Flow cytometry is great, it compliments other proliferative tests and you can follow specific subset proliferation
It would be of help reading:
Hodgkin, P.D.; Hawkins, E.D.; Hasbold, J.; Gett, A.V.; Deenick, E.K.; Todd, H.F.; Hommel, M. (2005). Monitoring T cell proliferation, pp 123-141. In: Analyzing T Cell Responses. Nagorsen D. and Marincola F. M. Editors. Springer. Netherlands.