林 燕,梁 萍
解放軍總醫院 介入超聲科,北京 100853
熱消融治療調節機體抗腫瘤免疫研究進展
林 燕,梁 萍
解放軍總醫院 介入超聲科,北京 100853
近年來影像引導下的熱消融技術在肝、腎等腫瘤的治療中發揮了重要的作用。局部熱消融技術能夠在一定程度上激活機體的抗腫瘤免疫,是真正意義上的體內腫瘤疫苗,但其誘發的免疫反應尚不足以完全消滅腫瘤或長期發揮預防腫瘤復發,因此與其他免疫調節手段同時應用的聯合療法可能發揮更有效的作用。
熱消融;免疫調節;抗原;免疫治療
近20年來局部腫瘤熱消融技術迅速發展,極大提高了失去手術機會病人的生存率,并在一定程度上取代了外科手術。局部熱消融技術是應用極熱(射頻、微波消融)或極冷(冷凍消融)的溫度變化在局部破壞腫瘤組織,進而達到治療的目的。此外熱消融過程本身能夠在原位留下腫瘤壞死殘骸,這些殘骸作為抗原能引發抗腫瘤免疫應答,有助于預防局部腫瘤復發。本文對腫瘤熱消融后機體產生的免疫應答及不同熱消融技術激活機體免疫反應的區別進行綜述,為局部熱消融聯合免疫調節方法預防腫瘤局部復發提供理論支持。
射頻消融是將1根或者多根射頻電極置于腫瘤病灶內,通過高頻交變電流的作用在局部產生60 ~ 100℃的高溫,使腫瘤組織發生凝固性壞死[1-2]。微波消融是通過微波輻射器把某頻率的電磁波能量轉換成輻射能,后者被組織吸收轉換為熱能,進而對腫瘤組織造成凝固性破壞。兩種消融技術都會在局部遺留凝固性壞死殘骸,因此二者對機體局部和全身的免疫狀態產生類似的影響。
與射頻和微波消融不同,冷凍消融對免疫系統的作用可以表現為激活或者抑制性作用。以往的研究認為,冷凍消融主要導致細胞發生凋亡,細胞發生凋亡時不釋放細胞內容物(抗原、熱休克蛋白和高遷移率族蛋白B1)進而導致免疫耐受,局部的壞死細胞則可作為免疫激活劑,而凋亡細胞可導致局部免疫耐受和免疫抑制,近期的研究認為,冷凍消融的頻次影響腫瘤的生長和局部的T細胞募集,并且是機體冷凍消融后處于免疫活化或免疫抑制狀態的決定性因素[3-6]。
多項研究對射頻消融后細胞因子、炎癥趨化因子和應激素變化情況進行了檢測,發現射頻消融后數小時至數天機體血清中的促炎性細胞因子如IL-1β、IL-6、IL-8及TNF-α水平在射頻消融后出現暫時性的升高,引起明顯的體溫升高伴腎上腺素水平升高,但不導致嚴重的全身性炎癥反應綜合征(systemic inflammatory response syndrome,SIRS)及多器官功能衰竭[7-11]。而冷凍消融可引發較嚴重的全身炎癥反應綜合征,部分病人伴隨冷休克現象,主要發生于肝組織的冷凍消融[12-17]。動物實驗證實,發生SIRS的風險與冷凍消融區的范圍呈正相關,消融的肝組織>35%時發生SIRS的風險明顯升高[15]。冷凍消融后數小時內血清中一系列細胞因子(如IFN-γ、TNF-α、IL-6、IL-12)水平升高,但不出現IL-10水平的升高[14,18-19]。射頻消融、冷凍消融后大鼠血清中細胞因子水平的對比研究發現在冷凍消融后1 ~ 6 h血清中IL-6水平明顯升高,IL-10水平僅有輕微升高[16]。而在前列腺癌病人冷凍消融后,血清TNF-α和IFN-γ可以持續增高達4 h以上[20]。
動物實驗證實射頻消融可導致肝組織中HSP-70、HSP-90、糖蛋白96轉錄、蛋白水平的表達上調以及HMGB1轉位至腫瘤細胞質內和細胞間質中,且HSP-70的表達升高主要位于射頻消融區的邊緣[21-26]。對大鼠肝的不同部位進行射頻消融,發現HSP-70的表達程度與消融區距大血管的相對位置有關,滋養血管能促進周邊肝細胞的合成代謝以及熱休克蛋白的表達[27]。此外HSP-70/HSP-90的表達水平與射頻消融應用的能量具有相關性[22]。微波消融正常大鼠腎組織后,通過ELISA方法可檢測到HSP-70的表達,然而與射頻消融相比,微波消融后HSP-70的表達上調低于射頻消融[28]。
臨床研究發現射頻消融后腫瘤病人血清中的HSP-70水平顯著升高,然而血清HSP-70水平與消融區大小、腫瘤的組織學類型以及臨床和實驗室檢測指標并無明確相關性,但預后較好的病人常伴有消融后次日血清HSP-70水平的升高[29]。
