Background: Interleukine-2 and Cyclophosphamide are known to influence the circulating T cells and are used for immune manipulation in cancer patients. We analyzed the influence on the Treg population in three different dendritic cell (DC) vaccine trials including either concurrent interleukine-2 (IL-2), combined IL-2 and metronomic Cyclophosphamide (MCy), or only MCy. Methods: Melanoma patients received treatment with autologous DCs. IL-2 was applied in trial I and II and MCy was applied in trial I and III. Flowcytometry analysis was performed on fresh drawn blood-samples measuring CD4, CD25 and CD127. Results: In the trials where IL-2 was applied a marked increase in the proportion of CD4 + CD25 + CD127 -Tregs from baseline to the 4th vaccine was observed. This was followed by a decrease, although not to baseline values. Additional analysis showed that the inhibitory function was predominant in the CD49d -subpopulation of Tregs which only increased slightly during treatment. The absolute lymphocyte count (ALC) and the number of CD4 + T cells also increased in these trials. In the trial where only MC was applied the Tregs remained stable throughout the trial whereas \ decrease in the ALC and CD4 + T cells were observed. Conclusion: We found that adjuvant treatment with low doses of IL-2 during DC vaccination therapy causes a significant increase in blood level of classically defined, CD4 + CD25 + CD127 -, Tregs but far less in the CD49d -sub-population and that the use of MC was unable to reduce Treg blood level and unable to counteract IL-2 dependent increase in the CD4 + CD25 + CD127 -T cells.