Renal Allograft Tolerance Through Mixed Chimerism - SMC/MGH

Inclusion Criteria: * Male or female 18-65 years of age. * Candidate for a living-donor renal allograft from an HLA mismatched donor * Subjects with chronic kidney disease stage or ESRD who are treated with either hemodialysis or peritoneal dialysis. * First transplant. * Use of FDA-approved methods of contraception * Ability to understand and provide informed consent. * Negative COVID at screening and 2 days before procedure Exclusion Criteria: * ABO blood group-incompatible renal allograft. * Participant with a (non DSA) PRA \> 20% within 6 months prior to transplant * Persistent Leukopenia (WBC less than 2,000/mm3) or thrombocytopenia (\<100,000/mm3). * Seropositivity for HIV-1, hepatitis B core antigen, or hepatitis C virus (confirmed by hepatitis C virus RNA); or positivity for hepatitis B surface antigen. * Active infection * Left ventricular ejection fraction \< 40% as determined by TTE or clinical evidence of heart failure * Forced expiratory volume FEV1 or DLCO \< 50% of predicted. * Lactation or pregnancy * History of cancer (following the American Transplant Society Guidelines) * Underlying renal disease etiology with a high risk of disease recurrence in the transplanted kidney (such as focal segmental glomerulosclerosis). * Prior dose-limiting radiation therapy * Known genetic disease or family history that may result in greater sensitivity to the effects of irradiation, or a physical deformity that would preclude adequate shielding or appropriate dosing during the irradiation component of the conditioning regimen * Enrollment in other investigational drug studies within 30 days prior to enrollment * Abnormal (\>2 times lab normal) values for (a) liver function chemistries (ALT, AST, AP), (b) bilirubin, (c) coagulation studies (PT, PTT). * Allergy or sensitivity to any component of Siplizumab, Fludarabine, Cyclophosphamide, tacrolimus, DMSO, MMF or rituximab. * The presence of any medical condition that the investigator deems incompatible with participation in the trial. * Subjects who have non-insulin dependent diabetes (NIDDM) without good blood glucose control (HbA1c\<7). Subject with severe retinopathy, gastroparesis, or severe neuropathy which prevent subject's normal independent daily activities will be excluded from the study