 + and CD8 + T-cell responses; (b) repeated yeast-CEA administration causes increased antigen-specificT-cell responses after each vaccination; (c) vaccination with yeast-CEA at multiple sites induces a greater T-cell response than the same dose given at a single site; and (d) tumor-bearing mice vaccinated with yeast-CEA show a reduction in tumor burden and increased overall survival compared to mock-treated or control yeast-vaccinated mice in both pulmonary metastasis and s.c. pancreatic tumor models. Conclusions: Vaccination with a heat-killed recombinant yeast expressing the tumor-associated antigen CEA induces CEA-specific immune responses, reduces tumor burden, and extends overall survival in CEA-Tg mice. These studies thus form the rationale for the incorporation of recombinant yeast-CEA and other recombinant yeast constructs in cancer immunotherapy protocols.