Previous studies have identified murine and human regulatory CD8+ T cells specific for TCR-Vβ families expressed on autologous activated CD4+ T cells. In the mouse, these regulatory CD8+ T cells were shown to be restricted by the MHC class Ib molecule, Qa-1. In the present study, we asked whether HLA-E, the human functional equivalent of Qa-1, binds Vβ peptides and whether the HLA-E/Vβ-peptide complex induces and restricts human CD8+ CTLs. We first created stable HLA-E gene transfectants of the C1R cell line (C1R-E). Two putative HLA-E binding nonapeptides identified in human TCR Vβ1 and Vβ2 chains (SLELGDSAL and LLLGPGSGL, respectively) were shown to bind to HLA-E. CD8+ T cells could be primed in vitro by C1R-E cells loaded with the Vβ1 (C1R-E/V1) or Vβ2 (C1R-E/V2) peptide to preferentially kill C1R-E cells loaded with the respective inducing Vβ peptide, compared with targets loaded with the other peptides. Priming CD8+ T cells with untreated C1R-E cells did not induce Vβ-specific CTLs. Of perhaps more physiological relevance was the finding that the CD8+ CTLs primed by C1R-E/V1 also preferentially killed activated autologous TCR Vβ1+. Similar results were observed in reciprocal experiments using C1R-E/V2 for priming. Furthermore, anti-CD8 and anti-MHC class I mAbs inhibited this Vβ-specific killing of C1R-E and CD4+ T cell targets. Taken together, the data provide evidence that certain TCR-Vβ peptides can be presented by HLA-E to further induce Vβ-specific CD8+ CTLs.

Previous studies have identified murine and human regulatory CD8(+) T cells specific for TCR-V beta families expressed on autologous activated CD4(+) T cells. In the mouse, these regulatory CD8(+) T cells were shown to be restricted by the MHC class Ib molecule, Qa-1. In the present study, we asked whether HLA-E, the human functional equivalent of Qa-1, binds V beta peptides and whether the HLA-E/V beta -peptide complex induces and restricts human CD8(+) CTLs. We first created stable HLA-E gene transfectants of the C1R cell line (C1R-E). Two putative HLA-E binding nonapeptides identified in human TCR V beta1 and V beta2 chains (SLELGDSAL and LLLGPGSGL, respectively) were shown to bind to HLA-E. CD8(+) T cells could be primed in vitro by C1R-E cells loaded with the V beta1 (C1R-E/V1) or V beta2 (C1R-E/V2) peptide to preferentially kill C1R-E cells loaded with the respective inducing V beta peptide, compared with targets loaded with the other peptides. Priming CD8(+) T cells with untreated C1R-E cells did not induce V beta -specific CTLs. Of perhaps more physiological relevance was the finding that the CD8(+) CTLs primed by C1R-E/V1 also preferentially killed activated autologous TCR V beta1(+). Similar results were observed in reciprocal experiments using C1R-E/V2 for priming. Furthermore, anti-CD8 and anti-MHC class I mAbs inhibited this V beta -specific killing of C1R-E and CD4(+) T cell targets. Taken together, the data provide evidence that certain TCR-V beta peptides can be presented by HLA-E to further induce V beta -specific CD8(+) CTLs.

Activation-induced cell surface molecules are involved in mediating bidirectional T-B lymphocyte signaling that is important in the induction of T or B lymphocyte effector functions. In this regard, T-BAM/CD40-L is an activation-induced CD4+ T cell surface molecule known to be important in inducing B cell effector functions. This report demonstrates that T-BAM/CD40-L molecules on a Jurkat T cell leukemia subclone (D1.1) or nonlymphoid 293 kidney cell transfectants induce B cells or B-CLL cells to express CD80 (B7/BB-1) in a manner that is specifically inhibited by anti-T-BAM/CD40-L mAb 5C8. Because activation-induced B cell surface molecules, such as CD80, deliver costimulatory signals to T cells that augment T cell proliferation, the functional costimulatory capacity of T-BAM/CD40-L-primed B cells and B-CLL cells was studied. T-BAM/CD40-L-primed B cells or B-CLL cells augment the proliferative responses of allogenic T cells. Furthermore, T-BAM/CD40-L priming is specifically inhibited by mAb 5C8. Together, these studies demonstrate that T-BAM/CD40-L induces CD80 expression on resting B cells or B-CLL cells. Moreover, T-BAM/CD40-L signaling enhances B cell costimulatory capacity. These studies suggest that T-BAM/CD40-L molecules not only induce B cell differentiative processes that result in Ab secretion, but also enable B cells to prime Ag-specific T cells for subsequent clonal expansion.