HIV and secondary causes of immune deficiency Flashcards
What type of Virus is HIV?
A retrovirus which infects immune system cells (can cause AIDS)
It is also a lentivirus- slow evolution of disease
What is a retrovirus?
A virus with (ds)RNA that uses reverse transcriptase to convert RNA to DNA to integrate into host cell genes.
What is the organisation of HIV?
Icosahedral (20 sided)
Diploid genome (Plus ssRNA)
9 genes
15 structural/ regulatory/ auxiliary proteins
What are the important proteins in HIV?
gp120 gp41 p17 p24 p9 p7 RT IN PR
What is the structure of HIV?
RNA + p7 + p9 + Reverse transcriptase
Surrounded by p24 capsid
Surrounded by p17 matrix
Surrounded by host derived lipid bi layer
With surface protein gp 120, transmembrane protein gp41 and myristic acid in the lipid bilayer
Which cells does HIV target?
CD4+ T helper cells
Also monocytes
Can the body protect against HIV?
Yes- immunity required antibodies (B Cells) to prevent and neutralise the virus and CD8 (CTL) cells to kill infected cells
Why may the immune system fail to control HIV?
One reason that the immune system fails to control HIV-1 infection is that the CD4+ T helper cells are the target of the virus.
Progressive decline in CD4 T-cell function & numbers: HIV-specific, Recall, Allo, and Mitogen (and even IL-2).
How does HIV-1 enter target cells?
Using CD4R and CCR5/ CXCR4
Other chemokine receptors may be necessary for entry also
How id HIV transmitted?
Sexual contact (Mucosal entry via damage to blood and LN)
Infected blood (penetration)
Vertical transmission (Mother to child)
How does natural immunity play a part in defence against HIV?
Within hours: inflammation, non specific activation of macrophages, NK cells and complement
Release of cytokines and chemokines
stimulate pDCs via TLRs
How does acquired immunity (B cells) defend against HIV?
Specific Abs
Anti gp120 and Anti gp41
Non neutralising anti p24 gag IgG
BUT HIV infectious even when coated with Abs
This response (antibody mediated cellular cytotoxicity) peaks at 6 months
How does acquired immunity (CD4 T cells) defend against HIV?
White blood cells that orchestrate the immune response, signalling other cells in the immune system to perform their special functions.
Recognise processed antigen - especially Gag p24 (peptides) - in the context of class II HLA molecules.
Also known as T helper (Th) cells, these cells are infected, killed or disabled during HIV-1 infection.
Selective loss of CD4+ T cells.
How does acquired immunity (CD8 T cells) defend against HIV?
White blood cells that kill cells infected with HIV or other viruses, or transformed by cancer (CTL). Also able to suppress viral replication.
Secrete soluble molecules (cytokines and chemokines such as MIP-1a, MIP-1b, and RANTES) which are able to prevent infection by blocking entry of virus into CD4+ T cells.
Recognise processed antigen - (peptides) - in the context of class I HLA molecules.
How does HIV interfere with CD8 activation?
Activated infected CD4+ helper T cells die and are lost
Infected CD4+ T cells are also disabled (ANERGISED) by the virus
MO/DC are not activated by the CD4+ T cells and can not prime naïve CD8+ CTL
CD8+ T cell and B cell responses are diminished without help
CD4+ T cell memory is lost
Infected MO/DC are killed by virus or CTL
Defect in antigen presentation
Failure to activate memory CTL
How does HIV become mutated?
Reverse transcriptase lacks proof reading - retrovirus genome is copied into DNA with low fidelity
Transcription is low fidelity
What escape tactics do HIV have?
Escape from neutralising antibodies.
Escape from HIV-1-specific T cells.
Resistance and escape from antiretroviral drugs.
How can we target mutation for Vaccines?
Vaccine strategies that focus on highly conserved and functionally important regions of the virus could result in ether an inability of the virus to escape or the emergence of an escape variant that replicates poorly.
What is the life cycle of HIV?
- Attachment/Entry
- Reverse Transcription & DNA Synthesis
- Integration
- Viral Transcription
- Viral Protein Synthesis
- Assembly of Virus & Release of Virus
- Maturation
How do we target attachment for treatment?
Attachment inhibitors
Fusion inhibitors
How do we target Reverse transcriptase for treatment?
Reverse transcriptase inhibitors
How do we target Integration & Transcription for treatment?
Integrase inhibitors
How do we target viral protein synthesis for treatment?
Protease inhibitors
What is the clinical course of the disease?
Median time from infection with HIV to development of AIDS is 8 - 10 years.
Viral burden (set point) predicts disease progression.
Rapid progressors (10%) in 2 - 3 years.
LTNP (<5%) stable CD4 counts and no symptoms after 10 years. >8 years, > 500 cells/ul, <50 copies/ml, no symptoms & no history of ART (group is however heterogeneous).
ESN
Effect of HAART.
