Transplantation Lecture 2024 PDF

Adjuvant  Agent added to a vaccine to induce an enhanced immune responses to vaccine antigens  Used for over 80 years  Technology continually evolving  Advances in immunology  Advances in chemistry  Recombinant proteins and peptides can be poorly immunogenic Different Adjuvants...

Adjuvant  Agent added to a vaccine to induce an enhanced immune responses to vaccine antigens  Used for over 80 years  Technology continually evolving  Advances in immunology  Advances in chemistry  Recombinant proteins and peptides can be poorly immunogenic Different Adjuvants – Different Strategies Carriers which stabilize vaccine antigens and allow them to be present for extended Delivery periods of time. Exert direct stimulatory effects on immune cells and initiate the immune response Immune through activation of innate immunity potentiator DANGER SIGNAL  The “Perfect” Adjuvant  “Perfect” adjuvant achieves both strategies  Delivery - Enhance the amount of antigen reaching the cells that are responsible for the induction of the immune response  Immune potentiator - Directly activates these cells.  Goal = Activate only the elements of the immune response required for protection, and avoid triggering a generalized activation of the immune response.  In other words “Effective and Safe”  Alums  Primarily aluminum adjuvants  Used extensively in veterinary vaccine products  Most commonly used adjuvant in human vaccines  Strong inducer of Th2 responses  Examples  Aluminum hydroxide  Aluminum potassium sulfate (often called “Alum”) - Used in many toxoid formulations (Clostridial vaccines)  Lipid/Oil Emulsions  Detergent-stabilized emulsions of oil and water  Precise mode of action is still not clearly understood  Depot  Induction of MHC responses  Primarily used in veterinary vaccine formulations  Gaining acceptance in Human vaccine formulations (MF59)  3 basic forms – multiple formulations  Oil in Water (O/W)  Water in Oil (W/O) (Freund’s)  Water in Oil in Water (W-O-W)  Oil Based Adjuvants Used in Veterinary Vaccines  Water in Oil Emulsions (W/O) – antigen-containing water droplets within external continuous oil phase  Oil in Water Emulsions (O/W) – emulsified oil droplets within continuous antigen-containing aqueous phase  Water-in-Oil-in-Water Emulsions (W/O/W) – antigen- containing water droplets entrapped inside of larger oil droplets, which in turn dispersed in continuous antigen containing water phase W/O/W ADJUVANT SYSTEM Water-in-Oil-in-Water (WOW) Adjuvant = Oil phase = Antigen = Surfactant 2 = Aqueous phase = Surfactant 1  PRR and Other Ligands Microbial PAMP’s – induce Th1 response LPS – interacts with APC, releases pro-inflammatory Derivatives cytokines CpG – Bacterial DNA Mucosal Heat labile E. coli enterotoxin (LT) Cholera toxin (CT) Plant derivative – Primary function is induction of cytokines Saponins Potentiates Th1 response (IL2, IFN-γ, IgG2a) Can be toxic in certain species (humans, mice) Commonly used in veterinary vaccine formulations  Delivery Vehicles  Membrane bound phospholipid vesicles (liposomes) with antigen trapped in lumen or incorporated in membrane  Targets increased antigen uptake by APC  ISCOMS (Immune Stimulating Complexes)  Liposomes containing saponin  Virosomes  Liposomes prepared from viral membranes  Virus-like Particles  30-90 nm self-assembled virus proteins with a nucleic acid or lipid genome  Vaccine Side Effects  Typically side effects- redness or pain at an injection site, sneezing or nasal congestion after intranasal administration, fatigue or headaches  Vaccine Adverse Events Reporting System (VAERS)-monitor adverse reactions-  Examples- Urban Legends  DTaP –sudden infant death syndrome (SIDS) – children vaccinated less likely to die SIDS  HBV-multiple sclerosis- no risk  Inactivated poliovirus vaccine (IPV)- contaminated with SV40, monkey virus- cancer- no increase  Polio vaccine and HIV- no evidence that HIV contaminated  Lyme Disease vaccine- caused arthritis- result of chronic Lyme Disease  MMR- the worst- connection with autism- completely made up  Future Vaccines  Prophylactic vaccines  Lots of targets- HIV, Ebola, hepatitis C virus, malaria  