ic2 Flashcards
MHC stands for
major histocompatibility complex
HLA stands for
human leukocyte antigen
MHC is a cell surface protein?
yes
main function of MHC
to bind peptide fragments (antigenic fragments) and display them for recognition by T cells –> aids the immune system to distinguish self from non-self or foreign antigens
another function of MHC
help to determine the compatibility of organ transplant donors
are MHC genes germline-coded
are all MHC genes encoding proteins meant to have immune functions?
yes.
no. MHC molecules do not have immune function
which class of MHC proteins are involved in antigen presentation?
class 1 & 2
how many percent of MHC region are encoding proteins having immune functions?
50%
where are class 1 MHC present in?
nucleated cells and platelets (in the nucleus) ; absent in rbc
where are class 2 MHC present in?
present in antigen presenting cells (APCs) including macrophages and dendritic cells; present in B cells
class 1/2 bind to peptide fragment of ENDOGENOUS/EXOGENOUS antigens?
class 1 - endogenous
class 2 - exogenous
CD8+ and CD4+ receptors binding. would there be any errors?
no, because there are 2 receptors involved, one is the CD4+ & CD8+ and also TCR for cytotoxic T cells and helper T cells. SPECIFIC binding.
2 key characteristics of MHC molecules (1 and 2)
- polygenic (made up of multiple gene) - different sets of MHC class 1 and 2 molecules can present different antigens to T cells
- polymorphic (each MHC gene have different alleles) - peptide binding domains different, varied antigen recognition by T cells in different individuals
class 1 MHC molecules bind to which type of T cells?
CD8+ cytotoxic T cell
class 2 MHC molecules bind to which type of T cells?
CD4+ helper T cell
where does the processing of peptide-MHC 1 molecules happen?
ER and golgi apparatus
where does the processing of peptide-MHC 2 molecules happen?
ER
how is the level of MHC molecule expression regulated?
cytokines and interferons
level of MHC molecules expression affects extent of ___ activation
T cell
how does interferon alpha help to activate appropriate T cells in times of infection?
- ifn alpha is produced as an early response to viral infection.
- it increases transcription
- increases expression of MHC molecules to activate appropriate T cells
how does interferon gamma help to activate appropriate T cells in times of infection?
- is an immunomodulatory cytokine
- increases expression of MHC molecules to activate appropriate T cells
what is an immunotherapy?
treatment of a disease by intervening the immune system (not cure)
types of immunotherapies
- activation of immune system by using agents that increase or reestablish the immune system’s ability to prevent and/or fight the disease
- suppression of immune system by using agents that reduce or suppress an immune response
are vaccines a kind of immunotherapy?
yes
is transfusion of whole blood a good therapeutic strategy for immunotherapy?
no, because there are other components that are not involved in immune response
what is anticytokine?
compete with cytokines to bind to the cytokine receptors, prevent and stop subsequent activation
what are anticytokines used for?
treating acute/chronic inflammation conditions
what are recombinant cytokines?
synthetically made cytokines that help to increase the activation of cytokine receptors and signal transduction
what are recombinant cytokines used for
create an antiviral state for host body
*Antiviral state means the virally infected cells release cytokines like IFN to prevent infection of other cells
3 types of ACT (adoptive cell transfer)
- TIL (tumour infiltrating lymphocyte therapy)
- TCRT (t cell receptor therapy)
- CART (chimeric antigen receptor T cell)
principles of TIL therapy
- Isolate lymphocytes in the tumour by centrifuging and spinning down the lymphocytes (consisting of T cells and NK cells)
- Isolated T cells are polyclonal, have diverse antigen specificity
- After isolation, may have problems Where the tumour is not very big and hence the number of lymphocytes present is not big
- Hence, growing/expansion of T cells in vitro by a rapid expansion process (REP)–> outside of body but same condition as body (there is no genetic modification of the cells)
Conditions: IL2, anti-CD3, feeder cells, irradiate
what is the purpose of IL2
it will induce the growth of the T cells
- IL2 is produced by CD4+ T cells that is exposed to the APC
- IL2 receptors is found on both immature T and B cells –> activated T and B cells
what is the purpose of adding anti-CD3 antibody?
Upon binding to the cell surface protein of T cells, then it activates the CD3 in the T cells
purpose of adding feeder cells
to quicken process
where is the feeder cells derived from?
obtained from the patients (autologous) –> usually autologous PBMCs (peripheral blood mononuclear cells) –> draw blood from peripheral
–> Centrifuge able to get PBMCs
what is the purpose of irradiating the expansion of cells?
To stimulate PBMCs cells to enter into cell cycle cell division to get the T cells to proliferate
PBMCs when stimulated also produce cytokines
what are the disadvantages of TIL?
