科普專欄–薯不揀單 - 深入淺出–以免疫治療(Immunotherapy)手段醫治癌細胞(二)

上集講述了PD1/PDL1在醫治癌細胞免疫治療方面的重要性，接下來我們將會繼續深入探討問題。1418Please respect copyright.ＰＥＮＡＮＡjVRGturpqq
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上集：https://www.penana.com/article/4711251418Please respect copyright.ＰＥＮＡＮＡeXajLVyrBt
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（圖1）雖然阻擋PD1/PDL1可以增強T cell辨認癌細胞的能力，但另一個重要的問題是，如何確保有足夠的T cell殺滅癌細胞呢?1418Please respect copyright.ＰＥＮＡＮＡJSUd3Rn5c7
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就算成功糾正免疫系統細胞懂得把癌細胞辨認為外來之物，但免疫系統細胞數量不足的話，依然是不會達到重大效果的。1418Please respect copyright.ＰＥＮＡＮＡyapXaFM1de
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換句話說，我們需要一道能夠提升針對癌細胞的T cell數量手段。1418Please respect copyright.ＰＥＮＡＮＡh2HZlYWlw0
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（圖2）T cell的產生數量，接近可以說是由Antigen Presenting Cells(APC)來決定;1418Please respect copyright.ＰＥＮＡＮＡuzH2DudmyJ
APC可以睇成為一堆負責把癌細胞獨特Neoantigen帶來T cell面前的細胞。1418Please respect copyright.ＰＥＮＡＮＡ8vpP9ZwLvc
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忘記甚麼是Neoantigen的話，可重溫上一集。1418Please respect copyright.ＰＥＮＡＮＡjff1snwo61
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當APC展示癌細胞的Neoantigen予T cell的receptor後，另一個必需的動作就是T cell表面的CD28與APC表面的B7合併。1418Please respect copyright.ＰＥＮＡＮＡEkLO2F4bJD
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只要兩者條件達成的話，負責對付對應癌細胞的T cell數量及效力便會大增。1418Please respect copyright.ＰＥＮＡＮＡzx3YT0sFpZ
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（圖3）然而，當T cell數量產生至一定程度的時候，T cell便會產生出CTLA4。CTLA4會搶奪CD28的位置，與B7合併。1418Please respect copyright.ＰＥＮＡＮＡUDJYqvbmO2
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而當CTLA4與B7合併後，T cell所產生的數量及威力就會大減。1418Please respect copyright.ＰＥＮＡＮＡekDYueE5af
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這個CTLA4產生的機制是與生俱來的，目的就是為了避免產生過量的T cell，以免身體會產生不良反應。1418Please respect copyright.ＰＥＮＡＮＡHO6yNllZ0P
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（圖4）只不過的是，現時癌細胞大敵當前，燃眉之急就是要調動大量的T cell前往討伐癌細胞。1418Please respect copyright.ＰＥＮＡＮＡnaz9rIs6UE
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為此，我們重施應對PD1/PDL1故技，利用抗體阻擋CTLA4，確保CD28及B7持續合併，不斷產生效力高強的T cell。1418Please respect copyright.ＰＥＮＡＮＡmDS5GIQx8t
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（圖5）簡略的總結來說，為了確保有足夠的T cell消滅癌細胞，我們不惜採用阻擋CTLA4的抗體，號令身體持續產生效力高強的T cell。1418Please respect copyright.ＰＥＮＡＮＡ6JWlgbgAIp
而另一邊廂，我們亦同時利用阻擋PD1/PDL1的抗體，確保T cell能夠順利把癌細胞辨認成為外來物，將其制裁。1418Please respect copyright.ＰＥＮＡＮＡAXd3K99Gii
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這CTLA4抗體及PD1/PDL1抗體的雙管齊下療法，將能大大提升免疫治療的效率。1418Please respect copyright.ＰＥＮＡＮＡF1MOaatYWm
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但是，並不是所有病人也能依靠這方法而得益，原因是T cell沒法能夠順利抵達癌細胞的位置以及滲入癌細胞的內部作有效的消滅。1418Please respect copyright.ＰＥＮＡＮＡk8rRx6jCXk
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這一方面，我們將會在下一篇免疫治療的最終章再作探討。1418Please respect copyright.ＰＥＮＡＮＡs3TjweuzUC
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