Eur. J. Immunol. 1989.19: 599-604 T cell response to HLA-A2 in HLA-transgenic mice 599 Gunter J. Hammerling', Thurman Hunt', Othmar Dill' and zyxwvutsrq J& MorenoO Institute for Immunology and Genetics', German Cancer Research Center, Heidelberg, Stanford University Medical School', Stanford and Division of Immunochemistry', Unidad de Investigacion Biomedica, Instituto Mexican0 de Seguro Social, Mexico Cytotoxic T lymphocyte recognition of HLA-A2 antigens in normal and HLA-Cw3-transgenic mice* It is well established that a large fraction of murine cytotoxic T cells can recognize allogeneic major histocompatibility complex (MHC) antigens, and that the majority of this response are not restricted by H-2 antigens of the responding host. In contrast, the murine response against the xenogeneic HLA class I antigens is relatively weak. Moreover, a large proportion of the responding murine T cells do not recognize the HLA antigen per zyxwv se but only in an H-Zrestricted manner, probably as an HLA peptide bound to H-2. Considerable evidence suggests that in mice the T cell repertoire is selected by thymic H-2 antigens. Therefore, we asked the question whether in transgenic mice expressing an HLA class I antigen the T cell repertoire would be shaped toward a more effective recognition of other HLA alleles. Normal C57BL/6 (B6) and HLA-Cw3 -transgenic B6 mice were immunized with a B6-derived cell line transfected with HLA-A2. The resulting AZspecific zyxwvu CTL were tested on L cells transfected with either A2 alone, which should identify the H-Zunrestricted CTL, and on L cells transfected with A2 plus H-2b genes, which should identify the sum of H-2b-restricted and unrestricted CTL. Both bulk culture and limiting dilution experiments showed that the CTL precursor frequencies for A2-specific CTL were not increased in the transgenic mice, and that both strains produced comparable proportions of H-2b-restricted and of unrestricted AZspecific CTL. The B6.Cw3 mice seemed to respond less well to HLA- A2 than the normal B6 mice, suggesting the possibility of tolerance for peptides shared by the Cw3 and A2 molecules. In conclusion, the T cells in the B6.Cw3 transgenic mice did not seem to be selected towards a stronger and more unrestricted recognition of an allo-HLA antigen. The possible reasons are discussed. 1 Introduction It is well established that a large fraction of T lymphocytes can recognize allogeneic major histocompatibility antigens (MHC). Estimates of the respective precursor frequencies of cytotoxic T lymphocytes (CTL) with specificity for one par- ticular MHC alloantigen range between 1/300 to 1/2000. These are about 100 to 1000 times higher than the precursor frequen- cies of CTL recognizing foreign antigens or peptides thereof in the context of syngeneic MHC (reviewed in [ l , 21). The pep- tide model of MHC-restricted antigen recognition offers an explanation for this high alloreactivity [3-51. According to this hypothesis the peptide-binding grooves of the MHC molecules are always occupied by a large number of different self-pep- tides, thus creating a multitude of epitopes which can be recog- nized by allogeneic T lymphocytes. In contrast to the high alloreactivity stands the relatively weak response to xenogeneic MHC antigens which has been documented in many experimental systems [6-91. In more [I 72351 * This study was supported by a grant of the Deutsche Forschungs- gemeinschaft HA 731/8-1 and by stipends of the German Cancer Research Center to visiting scientists Dr. Thurman Hunt and Dr. Jost Moreno. Correspondence: Gunter J. Hammerling, Institute for Immunology and Genetics, German Cancer Research Center, Im Neuenheimer Feld 280, D-6900 Heidelberg, FRG Abbreviations: MHC: Major histocompatibility complex CTL(p): Cytotoxic T lymphocyte(s) (precursor) zyxwvut E : T ratio: Effector : target cell ratio mAb: Monoclonal antibody(ies) LD: Limiting dilution recent studies it was observed that human CTL raised against HLA class I antigens on human cells were, in general, not able to lyse efficiently murine cell targets transfected with the respective HLA genes [lo-133, but some exceptions have been reported [14, 151. The failure to lyse the HLA' murine targets could have been due to a species barrier of accessory molecules (LFA-3, etc.) which are required for an efficient interaction between CTL and target cells. However, when mice were immunized with murine cells transfected with HLA genes again only a relatively weak response against the respec- tive HLA antigen was observed. In addition, most CTL clones generated in this manner recognized the HLA molecules in an H-Zrestricted way [16-181. In further studies it has been found that peptides of the HLA molecules were recognized together with the murine H-2 class I molecules [19]. These observations are in striking contrast to murine CTL responses to allogeneic cells or mouse cell lines transfected with allogeneic H-2 class I antigens which always resulted in the exclusive or predominant generation of CTL which were not restricted by the H-2 class I molecules of the responding mouse. It can be assumed that the overall structures of HLA and H-2 class I antigens are very similar [4]. It is not clear why mice see the HLA antigens predominantly like a nominal antigen and therefore so drastically different from murine H-2 antigens. On the other hand, recent work with HLA class I transgenic mice established that these mice can use the transgenic HLA antigens as restriction elements for nominal antigens similarly to their own H-2 molecules although not as efficiently. In HLA-Cw3-transgenic mice generated in this laboratory the Cw3 antigen was not only expressed in the same tissues as the endogeneous H-2 class I molecules, including the thymus, but also functioned as an MHC restriction molecule in zy CTL responses to influenza virus and to Sendai virus [20]. Similar z 0 VCH Verlagsgesellschaft mbH, D-6940 Weinheim, 1989 0014-2980/89/0404-0599$02.50/0