The T cell immune response to cytomegalovirus across the adult lifecourse

Lead Research Organisation: University of Birmingham
Department Name: Institute of Immunology & Immunotherapy

Abstract

Cytomegalovirus (CMV) is one of the human herpesviruses and infects over 80% of people. Once a person has been infected with CMV the virus can never be cleared from the body and our immune system needs to constantly 'fight' the virus to stop it dividing and causing tissue damage. This balance is quite finely set and CMV is a major problem in patients whose immune system is suppressed, such as those undergoing transplantation.
Perhaps because of this 'war of attrition' between the virus and immune system, the T cell immune response that develops against CMV in the blood is the largest that has been recorded against any pathogen. Moreover, studies in populations have shown that this large immune response can be associated with health problems in certain people, such as the elderly or those with kidney disease.
In this grant we propose to extend work that we have undertaken over several years to understand exactly how T cells fight CMV and to develop approaches to control the immune response in situations where it becomes a health risk.

The work has 4 sections.
In the first part we will investigate how the magnitude and composition of the immune response to CMV is established and maintained in people of all ages. We will assess if it is related to the level of virus that people are exposed to when they are first infected and if the level of the 'viral load' that people carry during chronic infection within the blood or liver is also a critical factor. We will also investigate the importance of lymphocytes that kill CMV-infected cells by acting through a molecule called HLA-C. We have shown that these T cells accumulate over the lifetime such that they become extremely common in older people. These cells are highly effective 'killers' of infected cells and, as well as investigating how they develop, we will also assess their potential use for the immunotherapy of CMV infection.

In the second part we will exploit the unique features of CMV, and development of powerful technologies, to study fine details of the differentiation of the CD4+ and CD8+ T cell response to CMV. Here we will use HLA-peptide tetramers to isolate virus-specific cells from tissue samples and immediately undertake a detailed assessment of their phenotype using a technology called CyTOF. Moreover, we will determine the transcriptome ('RNA profile') of the cells and also assess their epigenetic status. This will allow us, for the first time, to see how genomic regulation defines how human antigen-specific T cell responses develop. An important comparison will be between the results in younger and older people as there is evidence that the 'stem cell like' potential of these cells decreases during ageing. In addition, we hope that the comprehensive nature of this work will help understanding of the immune response to diseases such as cancer.

Part 3 will address how an important family of 'immune checkpoint receptor (ICR)' proteins such as PD-1 operate in CMV infection. These molecules act to 'suppress' T cell function and antibodies that block their activity are very important in cancer therapy. Here we will take advantage of the CMV model to understand the function of the ICR proteins, in both healthy donors and patients on PD-1 blocking therapy.

Finally, we are using anti-viral drugs to control CMV when it becomes a danger to health. We have undertaken two such studies in donors and patients and find that this does indeed suppress the level of CMV in the body. In this work we will undertake a detailed analysis of how treatment influenced the immune response to CMV. The aim here is that this will guide the introduction of anti-viral treatment for patient groups where it may be beneficial, such as the elderly.

The work represents one of the most comprehensive studies of how our white cells respond to CMV and we are confident that this will contribute to substantially improving health outcomes, both within CMV infection and beyond.