What are the possible mechanisms of long term non progressors (LTNP) with HIV?
Host genetic factors
Host immune response factors
Virological factors (e.g. infection with attenuated strains of HIV)
Which host genetic factors may impact LTNP?
Slow progressor HLA profile Heterozygosity for 32-bp deletion in CCR5 Mannose binding lectin alleles TNF c2 microsatellite alleles Gc vitamin D-binding factor alleles
Which host immune response factors may impact LTNP?
Effective CTL & HTL responses
Secretion of CD8 antiviral factor
Secretion of chemokines that block HIV entry co-receptors CCR5 (e.g., MIP-1a, MIP-1b, and RANTES) and CXCR4 (e.g., SDF-1)
Secretion of IL-16
Effective humoral immune response
Maintenance of functional lymphoid tissue architecture
How do we detect HIV?
ELISA (anti HIV Abs) + Western blot (confirmatory)
PCR (viral load)
What are the 4 steps of PCR?
- Reagent Preparation (Pre-PCR)
- Specimen Preparation (Pre-PCR)
- Amplification (Post-PCR)
- Detection (Post-PCR)
How do we do a CD4 count?
Flow Cytometry
Which markers are use in flow cytometry?
Cell surface markers (anti human CD3, CD4, CD8, CD19 and CD56)
Activation markers (Anti human CD57 and CD158b)
How do we establish drug resistance?
Phenotypic: Viral replication is measured in cell cultures under selective pressure of increasing concentrations of antiretroviral drugs – compared to wild-type
Genotypic: Mutations determined by direct sequencing of the amplified HIV genome (so far limited to sequencing of RT and P)
What is HAART?
Highly active antiretroviral therapy (HAART)
Why is HAART good?
Substantial control of viral replication
Increase in CD4 T cell counts
Improvement in their host defences (dramatic decline in opportunistic infections (AIDS-related disease) & deaths (mortality))
Causes:
Suppression of VL
Initial CD4 rise – memory T-cells redistributed
Later CD4 rise is thymic naïve T-cells
How do you prescribe HAART?
Two drug backbone (NRTI) + One binding agent (NNRTI/ PI/ INI/ AI/ FI)
Give an example of a drug regimen for HAART
Abacavir + Lamivudine
+ Dolutegravir
Bictegravir + Tenofovir alafenamide
+Ritonavir
When do you initiate HAART?
All symptomatic patients All CD4 <200 cells/ml START: CD4 200-350 cells/ml (All offered immediate treatment) Choices: 2NRTIs + NNRTI or boosted PI
What are the disadvantages of HAART?
Effective HAART does not eradicate latent HIV-1 in the host
Fails to restore HIV-specific T-cell responses
Is dogged by the threat of drug resistance
Significant Toxicities
High pill burden
Adherence problems
Quality of life issues
Cost (>40%)
What is the most common cause of secondary immune deficiency?
Malnutrition
What else causes secondary immune deficiencies?
Drugs
Age
Surgery/ trauma
Environment
What are the features of immune deficiencies?
Susceptible to infections (severe)
AI conitions/ allergy
Persistent inflammation
Cancer (viral associated EBV/ HHV-8)
Common secondary ID
Malnutrition Measles - mortality/ morbidity Mycobacterium TB - inflammatory immune re constitution syndrome HIV SARS CoV 2
Which drugs can cause ImmuneD?
Small molecules (Steroids, cytotoxic agents (methotrexate, azathrioprine etc.), calcineurin inhibitors, antiepileptic drugs, DMARDs (sulphasalazine)
JAK inhibitors (Tofacitinib etc.)
How do mabs affect ID?
Biologic agents (Anti- CD20 etc.)
Cellular therapy (Anti CD19/ CAR-T cell therapy)
Antibody deficiency in rituximab
Risk of infection increased
Anti TNF linked to TB infection reactivation
How does cancer affect ImmuneD?
B/ Plasma cell cancers (Multiple myeloma, CLL, NHL, MGUS)
Chemo + drugs
Goods’ syndrome [thymoma + antibody deficiency] (T/ B cell absent, CMV/PJP/ muco cutaneous candida, AI disease)
What do you ask for in the history?
Clinical Hx of infection, unusual complication of childhood inf., reaction to vx
Hx of other illness
FHx
MED
Vx history (childhood, flu etc.)
How do you FISH for an immune deficiency?
F- FBC- Hb<10, differential white cell count
I- Immunoglobulins (IgG, igA, IgM, IgE)
S- Serum complement (C3,4)
H - HIV test (18-80yrs)
What are front line investigation for immunodeficiency?
Renal/ liver profile calcium/ bone profile total protein/ albumin Urine protein/ Cr ratio Serum protein electrophoresis
Serum free light chains
What may you have if you have an Isolated reduction in IgG?
Protein losing enteropathy
Pred >10mg/day
What may you have if you have a reduced IgG and IgM?
