<qa>  What is the effect of giving low doses of chemotherapy before a donor stem cell transplant?RATIONALE: Giving low doses of chemotherapy before a donor stem cell transplant using stem cells that closely match the patients stem cells, helps stop the growth of cancer cells. It also stops the patients immune system from rejecting the donors stem cells. The donated stem cells may replace the patients immune system and help destroy any remaining cancer cells graft-versus-tumor effect. Giving an infusion of the donors T cells donor lymphocyte infusion after the transplant may help increase this effect. Sometimes the transplanted cells from a donor can also make an immune response against the bodys normal cells. Giving antithymocyte globulin before transplant and cyclosporine and mycophenolate mofetil after transplant may stop this from happening. 