The Immune System and Its Dysregulation with Aging.

Aging leads to numerous changes that affect all physiological systems of the body including the immune system, causing greater susceptibility to infectious disease and contributing to the cardiovascular, metabolic, autoimmune, and neurodegenerative diseases of aging. The immune system is itself also influenced by age-associated changes occurring in such physiological systems as the endocrine, nervous, digestive, cardio-vascular and muscle-skeletal systems. This chapter describes the multidimensional effects of aging on the most important components of the immune system. It considers the age-related changes in immune cells and molecules of innate and adaptive immunity and consequent impairments in their ability to communicate with each other and with their aged environment. The contribution of age-related dysregulation of hematopoiesis, required for continuous replenishment of immune cells throughout life, is discussed in this context, as is the developmentally-programmed phenomenon of thymic involution that limits the output of naïve T cells and markedly contributes to differences between younger and older people in the distribution of peripheral blood T-cell types. How all these changes may contribute to low-grade inflammation, sometimes dubbed "inflammaging", is considered. Due to findings implicating elevated inflammatory immuno-mediators in age-associated chronic autoimmune and neurodegenerative processes, evidence for their possible contribution to neuroinflammation is reviewed.

Weakly self-reactive T-cell clones can homeostatically expand when present at low numbers.

T-cell division is central to maintaining a stable T-cell pool in adults. It also enables T-cell expansion in neonates, and after depletion by chemotherapy, bone marrow transplantation, or infection. The same signals required for T-cell survival in lymphoreplete settings, IL-7 and T-cell receptor (TCR) interactions with self-peptide MHC (pMHC), induce division when T-cell numbers are low. The strength of reactivity for self-pMHC has been shown to correlate with the capacity of T cells to undergo lymphopenia-induced proliferation (LIP), in that weakly self-reactive T cells are unable to divide, implying that T-cell reconstitution would significantly skew the TCR repertoire toward TCRs with greater self-reactivity and thus compromise T-cell diversity. Here, we show that while CD4+ T cells with low self-pMHC reactivity experience more intense competition, they are able to divide when present at low enough cell numbers. Thus, at physiological precursor frequencies CD4+ T cells with low self-pMHC reactivity are able to contribute to the reconstitution of the T-cell pool.

Self-reactivity of CD8 T-cell clones determines their differentiation status rather than their responsiveness in infections.

Mature T cells are selected for recognizing self-antigens with low to intermediate affinity in the thymus. Recently, the relative differences in self-reactivity among individual T-cell clones were appreciated as important factors regulating their fate and immune response, but the role of self-reactivity in T-cell biology is incompletely understood. We addressed the role of self-reactivity in T-cell diversity by generating an atlas of mouse peripheral CD8+ T cells, which revealed two unconventional populations of antigen-inexperienced T cells. In the next step, we examined the steady-state phenotype of monoclonal T cells with various levels of self-reactivity. Highly self-reactive clones preferentially differentiate into antigen-inexperienced memory-like cells, but do not form a population expressing type I interferon-induced genes, showing that these two subsets have unrelated origins. The functional comparison of naïve monoclonal CD8+ T cells specific to the identical model antigen did not show any correlation between the level of self-reactivity and the magnitude of the immune response.

Translational analysis and final efficacy of the AVETUX trial - Avelumab, cetuximab and FOLFOX in metastatic colorectal cancer.

Introduction: In metastatic colorectal cancer (mCRC), the efficacy of immune checkpoint blockade (ICB) has so far been limited to patients with microsatellite instability high tumors (MSI-H). Unfortunately, most mCRC patients suffer from non-immunogenic microsatellite stable (MSS) tumors. Therefore, new combinatorial strategies are urgently needed to enhance the immunogenicity of MSS tumors to finally increase the number of patients benefiting from ICB. Methods: The AVETUX trial aimed to combine the PD-L1 antibody avelumab with the standard of care chemotherapy combination FOLFOX and the anti-EGFR antibody cetuximab. Furthermore, we performed a central radiological review of the pre- and on-treatment computed tomography scans to better define the individual response to treatment. Results and Discussion: In total, 43 patients were treated of which 39 patients were confirmed as RAS/BRAF wildtype in central tissue review and finally response evaluated. A final progression-free survival (PFS) of 11.1 (range: 0.8 to 22.3 months) and a herein updated final overall survival (OS) of 32.9 months (range: 0.8 to 47.1 months) was reached. We observed a strong median depth of response of 67.5% tumor shrinkage and deepness of response correlated significantly with survival. On the other hand, early tumor shrinkage was not an indicator of better outcome at a cut-off of 20% (median values). In a next step, we correlated the individual best radiological response with potential ICB response biomarkers and found that the clonality and diversity, but not frequency of tumor infiltrating lymphocytes (TiLs) and peripheral blood mononuclear cells (PBMCs), strongly correlated with response. In summary, we report the final overall survival of the AVETUX trial and propose T cell clonality and diversity as a potential marker to predict response to chemo-immunotherapy combinations in MSS mCRC by performing a central radiological review. Clinical Trial Registration: ClinicalTrials.gov, identifier (NCT03174405).

Blood T cell diversity associated with the prognosis of advanced non-small cell lung carcinoma treated with first-line pemetrexed based chemotherapy.

