Suppressor deletion therapy: selective elimination of T suppressor cells in vivo using a hematoporphyrin conjugated monoclonal antibody permits animals to reject syngeneic tumor cells

A MAb (B16G) which recognizes a constant epitope on TsC and their soluble factors in DBA/2 mice has been described previously. In this study, we show that when this MAb is covalently linked to the photoactivable molecule Hp, and injected i.v. into P815 tumor-bearing mice which were subsequently exposed to light, tumors undergo permanent regression in 10%–40% of these mice (depending on the individual experiment). All control animals died within an average of 22–24 days after tumor cell injection. It is suggested that tumor regression is attributable to immune mechanisms facilitated by the elimination of a population of TsC. When splenocytes of B16G-Hptreated mice were assayed in vitro for the generation of CTL active against P815 tumor cells, it was found that 24 h after treatment, a significant increase in killer cell activity was noted but that this effect was gone by 48h. We also show that B16G-Hp conjugates are capable in vitro of specifically killing cells of a TsC hybridoma, A10 (which has been shown previously to secrete a T suppressor factor reactive with P815 cell surface antigens). This conjugate had no cytotoxic effect on P815 cells under conditions in which A10 cells were killed.