CELLULAR IMMUNOLOGY $3, 302-3 12 ( 1984) T Helper Cell Lines That Augment in Viva Cytotoxic T-Cell Responses to Minor Alloantigens NICHOLAS R. J. GASCOIGNE’ AND PATRICK K. LAI Imperial Cancer Research Fund, Tumour Immunology Unit. Department of Zoology. University College London, Gower Street, London WClE 6BT, England Received August IS, 1983; accepted September 22, 1983 We have investigated the ability of long-term cultured T helper (Th) cell lines to help an in vivo cytotoxic T lymphocyte (CTL) responseto non-H-2 alloantigens (minor antigens). Th cell lines specific for various single or undefined minor antigens were selected by regular restimulation with antigen in vitro. They were antigen specific and H-2 restricted in proliferation assaysand were found to be able to help primary CTL responses to multiple minor antigens and secondary GIL responsesto single minor antigens. Although the Th were antigen specific they did not determine the specificity of the CTL. Th cells were both necessary and limiting for an effective CTL response indicating that “helper-independent” CTL are not in themselves sufficient to generate a strong in vivo response. Under conditions where a CTL response was clearly H-2 restricted, Th cells were not. Thus, the Th cells appeared to be activated by reprocessed antigen rather than antigen on the surface of the injected antigenic cells even though the CTL themselves reacted directly to the injected antigen. INTRODUCTION The requirement for T helper (Th)2 cells in the generation of cytotoxic T lymphocytes (CTL) has been recognized for some time (I), although most of the data that have accumulated over the last few years, and the concepts based upon them (2) have come from in vitro studies. These experiments have shown that Ly 1+2,3- T cells react with antigen presenting cells (APC) in an antigen-specific manner restricted by Class II H-2 molecules to produce a T cell growth factor (interleukin (IL)-2) which is neither antigen specific nor H-2 restricted (1, 3-8). IL-2 provides a proliferation signal for precursor CTL (CTLp), but is not sufficient in itself to induce CTL activity. The CTLp require direct contact with antigen (9) and stimulation by another soluble differentiation factor or factors (10, 11). The function of factors in vivo is not clear since IL2 at least is cleared from the serum very quickly ( 12, 13). There is uncertainty whether the requirement for Th cells in the CTL response is absolute, since some CTL clones themselves produce enough growth factors to act independently of extraneous factors in short-term proliferation assays in vitro (14- 16). Such cells are restricted by ClassI molecules for both proliferation and cytotoxicity ’ Present address:Department of Medical Microbiology, Fairchild Building, Stanford University School of Medicine, Stanford, Calif. 94305. * Abbreviations used: Th, T helper cells; CTL, cytotoxic T lymphocytes; CTLp, CTL precursor; IL-2, interleukin-2; APC, antigen presenting cells; FCS, fetal calf serum; CS, calf serum; LU, lytic units; MEM, minimal essential medium; Con A, concanavalin A, [‘251]Udr, [‘251]iodo-2’deoxyuridine. 302 0008-8749184$3.00 Copyri&l 0 1984 by Academic Press. Inc. All rights of reproduction in any fom reserved.