今年1月31日，史丹福大學醫學院(Stanford University School of Medicine)，免疫治療權威羅納•利維(Ronald Levy)教授與其研發團隊在國際重量級期刊《Science Translation Medicine》發表了一種革命性的新型免疫檢查點治療方式。這種新方式只需「局部、單次、低劑量」的投以免疫檢查點藥物，即可治癒多種不同類型的小鼠腫瘤，更成功讓小鼠對腫瘤產生全身性的免疫治療效果。鑑於此療法在動物實驗取得的驚人成效，史丹佛大學目前已著手進行臨床試驗準備，預計前期將招收15位淋巴癌病患進行人體實驗，並視實驗進展再擴及到其他腫瘤治療。
CpG DNA是細菌體內常見的未甲基化特殊DNA序列，主要與TLR9接受器結合並活化多種免疫細胞，CpG DNA過去即被證明在腫瘤治療上具顯著療效，然而由於藥物無法專一性運送至病灶，而系統性注射又容易導致副作用過強等問題，因此CpG DNA過去大多被當成疫苗佐劑使用。
目前所有的免疫檢查點藥物療程與大部分的結合治療研究，都是沿用傳統癌症藥物的邏輯，以高劑量持續的全身性給藥方式。這種治療方式，對於生物體複雜的免疫系統或許不是最好的選擇。去年10月15日，在《Clinical Cancer Research》和《Cancer Immunology Research》上，同日發表的兩篇文章便發現，合併兩種免疫檢查點藥物治療時，兩藥分別投藥的時間將嚴重影響治療效果，一味持續性的給藥反有不利影響。
Cancer “vaccine” makes tumours vanish
A DNA-antibody combination banishes cancer in mouse models, with human trials about to start. Andrew Masterson reports.
A vaccine effective against a wide range of cancers is one step nearer.
GOMBERT, SIGRID/GETTY IMAGES
A combination of a tiny segment of DNA and a specific antibody injected into a solid tumour has been shown to remove not only the target tumour, but also others in the body, at least in mice.
So confident are they of the effectiveness of their approach, scientists at the Stanford University School of Medicine in the US are this month starting a clinical trial using human patients.
Like several other treatments, the combination therapy, reported in the journal Science Translational Medicine, prompts the body’s own immune system to tackle tumours. However, unlike others, it functions as a one-size-fits-all strategy. To a significant extent, it seems, it is not necessary to first identify the type of cancer involved.
“When we use these two agents together, we see the elimination of tumours all over the body,” says oncologist Ronald Levy, one of the authors of the study.
“This approach bypasses the need to identify tumour-specific immune targets and doesn’t require wholesale activation of the immune system or customisation of a patient’s immune cells.”
The Stanford team’s strategy works by exploiting the curiously ambivalent relationship between cancer tumours and immune cells called T cells. The latter function to attack bodily invaders through detecting abnormal proteins.
Initially the T cells will recognise such proteins on the surface of cancer cells and enter the developing tumour. However, as the tumour continues to grow, T cell activity drops off. In a sense, the immune system gives up.
Levy and his colleagues found a way to reactivate the moribund T cells. To do this, they inject a target tumour with a couple of micrograms of a short stretch of DNA called a CpG oligonucleotide. This works with nearby immune cells to activate a receptor called OX40 on the surface of the T cells.
CpG oligonucleotide is already used to bolster several types of cancer treatment.
At this point, the second agent – an antibody that binds to OX40 – comes into action, revivifying T cells, but only those within the tumour. This is important, because the combination effectively generates a cohort of immune cells pre-programmed to attack only cancer-specific proteins.
Once the process is under way, the scientists report, the tumour-hungry T cells leave the initial site and distribute through the body, attacking any and all other similar tumours they find.
“Our approach uses a one-time application of very small amounts of two agents to stimulate the immune cells only within the tumour itself,” explains Levy.
“In the mice, we saw amazing, body-wide effects, including the elimination of tumours all over the animal.”
The therapy has been trialled against several different types of cancers in mice. The first trial involved 90 animals with lymphoma tumours on both sides of their bodies. In each, only one tumour was treated. The paper details that 87 out of the 90 were cured. The cancer returned in three cases, but went into permanent remission after a second treatment.
Mice carrying breast, colon and melanoma tumours were also treated successfully. Trials were also conducted on mice genetically engineered to develop multiple breast cancers. In many cases treating the first tumour to appear prevented others arising.
While the treatment is effective against a range of cancers, each application conditions T cells to fight only one. Tests on mice with two types of tumour found that only the type treated went into remission, leaving the other unaffected.
“This is a very targeted approach,” Levy says. “Only the tumour that shares the protein targets displayed by the treated site is affected. We’re attacking specific targets without having to identify exactly what proteins the T-cells are recognising.”
An initial human trial will get underway soon, with the researchers looking to recruit about 15 patients with low-grade lymphoma.
Injection helps the immune system obliterate tumors, at least in mice
Tumors are growing on each side of this mouse’s body just behind its forelegs.
SAGIV-BARFI ET AL./SCIENCE TRANSLATIONAL MEDICINE
Our immune cells can destroy tumors, but sometimes they need a kick in the pants to do the job. A study in mice describes a new way to incite these attacks by injecting an immune-stimulating mixture directly into tumors. The shots trigger the animals’ immune system to eliminate not only the injected tumors, but also other tumors in their bodies.
“This is a very important study,” says immunologist Keith Knutson of the Mayo Clinic in Jacksonville, Florida, who wasn’t connected to the research. “It provides a good pretext for going into humans.”
To bring the wrath of the immune system down on tumors, researchers have tried shooting them up with a variety of molecules and viruses. So far, however, almost every candidate they’ve tested hasn’t worked in people.
Hoping to develop a more potent approach, medical oncologist Ron Levy of Stanford University in Palo Alto, California, and colleagues used mice to test the cancer-fighting capabilities of some 20 molecules, including several types of antibodies that activate immune cells. The researchers first induced tumors by inserting cancer cells just below the skin at two different locations on the animals’ abdomens. After tumors started growing at both sites, the scientists injected the molecules, alone or in combination, into one tumor in each mouse. They then tracked the responses of both tumors.