Therapeutic vaccines  Cancer  Dendritic Cell culture  Autoimmune and Allergy  Domestic animals- castration  Summary  Whole Organism  Modified live  Inactivated  Subunit  Recombinant Live  DNA  Adjuvant  Vaccine Usage  Vaccine Side effects outway disease  Transplantation  The Nature of Transplantation  Molecular Basis of Graft Rejection  Allo/Auto Antigens, Minor Histocompatibility Antigens  Solid Organ Transplants  Graft Rejection, Graft-Versus Host Disease  Therapy  Pre-therapy Screening, Post-Transplant Drugs, Tolerance  Stem Cell Transplantation  Use, Rejection, Graft-versus-Host, Reconstitution  Transfusions  Terminology  Syngeneic: Refers to a graft between genetically identical individuals.  Allogeneic: Refers to a graft between genetically diverse individuals.  Autograft: self tissue transplanted to an alternate site: eg. Skin grafts in burns  Isograft: Tissue transferred between genetically identical individuals. Mostly experimental, rarely occurs clinically  Allograft: Tissue transferred between genetically different individuals of the same species.Most common  Xenograft: Tissue transferred between species. Experimental  Tissue Antigens  The regulation of graft rejection is due to differences in the HLA/MHC haplotypes of the recipient and the donor.  Rejection involves both T and B cell responses  Molecular Basis of Graft Rejection  The most important thing to remember is that the immune response against grafts follows all the rules and processes that apply to other immune responses!  Recognition either occurs through MHC-mediated recognition of “altered self” or disparate MHC (Allorecognition, Direct or Indirect), or through disparate recognition of MINOR histocompatibility antigens.  Direct Recognition  Recall that the basis of positive/negative selection of T cells involves the ability of T cells to recognize self-MHC at a certain level.  Addition of the peptide is what specifies recognition for normal tissues (altered-self).  Foreign MHC molecules can appear as if they are self, but altered. Hence, the molecule itself is close enough to bind T cells, but different enough to activate T cells. B cells just see them as foreign.  So-called Passenger Leukocytes in the graft can provide immune stimulation to recipient T cells. Fig. 17.1 19 Copyright © 2014 Elsevier Inc. All rights reserved.  Indirect Allorecognition  In this case, it is a more direct stimulation.  Foreign peptides produced as a result of antigens shed from the graft (dying cells, etc).  In the case of self-proteins, these will fail to be recognized  In the case of all-MHC, these may produce immunostimulatory T cell peptides. Fig. 17.2 Copyright © 2014 Elsevier Inc. All rights reserved. 22  Minor Histocompatibility Antigens  Minor histocompatibilty antigens (MiHA) generally provoke chronic rejection, or a slower response, due to minor differences in allelic coding between similar proteins.  For example, if the protein coding for “blue” eyes is presented on the graft as a peptide to the recipient who has “brown” eyes, then this may provoke an immune response due to these slight differences. Fig. 17.3 Copyright © 2014 Elsevier Inc. All rights reserved. 24 Solid Organ Transplantation  Note that transplantation of any organ is naturally a “traumatic” experience.  There will be damage to tissue, endothelium, blood vessels, etc. as a result of the transplant.  This can activate DAMPs and PAMPs on the graft, recognized by and activating the innate immune system.  Adaptive Immune Responses.  These will occur, in general, as you’d expect.  Presence of pre-formed antibodies may directly kill graft tissue (hyperacute rejection)  Passenger antigens and leukocytes will be transported to the regional lymph node, where they will initiate germinal center formation and cellular activation.  CTLs, Antibodies, and helper T cells produced against the graft can travel to the affected tissue, and destroy it as a “foreign body”.  Terminology Cont’d  Hyperacute Rejection: Occurs within minutes due to existence of preformed antibodies.  Acute Rejection: Occurs within days/weeks, due to normal immune response.  Chronic Rejection: Occurs over months/years. Mechanisms unknown.  