Is monitoring of FOXP3 Treg cells in renal transplants during acute cellular rejection episodes useful?

BACKGROUND: The FOXP3 (forkhead Box p3) transcription factor is a marker for T regulatory cells (Treg). During cellular immune responses, Treg are expected to increase in number to ultimately control and limit this response. In renal transplants massive infiltration by T cells is often seen during rejection crises. This prompted us to examine changes in the numbers of FOXP3 positive T cells accompanying acute cellular rejection events. METHODS: A total of 32 transplant biopsies from 23 patients were studied retrospectively, these 16 protocol biopsies and 16 biopsies taken during rejection episodes included 9 serial pairs (protocol-rejection). To quantify FOXP3 positive T cells, frozen sections were double immunostained with anti-CD3 and anti-FOXP3 antibodies. Areas revealing T cell infiltrates were measured morphometrically and the number of FOXP3 positive cells per 1,000 µm2 of CD3 positive cells was taken as an FOXP3 index. RESULTS: This index was 0.46 (median, range 0.00-1.00) in the 16 protocol biopsies and 0.48 (median, range 0.16-2.31) in rejection episode biopsies. The highest values were seen during rejection crises, exceeding 1.00 in 6/16 biopsies, whereas no protocol biopsies had values greater than 1.00 (0/16) (difference significant p<0.02). In serial biopsies no consistent behavior was observed; the FOXP3 index remained unchanged, fell slightly or rose to a maximum of 13 fold. Expression levels of FOXP3 could vary within weeks. No correlations were found between donor type, initial therapy, therapy at biopsy, serum creatinine at the time of biopsy, at 3 months or 1 year later, and any of the morphometric parameters (CD3 and FOXP3) studied. CONCLUSIONS: During rejection of renal allografts the fraction of FOXP3+ Treg cells within the infiltrating T-cell population can increase transiently. This phenomenon was not consistently seen in acute cellular rejection and the information does not appear to be of value for individual patient management in such cases.