Researchers at the University of Pittsburgh Cancer Institute are carrying out ground-breaking work on tumor immunology. Modern technology is enabling scientists to learn more and more about how cancer evades the immune system. SelectScience® speaks to Theresa Whiteside, professor of pathology, immunology and otolaryngology to find out more.
Introduce yourself and your place of work
TW: I am Theresa Whiteside, and I’m a professor of pathology, immunology and otolaryngology at the University of Pittsburgh Cancer Institute located in Pittsburgh, Pennsylvania. I carry out research in the field of tumor immunology; by training I’m an immunologist, but for many years my interest has been cancer and how the immune system either promotes cancer or helps us to fight cancer.
Extracellular vesicle research
Would you please describe your work on tumor-derived exosomes and the need for this research?
TW: Tumors are very smart, they develop ways or steal ways from normal cells on how to manipulate their microenvironment. My interest lies in the mechanisms through which tumors suppress a patient’s immune system so that it cannot eliminate cancer.
It has been observed that if you obtain plasma, serum or any other body fluid from a cancer patient with an advanced disease, there is something in the patient’s specimen that kills activated immune cells. We made this observation many years ago, and at the time we didn’t know what to make of it.
Approximately 10 years ago, I heard about the existence of exosomes, which are extracellular vesicles found in plasma. We isolated these vesicles by high-speed ultracentrifugation of plasma and incubated the recovered vesicles with human activated T lymphocytes. We were fascinated to find that these vesicles disrupted the functions, and even survival of normal T-cells. That discovery led us to postulate that these tiny, virus-sized vesicles (now called “exosomes”), which are produced in large numbers by tumor cells, have the ability to somehow interfere with functions and induce apoptosis of normal immune cells. This theory emerged as a novel mechanism of tumor escape from the immune system, and that is how our research into these micro-vesicles began.
We’ve since learned that these extracellular vesicles (EVs) are quite heterogenous, containing EV subsets of various sizes derived from different cellular compartments of parent cells. We have now carried out extensive work on exosomes, the smallest subset of EVs, although we now use size exclusion chromatography instead of ultracentrifugation to isolate the vesicles from human body fluids.
A better indicator of disease
How do you intend to use the Quanterix Simoa HD-1 technology in your research?
TW: We are just beginning our collaboration with Quanterix, but our idea is the following: we know that the exosome lumen contains cytokines, albeit in femtomolar quantities. We also know that when people look for cytokines in the plasma of patients with cancer, sometimes only very low levels of the cytokines known to modulate tumor growth are found. This is strange, because with tumors that induce big changes in the tumor microenvironment (TME), you would expect the presence of cytokines that are involved in the tumor development and growth. Thus, we postulated that many of the cytokines in the TME do not circulate but are enclosed in exosomes, which deliver them to recipient cells.
We are developing a method that enables us to disrupt the vesicles carrying cytokines and measure the exosome cytokine content, but because the cytokines are present in femtomolar quantities, we needed an extremely sensitive assay to be able to detect intra-luminal cytokines. And that is where the Simoa technology comes into play.
It is our intention to use a Simoa-based assay to measure the cytokines released when we disrupt the exosomes. This is a very exciting possibility, because it is not what is readily floating in the plasma that will provide a good biomarker of cancer. The cytokines and factors inside the vesicle have been protected from degradation by proteolytic enzymes and so should be a much better indicator of disease.
We are currently working out the logistics and trying to make sure the vesicle disruption process (using mild detergents) does not interfere with the function of the cytokines and other factors that we want to measure. It is logical that this technology, with its ultra-high levels of sensitivity, will be good for further expanding our research.
What do you see as the future of your research?
TW: I think that the significance of exosomes as a ‘liquid biopsy” is s a very important concept. Exosomes are emerging as potentially one of the best biomarkers we’ve ever had for cancer as well as for the host immune system. Tumor cells and immune cells produce and release into extracellular space exosomes which carry the unique protein and genetic cargos that resemble their respective parent cells. These circulating exosomes represent “liquid biopsies” which faithfully inform about the content of their parent cells. However, these are very preliminary studies, and the work on exosomes as biomarkers in cancer has yet to be validated. Furthermore, we have shown that these exosomes are involved in epithelial mesenchymal transition (tumor promotion), angiogenesis and cellular communication. In fact, exosomes are involved in modulating multiple cellular pathways using molecular/genetic, mechanisms now under intensive investigations.
My research is clinically oriented. I want to know what is the clinical usefulness of exosomes as diagnostic, prognostic and treatment response biomarkers in cancer. Tumor-derived vesicles are very effective at re-programing functions of normal cells, converting them into tumor-supporting cells. I want to understand mechanisms underpinning this ability of exosomes to reprogram other cells in the TME to be able to develop strategies to prevent or inhibit reprogramming that promotes tumor growth. Thus, exosome-mediated interactions between cells in the TME are very important for us to understand, and uncovering the truth of what is contained inside exosomes will play a key role in the future of cancer research.
Article based on an interview with Theresa Whiteside at the Powering Precision Health Summit 2017 (PPHS 2017), MA, USA, October 24-25, 2017.
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