Monitor for B cell neoplasia
History of Rituximab ues
what may you have if you have a reduced IgA and IgG?
? Primary antibody deficiency?
What can SPE miss?
Serum protein electrophoress can miss free light chain disease (e.g. in 20% myeloma)
What are second line investigation for immunodeficiency?
Measure conc of Vx Abs (Tetanus toxoid- protein ag, pneumovax vaccine-carbohydrate ag)
How may the test for PADS be used?
If Abs low- offer test immunisation with pneumovax II + tetanus
Dynamics test for primary antibody deficiency syndromes
Criteria for receipt of certain therapy for secondary Antibody Deficiency Syndromes
What are the third line investigations for immune deficiencies?
Analysis of T cell and B cell subsets
Assessment of IgG subclasses
Determination of anti cytokine and complement Abs
Genetics/ genome sequencing
Management of Secondary immune deficiency?
Treat underlying cause
Advise in measures to reduce exposure to infection
Immunisation against respiratory viruses/ bacteria + offer household contacts
Education to treat bacterial infections promptly (may require higher and longer therapies) (co amox 625 mg TDS for 10-14 days rather than 375 mg for 5-7 days)
Prophylactic antibiotics for confirmed recurrent bacterial infection
How do you decide on giving IgG replacement therapy?
If irreversible IgG drop OR lack of B cells through cancers etc.
AND
Recurrent bacteria
IgG<4g
did not respond to other vaccine challenges
What is the epidemiology of HIV?
75 mil over 40 yrs
21/37 mil on ART
101,200 people in UK with HIV
Incidence of new HIV dropped by 70% in 4-5 yrs
How does HIV get into cells?
Binds to CD4 then coreceptors replicates via DNA intermediate Integrates into host genome HIV DNA to translation to viral mRNA Viral RNA transcribed to viral proteins Makes viral enzymes
What is the origin of HIV?
4 distinct lines (MNOP)
From Chimpanzees
What is the natural history of HIV?
Acute phase - 2 weeks - 6 months ish [High risk of transmission]
Asymptomatic phase (steady state) - up to 10 years [Lower risk of transmission and increasing diversity]
Symptomatic phase [Highest viral diversity and high risk of transmission]
How does latent infection happen?
Integration of HIV virus in memory CD4 T cells within 72 hours = latent infection which don’t respond to current ART
How do cells change in HIV?
Look at picture notes
What are the key features of the immunology of HIV-1 infection?
CD4 T cell depletion
Chronic immune activation
Impairment of CD4 and CD8 function (exhaustion)
Disrupt LN architecture and impaired ability to generate protective T and B cell immune responses
Loss of antigen-specific humoral immune responses
What happens in acute phase?
Significant increase in HIV 1 viral load
Flu like symptoms
Significant viral transmission
Diagnosis
4th generation combine HIV-1
Assay: p24, gp41 (HIV1O), gp160 (HIV1M), gp36 (HIV2)
rapid POC testing (less sensitive)
HIV-1 RNA tests in cases where HIV-1 serological tests are negative but high clinical suspicion of acute HIV-1 infection
HIV RNA/ DNA test are used to diagnose infection in children <18months
What is the non pharmacological management of HIV?
Education
Co morbidities
Sexual health history and Vx
Discuss partner notification to prevent transmission
Screen for factors which may adherence to ART (Psych etc.)
What baseline tests should you do in clinic?
FBC REnal liver bone Sexual health TB - IGRA Baseline CXR Toxoplasma serology
Which HIV-1 specific tests do you do?
HIV 1 viral load
HIV-1 genotype for ART resistance
HIV-1 tropism test
HLA-B*5701 to avoid Abacavir (sensitivity)
Analysis of T cell counts (CD4 cell count and %, CD4:CD8 T cell ration)
What is Viral load set point linked to?
Viral load set point linked to outcomes
At what CD4 levels do you get PCP?
200 x 10^9
At what CD4 level do you get Toxoplasmosis?
100 x 10^9
What do you get at a CD4 level of 75 x 10^9?
MAC disease
How can you use ART?
Test and Treat
Treat to prevent
Prophylaxis
What drugs are used in ART?
Reverse transcriptase inhibitors
Boosted protease inhibitors (Ritonavir + PI)
Integrase inhibitors (DTG, RTG and EVG)
CCR5 antagonists (Maraviroc)
Fusion inhibitors
What does ART do?
Prevent new cells not old
Cannot eliminate if DNA integrated already
Cannot reverse chronic immune inflammation - bad for morbidity
How do you monitor people on ART?
Check for compliance
Regular HIV viral load
Monitor liver renal bone and lipids
CD4 T cell monitoring not needed if count >350 cells/ ul
Assess cardiovascular and osteoporosis risk
What are the challenges for HIV?
HIV prevention: Education, protection
Vx: new strategies and use of new research still needed
Cure: Allogenic stem cell transplant, shock and kill strategy
