Methods for treatment and diagnosis of cancer by targeting glycoprotein A repetitions predominant (GARP) and for providing effective immunotherapy alone or in combination

Isolated or recombinant monoclonal antibodies that bind to GARP are provided. In some cases, antibodies of the embodiments can be used for the detection, diagnosis and/or therapeutic treatment of human diseases, such as cancer. Further provided herein are methods and compositions for treating cancer in an individual comprising administering to the individual an effective amount of an anti-platelet agent and a T cell therapy.