This study will evaluate the safety, PK, and efficacy of AT 1501 in patients undergoing kidney transplantation.

This study will evaluate the safety, PK, and efficacy of AT 1501 in patients undergoing kidney transplantation. Up to 48 de novo kidney transplant recipients will receive AT-1501 in combination with rATG induction with corticosteroids (CS), and mycophenolate as maintenance therapy.

Inclusion Criteria:

1. Male or female ≥ 18 years of age
2. Recipient of their first kidney transplant from a living or deceased donor
3. Agree to comply with contraception requirements during and for at least 90 days after the last administration of study drug

Exclusion Criteria:

1. Induction therapy, other than study assigned rATG, planned as part of initial immunosuppressive regimen

2. Currently treated with any systemic immunosuppressive regimen, including immunologic biologic therapies, with the exception of 5 mg prednisone or equivalent daily;

3. Previous treatment with AT 1501 or any other anti CD40LG therapy

4. The patient has previously received a bone marrow transplant or any other solid organ transplant, including a kidney, or will be undergoing a multi organ or dual kidney transplant

5. Will receive a kidney with an anticipated cold ischemia time of > 30 hours;

6. Will receive a kidney from a donor that meets any of the following criteria:

   • Donation after Cardiac Death (DCD) criteria; or
   • Extended Criteria Donor (ECD) criteria, defined as:
   • Is blood group (ABO) incompatible; or
   • Age ≥ 60 years; or Age 50-59 years with any 2 of the following criteria:
   • Death due to cerebrovascular accident
   • History of hypertension
   • Terminal creatinine ≥ 133 μmol/L (1.5 mg/dL)

7. Human leukocyte antigen identical (two haplotype match or zero HLA mismatch) donor

8. Medical conditions that require chronic use of systemic steroids at a dose higher than 5 mg prednisone or equivalent per day

9. History of a TE event, known hypercoagulable state, or condition requiring long term anticoagulation:

10. Positive T- or B-cell crossmatch that is due to HLA antibodies or presence of a DSA at Screening

None ( Open Label)