In the present phase 1-2 study the investigators aim to determine whether depletion of Tregs using metronomic cyclophosphamide can enhance the antitumor efficacy of everolimus in patients with mRCC not amenable to or progressive after a VEGF-receptor tyrosine kinase inhibitor containing treatment regimen. In the phase 1 part of the study the investigators will determine the optimal CD4+CD25+ regulatory T cell-depleting dose and schedule of metronomic oral cyclophosphamide when given in combination with a fixed dose (10 mg daily) of everolimus. In the phase 2 part of the study the investigators will subsequently evaluate whether the number of patients who are cancer progression free at 4 months can be increased from 50% to 70% by adding metronomic cyclophosphamide (in the dose and schedule determined in the phase 1 part) to everolimus. In addition to efficacy, the investigators will evaluate treatment toxicity to determine whether this combination strategy is feasible and safe.