BACKGROUND: The tumor microenvironment is associated with prognosis in advanced non-small cell lung carcinoma (NSCLC). The aim of this study was to explore the relationship between blood T cell diversity and survival of patients treated with pemetrexed-based chemotherapy for nonsquamous NSCLC. METHODS: This prospective clinical study enrolled 26 patients with advanced NSCLC treated with 4-6 cycles of first-line pemetrexed combined with platinum-based therapy. The complementarity-determining region 3 (CDR3) located in the T cell receptor beta chain (TCR ß chain) was captured and deeply sequenced using next-generation sequencing (NGS) technology, and the correlation between TCR changes and efficacy after chemotherapy was analyzed. RESULTS: Patients with an inferior quarter diversity index showed a significantly shorter progression-free survival (PFS) than the others (median, 5.0 months vs. 8.1 months, P = 0.014). After two cycles of chemotherapy, the TCR diversity was significantly higher than the baseline (P = 0.034). Just as with the baseline, patients with an inferior quarter diversity index at the endpoint of cycle 2 showed a shorter progression-free survival (PFS) than the others (median, 5.0 months vs. 8.4 months, P = 0.024). CONCLUSIONS: In advanced NSCLC patients treated with first-line pemetrexed combined with platinum, the low level of blood TCR diversity at baseline with an endpoint of two cycles of chemotherapy was correlated with a poor prognosis.

Dynamics of T cell receptor distributions following acute thymic atrophy and resumption.

Naive human T cells are produced and developed in the thymus, which atrophies abruptly and severely in response to physical or psychological stress. To understand how an instance of stress affects the size and "diversity" of the peripheral naive T cell pool, we derive a mean-field autonomous ODE model of T cell replenishment that allows us to track the clone abundance distribution (the mean number of different TCRs each represented by a specific number of cells). We identify equilibrium solutions that arise at different rates of T cell production, and derive analytic approximations to the dominant eigenvalues and eigenvectors of the mathematical model linearized about these equilibria. From the forms of the eigenvalues and eigenvectors, we estimate rates at which counts of clones of different sizes converge to and depart from equilibrium values-that is, how the number of clones of different sizes "adjusts" to the changing rate of T cell production. Under most physiological realizations of our model, the dominant eigenvalue (representing the slowest dynamics of the clone abundance distribution) scales as a power law in the thymic output for low output levels, but saturates at higher T cell production rates. Our analysis provides a framework for quantitatively understanding how the clone abundance distribution evolves under small changes in the overall T cell production rate.

TCR diversity - a universal cancer immunotherapy biomarker?

Sipuleucel-T was approved as a treatment for men with advanced metastatic, castration-resistant prostate cancer on the basis of improved survival in randomized clinical trials. A major challenge for this therapy, as well as other newer cancer immunotherapy agents, has been to identify markers that can identify patients who benefit from these therapies. In a recent manuscript by Sheikh and colleagues, the investigators evaluated changes in T cell clonality in the peripheral blood and tumors of patients treated with sipuleucel-T using next generation sequencing of T cell receptor Vß CDR3 sequences. Their findings are discussed in the context of this trial and other cancer immunotherapies.

Lower Affinity T Cells are Critical Components and Active Participants of the Immune Response.

Kinetic and biophysical parameters of T cell receptor (TCR) and peptide:MHC (pMHC) interaction define intrinsic factors required for T cell activation and differentiation. Although receptor ligand kinetics are somewhat cumbersome to assess experimentally, TCR:pMHC affinity has been shown to predict peripheral T cell functionality and potential for forming memory. Multimeric forms of pMHC monomers have often been used to provide an indirect readout of higher affinity T cells due to their availability and ease of use while allowing simultaneous definition of other functional and phenotypic characteristics. However, multimeric pMHC reagents have introduced a bias that underestimates the lower affinity components contained in the highly diverse TCR repertoires of all polyclonal T cell responses. Advances in the identification of lower affinity cells have led to the examination of these cells and their contribution to the immune response. In this review, we discuss the identification of high- vs. low-affinity T cells as well as their attributed signaling and functional differences. Lastly, mechanisms are discussed that maintain a diverse range of low- and high-affinity T cells.

Cancer Immunotherapy Using γδT Cells: Dealing with Diversity.

The broad and potent tumor-reactivity of innate-like γδT cells makes them valuable additions to current cancer immunotherapeutic concepts based on adaptive immunity, such as monoclonal antibodies and αßT cells. However, clinical success using γδT cells to treat cancer has so far fallen short. Efforts of recent years have revealed a striking diversity in γδT cell functions and immunobiology, putting these cells forward as true "swiss army knives" of immunity. At the same time, however, this heterogeneity poses new challenges to the design of γδT cell-based therapeutic concepts and could explain their rather limited clinical efficacy in cancer patients. This review outlines the recent new insights into the different levels of γδT cell diversity, including the myriad of γδT cell-mediated immune functions, the diversity of specificities and affinities within the γδT cell repertoire, and the multitude of complex molecular requirements for γδT cell activation. A careful consideration of the diversity of antibodies and αßT cells has delivered great progress to their clinical success; addressing also the extraordinary diversity in γδT cells will therefore hold the key to more effective immunotherapeutic strategies with γδT cells as additional and valuable tools to battle cancer.