Early animal models predicted that the effectiveness of cell transfer therapies could be improved by administering either total body irradiation or lymphodepleting chemotherapy prior to the cell transfer. The limited persistence of the transferred cells in our early human trials thus led us to explore the use of lymphodepletion in patients with metastatic melanoma prior to receiving ACT with TIL. A series of clinical trials have been performed in a total of 93 patients with metastatic melanoma exploring the use of increasing levels of lymphodepletion4–6,20
. In the conduct of these recent trials a change was made in the procedures used to generate TIL for cell transfer. In the earlier trials entire excised tumors were subjected to enzymatic digestion to form a single cell suspension which was then cultured in 6,000IU/ml IL-2. Lymphocytes infiltrating into the tumor stroma grew and after 2–3 weeks, cultures were generally cleared of tumor cells and lymphocytes were continued in culture until the target number of cells was obtained. In the earlier trials these entire populations of TIL were administered without further selection. In the current trial a modified procedure was utilized10
. Excised tumors were minced into tiny fragments and individual fragments placed in the wells of a 24 well culture plate, or alternatively limited numbers of cells from a single cell suspension were put in individual wells of a 24 well plate. All wells then were individually grown and separately tested for their ability to recognize either the autologous tumor or tumors sharing MHC antigens. Individual cultures showing appropriate reactivity were then further expanded, generally to a total of 1010
cells before they were infused into patients. Although more labor intensive, this latter technique had the advantage of identifying cultures with anti-tumor activity but potentially had the disadvantage of limiting the heterogeneity or polyclonality of the cells administered21,22
Utilizing this new method of cell preparation, three consecutive protocols were performed using increasing levels of lymphodepletion (). In the first protocol, 43 patients were treated with autologous lymphocytes following the administration of a non-myeloablative chemotherapy regimen consisting of 60 mg/kg cyclophosphamide given on two consecutive days followed by five days of 25mg/m2 fludarabine. A second trial was then conducted in 25 patients in which the same chemotherapy was given (but condensed to a five day period) followed by 200cGy whole body irradiation the day before cell administration. In a third trial in 25 patients the total body irradiation was intensified by giving 200cGy twice a day for three consecutive days for a total of 1200cGy. In the latter two trials, circulating CD34+ hematopoietic stem cells were administered. In all protocols 720,000IU/kg IL-2 was administered to tolerance. The objective response rates by RECIST criteria in the three sequential protocols were 49%, 52% and 72% respectively (). Responses were often durable and many patients have ongoing responses beyond three years, and in the earliest trial beyond five years. All but one of the 12 complete responses are ongoing from 18 to 75 months. Objective cancer regressions were seen at all sites in the body including lung, liver, brain, lymph nodes, subcutaneous tissues and bone. Examples of these responses are shown in . The overall survival of patients in these three trials is shown in which also includes the survival of the original 86 patients who received T cell transfer without major lymphodepletion. It should be emphasized that these clinical trials are consecutive rather than randomized and thus, although it appears that increasing lymphodepletion has led to improvement in survival, this conclusion must be drawn with caution.
Schema of the lymphodepleting preparative regimens used in the adoptive cell transfer protocols in the Surgery Branch, NCI.
Figure 2 Objective clinical regressions in patients with metastatic melanoma treated with cell transfer therapy. A. Regression of melanoma metastases in the heart (upper), adrenal (middle) and peritoneal cavity (lower) now ongoing at 34 months in a 53 year old (more ...)
Figure 3 Survival of patients treated with cell transfer therapy in four consecutive clinical trials using increasing regimens of a lymphodepleting preparative regimen prior to adoptive cell transfer (NMA, non-myeloablative chemotherapy; TBI, total body irradiation). (more ...)
These studies have shown that T cell based immunotherapy is capable of mediating the regression of large vascularized invasive metastatic melanoma in humans. It should be emphasized that the widely held belief that immunotherapy can only affect minimal disease in the adjuvant setting is thus not correct.