Factors influencing the patterns of T lymphocyte allorecognition

Effective adoptive therapy of tap-deficient lymphoma using diverse high avidity alloreactive T cells

High avidity for antigen and diversity of T cell receptor (TCR) repertoire are essential for effective immunity against cancer. We have previously created a transgenic mouse strain with increased TCR avidity in a diverse T cell population. In this report, we show that strong alloreactive responses of transgenic T cells against targets with low MHC class I expression can be used for effective adoptive transfer of tumor immunity in vivo. Alloreactive transgenic T cells could be an effective therapeutic approach counteracting tumor evasion of the immune system.

Local production and activation of complement up-regulates the allostimulatory function of dendritic cells through C3a-C3aR interaction

Donor cell expression of C3 enhances the alloimmune response and is associated with the fate of transplantation. To clarify the mechanism for enhancement of the immune response, we have explored the role of C3a receptor (C3aR)-ligand interaction on murine bone marrow dendritic cells (DCs). We show that DCs either lacked receptor for C3a (a C3 cleavage product) or were treated with C3aR antagonist, elicited defective T-cell priming against alloantigen expressed on the DCs. This was associated with reduced surface expression of major histocompatibility complex (MHC) and costimulatory molecules on the DCs, and with defective priming in skin allograft rejection. In addition, DCs lacking factor B were unable to generate potent T-cell responses against donor antigen, whereas lack of C4 had no detectable effect, suggesting a role for the alternative pathway contributing to allostimulation. Furthermore, therapeutic complement regulator can down-regulate DC allostimulatory function. These findings suggest that the capacity of DCs for allostimulation depends on their ability to express, activate, and detect relevant complement components leading to C3aR signaling. This mechanism, in addition to underpinning the cell-autonomous action of donor C3 on allostimulation, has implications for a wider range of immune responses in self-restricted T-cell priming.

TCRβ Chain That Forms Peptide-Independent Alloreactive TCR Transfers Reduced Reactivity with Irrelevant Peptide/MHC Complex

A major feature of the TCR repertoire is strong alloreactivity. Peptides presented by allogeneic MHC are irrelevant for recognition by a subset of alloreactive T cells. To characterize peptide-independent TCRs at the molecular level, we forced the expression of a TCRbeta chain isolated from a peptide-independent alloreactive CD8+ T cell line. The alloreactive TCR repertoire in the transgenic mouse was peptide dependent. However, analysis of essential TCR contacts formed during the recognition of self-MHC-restricted Ag showed that fewer contacts with peptide were established by the transgenic TCRbeta chain, and that this was compensated by additional contacts formed by endogenous TCRalpha chains. Thus, reduced interaction with the peptide appears to be a transferable feature of the peptide-independent TCRbeta chain. In addition, these findings demonstrate that reactivity to peptides is preferred over the reactivity to MHC during the formation of the TCR repertoire.