Ultrastructural basis of enhanced antitumor cytotoxicity of cord blood-derived CTLs: a comparative analysis with peripheral blood and bone marrow.

Umbilical cord blood cells (UCBC) are a rich source of immature immune effector and accessory cells, including dendritic cells. UCBC-derived cytotoxic T lymphocytes (CTLs) generated against human breast cancer or neuroblastoma have shown an increased tumor-specific cytotoxicity compared to peripheral blood (PB)-derived CTLs. The precise mechanism of this increased cytotoxicity is not known. Since dendritic cells (DCs) play a central role in the immunostimulation, we compared the ultrastructure and antigen presenting nature of DCs from UCBC, PB and bone marrow (BM) at various stages of maturation using scanning and transmission electron microscopy as well as fluorescent microscopy to elucidate the mechanism underlying the increased cytotoxicity of UCBC-derived CTLs. DCs were examined for their immunophenotype nuclear morphology, dendritic processes and cytoplasmic endosomal vesicles after 0, 3, 7 and 10 days in culture with antigen priming on day 6. Results showed that there were smaller and more vesicles in UCB-DCs compared to DCs from the other two sources, while the endosomal vesicles in PB-DCs were heterogenous in size. The antigen processing ability of the UCB-DCs showed an increase in antigen-positive endosomes compared to PB-DCs as determined by the fluorescent microscopy. Thus, our results provided the comparative analyses of DCs from cord blood, peripheral blood and bone marrow, and suggested that UCBC-DCs might have better antigen presenting ability leading to increased CTL-mediated antitumor cytotoxicity.

Immunotherapy of human neuroblastoma using umbilical cord blood-derived effector cells.

Tumors of the nervous system, including neuroblastoma and glioblastoma, are difficult to treat with current therapies. Despite the advances in cancer therapeutics, the outcomes in these patients remain poor and, therefore, new modalities are required. Recent literature demonstrates that cytotoxic effector cells can effectively kill tumors of the nervous system. In addition, we have previously shown that umbilical cord blood (UCB) contains precursors of antitumor cytotoxic effector cells. Therefore, to evaluate the antitumor potential of UCB-derived effector cells, studies were designed to compare the in vitro and in vivo antitumor effects of UCB- and peripheral blood (PB)-derived antigen-nonspecific and antigen-specific effector cells against tumors of the nervous system. Mononuclear cells (MNCs) from UCB were used to generate both interleukin-2 (IL-2)-activated killer (LAK) cells and tumor-specific cytotoxic T lymphocytes (CTLs). UCB-derived LAK cells showed a significant in vitro cytotoxicity against IMR-32, SK-NMC, and U-87 human neuroblastoma and glioblastoma, respectively. In addition, the CTLs generated using dendritic cells primed with IMR-32 tumor cell lysate showed a selective cytotoxicity in vitro against IMR-32 cells, but not against U-87 or MDA-231 cells. Furthermore, treatment of SCID mice bearing IMR-32 neuroblastoma with tumor-specific CTLs resulted in a significant (p < 0.01) inhibition of tumor growth and increased overall survival. Thus, these results demonstrate the potential of UCB-derived effector cells against human neuroblastoma and warrant further preclinical studies.