Publications

Human CD4+ CD25hi Foxp3+ regulatory T cells are derived by rapid turnover of memory populations in vivo.

Vukmanovic-Stejic M, Zhang Y, Cook JE, Fletcher JM, McQuaid A, Masters JE, Rustin MH, Taams LS, Beverley PC, Macallan DC, Akbar AN.

Journal of Clinical Investigation 2006 Sep;116(9):2423-33.

Abstract

While memory T cells are maintained by continuous turnover, it is not clear how human regulatory CD4+ CD45RO+ CD25hi Foxp3+ T lymphocyte populations persist throughout life. We therefore used deuterium labeling of cycling cells in vivo to determine whether these cells could be replenished by proliferation. We found that CD4+ CD45RO+ Foxp3+ CD25hi T lymphocytes were highly proliferative, with a doubling time of 8 days, compared with memory CD4+ CD45RO+ Foxp3- CD25- (24 days) or naive CD4+ CD45RA+ Foxp3- CD25- populations (199 days). However, the regulatory population was susceptible to apoptosis and had critically short telomeres and low telomerase activity. It was therefore unlikely to be self regenerating. These data are consistent with continuous production from another population source. We found extremely close TCR clonal homology between regulatory and memory CD4+ T cells. Furthermore, antigen-related expansions within certain TCR Vbeta families were associated with parallel numerical increases of CD4+ CD45RO+ CD25hi Foxp3+ Tregs with the same Vbeta usage. It is therefore unlikely that all human CD4+ CD25+ Foxp3+ Tregs are generated as a separate functional lineage in the thymus. Instead, our data suggest that a proportion of this regulatory population is generated from rapidly dividing, highly differentiated memory CD4+ T cells; this has considerable implications for the therapeutic manipulation of these cells in vivo.

Skin resident cells in melanoma

This project focuses on investigating T cell differentiation in patients with melanoma. It is known that chronic viral infection (such as Cytomegalovirus) can drive T cells into end-stage differentiation due to constant immune stimulation in the absence of resolution. Increased differentiation is often associated with loss of function in T cells and is one of the parameters that are thought to impact on immune function in older individuals. We want to know if this process also occurs in melanoma where there is evidence of an immune response despite lack of tumour regression.

We investigated circulating T cells in more than 100 melanoma patients of all ages and disease stages and compared their differentiation pattern to those of healthy controls. Melanoma patients have increased T cell differentiation in both T cells subsets (CD4+ and CD8+ T cells).

The skin is also known to harbour large populations of T cells which might be relevant for tumour immunity, but little is known about the phenotype and behaviour of these cells. We have discovered that in both in healthy control and melanoma patients skin resident T cells show different characteristics to those seen in circulation. We are currently investigating if manipulation of certain inhibitory pathways can lead to improved function of these cells.

This work has been presented at international conferences including the Keystone Symposium: “Tissue-Resident Memory T Cells” (poster title: “Skin resident effector memory CD8+ T cells display low cytotoxic potential in steady state conditions”) and is currently being prepared for publication.

Atopic dermatitis and resident T cells

The aim of this project is to focus on investigating differentiation and function of skin resident T cells in patients with atopic dermatitis. Our hypothesis is that these cells may be chronically exposed to stimulation and that this may in part contribute to immune dysfunction such as increased infections in these patients.

We will investigate differentiation status, expression of markers that indicate loss of function, expression of inhibitory receptors and telomere lengths to try and identify factors which may impact on the function of skin resident T cells in these patients.  Changes in both lesional and non-lesional (apparently healthy) patient skin will be compared to skin of healthy volunteers. As the role of skin resident T cells becomes clearer, we hope that better understanding of T cell defects in AD patients will lead to better understanding of the disease pathogenesis and can be utilised in devising future therapeutic strategies.

We have just been granted ethical approval to collect skin and blood samples from patients with eczema and will shortly commence with recruitment.

The regulation of cutaneous immunity (by Tregs)

Over the last 15 years one particular subset of T cells, known as regulatory T cells has been the subject of many studies attempting to improve our understanding of immune responses to self (autoimmune disease, cancer), pathogens (infections) or harmless antigens (allergy). Regulatory T cells are thought to play an important role in controlling immune responses and therefore represent a potential target for manipulation in situations of inadequate or overly-exuberant activation.