Technical Summary

Cytomegalovirus (CMV) infection establishes a state of chronic infection in which viral replication is suppressed by the immune system and is thus an outstanding example of how the immune system can control chronic antigenic stimulation without excessive immunopathology. Greater understanding how the immune system controls chronic infection will directly impact upon and translate into improved understanding of immunotherapy therapy and vaccine regimens.
CMV is however an important cause of mortality and morbidity both within the UK and across the world. Although infection is well tolerated by immune competent people it is a major problem in patients who are immunosuppressed. Additionally, CMV is the major global infectious cause of congenital abnormalities. In addition, CMV has emerged as an important risk factor for health problems in the elderly and those with inflammatory disease due in part to a marked increased risk of death from cardiovascular disease (CVD).
The work will take advantage of several MRC supported, large and richly phenotyped population cohorts
Healthy Donors: >100 regular healthy donors aged 18-70 years; 1000+ donors aged 65-90+ years in the 'Thousand Elders' Cohort and a 5 year prospective study of 1000 medical students. '1000 Elders' donors give blood samples prospectively and have participated in a recent trial to assess valaciclovir therapy for suppression of CMV load and immune response (MRC funded DPFS, Moss PI)
Patients: 100+/year stem cell transplant patients, 170/year renal transplant patients, >100 patients with chronic lymphocytic leukaemia (CLL) and 100+ patients with vasculitis.
This research proposal will
- Study the virus-host balance across the human life course.
- Analyse the role or checkpoint protein expression on virus-specific T cells in CMV infection.
- Investigate CMV-specific T cell responses restricted by HLA-C.
- Assess the mechanisms of CMV-mediated immune pathogenesis and potential therapeutic intervent

Planned Impact

This Programme addresses the mechanisms that enable the human immune response to control infection with cytomegalovirus (CMV): how control is established, how it is maintained, how it is lost and how the virus host balance may be restored. The Programme will impact on scientists, the commercial sector but most relevantly on patients.
Impact on scientists
The access to unique cohorts we have established allows us to address key questions pertinent to studies by scientists working in related areas. The improved understanding of early events that control infection will support the development of vaccines capable of eliciting the sterilising immunity needed to prevent infection. Our work will further elucidate why immune control of CMV is lost in pathological states and in other situations such as ageing, HIV infection and malignancy. We highlight the fact that studies on CMV have provided fundamental insights into human immunology that have informed wider immunology research and have had direct translational relevance.
Impact on commercial sector
CMV vaccines are considered as a public health priority and a number of candidates are under investigation. They include recombinant protein, live attenuated, DNA and other vaccines. The latest trial is a phase 1 trial instigated this year by VBI vaccines. Our research will uncover novel features of the host-virus balance which will support similar advances.
We have established links with pharmaceutical companies and will continue to develop these links and establish new ones to exploit the findings of the research. Impact on the commercial sector will also come from our links with clinical staff who are conducting clinical trials with immune checkpoint inhibitors from pharmaceutical companies, primarily in a malignancy setting. As we plan to determine how this alters the virus host balance, such interventions may find use as clinical therapies for CMV related disease. The interaction with these pharmaceutical companies also opens the way for study of other interventions that are developed and administered through clinical trials conducted through the University of Birmingham.
Impact on patients
CMV is an important cause of morbidity and mortality. The identification of how the immune system effectively controls the virus will allow the development of rational interventions to restore the virus host balance. Whilst we will not administer interventions, we will study situations where the immune response is being altered by therapeutic intervention in a malignant setting. These data will together support the development of interventions leading to the alteration of clinical practice. In the longer-term, development of effective vaccines built on improved understanding of immune control could have a major impact globally.
Impact on general public

The impact on the general public will come primarily from public involvement in our engagement programmes where we disseminate information on our research and why these topics are important. We have a strong, successful record of outreach programmes in the Institute and we are committed to improving the public understanding of science.

Impact on all staff and students
Students: We have a strong track record of postgraduate education and the samples and data generated during these studies will allow us to continue educating PhD students in our and our collaborators' laboratories.
Staff: The diverse range of novel techniques that we are developing and our interaction with interdisciplinary collaborators from outside of our own field offer unparalleled opportunities for staff involved in this project to enhance their skill sets and be more productive. In particular, the access to clinical staff who manage the cohorts we will use will provide staff on this programme greater exposure to more translational aspects of the work.

Publications

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Wall N (2021) Latent Cytomegalovirus Infection and Previous Capsular Polysaccharide Vaccination Predict Poor Vaccine Responses in Older Adults, Independent of Chronic Kidney Disease. in Clinical infectious diseases : an official publication of the Infectious Diseases Society of America