問：什么是腫瘤移植模型？
答：人的腫瘤移植到小鼠體內(nèi)構(gòu)建的人源化腫瘤模型
問：這種模型意義在哪？
答：篩藥，為人民服務(wù)。（請為偉大的小鼠致敬�。�
問：為啥要構(gòu)建腫瘤模型，不能跳過直接上臨床？不也可以篩藥嗎？
答：嗯，好主意，要不你先來好不好？
.......
問：什么是CDX , PDX?
答：急什么，認真聽小編講就是了。
 

       人源腫瘤細胞系異種移植（cell derived xenograft, CDX），即將體外傳代培養(yǎng)的腫瘤細胞接種至免疫缺陷小鼠，接種部位常為皮下，靜脈或原位。 
 
       話說早在20世紀90年代早期，美國國立癌癥研究所（National Cancer Institute, NCI)就 依據(jù)來源于9種不同類型腫瘤（腦，結(jié)腸癌，白血病，肺，黑素瘤、卵巢癌、腎癌、乳腺癌和前列腺癌) 的60位癌癥患者腫瘤細胞系，引入了一種"disease-oriented"的藥物篩選策略，簡單來說，就是先用人腫瘤細胞系進行高通量體外藥物篩選，再用CDX模型進行體內(nèi)驗證，【Cancer Cell Lines for Drug Discovery and Development 】
 
       由于CDX模型細胞系容易獲得，有大量已發(fā)表的文獻關(guān)于其基因組學(xué)、細胞功能學(xué)及藥效反應(yīng)的數(shù)據(jù)可供參考，建模成本低等優(yōu)勢，【PDX模型與腫瘤個體化用藥指導(dǎo)】在當時可以說是風(fēng)靡各大實驗室。
 
       但是2016年，NCI卻決定從其藥篩系統(tǒng)中讓已經(jīng)使用了25年的NCI60細胞系“退休！
 
       為什么會發(fā)生這種轉(zhuǎn)變？！
 
       原來，研究者逐漸發(fā)現(xiàn)人源腫瘤細胞系經(jīng)長期體外培養(yǎng)后， 其腫瘤細胞生物學(xué)行為及基因譜表達水平、 腫瘤異質(zhì)性都與原始腫瘤組織存在較大的差異， 從而在預(yù)測臨床藥效方面不甚理想。有研究表明， 經(jīng)此模型鑒定篩選的藥物僅約 1/3在二期臨床試驗中驗證有效【Relationships between drug activity in NCI preclinical in vitro and in vivo models and early clinical trials.】，【PDX 模型在腫瘤轉(zhuǎn)化醫(yī)學(xué)中的應(yīng)用與發(fā)展】
 
       不過嘛，長江后浪推前浪，退休了CDX，就會有更優(yōu)秀的腫瘤模型崛起！這就是接下來小編要為大家重點介紹PDX啦~
 

       人源腫瘤組織來源移植瘤模型 (patientl derived xenograft ，PDX)，通過將病人新鮮的瘤組織直接移植到免疫缺陷小鼠體內(nèi)而建立的腫瘤模型，常見接種部位為皮下，原位。具體流程如下圖。

Fig. 1 Engraftment and expansion of patient-derived solid tumor xenografts. Young adult NSG mice are engrafted with solid tumors (shown as red) Human stroma accompanying the tumor is shown in blue. Primary solid tumors are engrafted subcutaneously, orthotopically, or under the renal capsule. Established grafts are excised from primary recipients, a portion is cryopreserved, and a portion is analyzed for gene expression, including copy number variation (CNV). The remainder is expanded through serial transplantation in secondary and tertiary NSG recipients to generate cohorts of sufficient size for therapeutic trials. At each stage tumor samples are cryopreserved and gene expression analyzed to compare with the primary tumor analyzed directly ex vivo from the patient. The primary recipients of solid tumors retain human-derived stroma (blue). Tumors in secondary recipients contain a mixture of human-derived and mouse-derived stroma (mixture of blue and green). Tumors
in tertiary recipients contain predominantly mouse stroma (green) 【Human Cancer Growth and Therapy In NOD/SCID/IL2Rγnull (NSG) Mice 】

