A new optogenetic medical technology called “optogenetic immunomodulation” that uses light to kick-start immune system response is being developed by scientists at the University of Massachusetts Medical School in Worcester 
(UMMS) and the Center for Translational Cancer Research at the Texas A&M Health Science Center Institute of Biosciences & Technology in College Station, Texas.
In the lab, optogenetic immunomodulation has been demonstrated to work by using near-infrared light to stimulate immune cells to attack melanoma tumors in mice, with the research team showing they can selectively activate an immune response by controlling calcium ion flow (Ca2+) into cells — heralded as a breakthrough that could facilitate less invasive, better controlled, and more selective immunotherapies for treating cancer.
“This is the first time anybody has used optogenetic techniques to stimulate the immune system, much less to fight cancer cells,” says study co-author and UMMS assistant professor of biochemistry and molecular pharmacology Gang Han, PhD, in a release. “The advantage an optogenetic approach has over other immunotherapies, which typically activate global immune responses, is that we now have the tools to closely monitor the dose and location of the treatment to mitigate potential side effects to healthy tissues.”
An Open Source paper explaining the research has been published in the journal eLife, entitled “Near-infrared photoactivatable control of Ca2+ signaling and optogenetic immunomodulation,” published in eLife, co-authored by Han, with Lian He, Yuanwei Zhang, Guolin Ma, Peng Tan, Zhanjun Li, Shengbing Zang, Xiang Wu, Ji Jing, Shaohai Fang, Lijuan Zhou, Youjun Wang, Yun Huang, Patrick G. Hogan, and Yubin Zhou, variously representing the University of Massachusetts Beijing Normal University and La Jolla Institute for Allergy and Immunology.
The investigators present an NIR-stimulable optogenetic platform (termed Opto-CRAC) that selectively and remotely controls Ca2+ oscillations and Ca2+-responsive gene expression to regulate the function of non-excitable cells, including T-lymphocytes, macrophages, and dendritic cells, thus overcoming limitations of the technology imposed by a lack of strict ion selectivity and inability to extend the spectra sensitivity into the near-infrared (NIR) tissue transmissible range.
The researchers note that when coupled to upconversion nanoparticles, the optogenetic operation window is shifted from the visible range to NIR wavelengths to enable wireless photoactivation of Ca2+-dependent signaling and optogenetic modulation of immunoinflammatory responses.
The coauthors explain that in a mouse model of melanoma by using ovalbumin as surrogate tumor antigen, Opto-CRAC has been shown to act as a genetically-encoded “photoactivatable adjuvant” to improve antigen-specific immune responses to specifically destruct tumor cells, concluding that their study “represents a solid step forward towards the goal of achieving remote and wireless control of Ca2+-modulated activities with tailored function.”
The UMMS release notes that nerve cells incorporate with light-sensitive proteins that enable researchers to activate or deactivate nerve impulses by exposing them to a particular color of light, but that adapting this technology for use in other cells has proved to be a challenge. Researchers explain that while optogenetic technologies rely on electrical impulses in neurons to efficiently transmit messages, other types of cells employ different, more diverse, communication methods, which makes them more difficult to activate and deactivate. Often target cells are also located deeper in the body where light has difficulty penetrating.
Han and his team have been working in collaboration with Yubin Zhou, PhD, a co-author of the eLife paper and an assistant professor at the Center for Translational Cancer Research at the Texas A&M Health Science Center Institute of Biosciences & Technology, jointly approaching these problems by focusing on calcium ion flow into cells as a potential on/off switch and relying on specially engineered up-conversion nanoparticles to activate and deactivate.
On his TAMU HSC website, Zhou observes that very recent identification of novel proteins responsible for calcium entry across the plasma membrane and mitochondria heralds the “opening of a Pandora’s box” in the quest of new mechanisms underlying calcium and its downstream signaling pathways. Research interests in the Zhou lab at TAMU HSC are currently directed toward developing greater understanding of the molecular and structural basis of novel calcium channels.
Zhou said that by integrating knowledge learned from the calcium channel research, and by combining parallel chemical biology and protein engineering approaches, his team seeks to devise “light-switchable optical tools” for non-invasive control of calcium signaling at high spatial-temporal resolution.
He explained that these tools will be applied to interrogate calcium signaling in mammalian cells and mouse models at precise locations and times, thus helping to reveal pathogenic mechanisms of tumorigenesis, autoimmune, and inflammatory disorders, and that similar strategies can, in the future, be extended to photo-manipulate other important signaling pathways as opportunities emerge. He is confident that knowledge gained from these studies is likely to facilitate discovery of improved or new immunomodulating and neuromodulating therapies.
Meanwhile, Han and his team at UMMS have been genetically engineering dendritic cells with a light-sensitive calcium gate-controlling protein. The release notes that when exposed to blue light, calcium ion gates on the dendritic cell open, activating it, and that once activated, the role of dendritic cells is to program T-cells that then attack infected or cancerous cells. Conversely, when the light is turned off, the calcium gates close and the dendritic cells deactivate.
Unlike blue light, near-infrared light being employed by Han and his team can penetrate tissue up to a depth of two centimeters, and when this near-infrared light reaches the nanoparticle inside an animal, it is converted to blue light, which in turn activates the light sensitive protein controlling calcium flow to the cell.
“When we exposed a near-infrared laser beam to these animal models injected with both the nanoparticle and the genetically engineered immune cells, this caused calcium channels on the dendritic cells to open and we saw a corresponding increase in the number of T-cells that were activated,” Han said, adding, “More importantly, we saw significantly suppressed tumor growth and reduced tumor volume in these animals. This suggests that the activated dendritic cells were successfully programming T-cells to attack the tumor.”
One advantage of this method is that it enables fine-tuning of which cells get activated and where in the body, a specificity with potential to reduce systemic side effects often associated with other types of targeted cancer immunotherapies.
“It’s also likely that this technique can be adapted to study other immune, heart, endocrine, or hematopoietic cells. Any cell that used calcium to perform its task could potentially be activated using this newly developed technology,” Han said. “The flexibility of this system means it can be adapted to explore other cellular processes while minimally interfering with other physiological or biological functions.”
