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治疗重点 - 如何解决Car-T疗法中的复发难题?

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发表于 2016-1-4 21:44:13 | 显示全部楼层 |阅读模式
治疗重点 - 如何解决Car-T疗法中的复发难题?
        Several companies’ CAR-T therapies have already produced impressive remission rates in leukaemia patients, but a high rate of relapses continues to cloud their long-term potential, especially considering the likely cost.
Several strategies have emerged to overcome this, one of which is Novartis ’s design of a CAR construct with a humanised antigen-binding region, the theory being that the commonly used murine CARs are being rejected by the immune system. But if this is the way forward it could leave Novartis ’s CTL019 – the industry‘s most-advanced CAR-T asset – and other murine constructs in a bind.
There is little data to go on at present, but one of the most hotly awaited presentations of the recent ASH meeting concerned the first data from a trial of six CTL019 -treated patients retreated with Novartis ’s new humanised, CD19 -targeting CAR, CTL119. Three of these went into complete remission, one of which was still ongoing at almost six months.
Dr Shannon Maude, of the Children's Hospital of Philadelphia, said it was particularly impressive that one of the remitting patients had had no response to the murine CTL019 . It is early days, but further positive data in a larger patient set would put Novartis in a quandary: should the group even bother filing CTL019 , or should it just switch to CTL119?
This might hit sentiment behind Novartis and the entire CAR-T space alike, given that the Swiss firm is the furthest advanced here, and it still hopes to submit CTL019 for approval next year. Switching to CTL119 would naturally imply a later filing.
Little is known about other players’ plans to develop humanised CARs; Kite has made a patent filing for one, while Juno refers to a bonus due to its R&D head, Mark Frohlich, on first patient dosing in a pivotal trial with a fully humanized CAR-T cell product.
CD19 -positive or antigen escape?
Of course such considerations relate to so-called CD19 -positive relapses – where patients’ leukaemia continues to express the CD19 antigen, with relapse due to waning CAR-T cells or loss of the CAR construct.
In the latest cut of Novartis ’s CTL019 data a highly impressive 93% of ALL patients went into complete remission after a month, though less impressively this rate was down to 30% by one year. At ASH the Children's Hospital of Philadelphia’s Dr Stephan Grupp said CD19 -positive relapse was responsible for a third of recurrences (ASH – CAR-T struggles to travel beyond leukaemia, December 8, 2015).
The remaining two thirds relapse because of loss of the CD19 antigen, and clearly require an entirely different retreatment approach. One strategy is to target a separate antigen, and fortunately in B-cell malignancies an alternative one seems to exist: CD22.
The leading project here is JCAR018 , an anti-CD22 CAR derived from work at the NIH that Juno bought from Opus Bio last year for about $120m. A first-in-human trial of JCAR018 featured at a separate ASH poster detailing a cohort of seven evaluable ALL patients, six of whom had been treated with an anti-CD19 CAR , and five of whom had had CD19 -negative relapse.
Complete remission was seen in two patients. It is early days here, too, and the best that can be said beyond initial efficacy hints is that there was no severe cytokine release syndrome, suggesting relative safety of JCAR018 , though most of the patients were given the lowest CAR-T cell dose.
Selection of antigens against which CAR-T therapies are being developed has tended to follow development of antibodies, and CD22 is no exception, but it is interesting that anti-CD22 MAbs, including MEDI-553 and IMTOX 22-97, have all failed in oncology, while’s epratuzumab failed in lupus.
Several antibody-drug conjugates are in development, as well as UCART22 , an allogeneic CAR-T therapy from Cellectis that also has a dCK gene knockout to confer fludarabine resistance.
At ASH the NCI’s Dr Daniel Lee said he was continuing to enrol CD19 -escaped patients into a CD22 CAR-T study, though all the data and IP arising from this will presumably belong not to the NCI’s CRADA partner Kite , but rather to Juno.
Dr Lee also cited a planned study of a bivalent CD19 -CD22 CAR, a highly unusual single CAR construct that was featured at an ASH poster. The NCI authors concluded that the order of the CD19 and CD22 binding domains, and the length of the linker, affected function, and despite some evidence of activity further optimisation is needed before this enters the clinic.
Persistence problems
When it comes to CD19 -positive relapses, developers of CAR-T therapies have to contend with a separate problem, namely the lack of persistence of the CAR construct on the T cells, or its inability to generate a sufficiently sustained response.
Since there are differences in the design of different players’ CAR constructs it is hoped that further data will shed light on which of these differences might affect persistence. For instance, Kite employs a gamma-retrovirus to transfect its construct, which uses a CD28 co-stimulatory domain, while Novartis ’s uses lentiviral transfection and a 4-1BB co-stimulatory element.
Juno has both: JCAR015 , a CD28 /gamma-retroviral construct from Memorial Sloan Kettering (MSK ), and JCAR017 , a 4-1BB/lentiviral one from the Fred Hutchinson Cancer Research Center . Again there is a lack of hard evidence, but Dr Grupp of the Philadelphia children's hospital says his construct, which is used by Novartis , enables persistence of around four years, versus around 30 days for the MSK /Kite projects.
During a recent investor call Dr Grupp stated that CD28 co-stimulation tends to give a strong early response but the T cells then “burn out”, while gamma-retroviruses are known to risk causing gene silencing.
“Solely based on the data that’s published right now, I’d say there’s more compelling data that CD28 versus 4-1BB is a bigger part of the [persistence] equation than lentiviral versus gamma-retroviral,” he speculated. “But that is just a guess.”
