Chakrabarti Rabindranath, Zhou Zheng F, Chang Yigang, Prud'homme Gérald J
Department of Laboratory Medicine and Pathobiology, St. Michael's Hospital and University of Toronto, 30 Bond Street, Toronto, Ontario, Canada M5B 1W8.
Vaccine. 2005 Aug 31;23(37):4553-64. doi: 10.1016/j.vaccine.2005.05.002.
We have shown that a plasmid encoding a B7-1/Ig fusion protein enhanced DNA vaccination against human carcinoembryonic antigen (CEA) more effectively than the plasmid encoding membrane-bound B7-1. However, it was not known if B7-1/Ig acted only by binding CD28 (amplifying a stimulatory signal) or by blocking CTLA-4 on T cells (removing inhibitory signals). Here, we aimed to determine this using a plasmid encoding mutant B7-1/Ig (B7-1wa/Ig), which binds only to CTLA-4 but not to CD28. Our results showed that both the B7-1/Ig and B7-1wa/Ig plasmids, when co-administered with a CEA plasmid, enhanced tumor rejection and the in vitro anti-CEA response. Therefore, B7-1wa/Ig ameliorates DNA vaccination, presumably by binding to CTLA-4. This could result from a number of non-exclusive mechanisms, such as a reduced threshold for T-cell activation, or blockade of CTLA-4/B7-mediated tolerogenic signals in DCs or T cells. We found that, in vitro, a significant fraction of CD3/CD28-activated T cells (in the absence of DCs) expressed CTLA-4 and B7-1. Primed T cells of CTLA-4(+)B7-1(+/-) phenotype acted as regulatory T cells by inhibiting IFNgamma production by re-stimulated CTLA-4(-)B7-1(-) cells, and this was reversed by antibodies against IL-10 or TGF-beta1. Both B7-1wa/Ig and CTLA-4/Ig, which bind to CTLA-4 and B7-1/B7-2 respectively, enhanced IFNgamma production, but not the proliferation or IL-4 release in mixed T-cell populations containing these two cell types. In contrast, CTLA-4(-)B7-1(-) T cells produced IFNgamma which was not affected by B7-1wa/Ig or CTLA-4/Ig. These results suggest that blocking of CTLA-4/B7-1 binding in T cell/T cell interactions blocks negative regulatory signals. This might be the mechanism, at least in part, of the enhancement of anti-tumor immunity by the B7-1wa/Ig and B7-1/Ig plasmids.
我们已经证明，编码B7-1/Ig融合蛋白的质粒比编码膜结合型B7-1的质粒更有效地增强了针对人癌胚抗原（CEA）的DNA疫苗接种效果。然而，尚不清楚B7-1/Ig是否仅通过结合CD28（放大刺激信号）起作用，还是通过阻断T细胞上的CTLA-4（去除抑制信号）起作用。在此，我们旨在使用编码仅与CTLA-4结合而不与CD28结合的突变型B7-1/Ig（B7-1wa/Ig）的质粒来确定这一点。我们的结果表明，当B7-1/Ig和B7-1wa/Ig质粒与CEA质粒共同给药时，均可增强肿瘤排斥反应和体外抗CEA反应。因此，B7-1wa/Ig大概是通过与CTLA-4结合来改善DNA疫苗接种效果的。这可能是由多种非排他性机制导致的，例如降低T细胞活化阈值，或阻断DC或T细胞中CTLA-4/B7介导的致耐受性信号。我们发现，在体外，很大一部分CD3/CD28激活的T细胞（在没有DC的情况下）表达CTLA-4和B7-1。具有CTLA-4(+)B7-1(+/-)表型的致敏T细胞通过抑制再次刺激的CTLA-4(-)B7-1(-)细胞产生IFNγ而发挥调节性T细胞的作用，而抗IL-10或TGF-β1抗体可逆转这种作用。分别与CTLA-4和B7-1/B7-2结合的B7-1wa/Ig和CTLA-4/Ig均可增强IFNγ的产生，但在含有这两种细胞类型的混合T细胞群体中，对增殖或IL-4释放没有影响。相反，CTLA-4(-)B7-1(-) T细胞产生的IFNγ不受B7-1wa/Ig或CTLA-4/Ig的影响。这些结果表明，在T细胞/T细胞相互作用中阻断CTLA-4/B7-1结合可阻断负调节信号。这可能至少部分是B7-1wa/Ig和B7-1/Ig质粒增强抗肿瘤免疫的机制。
