Immuno Flashcards
Stroke
The 2nd leading cause of death and the leading cause of adult disability world wide
- affects 9,000 kiwis/year
- cost/person >200,000$$
Risk factors for ischaemic stroke
- being male
- high blood pressure
- sedentary lifestyle
- smoking
- high alcohol consumption
- diabetes
- cardiac issues
- SARs-CoV2 infection
Cardioembolism
The pumping of blood containing unwanted materials into the brain due to:
- atrial fibrillation (irregular and often rapid heartbeat)
- carotid/parent artery atherosclerosis (hardening of arteries)
- small vessel disease (increased risk of obstruction)
Results in ischaemic infarct and re-perfused penumbra
Diagnosis of ischaemic stroke
- Non-contrast computerised tomography (CT) shows loss of grey/white matter differentiation
- IV injection of iodinated contrast agent shows blockage and re-perfusion through CT angiography or time resolved series
Alteplase and Tenecteplase
structural analogues of tissue plasminogen activator (tPA)
- bind to fibrin in clots and convert entrapped plasminogen to plasmin facilitating clot degradation
- given via I.V. within 4.5 hours of stoke
- 28% decrease in disability and 6% risk of haemorrhage at day 90
- only applicable to ~10% of patients
Consequence of ischaemic
Blood vessel occlusion reduces cerebral blood flow
- reduced oxygen and glucose
- lack of available energy
- stress response occurs in neurons and glia
- excess glutamate
- excess calcium influx resulting in:
- neurons: apoptotic cell death due to free radical production in neurons
- glia: release of trophic factors (all), cytokines (microglia), formation of scar tissue (astrocytes)
= inflammatory signalling and BBB dysfunction
= SPREAD OF NEURONAL DEATH
Acute immune response of ischaemic stroke (central & peripheral)
The ischaemic injury causes an increase in endothelial adhesion molecules, DAMPs, complement, and cytokines
- invasion of neutrophils via damaged BBB
- neutrophils produce ROS, cytokines, and NETs resulting in further neuronal damage
Peripherally, the adrenal glands are activated, causing release of glucocorticoids and catecholamines
- post-stroke immuno-depression (increased risk of infection)
- DAMPs leak from brain and mobilise lymphocytes in the lymph and gut
NET
neutrophil extracellular trap
Sub-acute inflammation in ischaemic stroke
In the days/weeks following ischaemic injury macrophages enter the CNS via the choroid plexus and BBB
- phagocytose clot debris, apoptotic neutrophils/neurons
- differentiate into reparative macrophages
- produce growth factors that dampen inflammation and induce glial scarring
Glial scar
Tissue formed from astrogliosis that acts to separate healthy tissue from damaged tissue
- creates an optimum environment for regeneration
Chronic stage of ischaemic inflammation
Antigen presenting cells encounter CNS antigens released due to ischaemic injury
- migrate to peripheral lymph nodes, and trigger differentiation and expansion of T/B cells
Days/weeks after stroke these auto-reactive T/B cells enter the brain through the choroid plexus and cause chronic inflammation and impair neural regeneration
Contributes to post-stroke depression, fatigue, and dementia
Neuronal regeneration
A naturally occurring process that is initiated by the secretion of growth factors (BDNF, NGF, neuregulin) from reparative microglia
- astrogliosis
- differentiation of NSPCs into neurons and glia
- migration and regeneration of synapses
Results in functional improvement in days/weeks/months following stroke
Current state of immunotherapy for ischaemic stroke
No drugs approved, but many in clinical trials
- generally target early stages of immune cell adhesion or recruitment (within 24hours)
- off-label use
Fingolimod Mechanism
(ischaemic stroke)
A structural analogue of S1P that activates the S1P1 GPCR on T cells
- transient activation, b-arrestin recruitment, and receptor internalisation
- prevents T cells from exiting lymph nodes
Action of S1P3/S1P5
- promotes neuronal and oligodendroglial survival
Fingolimod Clinical Trial
5 RCTs with 228 participants
- first (0.5mg) dose within 4.5 hours + two more doses each following day
- decreased infarct growth by 26% by day 1, and by 17% at day 7
- improvement of clinical function by 2.6 fold at day 90
Safe
Micocycline Mechanism
(ischaemic stroke)
Lipophilic antibiotic derivative of tetracycline
- antioxidant (inhibits ROS)
- chelates Fe2+, Ca2+, Mg2+ thus interferes with NFAT, MAPK, MMPs, iNOS, COX, sPLA2
