Age-associated T-cell Clonal Expansions (TCE) in vivo—Implications for Pathogen Resistance

Effect of cellular aging on memory T-cell homeostasis

The fact that T-cell numbers remain relatively stable throughout life, and that T-cell proliferation rates increase during lymphopenia, has led to the consensus that T-cell numbers are regulated in a density-dependent manner. Competition for resources among memory T cells has been proposed to underlie this ‘homeostatic’ regulation. We first review how two classic models of resource competition affect the T-cell receptor (TCR) diversity of the memory T-cell pool. First, ‘global’ competition for cytokines leads to a skewed repertoire that tends to be dominated by the very first immune response. Second, additional ‘cognate’ competition for specific antigens results in a very diverse and stable memory T-cell pool, allowing every antigen to be remembered, which we therefore define as the ‘gold-standard’. Because there is limited evidence that memory T cells of the same specificity compete more strongly with each other than with memory T cells of different specificities, i.e., for ‘cognate’ competition, we investigate whether cellular aging could account for a similar level of TCR diversity. We define cellular aging as a declining cellular fitness due to reduced proliferation. We find that the gradual erosion of previous T-cell memories due to cellular aging allows for better establishment of novel memories and for a much higher level of TCR diversity compared to global competition. A small continual source (either from stem-cell-like memory T-cells or from naive T-cells due to repeated antigen exposure) improves the diversity of the memory T-cell pool, but remarkably, only in the cellular aging model. We further show that the presence of a source keeps the inflation of chronic memory responses in check by maintaining the immune memories to non-chronic antigens. We conclude that cellular aging along with a small source provides a novel and immunologically realistic mechanism to achieve and maintain the ‘gold-standard’ level of TCR diversity in the memory T-cell pool.

The role of checkpoint inhibitors immunotherapy in advanced non-small cell lung cancer in the elderly

INTRODUCTION

Immune checkpoint inhibition is a novel treatment modality that has brought a new hope to patients with advanced NSCLC. Several molecules targeting cytotoxic T-lymphocyte antigen 4 (CTLA4) or programmed cell death 1 receptor/programmed death ligand-1 (PD1/PD-L1) pathways are under evaluation in NSCLC and three of them are currently approved: nivolumab and atezolizumab for advanced NSCLC after prior chemotherapy and pembrolizumab for advanced NSCLC expressing PD-L1 ≥ 1% after at least one prior chemotherapy regimen and > 50% as a first-line response. Areas covered: To date, the efficacy and toxicity of immune checkpoint inhibitors in the elderly is unclear because available studies involved mainly a low number of elderly patients. In this paper, the authors discuss the frailty of the elderly patient and the challenges of choosing the best therapeutic strategy, focusing on the role of immune checkpoint inhibitors. Expert opinion: There are several outstanding goals that need to be met for the proper and safe use of immunotherapeutic drugs. In terms of the elderly, it is true that age-tailored clinical trials are needed to confirm the real impact of immunotherapy and harmonize the standard of care in this specific demographic.

The immune system in the elderly: a fair fight against diseases?

The immune system is a very dynamic network, consisting of various innate and adaptive cells acting via direct cell–cell contact, as well as indirect messaging mediated by soluble factors. Changes in the number or quality of receptors involved in these events alter the capacity of the immune system to respond properly. There is an increasing awareness that many chronic infections and diseases, such as cytomegalovirus, impact on the immune system. Concurrently, there are changes in immune profiles of healthy, as well as ill, elderly individuals. All these changes translate into obvious signs of immunological aging that are more profound in diseases. This review will discuss the manifestation of different diseases in the elderly and how the immune system behaves in such situations.