T cells are also called as T- lymphocytes. T represents Thymus. Thymus is an organ which is present above the heart. T cells produce from the Hematopoietic stem cells in bone marrow, from bone marrow t cells migrates to Thymus and matures there. Hematopoietic stem cells are the cells which can change into any type of cell in body. These cells protect the body from foreign organisms.