Tumour-associated B7-H3 was unlikely to be involved in an initial antigen-priming phase of CD8+ T-cell responses. A similar observation has been reported using B7-H3-transfected P815 cells and adoptive transfer in a P1A-specific CTL model system.25 B7-H3 expression on P815 tumour Vincristine cells enhanced CD8-mediated tumour immunity by amplifying local expansion of tumour-specific CTL in the absence of professional antigen-presenting cells. Unfortunately, the P815 cells used in our study lacked a P1A tumour antigen so we used OVA-specific TCR-transgenic CD8+ (OT-I CD8+) T cells and an OVA-expressing

tumour (E.G7) cell system to assess antigen-specific CTL responses. Another report also demonstrated enhanced tumour immunity by B7-H3 introduction into Colon 26 colon carcinoma cells.26 IFN-γ production from splenic CD8+ T cells of tumour-bearing mice was enhanced by co-culture with B7-H3+ tumour cells. In both reports, B7-H3-introduced tumours were not completely rejected in all individuals and some mice developed large tumours and died. Our results also showed a failure of complete tumour rejection. Although we have not observed this in parallel studies, it seems that

the effects of introducing B7-H3 is not as strong as those of CD80, CD86, 4-1BBL or GITRL both in vitro and in vivo.35,36,40,43–45 We also examined tumour vaccine effects of B7-H3-transduced tumours following Selleckchem Saracatinib several injections of B7-H3/SCCVII after pre-inoculation of live parental tumours; however, there was no effect on tumour growth Chloroambucil (data not shown). These observations are consistent with a previous report on B7-H3/P815 tumour vaccine effects.25 It is likely that the reason for the limited effect of B7-H3-transduced tumour cells was the few or no enhancing effects of

B7-H3 during the priming phase. The de novo induction of regulatory co-stimulatory ligands like B7-H1 and B7-H4 in tumour cells and others may override the effects of B7-H3-mediated anti-tumour immunity.22 The major reason for dominant involvement of CD8+ T cells in B7-H3-enhanced immunity could be the result of counter-receptor expression. In the steady state, TLT-2 is clearly expressed on splenic CD8+ T cells, whereas TLT-2 on CD4+ T cells is either weak or null (Fig. S2 and ref. 28). Nevertheless, we observed preferentially higher anti-CD3 mAb-induced re-directed cytotoxicity of CD4+ T cells against both parental P815 and B7-H3/P815 cells (Fig. 1). We have previously shown that the anti-CD3 mAb-induced re-directed cytotoxicity was greatly dependent on the Fas–Fas ligand pathway.33 In fact, the re-directed cytotoxicity of CD4+ T cells against P815 and B7-H3/P815 cells was efficiently inhibited by blocking anti-Fas ligand mAb (data not shown). CD4+ T cells rapidly increased TLT-2 expression by anti-CD3 mAb stimulation alone (Fig.