Dr. Gaber serves as Chair of Houston Methodist's Department of Surgery.  He received his first academic appointment in 1987, as an Assistant Professor in the Department of Surgery at the University of Tennessee in Memphis. He became an Associate Professor there in 1991, and received his full professorship and was named to the Baptist Memorial Health Care Foundation chair of excellence in transplantation in 1994. While at the University of Tennessee, Dr. Gaber also held professorships in the Departments of Pharmacy and in the College of Nursing. He was also the Medical Director for the University of Tennessee Bowld Hospital, and the Methodist University Transplant Institute.

Dr. Gaber is a prolific researcher and has authored over 300 scientific papers, as well as more than 340 abstracts and numerous book chapters, and his research has been funded by numerous grants from the National Institutes of Health, the Juvenile Diabetes Research Foundation, and several national and local foundations. Dr. Gaber assumed his positions at the Houston Methodist Hospital and Research Institute in Houston in 2006.

While also conducting transplant immunotherapy research for liver and kidney whole organ transplants and allografts, the main focus of Dr. Gaber´s research is in the transplantation of islets to alleviate diabetic complications. He and his collaborators have developed the protocol for long term islet culture and described the clinical transplantation of islets through the intestinal veins. Dr. Gaber´s current studies center on the testing of gene therapy and other approaches to test for islet viability and assist the transplanted islets to develop a sustaining blood supply and resist rejection by the recipient's immune system.