文獻報道肺腫瘤患者接受射頻消融1個月后外周血循環中Treg(CD4+CD25+Foxp3+)比例明顯降低[8]。對20位原發性肝癌患者射頻消融后的淋巴細胞亞群結果進行分析,發現在消融1個月后患者的T淋巴細胞亞群比例(初始/記憶性CD4+、CD8+)無明顯變化,但循環中自然殺傷(natural killer,NK)細胞及活化T細胞的比例有所升高,而在治療后1周、4周CD3-CD56dim效應NK細胞的比例明顯增加[30-31]。動物實驗發現多種免疫細胞(中性粒細胞、巨噬細胞、漿細胞、樹突狀細胞、CD3+和CD4+T細胞)在消融治療后數小時至數天內可浸潤至消融區邊緣[32-34]。通過IFN-γELISPOT實驗對20例原發性肝癌病人射頻消融前的自身腫瘤抗原刺激的外周血單個核細胞進行檢測,消融前在4例病人體內發現腫瘤抗原反應性T細胞,而在射頻治療后1個月在9例病人體內發現該反應性T細胞,這提示射頻治療在體內發揮了調節抗腫瘤免疫的作用,這一結果在另外兩組原發性肝癌和結直腸肝轉移癌的隊列研究中得到了驗證[30,35]。
射頻誘導的T細胞應答具有抗原特異性,在原發性肝癌病人體內存在針對MAGE-1、NY-ESO-1、GPC3抗原的CD8+T細胞應答,在射頻治療前可檢測到上述抗原的特異性免疫應答,而在射頻治療后約50%病人出現了抗原特異性免疫應答的上調[36]。在射頻消融后腫瘤特異性T細胞免疫活化的原發性肝癌病人局部和遠處部位的腫瘤復發率類似,但是腫瘤抗原特異性T細胞比例與原發性肝癌無病生存率呈正相關[30,36]。
冷凍消融對特異性抗腫瘤免疫的調節作用尚無明確結論,以往的研究認為,冷凍消融引發機體免疫抑制,盡管外周血循環中的免疫效應細胞增加但卻不具有明顯的殺傷腫瘤細胞的作用,冷凍消融有可能通過誘導Treg細胞或通過延遲抗腫瘤免疫來發揮負調節作用[37-38]。與上述結論相反,有研究認為,接受冷凍治療的實驗動物存在免疫激活的現象,對負荷淋巴瘤的小鼠進行冷凍治療時可發現外周血淋巴細胞和脾細胞殺傷活性增加[39]。在小鼠結腸癌模型冷凍消融后7 d發現腫瘤特異性殺傷性T淋巴細胞活性增加,但這一效應僅在消融單個腫瘤結節時出現,而在消融多個結節后這一免疫激活效應反而減退,提示冷凍消融組織的范圍可能對消融后機體免疫活化或抑制具有重要影響[40]。
在小鼠肝腫瘤模型中2只(共10只)小鼠在微波消融后對再次種植的腫瘤產生抑制,提示微波消融后機體出現保護性抗腫瘤免疫,這一保護性作用在瘤內注射負載GMCSF的微球后大大提高,腹腔內CTLA-4封閉效果更為明顯,三者的聯合應用對遠處轉移的腫瘤也具有抑制作用[41]。此外從處理組小鼠體內分離到的脾細胞能夠在體外殺死肝腫瘤細胞。體外單克隆抗體封閉實驗證實這種殺傷作用是由T細胞(CD4+和CD8+)及NK細胞介導的,而多種方法的聯合應用能夠發揮更強大的作用[41]。
冷凍消融聯合瘤內注射未成熟樹突細胞能夠誘導活化CD4+CD8+殺傷性T細胞[42]。冷凍治療前應用抗CD4或CD25單克隆抗體進行Treg耗竭能夠增強這一協同效應[43]。聯合治療雖然能夠延緩腫瘤的生長,但與單獨冷凍消融相比,生存率并沒有顯著差異。冷凍消融前1 d向結腸癌小鼠注射環磷酰胺可以促進腫瘤特異性CD4+T細胞生成IFN-γ,并提高小鼠的生存率甚至完全治愈腫瘤,對治愈小鼠再次種植腫瘤小鼠仍可存活,而過繼性移植存活小鼠的淋巴結細胞能夠提高其他荷瘤小鼠的生存率,CD8+效應T細胞在其中發揮了重要的清除腫瘤作用,提示小鼠體內已建立了抗腫瘤免疫記憶。
臨床應用方面有冷凍消融聯合GM-CSF注射治療前列腺癌的文獻報道,T細胞對自體腫瘤抗原的活性在治療后輕度增加,但是免疫應答與臨床血清中前列腺特異性抗原水平無相關性[20]。在接受冷凍消融和GM-CSF注射聯合治療的部分腎癌病人中殺傷性T細胞活性和血清中抗腫瘤抗體的增加都與較好療效存在相關性。
我們的前期研究發現,在微波消融1個月后10例脾亢病人出現短暫的外周血T輔助細胞(CD3+CD4+)和B淋巴細胞數量的增加[44]。在另外一項大樣本的肝癌患者隊列研究中,我們將微波消融前及微波消融后各時間點(3 ~ 30 d)的穿刺組織的免疫細胞浸潤情況進行了分析,發現在微波消融區內、消融區、正常肝組織邊緣以及遠處未消融病灶內淋巴細胞(主要是CD3+T細胞,CD56+NK細胞和巨噬細胞)有明顯的局部浸潤,且淋巴細胞、巨噬細胞和CD56+NK細胞浸潤入微波消融區內的數量與局部復發風險呈負相關[45]。隨后10例原發性肝癌患者在微波消融后當日、微波消融后11 d、微波消融后100 d接受Ⅰ期臨床過繼性免疫治療。將自身腫瘤抗原特異性的樹突細胞在超聲引導下分別注射入消融區與正常肝組織的邊緣、腹股溝淋巴結內、體外活化的淋巴細胞。治療后1個月進行外周T淋巴細胞亞群檢測發現Treg(CD4+CD25+)細胞比例降低,而CD8+T細胞(CD8+CD28-)細胞比例升高,部分病人還出現乙肝病毒復制量的降低[46]。聯合應用免疫治療有可能在一定程度上增強微波消融在局部的免疫激活作用,起到預防原發性肝癌微波消融后復發的作用。
