Role of tumor necrosis factor species in the sequence-dependent effects of interleukin-2--tumor necrosis factor immunotherapy in mice: implications for preclinical cytokine testing.

We previously demonstrated that recombinant human tumor necrosis factor (hTNF) is synergistic with human interleukin-2 (hIL-2) for in vivo regression of murine tumors. In mice, the timing of cytokine administration is critical in achieving synergy. Because hTNF exhibits negligible binding to the type II murine TNF receptor (TNF-R), we questioned whether murine TNF (mTNF) would have therapeutic benefits, scheduling requirements, and toxic effects similar to those of the hIL-2-hTNF combination. To evaluate the biological effects of TNF-R types I and II interaction, we directly compared the effects of mTNF and hTNF in combination with hIL-2 on in vivo tumor regression and in vitro activation of murine splenocytes. Our results demonstrate for the first time that (a) the cytokine combination hTNF-hIL-2 is consistently more efficacious than mTNF-hIL-2 in in vivo murine immunotherapy models; (b) the in vivo antitumor effects of hTNF-hIL-2 and not mTNF-hIL-2 are critically dependent upon cytokine scheduling; and (c) in vitro culture of splenocytes with mTNF-hIL-2 enhances cellular proliferation, Lyt 2, and TNF-RI expression compared with hTNF-hIL-2. Collectively, these studies extend the previous findings of species-specific mTNF-R responses and reveal that optimal scheduling and efficacy of TNF-hIL-2 combination therapy in murine tumor models is critically dependent upon the TNF species employed.