In most cases the medical condition of T-cell donors for our study was unknown, but in all probability some had been previously infected with common

viruses such as influenza and EBV, which may have introduced a bias toward higher affinity TCRs for these antigens. However, in cases where previous antigen exposure of the donor is highly likely, it has not always led to selection of robust TCR affinity. For example, the Her-2/Neu TCR, isolated from a breast cancer patient, has a relatively low affinity for the antigen (KD = 53 μM; Table 1). In contrast, the PSCA TCR was cloned from a healthy donor but has a slightly higher antigen affinity (KD = 48 μM; Table 1). We therefore suggest it is unlikely that the higher affinities observed for VA-specific TCRs manifest themselves solely as a consequence of previous antigen exposure in the donors. The observed differences in binding see more parameters between TCRs recognizing VAs or TAPAs will

confer significantly different levels of antigen sensitivity to T cells and are likely to affect their signaling pathways. T-cell activation is first and foremost driven by TCR binding to antigen, although it remains unclear whether the affinity or kinetics of binding is the determining factor; discrepancies in the correlation of a single-binding parameter with T-cell activation have been reported ([18-20] and reviewed in [13]). Despite this debate it is established that, in the naturally selected affinity range, T cells with TCRs that bind pMHCs with higher affinities and longer selleck screening library half-lives elicit a stronger and more effective immune response. It therefore follows from the data presented here that in general why VAs will draw a stronger CTL response than TAPAs. Indeed, we have shown that cancer-specific CTLs give a poor functional response to physiological levels of antigen (data

not shown). The lower affinity of TAPA-specific TCRs, in comparison with their VA-specific counterparts, could be a consequence of negative selection during T-cell maturation within the thymic medulla. Negative selection, in response to antigenic presentation of self-peptides, leads to the deletion of T cells bearing high affinity TCRs to self-antigens. Since many TAPAs are also self-antigens, high affinity TAPA-specific T cells will be simultaneously deleted from the repertoire. Even for antigens such as NY-ESO-1 [21], whose expression is usually restricted to immune privileged sites, low levels of mRNA have been detected in thymus [22]. Nevertheless, some TAPA-specific TCRs possessing low to moderate antigen affinity (in the region of 10 and 400 μM; Table 1) do escape thymic deletion; this may occur as a result of promiscuity within the T-cell repertoire.