近20年來熱消融技術以其微創性和不遜于外科手術的療效等優點逐漸被腫瘤患者認識和接受,除了較好的局部腫瘤控制效果,熱消融治療還可以增強機體抗腫瘤免疫進而控制腫瘤進展。目前的研究認為,可能的機制包括: 1)熱消融治療后局部腫瘤組織壞死可以引起炎癥反應和危險信號如熱休克蛋白的釋放; 2)促進壞死腫瘤組織內和附近微環境內樹突細胞的募集和活化; 3)激活特異性抗腫瘤免疫,包括CD4+T細胞、CD8+T細胞的活化以及抗體的產生,進而促進局部腫瘤細胞的清除,控制遠處的腫瘤微小轉移灶和建立長期的抗腫瘤免疫記憶[18,37-39]。熱消融同時也清除了局部的Treg,解除了局部的抑制性免疫狀態,使得局部的免疫平衡趨向于抗腫瘤免疫[40,42-43]。然而熱消融自身對免疫系統的調節作用仍較為微弱,其單一療法不足以為機體提供全面的抗腫瘤保護作用[39,41]。熱消融治療對單發小病灶的療效遠優于晚期腫瘤,而聯合其他提高機體抗腫瘤免疫的療法有較好的應用前景,例如抗CTLA-4抗體、Treg耗竭等方法以及應用免疫佐劑(白介素、趨化因子、GM-CSF和TLR激動劑),但是上述聯合治療方案尚未廣泛應用于臨床。
機體自身免疫能夠消滅較小的和亞臨床階段的腫瘤,而熱消融治療能夠同時激活和提升機體自身的免疫狀態。通過誘導機體自身的應激反應,熱消融治療能夠打破機體的免疫耐受并活化機體的天然免疫和特異性抗腫瘤免疫,與其他方法如化療、免疫調節療法協同應用則可發揮更為強大的抗腫瘤作用。針對病人的個體化選擇的微創熱消融技術以及合理聯用免疫療法,將是未來治療各種惡性腫瘤的必然趨勢。
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Advances in thermal ablation therapy for regulating anti-tumor immunity
LIN Yan, LIANG Ping
Department of Intervention Ultrasound, Chinese PLA General Hospital, Beijing 100853, China
Corresponding author: LIANG Ping. Email: liangping301@hotmail.com
Image-guided thermal ablation technique plays an important role in treatment of hepatic and renal tumors. Thermal ablation technique can activate the anti-tumor immunity in vivo. However, the immune response of patients to them cannot completely eliminate the tumor or prevent its relapse. Thermal ablation should therefore be applied in combination with other immune-regulating therapies in order to bring its effect into full play.
thermal ablation; immuneregulation; antigen; immunotherapy
R 445.1
A
2095-5227(2014)05-0509-04
10.3969/j.issn.2095-5227.2014.05.031
時間:2014-02-13 10:13
http://www.cnki.net/kcms/detail/11.3275.R.20140213.1013.003.html
2013-11-18
國家科技部國際科技合作項目(2012DFG32070)
Supported by International S&T Cooperation Program of China(2012DFG 32070)
林燕,女,在讀博士。研究方向:肝癌熱消融與腫瘤免疫。Email: linyan_911@hotmail.com
梁萍,女,主任醫師,教授,博士生導師,主任。Email:liangping301@hotmail.com