Cytokine-induced killer (cik) cell cultures for the adoptive immunotherapy of hematological malignancies: characterization and new therapeutic strategies for clinical application

Cytokine-induced killer (CIK) cells are a heterogeneous population of lymphocytes obtained in vitro within 21 days from mononuclear cells under the influence of cytokines. CIK cells show potent MHC-unrestricted cytotoxicity against a variety of tumor cells, in particular hematological malignancies, and minimal tendency to induce graft-versus-host disease. The expanded bulk CIK culture consists of over 90% CD3+ cells, of which the majority coexpress CD56 and the remaining cells are CD56-. CD3+CD56+ “true” CIK cells are terminally differentiated non dividing lymphocytes which could deliver potent MHC-unrestricted cytotoxicity for the immediate destruction of tumor cells. The other less cytotoxic CD3+CD56- cell subset represents a progenitor reservoir that could proliferate and differentiate into CD3+CD56+ CIK cells. CD3+CD56+ CIK cells express activating NK receptors including NKG2D, DNAM-1 and low levels of NKp30. Cell signalling not only through TCR/CD3, but also through NKG2D, DNAM-1 and NKp30, leads to CIK cell activation resulting in granule exocytosis and cytotoxicity. Antibody blocking experiments revealed that NKG2D, DNAM-1 and NKp30 are actually involved in tumor cell recognition and killing. Anti-CMV specific CIK cells could be expanded in standard CIK conditions and mediate both specific, MHC-restricted recognition of a CMV-pulsed autologous target and NK-like non specific cytolytic activity against leukemic cell targets. Antibody blocking of NKG2D and NKp30 only inhibited NK-like cytotoxicity. Their dual effector function suggests that CIK cells, when used in a clinical setting, may control both neoplastic relapses and viral infections, two frequently associated complications in transplanted patients. B-cell non-Hodgkin lymphoma is only partially susceptible to CIK-mediated lysis. The addition of anti-CD20 monoclonal antibodies GA101 or rituximab increased cytotoxicity mediated by CIK cell cultures by 35% and 15%, respectively. This enhancement was mainly due to antibody-dependent cytotoxicity mediated by the 1%-10% NK cells contaminating CIK cultures. The addition of human serum inhibited NK-cell activation induced by rituximab, but not activation induced by GA101. Overall lysis in presence of serum, even of a resistant B-NHL cell line, was significantly increased by 100 mcg/mL of rituximab, but even more so by GA101, with respect to CIK cultures alone. The combined use of CIK cells with anti-CD20 mAbs could represent a novel immunotherapy protocol for the treatment of B lymphoma patients with resistant disease.