= suppression of lymphocyte and microglia signalling and proliferation - Reduces caspase 1/3 expression and other pro-apoptotic features
- Competitively inhibits PARP-1 to prevent DNA fragmentation
= prevents apoptosis and enhances neuronal survival - promotes regulatory microglia phenotype
= REDUCTION OF CELL DEATH AND INFLAMMATION IN CNS AND PNS
Micocycline Clinical trial
seven RCTs with 426 participants
- improved clinical function 1.6 fold from standard care at day 30
- oral route more effective
Safe
Key point of immuno-therapeutic treatment of ischaemic stroke
There is a bias in stroke treatment that all treatments must be given within 24hours of stroke
- However, the inflammatory cascade of stoke occurs over months
- Thus drugs should be given at different time points based on their mechanism of action
- Combination treatment with different timings
Multiple sclerosis
A chronic neurodegenerative disease that is characterised by relapsing-remitting waves of inflammation that create worsening neurological deficits
- mainly affects young adults
Causes of multiple sclerosis
Genetic
- HLA-DRB1 (MHC that makes people more susceptible to autoimmune reaction)
- polymorphisms of IL2 and the IL7R
Environmental
- being female
- smoking
- herpes
- low vitamin D
- adolescent obesity
Pathology of multiple sclerosis
- focal plaques
- inflammation
- BBB breakdown
- leukocyte accumulation
- reactive gliosis
- demyelination
- axonal degeneration
Within lesions there is neuroinflammation characterised by macrophages and T cells & degeneration of myelin, which leads to atrophy
Symptoms of MS
- sensory disturbances
- visual disturbances
- motor impairments
- fatigue
- pain
- cognitive deficits
50% of patients are in a wheelchair 25 years following diagnosis
Autoimmune activation of MS
- T cells infiltrate the meningeal, perivascular, and ventricular spaces where
macrophages present self-antigen to T cells - Activation of patrolling T cells
- Microglia and astrocytes contribute to T cell activation through chronic, low grade inflammation
Immune induction of MS
Macrophages and T/Cell cells infiltrate the perivascular spaces via BBB, subarachnoid, and choroid plexus
- produce cytokines and antibodies against myelin that promote demyelination and oligodendrocyte injury
- this leads to axonal injury
Chronic inflammation of MS
Microglia and astrocytes contribute to chronic inflammation through production of cytokines, NO, ROS and RNS that exacerbate gliosis and prevent re-myelinaton by inhibiting the differentiation of progenitor cells into oligodendrocytes
Neurodegeneration in MS
- Chronic inflammation results in mitochondrial injury and metabolic stress in soma
+ - Glutamate excitotoxicity in axons
spreads in both anterograde and retrograde directions causing neuronal cell death
What is the clinical outcome for MS, and how is this assessed?
The target in clinical practise is NEDA (no evidence of disease activity) which is shown through MRI
- T1 = active inflammation
- T2 = all scarring
Escalation therapy for MS
- First-line treatment with moderate efficacy and good safety
(IFNa analogues) - Second-line treatment with high efficacy but more risky medication
(Clabidrine, Natalizumab, Fingolimod)
Induction therapy for MS
- First-line treatment with high efficacy but more risky medication to deplete lymphocytes and allow for disease remission
(Clabidrine, Natalizumab, Fingolimod) - Second-line treatment with moderate efficacy and good safety to provide long term maintenance
(IFNa analogues)
IFN-b analogues
Reduce T cell activation and adhesion thus preventing T cells from entering CNS
+
Increases anti-inflammatory cytokines and decreases pro-inflammatory cytokines
IFNb clinical trial
9 placebo-controlled with 3216 patients
- reduction in annual relapse rate
- no effect of administration route or dose
Cladribine
A small molecule prodrug and nucleoside analogue that is selectively activated in T/B cells and induces cell death
Cladribine clinical trials
Two comparative trials with 3149 patients
- reduced annual relapse rate by 58% (not better than fingolimod/natalizumab)
- best efficacy in highly active disease
Natalizumab
A humanised antibody against a4 integrin, which prevents the binding of lymphocytes to VCAM1 on the brain endothelium
= reduced CNS entry
Natalizumab clinical trial
- long term efficacy, reducing relapse rate by >90%
- half of participants did not relapse after 12 years
- serious adverse effects occurred in 4.6%, including PML
PML
progressive multifocal leukoencephalopathy