If further trials do substantiate this view then Kite especially will be left with some rethinking to do.
几个公司的CAR-T疗法已经在白血病患者中产生令人印象深刻的缓解率,但较高的复发率影响了它们长远发展的潜力,特别是考虑到有可能出现的成本。
为了克服这个问题,几种策略应运而生,其中之一是诺华公司设计的CAR结构,使用一个人源的抗原结合区,理论上,常规使用的鼠源CARs会被免疫系统所排斥。如果这就是前进发展的道路,那么就剩下诺华公司的CTL019技术,目前最先进的CAR-T技术,以及其他一些在结合区使用鼠源的CAR-T技术。
到目前为止,得到的数据仍然有限。但是最受期待的一个数据是在ASH年会上提到的一个包含6例使用CTL1019治疗的病人,再次使用诺华公司的新技术——CD19靶向CAR-T,即CTL119。6个病人中有三个得到了完全的缓解,其中有一位病人维持了近6个月的时间。
费城儿童医院的Shannon Maude,说道:一位缓解期的患者对鼠源的CTL019没有反应,这是非常让人印象深刻的一件事情。这是在早期的一个研究,但是进一步在大数据病人身上得到的数据会让诺华公司非常为难:CTL109治疗组会失败,或者它只是CTL119的开关?
这可能会打击到诺华公司和整个CAR-T发展空间,这家瑞士公司在这个领域是最先进的,这家公司希望提交CTL019治疗方案并在下年获得审批。转变成CTL119或许意味着推迟审批文件。
对于其他公司开发人源化的CARs的计划,我们所知甚少。Kite公司已经申请了一个专利,Juno公司由于其研究与发展部门的带头人Mark Frohlich的研究而获得红利,该公司第一次在临床试验中的病人身上使用了完全人源化的CAR-T细胞产品。
CD19 阳性或者抗原逃逸?
当然,这样的考虑涉及到所谓的CD19阳性的复发,这是因为病人的白血病细胞持续表达CD19抗原,从而由于CAR-T细胞的缺损和CAR结构的丢失,导致白血病细胞的逃逸。
在最近的诺华公司的CTL019治疗ALL病人的试验中,在治疗一个月后,出现了令人印象深刻的93%的完全缓解率,虽然1年后,这个完全缓解率下降到30%。在ASH年会上,费城儿童医院的Stephan Grupp先生提到,CD19阳性导致的逃逸这个原因占到了疾病复发的1/3 。(12月8日, 2015)
剩下的三分之二的复发是由于CD19抗原的损失,显然需要一个完全不同的治疗方法。一个策略是靶向另一个抗原,很幸运,在B细胞恶性肿瘤的表面存在一个替代的抗原:CD22。
在这个领域中,占主导地位的是JCAR018,一个靶向CD22的CAR,它来源于NIH,在去年被Juno花了12000万从Opus Bio公司买下。一个单独的ASH海报上详细报道了JCAR018的第一个人体试验,包含七个ALL病人,其中的6个患者曾经接受CD19 CAR的治疗,其中有5个病人曾经出现过CD19缺失导致的逃逸。
其中,有2位病人出现了完全的缓解。这是早期的试验,最好的能够被提及的并不是疗效,而是没有严重的细胞因子释放综合症的出现,预示着JCAR018的安全性,虽然大多数的病人给予的是最低剂量的CAR-T细胞量。
CAR-T细胞治疗基于对抗原的选择,它的发展趋向于跟随抗原的发展,CD22也不例外。但有趣的是靶向CD22的单克隆抗体,包括MEDI-553和IMTOX 22-97,在癌症的治疗中都已失败,就像优时比公司的epratuzumab在狼疮治疗中也失败了。
几种抗体偶联药物正在开发中,比如UCART22,Cellectis公司的一种同种异基因的CAR-T技术,它的DCK基因被敲除从而能够获得氟达拉滨的耐药性。
在ASH年会上NCI的Daniel Lee先生提到,他给予CD19逃逸的病人进行CD22CAR-T技术治疗,从这个试验中得到的数据很有可能是属于Iuno公司,而不是NCI的合作研究和发展合约伙伴Kite公司。
李博士还计划研究一个二价的CD19-CD22的CAR,一个很不寻常的单链CAR结构,在ASH海报中被描述过。NCI认为CD19和CD22结合域的顺序,以及连接器的长度会影响CAR-T的功能。在这个技术进入临床前,仍然需要进一步优化。
持续性的问题
当出现了CD19阳性导致的逃逸, CAR-T技术的研究者不得不面对一个问题,即T细胞上CAR的结构缺乏持续性,或者不能够产生足够的持续性的有效性。
由于不同的公司设计的CAR的结构有差异,希望进一步的数据能够揭示这些差异可能会影响到的持久性。例如,Kite采用伽马逆转录病毒转染进行结构构建,采用CD28共刺激域,而诺华的使用慢病毒转染和4-1BB共刺激域。
Juno公司有JCAR015和JCAR017。虽然缺乏更多的证据,费城儿童医院的Grupp博士介绍他们CAR的结构,能够持续将近4年,这与MSK和Kite公司的设计形成对比。
最近的一次投资者告诉Grupp博士,CD28共刺激在早期能够有一个强有力的有效性,但是T细胞逐渐消失,然而伽马逆转录病毒是已知的能够导致基因沉默的因素。
完全基于数据的公布,现在我想说,CD28和4-1BB比慢病毒与γ-逆转录病毒更加重要,”他推测,“但这只是一个猜测。
如果进一步的实验证实了这一观点,那么,Kite公司将会留下很多事需要重新思考。
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