Human T cells expressing affinity-matured TCR display accelerated responses but fail to recognize low density of MHC-peptide antigen

Abstract

We have tested whether affinity-matured TCRs that retain peptide specificity improve the ability of primary human CD8 ؉ T cells to mount antigen-specific responses. We found that TCR affinity correlated with the speed of T-cell responses. High affinity TCR-antigen interactions rapidly initiated T-cell responses, but low affinity TCR/antigen interactions required longer time periods to elicit the same responses. Within the "natural" affinity range, increased TCR-to-antigen affinity correlated with improved ability of T cells to recognize low concentration of antigen. However, affinity-matured TCR with 700-fold enhanced affinity for MHC-toantigen required 100-fold higher antigendensity to initiate T-cell responses than did wild-type TCR. Using modified peptides to reduce the affinity of TCR-toantigen interaction, we demonstrate that affinity-matured TCRs are not defective, being superior to wild-type TCR in recognizing low concentration of modified peptides. These data indicate that enhancing TCR affinity can accelerate the speed of T-cell activation and reduce the ability to recognize low density of MHC-to-peptide antigen. We predict that future studies of the human T-cell repertoire will reveal 2 types of low avidity T cells: fast and slow responders, with high-affinity and low-affinity TCR, respectively. (Blood. 2011;118(2):319-329) IntroductionT cells recognize antigens using the TCR that binds peptides displayed by MHC molecules. Compared with antibodies, the affinity of TCR for MHC-to-peptide is relatively low, with dissociation constants K D ranging from 100-1M. [1][2][3][4] Unlike antibodies, TCRs do not naturally undergo somatic hypermutation to enhance affinity for the TCR-recognized antigen. The reasons for the very limited range of TCR affinities is not fully understood, but might be related to the thymic selection process that eliminates TCRs with high affinity for self MHC-to-peptide while positively selecting low-affinity interactions. 5 In the field of antitumor TCR gene therapy, giving T cells high-affinity TCRs is a major goal for producing T cells capable of attacking tumor cells. 6,7 As most tumor-associated targets are self-antigens that are also expressed in normal tissues, central and peripheral tolerance mechanisms are likely to delete or inactivate T cells expressing high-affinity TCR for these tumor-associated antigens. 8,9 Several strategies have been explored to circumvent tolerance to tumor-associated self-antigens. This includes the use of the natural TCR repertoire of HLA-mismatched donors and HLA-transgenic mice. [10][11][12] In the HLA-mismatched setting the TCR repertoire is not tolerant to peptides presented by non-self HLA molecules, and in the HLA-transgenic setting mice are not tolerant to human proteins and antigens that are not conserved in mice.In vitro affinity maturation provides an additional strategy to select high-affinity TCR. In this setting affinity is not restricted to the physiologic range of naturally selected TCR, but provides an opportunity to enhance TCR affin...

Architecture of a minimal signaling pathway explains the T-cell response to a 1 million-fold variation in antigen affinity and dose

“…Studies performed over the last two decades have focused on empirically mapping the relationship between pMHC affinity and T-cell activation (5,(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24). A number of studies have reported an optimal pMHC affinity for T-cell activation, but other studies have failed to observe the optimum.…”

“…A specific example is the NY-ESO-1 cancer antigen, for which both high-affinity TCRs and CARs have been produced (26,27). The optimizing of these therapies has focused, in part, on trying to determine the optimal receptor affinity for clinical efficacy (20,22,(28)(29)(30); reviewed in ref. 31).…”

Target Density, Not Affinity or Avidity of Antigen Recognition, Determines Adoptive T Cell Therapy Outcomes in a Mouse Lymphoma Model

“…More importantly, our results indicate that the requirement to artificially engineer CTL TCR for higher-affinity recognition of MHC-peptide complexes may not be as critical as previously considered. Indeed, in some settings, increasing TCR affinity can impair, rather than enhance, CTL activity (20)(21)(22). Although it seems counterintuitive, this is likely due to the reduced ability of high-affinity CTL to undergo serial triggering, where one MHC-peptide complex sequentially engages several TCR to achieve a critical activation threshold (23)(24)(25).…”

Adoptive T-Cell Therapy for Cancer in the United Kingdom: A Review of Activity for the British Society of Gene and Cell Therapy Annual Meeting 2015

“…The group is also leading translational application of emerging nuclease reagents including TALENs for the generation of universal Tcells depleted of alloreactive T-cell receptors. Within University College London, Prof. Hans Stauss and Dr. Emma Morris have shown that TCR-redirected T-cells can function in vitro and in vivo targeting tumor or viral antigens supporting clinical trial activity 34,41,42 and also that modifications to TCR sequences or transfer of additional molecules can enhance TCR expression and in vivo T-cell function, 43,44 that clinical-grade gene-modified cell products can be generated, 45,46 and that tolerance to tumor-associated antigens may be overcome. 47 Moreover, the group has also shown that genetic engineering of HSCs can alter the specificity of developing T-cells 48 and, in collaboration with others, has shown that gene-modified antigen-specific Tregs have suppressive function in vivo.…”