Self-Reactive T Cell Receptor-Reactive CD8+ T Cells Inhibit T Cell Lymphoma Growth In Vivo

mRNA-Based Anti-TCR CDR3 Tumour Vaccine for T-Cell Lymphoma

Efficient vaccination can be achieved by injections of in vitro transcribed mRNA (ivt mRNA) coding for antigens. This vaccine format is particularly versatile and allows the production of individualised vaccines conferring, T-cell immunity against specific cancer mutations. The CDR3 hypervariable regions of immune receptors (T-cell receptor, TCR or B-cell receptor, BCR) in the context of T- or B-cell leukaemia or lymphoma are targetable and specific sequences, similar to cancer mutations. We evaluated the functionality of an mRNA-based vaccine designed to trigger immunity against TCR CDR3 regions in an EL4 T-lymphoma cell line-derived murine in vivo model. Vaccination against the hypervariable TCR regions proved to be a feasible approach and allowed for protection against T-lymphoma, even though immune escape in terms of TCR downregulation paralleled the therapeutic effect. However, analysis of human cutaneous T-cell lymphoma samples indicated that, as is the case in B-lymphomas, the clonotypic receptor may be a driver mutation and is not downregulated upon treatment. Thus, vaccination against TCR CDR3 regions using customised ivt mRNA is a promising immunotherapy method to be explored for the treatment of patients with T-cell lymphomas.

Concepts and ways to amplify the antitumor immune response

In this chapter, a detailed description of how the innate and adaptive immune responses interact with malignant cells is presented. In addition, we discuss how developing tumors establish themselves, and how they benefit on one hand and organize their defense against the immune system on the other hand. New data from three tumor model systems in mice are discussed; in particular, the intricate interactions between the immune cells and the tumor cells are highlighted. With the present data and knowledge, we conclude that a first prerequisite for the combat against tumors is the activation of the innate immune system via external danger signals or damage signals and internal danger signals. The second prerequisite for efficient tumor cell eradication is combined therapeutic approaches of physical, chemical, pharmacological, and immunological origin. Finally, we propose new ways for further investigation of the relationship linking tumor cells and our defense system. It appears mandatory to understand how the malignant cells render the adaptive immune cells tolerant instead of turning them into aggressive effectors and memory cells. Perhaps, the most important thing, for immunologists and clinicians, to understand is that tumor cells must not be viewed just as antigens but much more.

Natural immunity has significant impact on immune responses against cancer

The immune system defends the host against pathogenic attacks by micro-organisms and their products. It does not react against self-components due to the relatively efficient negative selection of developing T lymphocytes in the thymus. This process does permit T cells with low avidity against self to be present in the T cell repertoire. Such cells play an important physiological role as the host needs so-called autoimmune reactions in order to eliminate dying cells or transformed tumour cells. One of the mysteries in immunology is how the host maintains beneficial autoimmune reactions and avoids pathogenic autoimmune reactions. Activation of the adaptive T lymphocytes is mediated by the low avidity interaction between T-cell antigen receptors and antigenic peptides associated with major histocompatibility complex class I or class II molecules. This interaction is strengthened by T-cell co-receptors such as CD2, CD4, CD8, CD28 and CD154, which react with ligands expressed by cells of the innate immune system. In recent years, the importance of pre-activation of the innate immune system for initiation of adaptive T-cell immune responses has been appreciated. In the present review, I will summarize our work on how natural immunity plays an important role in determining the level of beneficial autoimmune reactions against cancer.

Allosteric Changes in the TCR/CD3 Structure Upon Interaction With Extra- or Intra-cellular Ligands

T lymphocytes are activated by the interaction between the T-cell antigen receptor (TCR) and peptides presented by major histocompatibility complex (MHC) molecules. The avidity of this TCR-pMHC interaction is very low. Therefore, several hypotheses have been put forward to explain how T cells become specifically activated despite this handicap: conformational change model, aggregation model, kinetic segregation model, sequential interaction model and permissive geometry model. In the present paper, we conducted experiments to distinguish between the TCR-aggregation model and the TCR-conformational change model. The results obtained using a TCR capture ELISA with Brij 98-solubilized TCR molecules from normal or activated T cells showed that the ligand-TCR interaction causes structural changes in the CD3 epsilon cytoplasmic tail as well as in the extracellular TCR beta FG loop region. Size-fractionation experiments with Brij 98-solubilized TCR/CD3/co-receptor complexes from naïve or activated CD4(+) or CD8(+) T cells demonstrated that such complexes are found as either dimers or tetramers. No monomers or multimers were detected. We propose that: (1) ligand-TCR interaction results in conformational changes in the CD3 epsilon cytoplasmic tail leading to T-cell activation; (2) CD3 epsilon cytoplasmic tail interaction with intracellular proteins may dissociate pMHC and co-receptors (CD4 or CD8) from TCR/CD3 complexes, thus leading to the arrest of T-cell activation; and (3) T-cell activation appears to occur among dimers or tetramers of TCR/CD3/co-receptor complexes interacting with self and non-self (foreign) peptide-MHC complexes.

Interactions between CD8alphabeta and the TCRalphabeta/CD3-receptor complex

CD8+ T cells recognize antigenic peptides bound to major histocompatibility complex (MHC) class I molecules on normal antigen-presenting cells (APC), as well as on virus-infected cells or tumour cells (pMHC). At least two receptor types participate in recognition of these complexes: T-cell receptor (TCR) alphabeta heterodimers and CD8alphabeta molecules. The former molecules react with antigenic peptide and variable regions of MHC class I molecules, whereas the latter molecules react with constant alpha3 regions of MHC class I molecules. As the avidity of both receptor-MHC interactions is low, it is believed that TCRalphabeta and CD8alphabeta heterodimers collaborate in T-cell recognition. We have established a TCR/CD3-CD8 capture ELISA, which can measure the interaction of pMHC with CD8alphabeta molecules and with TCR/CD3 complexes. The major findings are: (1) TCR/CD3 complexes derived from in vitro activated T cells and captured by anti-CD3 MoAb, do bind specific pMHC and (2) CD8+ T cells express at least three forms of CD8alphabeta molecules: single CD8alphabeta, CD3-CD8 and TCR/CD3-CD8 complexes. Only the latter complexes are associated with CD3zeta homodimers, and the quantity of TCR/CD3-CD8 complexes relative to total CD8alphabeta molecules appears to increase and to be selected into sucrose-gradient microdomains as a function of TCRalphabeta-mediated T-cell activation.