GENERATION OF TUMOR-SPECIFIC CYTOTOXIC T-LYMPHOCYTES FROM PEROPHERAL BLOOD OF COLORECTAL CANCER PATIENTS FOR ADOPTIVE T-CELL TRANSFER

Colorectal cancer (CRC) is the third most common cancer worldwide and the fourth most common cause of death in the developed Western countries. Adoptive T-cell transfer (ACT) refers to an immunotherapeutic approach in which anti-tumor T lymphocytes, usually the tumor infiltrating lymphocytes (TIL), are identified, grown ex vivo and then re-infused into the cancer patient. ACT of EBV-specific T-cell lines and T Cytotoxic Lymphocytes (CTLs) for the therapy of EBV-induced lymphomas is the best demonstration of clinically efficacious ACT, but there are many evidences also for leukemia and multiple myeloma. As regards to the solid tumors, ACT using autologous TIL, grown ex-vivo and then re-infused into the cancer patient, has emerged as an effective treatment for metastatic melanoma and renal cell carcinoma (RCC), that are the most immunogenic tumors in humans. Randomized clinical trials are ongoing for gastric cancer, hepatocellular carcinoma and lung cancer. These approaches mainly use the TIL and the definition of tumor associated antigen (TAA), tumor specific antigen (TSA) or cancer testis antigen (CTA), that are generally correlated with tumor progression and immunogenicity in various types of cancer. However these antigens are often found to be poorly expressed in CRC, and few is known about their relationship with this type of neoplasia. In addition, although a clear association between TIL and clinical outcome of CRC has been documented, active and adoptive immunotherapy do not play yet an important role in the treatment of advanced CRC. In order to develop an ACT protocol for CRC treatment, we designed an experimental approach that does not require neither the definition of molecular defined tumor antigens, nor the availability of TIL. Our strategy was based on the in vitro stimulation of patient’s CD8+-enriched T-cells from peripheral blood mononuclear cells (PBMCs) with dendritic cells (DCs), pulsed with apoptotic tumor cells as a source of tumor antigens, in order to generate autologous CTLs with strong anti-tumor activity. In this study, 78 CRC patients were enrolled. Tumor biopsies were obtained at surgery, together with 100 ml of heparinized peripheral blood (PB). Tumors were mechanically dissociated to a single-cell suspension and cultured to obtain tumor cell line from each patient. DCs were generated from previously separated PBMCs, using a magnetic positive selection of CD14+ monocytes, cultured in presence of recombinant human Interleukin-4 (rh IL-4) and recombinant human Granulocyte-Macrophage Colony-Stimulating Factor (rh GM-CSF). Anti-tumor CTLs were elicited in co/micro-culture using DCs as antigen-presenting cells, autologous apoptotic tumor cells as source of antigens and T CD8+ lymphocytes enriched effectors, with weekly stimulation. CTLs Interferon-γ (IFN-γ) secretion was assessed by ELISpot assay to evaluate their activation in response to autologous tumor. Tumor cell lines were obtained from 20 out of 78 patients (25,6%), because gut intestinal flora had adversly affected the establishment of primary tumor cell line and a loss of expansion of tumor cells was observed. DCs were generated from 26 patients, but only 6 patients had the corresponding tumor cell line, indispensable for the co-culture setting up. This was the reason why co/micro-cultures were set up only for 6 patients. ELISpot assay was performed at the end of co/micro-culture stimulations to evaluate effectors IFN-γ secretion. ELISpot results showed that strong and significant IFN-γ secretion was detected at the third, fourth and fifth stimulations for one patient and at the second for another patient, whereas for three patients a weak secretion was detected during the second and third stimulations. Although our immunological study must be performed on an increased number of CRC patients, and the CTLs expansion, together with CTLs lytic ability against autologous tumor cells, must be still performed, our results suggested that the generation of tumor-specific CTLs could be useful for supporting an ACT approach in CRC.