Our research has focused on the role Tregs play during immune response in the skin. We have previously developed a unique experimental model which allows us to study human responses to foreign antigens (bacterial, viral, fungal particles) after they are injected into the skin.  In this model we have discovered the kinetics of cellular accumulation after antigen challenge and we were able to demonstrate that the cells accumulating in the skin are specific for the antigen which has been injected. More importantly, regulatory T cells also accumulate in the skin at the same time, and are also able to recognise the same antigen.

Furthermore, we have shown that in those individuals who do not mount a good response to this challenge, regulatory T cells accumulate in larger numbers suggesting that this mechanism can be responsible for defects in cutaneous immunity that is notable in the elderly.

We have published extensively using this model, and this work has also been presented at many international and national meetings. Including:

 

1. Vukmanovic-Stejic M, Sandhu D, Sobande TO, Agius E, Lacy KE, Riddell N, Montez S, Dintwe OB, Scriba TJ, Breuer J, Nikolich-Zugich J, Ogg G, Rustin MHA, Akbar AN.

Publication Title: Varicella Zoster-Specific CD4+Foxp3+ T Cells Accumulate after Cutaneous Antigen Challenge in Humans.

Published in: J Immunol 2013: 190(3):977-86.

 

2. Akbar AN, Reed JR, Lacy KE, Jackson SE, Vukmanovic-Stejic, Rustin MHA.

Publication Title: Investigation of the Cutaneous Response to Recall Antigen in Humans in vivo.

Published in: Clin Exp Immunol 2013: 173(2):163-72.

Effect of inflammation in retarding skin immunity in the elderly

Over the last couple of years our group has been studying immune responses to foreign antigens by injecting into the skin of the forearm of old and young volunteers and subsequently sampling the injected skin site by either taking a biopsy or performing a suction blister. Our data indicates that old individuals do not mount effective responses to cutaneous challenge with bacterial, fungal or viral antigens and we are focusing on understanding the primary mechanism behind this defect.

In the current project we will investigate reasons why older humans have decreased immunity in the skin. Our work is focused on the varicella zoster virus (VZV) that induces chickenpox during childhood and which can also re-activate and cause shingles in older subjects. To better understand the age-related changes in the skin, which lead to the reduction in skin immunity, we investigated accumulation of cells at the site of challenge with VZV and also gene expression in young and old individuals. One of the possibly fundamental observations we have made is that old individuals respond more strongly to non-specific challenge such as injection with saline. This ‘background inflammation’ can have detrimental effect on the ability to respond to foreign antigens such as VZV and we are currently pursuing this avenue. We are investigating which cells may be responsible for inflammatory mediators and if this ‘non-specific’ inflammation can be modified to improve immune responses.

Publication Title: The Characterization of Skin-Resident Varicella Zoster Virus Specific T Cells During Ageing

Publication Type: submitted for publication

Impact of vaccination on VZV immunity in the skin

Varicella zoster virus (VZV) induces chickenpox during childhood but this virus can also re-activate and cause shingles in older subjects. Both chicken pox and shingles manifest in the skin making it a good model to study cutaneous immunity. The complication of post-herpetic neuralgia and the shingles itself produces a considerable loss of quality of life and incurs a large healthcare cost in older humans. For this reason a vaccine, known as Zostavax, was developed specifically for the prevention of shingles in old humans and it has been licenced in both the USA and the UK.

One of the measures of efficient immunity to VZV is called a skin test and involves injection of antigens (harmless proteins derived from the VZV virus) into the skin. Young people with a previous history of chickenpox respond to this injection by mounting a localised immune response in the skin, but many old individuals do not. We are interested in understanding the basis for this defect, which is most likely multifactorial. Better understanding of the mechanisms involved is important not only for understanding the pathogenesis of shingles but also basic mechanisms involved in skin immunity generally, as well as those mechanisms that are affected by age. Importantly these mechanisms may not be specific for skin and could also be involved in decreased immunity in other tissues such as the lung or intestine.

In this project we will investigate whether vaccination with Zostavax can improve responses to skin challenge and, if so, which changes in the skin are responsible for this improvement.