lymphocyte transformation, 1. the morphological changes accompanying lymphocyte activation, in which small, resting lymphocytes are transformed into large, active lymphocytes (lymphoblasts). 2. an in vitro immunity test process in which a patient’s lymphocytes are placed in a culture with an antigen. The rate of transformation, in terms of proliferation and enlargement of T memory cells, is measured by the uptake of radioactive thymidine by the lymphocytes, indicating protein synthesis.