1 Department of Clinical Chemistry and Pathobiochemistry, Medical Faculty, University of Technology, Pauwelsstr" D-5100 Aachen, federal Republic of Germany
2 Department of Immunology, University of Münster, Domagkstr. 3, D-4400 Münster, Federal Republic of Germany

We have shown previously that tumorspecific T suppressor (Ts) cells were induced in vivo in BALB/c mice by the syngencic plasmacytoma (PC) ADJ-PC-5 at very early stages of tumorigenesis [1, 2]. These Ts cells, which suppress a strong primary cytotoxic T cell response, have been characterized in detail [1- 3]. There is evidence that Ts cell-inducing antigens (Ts-Ag) on ADJ-PC-5 plasmacytoma cells are expressed to some extent on normal BALB/c spleen cells and are therefore "self' antigens rather than tumor-specific neoantigens [4]. These data were subsequently confirmed by independent comparable studies using the EL4 thymoma ofC57B1/6 mice [5]. Thus, the induction of Ts cells by tumor-associated self antigens seems to be a more general rule and might be an important tumor escape mechanism. To characterize Ts-Ag in more detail we have developed an in vitro system for the selective induction of tumor-specific Ts cells. Ts cell function would be masked in the in vitro Ts assay in the presence of activated cytotoxic T cells, which, like specific cytotoxic T cell clones, are not susceptible to suppression [2]. Activation of cytotoxic T cells is prevented by pretreatment of the ADJ-PC-5 stimulator cells with glutardjaldehyd (GA) (Fig. 1). In contrast, specific Ts cells were activated by this approach which suppress the

activation of specific cytotoxic T cells in the course of a primary mixed-lymphocyte tumor cell culture (MLTC) of BALB/c spleen cells against ADJ-PC-5 plasmacytoma cells, but not against the syngeneic control tumors ULMC (lymphoma) and MethA (fibrosarcoma) (Fig. 2). These Ts cells have been further characterized. Even in lectin-kill assays they have no cytolytic or NK-Iike activity, excluding a veto effect. In addition, suppression is not due to nonspecific effects like IL2 consumption, toxic effects by glutaraldehyde or PGE2 release (data not shown). The phenotype of these Ts cells was Thy 1.2+, Lyt2.2+, L3T4+, l-Ad-, l-Ed+ as cvidenced by treatment with cytotoxic monoclonal antibodies and complement. This in vitro system will be helpful for the isolation and characterization of TsAg, but it also allows us to study in morc detail the requirements for thc induction of Ts cells and Ts-cell effector mechanisms.

References

1. Haubeck H-D, Kölsch E (1982) Regulation of immune responses against the syngeneic AOJ-PC-5 plasmacytoma in BALB/c mice. I II. Induction of specific T suppressor cells to the BALB/c plasmacytoma ADJ-PC-5 during early stages of tumorigenesis. Immunology 47:503- 509

2. Haubcck H-O, Kölsch E (1986) Regulatioll of immune responses against the syngeneic AOJ-PC-5 plasmacytoma in BALB/c mice IV. Tumor-specific T suppressor cells, induced at early stages of tumorigenesis, act on the induction phase of the tumorspecific cytotoxic T cell response. Immunobiology 171:357-363

3. Haubeck H-O, Kölsch E (1985) Isolation and characterization of in vitro and in vivo functions of a tumor-specific T suppressor cell clone from a BALB/c mouse bearing the syngeneic AOJ-PC-5 plasmacytoma. J Immunol I35.4297-4302

4. Kloke 0, Haubcck H-O, Kölsch E (1986) Evidence for a T suppressor cell-inducing antigenic determinant shared by ADJ-PC-5 plasmacytoma and syngeneic BALB/c spleen cells. Eur J lmmunol 16:659-664

5. Grooten J Leroux-Roels G, Fiers W (1987) Specific suppression elicited by EL4 lymphoma cells in syngeneic mice. Specifity includes self-antigens. Eur J lmmunol 17:605