Types of Rejection of Solid Organ Transplants Hyperacute Acute Cellular Acute Humoral Chronic Time for Minutes Days/Weeks Days/Weeks Months/Years Rejection Targets on Donor ABO Antigens, Allo MHC Allo MHC Allo MHC Cell Allo MHC Mechanism Preformed Ab CTLs CD4+ T cells, Indirect allo, allo Ab Cytokine-induced ischemia Cells Infiltrating? No Lymphocytes PMNs Lymphocytes, PMNs C4d? Yes No Yes Yes Fibrosis? No No Yes Yes Treatment Pre-transplant Drugs, Steroids Drugs, None. screening, plasmapheresis plasmapheresis  Graft-Versus-Host Disease  This basically occurs due to passenger leukocytes in the graft failing to recognize that they are in a new individual!  Again, the immune processes involved are EXACTLY as you’d expect.  The Dendritic Cells and T cells present in the transplanted organ are capable of proliferating and attacking host tissue.  This is more common with transplant of immune tissues (blood, stem cells) than with solid organs. Passenger Leukocytes in solid organs are normally more of a danger for promoting rejection, as discussed previously.  Minimizing Graft Rejection  The most effective strategy to prevent rejection is to match, as closely as possible, the HLA/MHC haplotype of donor and recipient.  In the past, this was done using a Mixed-Leukocyte Culture (ie mix PBMCs from both donor and recipient, watch for cell division).  Currently, flow-cytometry based methods are generally used. Antibodies against individual HLA- alleles are used to “type” the donor and recipient leukocytes. In some labs, this is moving towards PCR and DNA-based approaches.  Screening for Pre-existing Antibodies  In general, making sure that there are no pre- existing antibodies in a recipient is important to graft success.  This is one reason that repeat transplants have a much lower chance of success – similar to a “memory” stimulation after primary “vaccination” with the prior organ.  Typically, this is done using either solid-phase or Flow Cytometry based-approaches to look for donor-specific responses in the recipient.  Immunosuppressive Therapy  This generally involves basically “turning off” the recipient immune response.  While many elegant techniques are being investigated, the majority of tools at our disposal now effectively “immunosuppress” the recipient generally against all antigens.  These are summarized in Table 17-6.  Originally, Cyclosporin A was the “go-to” drug, as it effectively shut down T cell proliferation by blocking IL-2 resposiveness.  Analogs have now been developed with fewer side effects, partially due to patent protection initiatives. Induction of Graft Tolerance  Elegant, highly targeted strategies are now being pursued to limit graft rejection through selective immunotolerance.  This “holy grail” of transplantation would selectively convince the immune system that the new organ is part of “self”, and in rare cases occurs spontaneously (e.g. Heart-Lung-Liver).  Basically, these tools involve selective inhibition of antigen-specific responses, through blockade or selective stimulation of regulatory T cells.  Hematopoietic Stem Cells  Hematopoietic Stem Cell transplantation is used clinically for treatment of a number of conditions.  Note that radiation/chemotherapy is destructive to immune stem cells.  This may also be used in an attempt to cure autoimmune disease, or in conjunction with organ transplantation to promote acceptance.  Primary challenges are limiting cell numbers in the bone marrow, and potentially for transplant of host leukocytes and initiation of GVHD.  Blood Transfusions.  Blood transfusions are probably the oldest example of organ transplantation.  Pre-existing antibodies directed against target antigens can be found in individuals, hence the great need for ABO bloodgrouping prior to blood transfusion.  If this is not done, these antibodies lyse the donor red cells, resulting in serum toxicity and anemia.  Blood Group Antigens/Antibodies Blood Type Genotype RBC Antibodies Compatible Antigens Donors A AA or AO A Anti-B A,O B BB, BO B Anti-A B,O AB AB A and B None A,B, AB, O O OO H Anti-A, Anti-B O  Next (final) lecture  Autoimmunity