       既然能使科研界沿用幾十年的CDX被“退休”，那就必然代表新生力量PDX青出于藍，目前該模型被研究者普遍認可的優(yōu)勢主要包括【人體腫瘤PDX移植模型的優(yōu)與劣 】：


1. 移植所用標本直接來源于人體腫瘤組織，未經(jīng)過體外培養(yǎng)，穩(wěn)定地保留了腫瘤的遺傳特性、組織學(xué)和表型特征，即腫瘤異質(zhì)性； 

       如下圖所示，為構(gòu)建的人源結(jié)直腸癌小鼠移植模型，通過不同形態(tài)學(xué)特征的組織染色，發(fā)現(xiàn)在某些情況下，新鮮病灶和傳代病灶均表現(xiàn)出良好的分化表型，某些樣本均出現(xiàn)透明細胞，黏液分泌細胞和細胞壞死區(qū)域等，同時，少數(shù)腫瘤表現(xiàn)出高度的多形性，保持未分化狀態(tài)（Fig2B）。

Figure 1. Setup and characterization of the xenopatient platform. A, generation of xenopatients. After surgical removal from patient, each metastatic colorectal cancer specimen was cut in small pieces and 2 fragments were implanted in 2 mice. After engraftment and tumor mass formation, the tumors were passaged and expanded for 2 generations until production of 2 cohorts, each consisting of 12 mice. These were randomized for treatment with placebo (6 mice) or cetuximab (6 mice). B, xenografted tumors retained the histopathologic characteristics of original samples. Hematoxylin and eosin stains of representative cases with different morphologic features. In some instances, both fresh and passaged lesions displayed a well-differentiated phenotype, with cells describing irregular pluristratified tubular/acinar structures with multiple lumens embedded in a scarce stromal matrix. Other samples had a clear-cell appearance or featured high nuclear grade and areas of necrosis. In some cases, discohesive mucus-secreting cells defined a moderately differentiated phenotype typical of mucinuos adenocarcinoma, with signet-ring elements showing peripheral nuclear delocalization and abundant intervening stroma associated with desmoplastic reaction. Finally, a few tumors exhibited high-grade pleomorphism and could be pathologically classified as poorly differentiated adenocarcinomas. Scale bar, 50 μm. C, genetic concordance between xenografts and their original counterparts. Similar groups of samples are evidenced by applying a Pearson-based hierarchical clustering to copy number calls
 
 
2. PDX可用于篩選化療藥物敏感或耐藥標記物，其試驗結(jié)果具有較好的臨床預(yù)見性
 
       以胃癌PDX為例，圖A表示對 cetuximab治療不敏感與敏感小鼠中EGFR DNA/mRNA/EGFR受體蛋白拷貝數(shù)差異，發(fā)現(xiàn)敏感小鼠中拷貝數(shù)普遍較高，并且通過腫瘤生長曲線，IHC, FISH對比，最終得出:對 cetuximab敏感的小鼠模型，其EGFR表達普遍上調(diào)。
 

 

Figure 1 | The response to cetuximab treatment and genetic profile of GC-PDX models. Panel A: The PDX-GC models are sorted by the tumor response to cetuximab (DT/DC). The responders at the right part display higher EGFR mRNA level and IHC staining intensity, and the only two cases (GA0075 and GA0152, CN . 5) of gene amplification. Panel B: The representative images of responders and non-responders. The responders GA0152 and GA0075 display IHC score 31, and gene amplification (GA0075, CN 5 5.8; GA0152, CN . 15), while non-responders GA0119 and GA0139 are with IHC low
expression and no gene amplification. Left: Representative tumor growth curves of responders and non-responders. Middle: IHC analysis of tumor models; Right: Dual-color FISH assay in gastric carcinoma. Probe for EGFR locus is labeled in red and CEP7 labeled in green. Blue: Nuclei.
 
