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

Age-related accumulation of T cells with markers of relatively stronger autoreactivity leads to functional erosion of T cells

Background

Thymic involution is a prominent characteristic of an aging immune system. When thymic function is reduced/absent, the peripheral T cell pool is subject to the laws of peripheral T cell homeostasis that favor survival/expansion of T cell receptors with relatively higher functional avidity for self-peptide/MHC complexes. Due to difficulties in assessing the TCR avidity in polyclonal population of T cells, it is currently not known whether high avidity T cells preferentially survive in aging individuals, and what impact this might have on the function of the immune system and development of autoimmune diseases.

Results

The phenotype of T cells from aged mice (18-24 months) indicating functional TCR avidity (CD3 and CD5 expression) correlates with the level of preserved thymic function. In mice with moderate thymic output (> 30% of peripheral CD62L^hi T cells), T cells displayed CD3^lowCD5^hi phenotype characteristic for high functional avidity. In old mice with drastically low numbers of CD62L^hi T cells reduced CD5 levels were found. After adult thymectomy, T cells of young mice developed CD3^lowCD5^hi phenotype, followed by a CD3^lowCD5^low phenotype. Spleens of old mice with the CD3^low/CD5^hi T cell phenotype displayed increased levels of IL-10 mRNA, and their T cells could be induced to secrete IL-10 in vitro. In contrast, downmodulation of CD5 was accompanied with reduced IL-10 expression and impaired anti-CD3 induced proliferation. Irrespective of the CD3/CD5 phenotype, reduced severity of experimental allergic myelitis occurred in old mice. In MTB TCRβ transgenic mice that display globally elevated TCR avidity for self peptide/MHC, identical change patterns occurred, only at an accelerated pace.

Conclusions

These findings suggest that age-associated dysfunctions of the immune system could in part be due to functional erosion of T cells devised to protect the hosts from the prolonged exposure to T cells with high-avidity for self.

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.

Paradoxical arrest in lupus activity in BXSB mice with highly autoreactive T cells

T cells with high avidity for antigens are thought to mediate more effective immunity against foreign antigens and cause more severe autoimmunity. The impact of T cell receptor (TCR) avidity on the development of lupus has not been investigated. We took advantage of a transgenic mouse strain (designated MTB) that has a diverse T cell population and a globally stronger reactivity to self. [MTBxBXSB]F1 mice displayed accelerated lupus relative to the [WTxBXSB]F1 controls. The severity of lupus and the activation of T cells subsided with aging, when elevated IL-10 production by Tr1 cells was observed. Thus, chronic high avidity interactions of T cells with self-antigens can lead to an age associated increase in IL-10 production. This could explain the age-associated reduction of the incidence of lupus, as well as other autoimmune diseases. Furthermore, the principle of Tr1 differentiation based on diverse T cells with high avidity for self may potentially be used as a therapeutic strategy in the treatment of lupus.

T-cell allorecognition: a case of mistaken identity or déjà vu?

T cells bearing alphabeta T-cell receptors (TCRs) are selected by a subset of peptide-laden major histocompatibility (pMHC) molecules in the thymus and in the periphery and therefore are restricted to recognising host or 'self' MHC molecules. Nevertheless, T cells are inherently cross-reactive and often react with 'foreign' allogeneic MHC molecules (direct T-cell alloreactivity), manifested clinically as organ transplant rejection. Although the basis of T-cell alloreactivity has remained a puzzle to immunologists for decades, studies on alloreactive TCRs have begun to shed light on the basic mechanisms underpinning this 'mistaken identity'. Here we review recent advances in the field, focusing on structural and cellular studies, showing that alloreactivity may sometimes result from cross-reactivity without molecular mimicry and at other times may result directly from TCR interactions with allogeneic pMHC surfaces that mimic the cognate ligand.