Immunotherapy 14/03/23 Flashcards
What is immunotherapy?
Immunotherapy is defined as harnessing the patient’s own immune system to fight disease.
What are immuno-oncology therapies?
Immuno-oncology therapies represent a significant advance in cancer treatment beyond traditional treatment.
How do immunotherapies work?
Immunotherapies engage and recruit the immune system to combat disease by inducing an antibody generation response against a specific antigen (foreign entity) typically present on the cell surface of a virus or cancer cell. This is very similar to a traditional vaccine approach seen for a whole host of diseases throughout history. These cell surface antigen targets typically evade the surveillance mechanisms of the immune system and thus persist and manifest disease within the host. As a result of the body’s inability to recognize and destroy these antigen targets via antibody generation and subsequent eradication, these antigens must be presented to the immune system exogenously. An option for the immune-tolerant host outside of traditional medical intervention is immunotherapy via exogenous delivery. Immunotherapies are directed at a specific antigen or cluster of antigens that compose the unique signature of a virus or cancer cell that is dissimilar to its host thus recognizing self from non-self.
Where has there been success with immunotherapies?
There are lots of different types of immunotherapy, but for all types, its success requires the tumour load being reduced first by surgery, irradiation, or chemotherapy for 2 reasons:
-Immune system cannot cope with large tumours
-If had lots of antigen shedding from the tumour it would stimulate the regulatory T-cells, and thus stop an immune response against tumour
-After debulking the tumour, smaller amounts of tumour are left as the main target for immunotherapy
What are humanised monoclonal antibodies?
Humanized monoclonal antibodies that target cell surface components of tumour cells are increasingly being used to treat cancer been approved for therapeutic use.
Antibodies reacting with antigens on the surface of tumour cells protect the host by complement mediated opsonization and lysis and also through recruitment of macrophage and NK ADCC. The FcR cells not only act as cytotoxic effectors but cause crosslinking of antibody coated cells which leads to apoptosis or exit from the cell cycle, and makes the cells sensitized to irradiation and DNA damaging chemotherapy.
What are immunoconjugates?
A lot of interest has been made into therapeutic immunoconjugates which consist of a tumour targeting antibody linked with a toxic effector component such as radioisotope, toxin or small drug molecule, or prodrug (antibody enzyme prodrug treatment-ADEPT-so drug gets activated at the site of the tumour-so highest concentrations delivered there).
What are some of the approved humanised monoclonal antibodies?
More than 20 humanized or fully human monoclonal antibodies and immunotoxins were approved by the US Food and Drug Administration by the end of 2019 for use in cancer. All of these antibodies listed target a cell surface component except the one targeting Vascular endothelial growth factor (VEGF), this neutralizes VEGF to prevent angiogenesis which is required for tumours to grow
Examples include:
-MAb approved for HER2 in breast cancer
-CD20 in lymphoma
-EGF in colorectal cancer
How do the humanised monoclonal antibodies work?
Therapeutic antibodies are specific for a protein on the surface of the tumor cells, such as the binding of rituximab to CD20. The antibodies coat a tumor cell with their Fc regions pointing away from the cell. These can then engage the FcγRIII receptors on an NK cell. Signals from the receptors activate the NK cell to kill the tumor cell. This is an example of ADCC (antibody mediated cell-mediated cytotoxicity). The monoclonal antibody bindstothetumorcellantigenwithitstwoFabarmsandtoFcγRIIIontheNKcellwith itsFcregion,thuscreatingastrongadhesionbetweenthetwocells. The activatingsignalsgeneratedbyFcγRIIIareaugmentedbysignalscomingfromNKG2 andotherNK-cellreceptorstoactivatethecytotoxicmachineryoftheNK cell.
Why are mouse monoclonal antibodies not used?
Monoclonal antibodies were originally produced using mouse hybridomas. Specificity of mouse monoclonal antibodies makes them very useful for treating a broad range of clinical conditions. Problem though, when mouse monoclonal antibodies are introduced into humans they are recognised as foreign, and evoke an immune response known as the HAMA response. Human anti mouse antibody, which quickly clears the mouse monoclonal antibodies from the bloodstream and lowers the therapeutic efficiency of subsequent administration.
It does not just reduce the efficiency of the treatment it can also cause a host of other complications including allergic reactions, or the accumulation of mouse and human ab complexes in organs such as the kidneys which can cause life threatening problems.
How are humanised monoclonal antibodies made?