       除此外，另有PDX在移植過程中較好地保留了腫瘤間質(zhì)和干細胞成分，使得腫瘤的生長微環(huán)境更接近實際情況，還可為腫瘤樣本的保存和傳代提供大量標本等。
 
       剛開始小編也說了，建模是為了什么？篩藥！
 
       這些荷瘤小鼠可以作為病人的“替身”(avatar)，代替病人去測試不同藥物方案的治療效果，從中篩選出最有效的治療方案，從而避免藥物毒副作用以及經(jīng)濟上的浪費【PDX模型與腫瘤個體化用藥指導(dǎo) 】，具體流程參照下圖。
 

Establishment and testing of PDTX models. Excess tumour specimens not needed for clinical diagnosis are obtained from the consented patients (F0). Non-necrotic areas of these tumours are sectioned into ~3 mm3 pieces and, after processing, implanted subcutaneously into anaesthetized 5-week to 6-week-old female athymic nude mice. During the engraftment phase, tumours are allowed to establish and grow and then are harvested upon reaching a size of 1,500 mm3 (F1). Similar protocols are employed for subsequent expansion cohort (F2) and treatment cohort (F3 … Fn). Typically, biological assays are performed on tumours in early generations (≤F5); these biological assays include drug efficacy studies, rational combination studies and the development of predictive biomarkers for novel targeted therapies. If the developed biomarkers achieved accurate prediction in a validation set of PDTX models (or ‘xenopatients’), they might be translated into early phase clinical trials as tools for patient selection strategies. Abbreviations: PDTX, patient-derived tumour xenografts; RES, resistant; SEN, sensitive. 【Patient-derived tumour xenografts as models for oncology drug development 】
 
       當然了，雖然PDX優(yōu)勢頗多，但局限性也不容忽視【PDX 模型在腫瘤轉(zhuǎn)化醫(yī)學(xué)中的應(yīng)用與發(fā)展 】
 
       目前PDX模型原始腫瘤的主要來源為手術(shù)切除，建模難度高且不能反復(fù)獲取，構(gòu)建時間長且成功率不穩(wěn)定，隨著傳代次數(shù)增加腫瘤微環(huán)境也會逐漸被小鼠細胞外基質(zhì)取代，因此對于傳代次數(shù)有一定限制。值得一提的是，負荷腫瘤的小鼠均為免疫缺陷的小鼠，因而該模型也無法用于篩選免疫相關(guān)藥物。
 
       總的來說，兩種模型各有千秋，某種程度上CDX可以被認為是傳代次數(shù)太多已經(jīng)難以追溯的PDX模型，【PDX模型與腫瘤個體化用藥指導(dǎo) 】經(jīng)過體內(nèi)外交替?zhèn)鞔��?strong>原始腫瘤組織中只有最適應(yīng)體外培養(yǎng)條件的單個克隆被保留下來，喪失了克隆異質(zhì)性，從而難以對臨床藥效進行預(yù)測。而PDX最大的優(yōu)勢也在于此，保留了腫瘤異質(zhì)性，更符合臨床腫瘤特征。

百奧賽圖
   百奧賽圖基因生物技術(shù)有限公司（簡稱“百奧賽圖”），公司總部現(xiàn)位于北京亦莊，在上海張江、江蘇海門、美國波士頓設(shè)有分公司，同時在武漢、廣州、成都等地設(shè)有辦事處。
   2008年在美國成立并成功運營，2009年北京百奧賽圖總公司成立，并于2012年將總部遷址到北京亦莊經(jīng)濟技術(shù)開發(fā)區(qū)。
   百奧賽圖是一家以穩(wěn)定、高效基因編輯技術(shù)平臺為依托，以模式動物定制服務(wù)、重要模式動物開發(fā)與規(guī)�；�繁殖與供應(yīng)、體內(nèi)藥理藥效評價服務(wù)、抗體藥物研發(fā)外包服務(wù)為一體的高科技生物醫(yī)藥企業(yè)。
  公司秉承以追求更好的人類健康為宗旨，旨在為新藥研發(fā)領(lǐng)域提供高品質(zhì)的產(chǎn)品與服務(wù)。