In this study, we will treat male and non-pregnant female subjects between the ages of 18 and 70 years (both inclusive) suffering from advanced MF/SS with an allogeneic peripheral blood stem cell (PBSC) transplant from an HLA-matched family donor or an HLA matched (10/10 allele level match) unrelated donor. A low intensity, nonmyeloablative conditioning regimen employing the anti-CD52 monoclonal antibody Campath-1H (alemtuzumab) and fludarabine will be used to induce host immunosuppression to facilitate donor hematopoietic and lymphoid engraftment. We anticipate minimal host myelosuppression and consequently reduced early transplant toxicity with this conditioning regimen. Immune and hematopoietic reconstitution will be achieved by infusion of unmanipulated donor-derived granulocyte colony stimulation factor (G-CSF) mobilized peripheral blood stem cells. Infusion of donor lymphocytes in incremental doses will be used to promote engraftment or diease regression when indicated. Cyclosporine A (CSA) will be used as prophylaxis against graft vs host disease (GVHD), with dose adjustments made as necessary to favor complete donor chimerism and disease regression.