MICA: Fundamental Role of Phosphoinositide 3-kinase delta in Infection and Immunity: Insights from a Novel Primary Immune Deficiency Syndrome, APDS

As a collaborative group of doctors, geneticists and scientists, we have recently discovered a new inherited disease, which causes increased susceptibility to infection. Affected patients suffer frequent and often severe bacterial infections of the lungs, sinuses and ears, often leading to permanent damage; they can also experience potentially life-threatening viral infections (particularly with the Herpes viruses such as those which cause chicken pox and shingles or glandular fever). Many of the patients die young from these devastating infections. We found that this disease is due to a genetic mutation that causes an enzyme called PI3Kdelta (which is found mainly in the cells of the immune system) to be more active and to 'work harder'. The overactive PI3Kdelta protein disturbs the chemical signals that control how immune cells develop and function in the body.
B and T lymphocytes coordinate the immune system to fight infections. We found that the B-lymphocytes from our patients do not make good quality antibodies (proteins which help to kill invading bacteria), and that their T-lymphocytes (which provide protection from viral infection) also function less effectively. We do not yet know how common the condition is, why the B and T cells don't work properly, or if other immune cells or lung cells are also affected. We also don't know if other abnormalities that affect the activity of PI3Kdelta or related proteins contribute to susceptibility to infection in a more general setting.
It is difficult to study immune cells from the patients, as most of them are unwell children, and because a feature of the disease is that the immune cells die rapidly outside the body. To solve this problem we have engineered a mouse with the same genetic defect, and will study how the immune cells of this mouse work. We will then take the findings from these mouse cells and see if they hold true in patients' cells; this strategy will enable us to use the limited number of patient cells available to us more effectively. We plan to expose the genetically altered mice to the same infections that the patients develop, to find out precisely why they are so susceptible. We will also test protective strategies such as drugs that reduce PI3Kdelta activity (PI3Kdelta inhibitors) to see if they prevent infection or reduce its severity. If this is the case, we will also treat patients who suffer from this disease with PI3Kdelta inhibitors and study the effects of this treatment; we believe such drugs will reduce the inflammation in their lungs and improve their ability to fight infection. Since too little PI3Kdelta activity is also detrimental immune, these medications will need to be carefully titrated, so we will need to monitor the effects on a range of biological markers of PI3Kdelta function as well as infection and inflammation.
This work will determine the role and importance of PI3Kdelta in infection. This knowledge will help not only patients with the newly described disease, but may also give new insights into why some otherwise healthy people are prone to develop bacterial and viral infections. This is of importance nationally and globally, since respiratory infections cause more illness and more deaths than all cancers combined.

Background
Respiratory infections account for more than 6% of the global burden of disease, causing more morbidity and mortality than all cancers combined. We have recently described a novel combined immune deficiency characterised by severe recurrent respiratory bacterial infections, viral infections and a marked predisposition to B cell lymphoma; this condition is caused by an activating mutation (E1021K) in the gene encoding the catalytic subunit of PI3 kinase delta (p110delta) and has been termed 'Activated PI3 kinase Delta Syndrome' (APDS). We wish to elucidate precisely how augmented p110delta function compromises lymphocyte and myeloid immune cell function, and to explore the potential therapeutic applications of p110delta inhibitors in our patients.

Scientific Objectives.
We wish to establish the importance of augmented p110delta function in susceptibility to infection, to ascertain precisely how increased p110delta-dependent signalling perturbs lymphocyte and myeloid cell function, and to explore the role of p110delta inhibitors in the prevention/treatment of respiratory infection in APDS.

Plan of Investigation
We have generated a transgenic mouse model of the human disease and will use this to explore immune cell function, susceptibility to bacterial and viral infection, and protection from such infections by administration of p110delta inhibitors. In addition, we will undertake an experimental medicine study using a novel inhaled p110delta inhibitor to establish the ideal profile of inhibition needed to restore aberrant immune cell function; this strategy will be guided and monitored by means of a number of biomarkers including sputum PIP3 levels.

Potential Future Applications
This work will generate improved understanding of infection susceptibility at the genetic, biochemical and cellular levels, and will help to clarify the role of p110delta inhibitors in prophylaxis and treatment of infections in APDS.

Who Will Benefit from this Research?
The overarching aim of the work described in this application is to delineate the role of PI3Kdelta in immunity and infection, and to explore its potential as a therapeutic target in immunodeficiency secondary to excessive PI3Kdelta activity. In addition to the accrual of scientific knowledge, this work may lead to novel diagnostic and therapeutic strategies in patients suffering recurrent respiratory infection, and other consequences of aberrant PI3Kdelta signalling. Given the burden of respiratory infection both within the UK and globally, this research has the potential to have a substantial and wide-ranging impact with multiple potential beneficiaries.
1. Patients suffering from the Activated PI3Kinase Delta Syndrome (APDS).
2. Additional patient cohorts suffering from recurrent infection or other consequences of aberrant PI3Kinase signalling.
3. Clinicians (respiratory physicians, immunologists and others) caring for the above patient groups.
4. Companies with an interest in developing and implementing novel diagnostic and therapeutic agents or strategies in these settings.
5. Government departments planning NHS strategy to implement care for conditions.
6. Academics studying the role of PI3kinase signalling in immunity, infection, inflammation and malignancy.

How Will They Benefit?
Direct benefit to patients with documented APDS is likely to accrue in the short term (within 3 years) as they are candidates for treatment with (already available) PI3K delta inhibitors; the identification of this patient group is likely to drive the development of improved therapeutic agents. The development of a transgenic mouse model will help to characterise the benefits of novel agents and compare them with existing compounds and other strategies such as vaccination. This research may also have implications for respiratory infection and infection susceptibility in the wider setting. There were an estimated 3.2 million deaths worldwide from lower respiratory tract infections in 2010, making this the third commonest cause of death globally, and bacterial pneumonia is the leading cause of childhood mortality worldwide.
This project includes development opportunities for the applicants through collaborative exposure to patient samples, to mouse models, to next generation sequencing platforms, and to novel assays. These skills will be shared among colleagues to support academic development in Cambridge and elsewhere. Methodologies and resources will be shared, to support UK academic excellence, raising the profile of UK-based research internationally.