All patients will receive alemtuzumab in a dose escalation fashion (3, 10, 30mg). Successive escalating doses will be administered if the previous dose is tolerated. Previously, Stock et al established the safety of 12 doses of 30mg of alemtuzumab in ALL. The treatment regimen is designed to have alemtuzumab administered prior to administration of clofarabine to allow dose escalation of the monoclonal antibody and decrease confounding acute toxicities such as infusion reactions and cytokine release. Clofarabine dose is modeled after previous trials in adult and pediatric ALL. The starting dose of clofarabine is lower than standard phase II doses for adult hematologic malignancy to conservatively evaluate tolerability and toxicity of clofarabine in combination with alemtuzumab. Alemtuzumab dosing will be limited to a total of 12. However, patients can continue with additional cycles of clofarabine if they do not show progressive disease or have unacceptable toxicity.