I am studying the proliferation profile of Tfh and Tfr cell and I use to stain them with CFSE afterward I stimulate them with anti-CD3 and anti-CD28, I take two measurements one after each 48 hour. I could observe a good proliferation during the first 48 hour however, after 96 hours I couldn't observe any difference the two measurements. What is the problem might be? Any suggestions will be quite helpful!