通常的癌癥疫苗是通過促進(jìn)腫瘤抗原（tumor antigen）的釋放，并且吸引抗原提成細(xì)胞（antigen presenting cells, APCs）將釋放的腫瘤抗原提呈給T細(xì)胞使其活化,，發(fā)揮效應(yīng)來殺滅癌細(xì)胞,。但是，這個策略用在惡性黑色素瘤（melanoma）的治療上,，就面臨一個問題——活化的T細(xì)胞在消滅腫瘤細(xì)胞的同時也誤傷正常的黑色素細(xì)胞（melanocyte）,，因為許多與惡性黑色素瘤相關(guān)的抗原是正常黑色素細(xì)胞在產(chǎn)生黑色素過程中的蛋白。
在最新的《Nature Biotechnology》advance on-line publication上,，Mayo Clinic的科學(xué)家卻用了一種新的癌癥疫苗策略來達(dá)到治療目的：利用刻意殺死健康的皮膚細(xì)胞來啟動免疫系統(tǒng),，最終消滅腫瘤。因為熱休克蛋白70（heat shock protein 70, hsp70）是免疫耐受（immunological tolerance）的重要開關(guān),，可以阻斷免疫耐受而使免疫系統(tǒng)對自身抗原（self-antigen）產(chǎn)生反應(yīng),。通過皮內(nèi)注射質(zhì)粒DNA疫苗，表達(dá)作用于轉(zhuǎn)錄的細(xì)胞毒性基因和hsp70基因,，研究者設(shè)想細(xì)胞毒性基因可以引起正常細(xì)胞的死亡,，而hsp70就可以促發(fā)自體的免疫反應(yīng)，而這個免疫反應(yīng)進(jìn)而消滅腫瘤細(xì)胞,。
通過激活免疫系統(tǒng)使癌癥疫苗的共同途徑,，但是不管用什么方式，都回面臨相同的風(fēng)險,。如果被激活的免疫系統(tǒng)“矯枉過正”,，開始大量進(jìn)攻正常的組織和細(xì)胞，就會出現(xiàn)自體免疫病的副作用,。這種新方法也不例外,，研究者也有同樣的擔(dān)心,。但是實驗結(jié)果卻出人意料,，大量被激活的T細(xì)胞殺死了惡性黑色素瘤；不過,，在它們引起自身免疫病之前,，由于調(diào)節(jié)性T細(xì)胞（regulatory T cell）的出現(xiàn)，而被抑制了,。
多么令人鼓舞?。翰坏诙啻沃委熀螅械膶嶒炐∈蟮钠つw癌都被根除了,；而且又不存在自身免疫病的問題,。
接下去,，研究會進(jìn)一步向兩個方面展開。一方面當(dāng)然是研究人體對這種免疫治療的反應(yīng),，如果順利,，則開始進(jìn)行臨床實驗。另一方面,，研究者希望將這種策略擴(kuò)展到其他的腫瘤類型,，例如乳腺癌、肺癌和前列腺癌,。
在通常情況下,，對正常細(xì)胞的破壞是治療中需要避免的。而這種新的治療策略卻反其道而行之,，利用殺傷正常細(xì)胞觸發(fā)免疫效應(yīng),，使癌細(xì)胞也“同歸于盡”。
A simple method to cure established tumors by inflammatory killing of normal cells
We describe a simple technology used to cure an established metastatic disease. Intradermal injection of plasmid DNA encoding a transcriptionally targeted cytotoxic gene, along with hsp70, not only promoted tissue-specific, inflammatory killing of normal melanocytes, but also induced a CD8+ T-cell–dependent, antigen-specific response in mice that eradicated systemically established B16 tumors. This CD8+ T cell response was subsequently suppressed in vivo within a few days. The data demonstrate that deliberate destruction of normal tissue can be exploited to generate immunity against a malignant disease originating from that tissue. This approach obviates the need to identify tumor antigens and does not require complex isolation of tumor cells or their derivatives. In addition, it provides a model system for studying the mechanisms underlying the etiology and control of autoimmune diseases. Finally, despite targeting normal tissue, therapy could be separated from development of overt autoimmune symptoms, suggesting that the strategy may be valuable against tumors derived from both non-essential and essential tissue types.
Figure 1. Intradermal injection of Tyr-HSVtk plasmid DNA leads to expression in melanocytes.
(a) Plasmids used in these studies. The Tyr-HSVtk plasmid uses a hybrid promoter of three tandem copies of a 200–base pair (bp) element of the murine tyrosinase enhancer47 upstream of a 270-bp fragment of the tyrosinase promoter28 to drive expression of the HSVtk gene27. In Tyr-LacZ, the HSVtk cDNA was replaced with the LacZ gene28. In CMV-hsp70, the murine hsp70 gene11 is driven by the CMV promoter in pCR3.1 (Invitrogen) (full details of plasmids available on request). (b) At 5 d after plasmid injections (days 1, 2, 3) and GCV or PBS treatment (days 1–5), skin samples at the site of intradermal plasmid injections (as indicated) from two separate mice per treatment were used to prepare cDNA, which was subsequently analyzed by PCR using primers specific for either murine tyrosinase or GAPDH as a loading control. (c) At 5 d after administration of nothing (none) or Tyr-HSVtk plasmid (10 g) (days 1, 2, 3) along with either PBS (Tyr-HSVtk + PBS) or GCV treatment (Tyr-HSVtk + GCV) on days 1–5, skin at the site of intradermal injection was analyzed for the L-DOPA oxidase activity of the tyrosinase enzyme in the samples. Results from two separate experiments (filled or hatched columns) are shown. Error bars represent standard deviations.
Figure 2. Immune consequences of Tyr-HSVtk + CMV-hsp70 intradermal injections.
(a–e) Sections of skin at sites of three daily intradermal injections of the following. (a) PBS; a displaced hair follicle at the needle injection site is shown, and white arrows indicate examples of pigmented hair bulbs, indicating the presence of intact melanocytes. (b) (10 g Tyr-HSVtk + 10 g empty plasmid) and GCV i.p. (c) (10 g CMV-hsp70 + 10 g empty plasmid) + GCV. (d,e) (10 g Tyr-HSVtk + 10 g CMV-hsp70) + GCV. Sections for a–e were recovered 72 h after the first injection, stained with H&E and examined for evidence of immune infiltrates. Regions encompassing dense infiltrates are delineated by white arrows. (f) Skin samples at the site of intradermal plasmid injections (72 h later, as indicated) from two separate mice per plasmid combination were snap frozen and used to prepare cDNA, which was subsequently analyzed by PCR using primers specific for murine cytokines including IFN- (f). PCR for GAPDH was used as a reference for levels of expression of each RNA.
