The purpose of this study is to compare mogamulizumab alone to using Hu5F9-G4 (magrolimab) plus mogamulizumab for the cutaneous T-cell lymphomas (CTCL), Mycosis Fungoides and Sezary Syndrome, as well as determining if the addition of Hu5F9-G4 could slow or stop the cancer’s growth or prevent it from returning.
   
This study will help the study doctors find out if this approach is better than the usual approach of retinoids, low-dose methotrexate, interferons (alpha and gamma), extracorporeal photopheresis, HDAC inhibitors (vorinostat, romidepsin), brentuximab vedotin, cytotoxic chemotherapeutic agents (pralatrexate, liposomal doxorubicin, gemcitabine), pembrolizumab, or mogamulizumab.

Hu5F9-G4 is considered investigational in this study, which means is not yet approved by the U.S. Food and Drug Administration for this use. Mogamulizumab is already approved by the FDA for use in T-cell lymphomas involving the skin, but it is not approved in combination with other therapies.
 
Participants will be randomized into 2 study groups. A computer will randomly assign each participant to one of the groups.

Participants in group 1 will receive mogamulizumab plus the study Hu5F9-G4 (magrolimab). Hu5F9-G4 (magrolimab) is administered through a vein in the arm every week for 9 weeks and every 2 weeks thereafter. Mogamulizumab is administered through a vein in your arm every week for 4 weeks and every 2 weeks thereafter. 

Participants in group 2 will receive mogamulizumab alone through a vein in the arm every week for 4 weeks and every 2 weeks thereafter.