Antoni Ribas, MD, PhD

Antoni Ribas, M.D., Ph.D. 

Professor, Medicine, Surgery, Molecular and Medical Pharmacology; Director, Parker Institute for Cancer Immunotherapy Center at UCLA; Director, UCLA Jonsson Comprehensive Cancer Center Tumor Immunology Program


Antoni Ribas, M.D., Ph.D., conducts laboratory and clinical research focused on malignant melanoma, an aggressive form of skin cancer for which few effective therapies exist. He is working to understand how a patient’s own immune system can be harnessed to attack melanoma. This research informs the development of new immunotherapies that utilize the body’s natural defenses to fight cancer.

Ribas’ laboratory has made major advancements in the treatment of melanoma. Most significantly, he led the clinical program that demonstrated the effectiveness of the drug pembrolizumab (marketed as Keytruda), which ushered in a paradigm shift in the way melanoma is treated. The drug blocks a protein called PD-1 that sits on the surface of immune cells and keeps them from recognizing and attacking cancer cells. This was the first of the class of PD-1 blocking antibodies to be approved by the Food and Drug Administration for the treatment of any cancer. Keytruda is now used in the treatment of inoperable, metastatic melanoma, non-small cell lung cancers and other malignancies including Hodgkin’s lymphoma.

Ribas is conducting several clinical trials of cutting-edge treatments including both immunotherapies and targeted stem cell-based therapies. In 2017, he launched a first-of-its-kind trial that involves genetically engineering blood-forming stem cells to produce cancer-fighting T cells to treat melanomas and sarcomas and later multiple myeloma. The clinical trial involves a dual approach intended to provide patients with both short and long-term immune responses to their cancer. This is accomplished by giving patients modified blood-forming stem cells and modified mature T cells in a single transplant.  Upon transplant, the modified mature T cells begin fighting the cancer immediately, while the modified blood-forming stem cells work to generate an on-going supply of new modified T cells, resulting in a lasting immune response to the cancer.    

Ribas also studies how the immune system responds to and develops resistance to immunotherapies, and how combination therapies may be used to overcome treatment resistance. One such treatment the Ribas lab is evaluating combines pembrolizumab with a targeted therapy that blocks a protein that leads to mutations in the BRAF gene. The BRAF gene makes a protein called B-RAF, which is involved in cell communication and growth. When BRAF genes are mutated, they can increase the growth and spread of cancer cells; approximately one‐half of all patients with melanoma have mutations in the BRAF gene.

An additional area of focus in the Ribas lab is molecular imaging and advanced monitoring of the immune system. Ribas and his team utilize molecular imaging technology such as PET scans to investigate and understand precisely how novel immunotherapies work on a molecular level. They aim to use these technologies to guide and evaluate new therapeutic strategies for melanoma.

Ribas earned both his medical and doctoral degrees from the University of Barcelona in Spain. He completed an internship and residency at Hospital Vall d'Hebron and fellowships in surgical oncology and hematology/oncology at the UCLA David Geffen School of Medicine. He is an elected member of the American Society of Clinical Investigation.


Honors & Affiliations



  • President-Elect, American Association for Cancer Research, 2019
  • Lloyd J. Old Award in Cancer Immunology, American Association of Cancer Research-Cancer Research Institute, 2018
  • Great Immigrant Award, Carnegie Corporation, 2018
  • Doctor Honoris Cause, University of Buenos Aires, Argentina, 2017
  • Richard and Hinda Rosenthal Memorial Award, American Association of Cancer Research, 2016
  • Member, Royal Academy of Medicine of Catalonia, 2015
  • Outstanding Investigator Award, National Cancer Institute, 2015
  • Physician of the Year, Melanoma International Foundation, 2013
  • Outstanding Research Award, Society for Melanoma Research, 2013
  • Elected member, American Society of Clinical Investigation, 2009


  • Board of Directors, American Association for Cancer Research
  • American Society of Clinical Oncology
  • American Association for Cancer Research
  • Chair, Melanoma Committee, SWOG Cancer Research Network
  • Advisory Board, UCLA General Clinical Research Center
  • UCLA Jonsson Comprehensive Cancer Center


Ribas’ work is funded by the California Institute for Regenerative Medicine, the National Institutes of Health, the Parker Institute for Cancer Immunotherapy, Stand Up to Cancer, the Caltech-UCLA Joint Center for Translational Medicine and the UCLA Broad Stem Cell Research Center.


Dr. Ribas: Portrait of a Physician/Scientist
In his office, Dr. Antoni Ribas has a special collection of books - his great grandfather's notes from medical school in the late 1800s. "It's a good reminder of how much we've improved, how much medicine has progressed,” says Ribas. “I think the textbooks have changed faster in cancer in the last 10-15 years than in all of the centuries before.” As a fourth generation physician, caring for patients is part of a deep family legacy for him. Dr. Ribas has spent the last 20 years at UCLA pioneering new treatments for malignant melanoma. "...Probably up to half of my clinic are patients who are coming back with the cancer being smaller than when we started - some of them going years with improvement." However, even despite all of his contributions toward treating the disease, in true scientific form Dr. Ribas pushes on. "But that is obviously not enough. Knowledge brought us so far and we should continue to improve." Watch to learn more about Dr. Ribas and for an intimate portrait of one of UCLA Health's leading physician/scientists. This video and imagery was captured in 2019 or earlier.

Clinical Trials