In this task, you are given a sentence from the research paper and your task is to classify the given sentence into the following categories: Background (Why is this problem important? What relevant works have been created before? What is still missing in the previous works? What are the high-level research questions? How might this help other research or researchers?), Purpose (What specific things do the researchers want to do? What specific knowledge do the researchers want to gain? What specific hypothesis do the researchers want to test?), Method (How did the researchers do the work or find what they sought? What are the procedures and steps of the research?), or Finding (What did the researchers find out? Did the proposed methods work? Did the thing behave as the researchers expected?). 
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Question: induces apoptosis in infected cells at late times postinfection.

Answer: purpose


Question: modern vaccination and therapeutic strategies with thrust on T cell biology.

Answer: purpose


Question: The coil-3 10 - helix conformational transition of the Ser139-Leu141 loop serves as an enzyme activity switch.

Answer:
finding