- activation of dormant JC virus causes demyelination
- manifests as clumsiness, progressive weakness, and death after 3/4 months
- biomarkers can be used to detect at risk individuals
Side effects of IFNb treatment
- flu-like symptoms
- reaction at injection site
- increased liver enzymes (which can lead to rare cases of liver toxicity)
Side effects of cladribine
- infection
- teratogenic (can cause birth defects in fetus)
Natalizumab side effects
- dizziness
- shivering
- nausea
- itchy skin
- rash
- herpes
- PML
Immune reconstitution therapy for MS
Used for patients that do not respond to other immuno-therapies
- Isolation of bone-marrow derived haematopoetic stem cells
- Expansion of stem cells via GM-CSF treatment
- Depletion of autoreactive lymphocytes via anti-metabolite cancer drugs or cell depleting antibody therapy
- I.V. administration of cultured stem cells, which differentiate into leukocytes (immune cell)
Stem cell clinical trial
24 (uncontrolled) studies with 1626 patients
- progression free survival at 74% after a year
- 50% remission after 5 years
- 30% remission after 10 years
- works best for earlier stage disease
- not impacted by prior treatment
Alzheimer’s disease
A progressive neurodegenerative disease characterised by Ab plaques and NFTs, neural atrophy and ventricle enlargement, astrogliosis and microgliosis
Forms of AD + risk factors
Familial: mutation in APP and PSEN1/2
Sporadic: mutations in TREM2 and APOE4 genotype, age, vascular health, being female
The amyloid cascade hypothesis
Amyloidogenic cleave by b-secretase and y-secretase producing Ab42
- oligomerisation
- plaque formation
hyper-phosphorylation of tau causing destabilisation of microtubules and aggregation of tau, which eventually leads to neuronal degeneration
Microglia pathology in AD
Impaired signalling though TREM2 leads to impaired phagocytic and migratory action against amyloid beta
Astrocyte pathology in AD
Astrocytes produce APOE (apopoliproteins) that act to transport cholesterol and regulate microglial survival and phagocytosis
- implicated by APOE4 risk factor
Diagnosis of AD
- Ab PET, although this is controversial as amyloid burden poorly correlated to clinical AD and disease severity (30% of healthy individuals have amyloid pathology)
- CSF biomarkers (Ab:ptau) being explored
Approved drugs for AD
- AChE inhibitors (donezapil, galantamine, rivastigmine) increase cholinergic transmission to give moderate benefit
- NMDA antagonists (memantine) inhibit excitotoxicity by preventing excess calcium influx
Broad drug classes being explored for AD treatment
Biologics: protein based molecules that stimulate that immune system to aid Ab clearance
Small molecules: target secretase enzymes to increase Ab breakdown
Three targets of anti-Ab antibodies
- Individual Ab peptides (aim to prevent aggregation)
- Aggregated plaques (aim to break up plaques and facilitate clearance)
- Microglia (increase plaque recognition and phagocytosis)
Aducanumab
- Preclinical testing showed reduction of amyloid PET
- two 18 month RCTs (EMERGE and ENGAGE) were conducted in patients with MCI/early AD
- Both showed a reduction in amyloid with CSF/PET biomarkers
- Only one trial showed a cognitive benefit of 0.45 (not meaningful), which arose from retrograde subgroup analysis of high dose group
- ARIA-E occurred in 29-43% of APOE4 carriers
Approved by FDA
- 9/10 advisory committee voted no (last was unsure)
- statisticians voted no
- neurological drugs voted yes, due to lack of existing treatments
- waiting on clinical benefit in phase 4
ARIA
amyloid-related imaging abnormalities
Antibody breakdown of amyloid causes
- increased perivascular drainage
- loss of vascular integrity
- BBB breakdown
Causes edema (ARIA-E) or micro-haemorrhage (ARIA-H)
- often asymptomatic but can cause headache, confusion, visuospatial impairment, stroke, or haemorrhage
- possible link to brain atophy
Lecanemab
tested in an 18-month RCT in patients with MCI/early AD
- reduced amyloid PET burden
- reduced cognitive decline by 27% (not clinically meaningful)
- infusion-related reactions in 26.4% of participants
- ARIA-R occurred in 15.8% of APOE4 carriers
Full approval by FDA
Reality of implementing Lecanemab
- Extremely expensive at 26,500$ USD per treatment
= prohibitive for low/middle income countries - need greater access to PET to ensure AD is detected early enough to provide clinical benefit ($$$)
- need clinics to facilitate bi-weekly infusion
- need access to MRIs to detect ARIA
