Int. Z Immunopharmac., Vol. 15, No. 1, pp. 1 - 10, 1993. Printed in Great Britain. 0192-0561/93 $5.00 + .00 Pergamon Press Ltd. International Society for Immunopharmacology. IN VITRO COMBINED EFFECTS OF HUMAN INTERFERONS AND INTERLEUKIN-2 ON NATURAL CELL-MEDIATED CYTOTOXICITY M. P. FUGGETTA,* A. AQUINO,t R. PEPPONI, t S. D'ATRI,* G. LANZILLI,* E. BONMASSAR t and G. GRAZIANI t* *Institute of Experimental Medicine, National Council of Research, Rome, Italy; and *Department of Experimental Medicine and Biochemical Sciences, University of Rome "Tor Vergata", Rome, Italy (Received 8 July 1992 and in final form 29 August 1992) Abslraet -- In vitro modulation of natural cell-mediated cytotoxicity (NCMC), following sequential treatment of human mononuclear cells (MNC) with cytokines was investigated. Recombinant Interleukin-2 (IL2) used in combination with interferons (IFNs) induced variable effects on the cytolytic function of different MNC preparations obtained from 16 healthy donors. When MNC were treated with IFNs on day 4, after IL2 induction of LAK cells, increase or no change in cytotoxic activity was found. On the other hand, either no change or decrease in LAK activity occurred when MNC were treated with IFNs on day 0 before exposure to IL2. In this case the effect of IFNs on NCMC did not correlate with their activity on cell proliferation or on TAC antigen expression. In conclusion the present study points out that the NCMC of MNC of healthy donors, subjected to IL2 treatment in vitro, can be significantly increased by IFNs. However this effect is largely schedule-dependent (i.e. detectable with IL2 - IFNs but not with IFNs- IL2 sequence), and can be obtained in a relatively limited number of cases. Moreover it is suggested that these in vitro studies could provide preclinical bases for a rational approach to in vivo treatment with cytokine cascade in a clinical setting. Interleukin-2 (IL2) has been shown to possess multiple and potent regulatory effects on lymphocyte functions. Early effects mediated by IL2 concern activation of the cytotoxic potential of natural killer (NK) cells (Phillips, Takeshita, Sugamura & Lanier, 1989), production of gamma-interferon (Young & Ortaldo, 1987) and expression of IL2 receptor alpha and HLA-DR antigen on CD3- large granular lymphocytes (Gravekamp, Van den Bulck, Vijg, Van de Griend & Bolhius, 1987). Moreover after 3-5 day lymphocyte culture, IL2 promotes cell proliferation and generates effector cells with natural cytolytic activity against a large variety of NK-resistant targets, including fresh tumor cells (i.e. LAK activity; Grimm, Mazumder, Zhang & Rosenberg, 1982). Interferons (IFNs), and especially alpha and beta- IFNs, are known to be potent activators of NK cell function in vitro and in vivo (Dieu, Heinbaugh, Holden & Herberman, 1979; Herberman, Ortaldo, Mantovani, Hobbs, Kung & Pestka, 1982). However their influence on cell proliferation appears to be quite different from that of IL2. Actually they mediate cytostatic rather than mitogenic effects upon interaction with IFN receptors in different types of susceptible target cells (Gresser, 1985). Combined effects of IL2 and IFNs on cells involved in natural immunity appear to be of primary interest, especially on the bases of the recognized activity of these agents in neoplastic diseases (Rosenberg et aL, 1987; West et al., 1987; Gastl et al., 1986; Neidhardt et al., 1984). A number of studies have been performed on in vitro interaction between IL2 and IFNs on cell- mediated cytotoxic functions (Brunda, Tarnowski & Davatelis, 1986; Iigo, Sakurai, Tamura, Saijo & Hoshi, 1988; Sone, Utsugi, Nii & Ogura, 1988). However the results of these studies appear to be controversial, presumably as a result of a limited number of observations on different effector cell *Author to whom correspondence should be addressed at: Grazia Graziani, MD, Department of Experimental Medicine and Biochemical Sciences, University of Rome "Tor Vergata", Via Orazio Raimondo, 00173 Roma, Italy.