| How is difference between vaccination and Ig immunotherapy? | . |
| What are current different preparations of human Igs used in biotherapies? | . |
| How is use of total human Igs? | Total immunoglobulin fraction purified from a pool of
plasma derived from several thousand random adult
healthy individuals, by cold ethanol fractionation
Contains 98% IgG, traces of IgA and IgM
Contains immunoglobulins with billions of different antigenic specificities
Includes a large spectrum of antimicrobial antibodies, each in tiny amounts
Two forms:
Intramuscular immunoglobulins (IMIG
Intravenous immunoglobulins (IVIG): obtained by nanofiltration of IMIG, may also be used subcutaneously |
| How is use of total human Ig in infection prevention? | IMIgs are used since 1952 in Ig replacement in patients with congenital humoral immunodeficiency (Bruton disease,
common variable immunodeficiency)
Objective: maintain constant blood IgG concentration > 500 mg/dl (50% at least of normal concentration)
IMIG are poorly efficient and are now replaced by IVIg
IVIG are administred in perfusion : 400-500 mg/kg every 3 to 4 weeks
IVIg subcutaneous administration (smaller amounts, more
frequently, self administration) allows higher patient autonomy |
| What are FDA approved clinical applications of total human IVIg? | Infection prevention in children > 2 years with congenital
(primary) immmunodeficiency
Very efficient prevention of serious bacterial infections
Good tolerance
Subcutaneous use: practical, less severe fluctuations in Ig
concentration
Infection prevention in leukemia patients with secondary
immunodeficiency
Treatment of pediatric infections in HIV + children |
| What is human hyper Ig? | Preparations of IMIg or IVIG that are enriched with specific antibodies against one given pathogen
Obtained from a pool of plasma of preselected adult donors with high specific antibody titers against the target pathogen
Clinical applications :
Immediate post-contact protection of unvaccinated individuals
IMIG: tetanus, rabies (in addition to vaccine)
IVIG : HBVIG, VZVIG
Treatment of serious established infections in immunosuppressed or immunocompetent |
| How is use of monoclonal Ab in tx of infectious diseases? | Limitations of hyper-Ig
Expensive, not always available
The active fraction represents less than 1% of the total injected Ig
Advantages of monoclonal antibodies
Pure
Specific for a single epitope
May be produced indefinitely, reproducibly and at low cost
Limited biohazard
Efficient a low dose |
| How is production of monoclonal Abs done by hybridoma? | . |
| What are limitations of use of monoclonal Abs mouse in humans? | Induce an isotypic human anti-mouse antibody (HAMA)
response
Reduced efficacy
Risk of allergic complications and serum sickness
Mouse and human Ig repertoires are different
Effector functions are less efficient |
| How is difficulty of production of human mAb by somatic fusion? | Experimental immunization of humans is ethical unacceptable
Immortalization of human B cells is difficult
No access to a good source of B cells
No adequate human myeloma cells
Need to find alternative techniques |
| How is production of different mAb by recombinant DNA technique? | . |
| How is production of chimeric MAb? | . |
| How is production of humanized Ab? | . |
| How are fully human monoclonal Ab made? | From transgenic mice (ex: Xenomouse model):
Endogenous mouse Ig (H and L chain) loci are deleted and replaced by human Ig (H and L chain) loci.
