Therefore, physiological regulatory functions cannot be distinguished easily from effects that are caused by homeostatic proliferation and clonal expansion of transferred cells (Bach, 2003; Barthlott et al., 2003).
Bach JF., Chair's introduction. Generation and effector functions of regulatory lymphocytes. Novartis Found Symp. 2003; 252: 1-5; discussion 106-14. Review.
Barthlott T, Kassiotis G, Stockinger B. T cell regulation as a side effect of homeostasis and competition. J Exp Med. 2003 Feb 17;197 (4): 451-60.
[...] and therefore physiological regulatory functions cannot be distinguished easily from effects that are caused by homeostatic proliferation and the clonal expansion of the transferred cells (see the reviews by J. F. Bach in this issue45 and by B. Stockinger and colleagues46)
45. Bach, J. F. Regulatory T cells under scrutiny. Nature Rev. Immunol.3, 189–198 (2003).
46. Kassiotis, G., Garcia, S., Simpson, E. & Stockinger, B. Impairment of immunological memory in the absence of MHC despite survival of memory T cells. Nature Immunol.3, 244–250 (2002).
The source is not given.
Note: there are two references "Bach, 2003" listed in the bibliography.