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。1363Please respect copyright.ＰＥＮＡＮＡtMhvtFBg1t
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上集：https://www.penana.com/article/4711251363Please respect copyright.ＰＥＮＡＮＡZAx1L8aFR4
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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?1363Please respect copyright.ＰＥＮＡＮＡOOQmYn371D
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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。1363Please respect copyright.ＰＥＮＡＮＡwBhJ3bOV6c
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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。1363Please respect copyright.ＰＥＮＡＮＡvkd2V7cDmN
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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;1363Please respect copyright.ＰＥＮＡＮＡPSychdpiTw
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。1363Please respect copyright.ＰＥＮＡＮＡN8dt1RsmSe
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忘記甚麼是Neoantigen的話，可重溫上一集。1363Please respect copyright.ＰＥＮＡＮＡcBKQPKKK99
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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。1363Please respect copyright.ＰＥＮＡＮＡqNL4oSabdE
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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。1363Please respect copyright.ＰＥＮＡＮＡBahvzSWoQJ
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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。1363Please respect copyright.ＰＥＮＡＮＡPvfdVWP7Ue
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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。1363Please respect copyright.ＰＥＮＡＮＡjmjOUChjSw
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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。1363Please respect copyright.ＰＥＮＡＮＡuB9f3bDhoM
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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。1363Please respect copyright.ＰＥＮＡＮＡ34GNT2hk5H
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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。1363Please respect copyright.ＰＥＮＡＮＡ6alc53xhJJ
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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。1363Please respect copyright.ＰＥＮＡＮＡDCdrYG86Vn
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。1363Please respect copyright.ＰＥＮＡＮＡPDaiJd4zlI
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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。1363Please respect copyright.ＰＥＮＡＮＡMbYnlL6Hb6
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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。1363Please respect copyright.ＰＥＮＡＮＡWagURrZaqJ
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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。1363Please respect copyright.ＰＥＮＡＮＡn4nPcQR6Fq
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