- individual based response –> high/low lymphocytes obtained from the patient
- polyclonal T cells –> different specificity to the antigen –> not that specific to the cancer cells –> unable to kill and eradicate cancer
- not genetically engineered and hence there could be chance of T cells that have low or no specificity/affinity to the cancer cells at all
principle of TCRT (T cell receptor therapy)
- genetically modified T cell receptors –> alpha and beta chain undergo gene engineering to obtain the specificity for the target cancer cells
- these genes that are specific to the antigen are cloned into retro or lentviral vectors
- these vectors are used to transduce T cells isolated from patient’s peripheral blood
- these genetically modified T cells have high transduction efficiency and more homogenous (less heterogenous)
- infuse the T cells back into the patients
2 advantages of TCRT
- effective against solid and hematological tumour
genetically modified TCR complex, more specific to the antigen –> able to bind to mhc-peptide molecules more effectively around the entire body (cell surface in blood and within the tumour cells/mass) - more effective than CART
they use full TCR complex, can have high signal transduction with the help of CD3 adaptor proteins –> activated at low target cell antigen densities. onset is slow but prolonged and hence more extended killing
disadvantages of TCRT
- require MHC binding because the full TCR complex is present –> need bind to mhc-peptide molecules.
however, some MHC cannot bind to the antigenic peptide fragment because they are polygenic and polymorphic - less safe than TIL
a) on-target-off tumour toxicity
b) off target toxicity
c) cytokine release syndrome
CDR1 in alpha & beta chain bind to which peptide/MHC in peptide-MHC molecule?
bind to each terminus of the peptide
CDR2 in alpha & beta chain bind to which peptide/MHC in peptide-MHC molecule?
recognise and bind to MHC
CDR3 in alpha/beta chain bind to which peptide/MHC in peptide-MHC molecule?
recognise and bind to peptide
principle of CART therapy (chimeric antigen receptor therapy)
- genetically modified T cells
- construct chimeric antigen receptor –> genetic sequence encoding for specific antigen binding sites within Vh and Vl in the Fab domain of the antibody –> are cloned into retro or lentviral vectors
- these genetic sequence uses scFv (single chain variable fragment)
–> they are not encoded by the variable chains of alpha and beta chain anymore - these vectors are used to transduce T cells isolated from patient’s peripheral blood
- transduced T cells express chimeric antigen receptor on the cell surface which are known as car-t cells
- in vitro expansion of car-t cells are then infused back into the patient
intracellular domain of the 1st gen of the CAR-T contains
1 signalling domain (CD3zita)
intracellular domain of the 2nd gen of the CAR-T contains
2 signalling domains
(CD3zita + additional co-stimulatory CD28 OR 4-1BB domain)
intracellular domain of the 3rd gen of the CAR-T contains
3 signaling domains
(CD3zita + additional co-stimulatory CD28 + 4-1BB domain)
intracellular domain of the 4th gen of the CAR-T contains
3 signaling domains + transgene
CD3zita + additional co-stimulatory CD28 + 4-1BB domain + TRANSGENE
in the 4th gen CART, what is the purpose of transgene?
transgene is activated to express cytokine (IL12)
can antigen-negative cancer cells be eliminated?
gen 1, 2, 3 cannot eliminated antigen negative cancer cells because they cannot detect such cells without the antigen
gen 4 can eliminated because of the presence of the transgene which produces IL12 which helps to activate other immune cells from the innate immunity to kill such cells because innate immune cells do not have memory
advantages of car-t
- independent of MHC molecules (car-t cells can recognise the antigens directly without the help of MHC) –> hence fast onset
- effective for hematological tumours but not the solid tumour cells because they cannot infiltrate
disadvantages of CART
- not as effective as TCR
a) short duration because only one subunit scFv binds to antigen –> weaker signaling and activation compared to 6CDRs on the T cell receptor
b) only activated at higher target cell surface antigen densities - adverse effects:
a) off-target toxicity
b) on-target off-tumour toxicity
c) cytokine storm syndrome - scFv misguide T cells into the wrong antigen due to lack of specificity (off-target toxicity)
types of cancer vaccines
- tumour cell vaccine
- dendritic cell vaccine
- nucleic acid vaccine
how are cell type of cancer vaccines different from TIL therapy?
cancer vaccines just need to draw blood from patient, TIL need remove tumour
how does tumour cell vaccine work
autologous or non-aotuologous tumour cells that may be or may not be genetically modified –> antigens expressed by tumour cells can induce T cells in patient –> activation therapy of immunotherapies
how does dendritic cell vaccine work specifically for prostate cancer
- autologous leukocyte extracted from patient’s peripheral blood
- DCs cultured ex vivo with a fusion protein consisting of:
a) antigen prostatic acid phosphatase (present in most prostate cancer cells)
b) immune signalling factor GM-CSF for APC maturation - activated APCs re-infused into patient –> evoke immune response against cancer cells carrying antigen
how does nucleic acid vaccines work (DNA or RNA vaccines)
DNA nucleic acid gets incorporated into host cell genome –> more lasting expression of antigenic proteins/peptides
RNA vaccines –> not incorporated into host cell genome