After immunization with antigen of interest, somatic fusion is performed resulting in isolation of specific fully human mAbs
From phage display libraries:
Total cDNA of VL and VH gene segments is purified from human B cells
The genes are inserted in tandem in phages that infect bacteria in culture: Billions of different recombinant phages express a random combination of VH and VL (Fab ou Fv fragment)
Phages binding to antigen of interest are amplified in bacterial cultures and resulting antibody fragment is purified |
| What are MAb used in clinics? | Palivizumab (Synagis); Medimmune): Humanized monoclonal antibody used in prophylaxis of respiratory syncitial virus infection in high risk children
Raxibacumab and Obiltaxaximab against anthrax: for postexposure defense against bioterrorism
Bebtelovimab: treatment of COVID-19 that retains activity against the omicron variant. Used for the treatment of moderate COVID-19 in patients who are at high risk for progression to severe COVID-19 for whom alternative treatment options are not clinically appropriate
Zmapp against Ebola. Efficacy not proven, used in emergency
VRC01 is in Phase 2 development as a broadly neutralizing antibody for HIV treatment. VRC01 is also being studied for HIV prevention |
| What are advantages and limits of MAbs in immunotherapy of infectious diseases? | Promising against:
Multi-resistant bacteria
Emerging diseases
Viruses
Limits
High cost
Narrow specificity
Limited market
In some cases:
Availability of anti-microbial drugs
Availability of vaccines |
| What is role of cytokines in innate antiviral immunity? | IFN a: Produced by infected cell
Inhibits viral infection: Induces enzymes that are able to degrade viral RNA or inhibit viral protein synthesis
Increases MHC-I expression to facilitate recognition of infected cell by CTL
Activates NK cells
IL2, IFN-g : activate B cell and Tc
IFN-g and TNF-b activate macrophages |
| What are applications of usage of recombinant cytokines in immunotherapy of chronic infections/ | Chronic hepatitis B and hepatitis C
IFN-a (Roferon): Inhibits viral propagation in healthy cells
Pegylated IFN-a (Rebetol) less degradable (adults only)
Approved by the FDA
HIV:
IFN-a for the treatment of Kaposi sarcoma (approved by the FDA)
IFN-g prevents mother-fetus transmission of HIV
IL-2 combined to 2 anti-retroviral drugs increases the number of CD4 cells
Herpes simplex: IFN a |
| What is CAR-T cell therapy? | Autologous live reprogrammed T cell therapy
Patients are treated with their own T cells transfected with a CAR
CAR: Chimeric Antigen Receptor
= scFv fragment of a specific Ab (VH+VL)
+ a trans-membrane region anchoring scFv to the cell membrane
One or more intra-cellular signaling domains containing ITAM, that activate the T cell upon Ag binding
Advantage:
Ag binding by Ab-binding site, not TCR: no need for APC, no MHC restriction
Higher number of specific T cells
Intracellular signaling domains overcome suppresive microenvironment |
| How was initial development of CAR-T cell therapy? | For cancer
1. Blood is collected from the cancer patient by leukapheresis
2. T cells are selected by purification on Ab coated beads.
3. T cells are transfected virally or nonvirally with a CAR molecule and expanded in vitro
4. Modified T-cells are reinfused to the patient with or without combined chemotherapy.
5. T cells bind to antigen-expressing tumor cells and kill them |
| How is CAR-T cell therapy in HIV tx? | Patient’s T-cells are transfected with both anti-CD4 and anti-HIV envelope protein (E) scFvs
they bind to both CD4 and E proteins on CD4 infected T-cells, inducing their death
The expression of C46 (an HIV-resistance protein) on the surface of the CAR-T-cell prevents the CAR T-cell itself from being infected by the HIV virus |
| What are immune checkpoint proteins? | Immune checkpoint proteins belong to the B7 family ligands and the CD28 family receptors. They act as co-inhibitory molecules between APC and T cells
In physiological conditions, they ensure that the immune system is activated only when needed, in order to avoid chronic inflammation or autoimmunity
The most important are:
CTLA4
PD-1 and PD1-L |
| How do immune checkpoints modulate immune responses to infections? | Induce a modulation of the duration and amplitude of
immune responses to pathogens that minimizes the risk
collateral tissue damage during acute and chronic infections
This leads to « exhausted T cell responses » that allow
pathogens to evade immunity. Examples: malaria, hepatitis B and HIV, tuberculosis
Targeting the checkpoint proteins may activate immunity and improve pathogen clearance |
| What is proposed role of PD1 in establishment and reverasl of HIV latency? | HIV infects CD4+T cells
Ag- or mitogen-stimulated T produce HIV virions and die by virus-mediated cytolysis.
Upregulated expression of immune checkpoint molecules limits T cell activation, favouring latent infection (integration of HIV progenome (yellow oval) but no virus production.
Administration of anti-PD1 antibody leads to activation of
these T cells and increased production of virus
This leads to either immunemediated clearance or virusinduced cell de |