One way to avoid these undesirable mouse reactions would be to use human monoclonal antibodies, produced by human hybridoma cell lines but this is not possible due to technical problems. So alternative methods of antibody engineering using recombinant DNA technology have been developed to overcome these difficulties. It is now possible to create ‘man made‘ abs that have less non-human protein in them.
Two main ways of making these:
-Design and construct genes so that you clone the promoter, leader and variable region from a mouse ab gene, and constant region exons come from a human ab gene. An ab produced this way using recombinant DNA technology is a mouse human chimera, and is called a chimeric ab, this type of ab is partially humanised. Its antigen specificity, which is determined by the variable region, is encoded by the mouse, and its isotype, which is determined by the constant regions, is derived from the human DNA. Because the constant regions are encoded by human DNA, the abs have fewer mouse antigenic determinants, and are far less immunogenic when administered to humans than mouse monoclonal antibodies. Of the 20 antibodies that have been approved for use in humans to treat various diseases, approximately half are chimeric. One such chimeric ab that is used for treatment is rituximab which targets CD20 of the B cells in non-Hodgkin’s lymphoma. When the chimeric antibodies were introduced, a human anti-chimeric antibody response (HACA) was observed.
-However because the entire mouse VH and VL regions are retained in chimeric abs, they contain significant amounts of mouse ig sequence, which can cause HACA (human anti chimera antibody) responses. It is now possible to engineer abs in which all of the sequence is human except the CDRs. This is known as CDR grafting-involves the substitution of non-human CDR domains from an mouse ab into the most closely related human ab sequence available, so that only the CDR domains are non-human. This is a fully humanized ab. These humanized abs retain the biological effector functions of human antibody and are more effective than mouse abs in triggering complement activation and fc receptor mediated processes such as phagocytosis in humans. They are also less immunogenic in human than mouse-human chimeric abs.
However even when graft CDR regions into the human framework region, you see and anti-variable region response. It is thought that only 20-30% of the residues in the CDRs are crucial for antigen binding called the specificity determining residues (SDRs). Minimally immunogenic molecules are generated by grafting the SDRs onto a human framework. Veneering is another approach, based on the premise that only the surface residues contribute to the immunogenicity of the variable regions-so it changes only exposed residues that differ from human amino acid sequence, while those residues which are buried within molecule are not modified. In both the chimeric and humanised abs the specificity was determined from the mouse (clone the sequence from the mouse hybridoma lines which can be readily generated), whereas the isotype of the ab is governed by cloning human gene sequences corresponding to constant segments. Because of these approaches the abs contain fewer mouse antigenic determinants, so are less immunogenic in humans. Another advantage to humanising abs is that mouse abs have very short half-life of a few hours, compared with the 3 week half lives of their human or humanized counterparts.
Process of production of full human Ig in mice by antibody engineering?
Chimerization and humanization of abs are labour intensive procedures, involving sequence analysis, engineering approaches, analysis and optimization of binding affinity, and evaluation of immunogenicity for each ab. So technological developments have been undertaken so that fully human antibodies are produced by engineering the Ig loci, rather than components within the Ig molecule.
Technology involves removal of the Ig H and L chain loci of mice which creates knock out mice.
Embryonic stem (ES) cells were collected from these KO mice from the blastocyst. Human artificial chromosome containing the Ig H (1.5 Mb) and lamda loci (1 mb) were transfected into ES cells.
These modified ES cells were put back into a blastocyst and transplanted into surrogate mothers. The B cells of the offspring produced human abs in response to antigen.
The transgenic mice produced completely human abs in response to antigenic challenge, in cells that you can make hybridomas from (because they’re produced in mice B cells). So can produce human moabs of any specificity by this method.
This approach particular useful for producing large quantities of human abs, for example, if replace cattle loci with human ig koci, larger quantities of human Moabs produced because contain ~60 litres of blood.
-Panitumab (colorectal Ca) and Zanolimumab (lymphoma) have been produced using this approach. Panitumab has been approved for tx of metastatic colorectal cancer, and zanolimumab is currently in phase III trials for t cell lymphoma.
What has changed in melanoma treatment since monoclonal antibodies?
Melanomaaccountsfor75%ofthedeathscausedbyskincancer.In2018,therewere61,000deathsfrommelanoma,and288,000newcasesofthediseasewerediagnose worldwide. At that time, 75% of patients with advanced melanoma survived less than 1 year so great need to develop more effective treatments, hence a lot of research done using immunotherapies for this disease. Since 2011, more than 17,000 patients have been treated with ipilumumab (binds to CTLA4), the 5 year survival rate of melanoma has increased from 8% to 18%.
What are the immune checkpoint inhibitors for antibodies?
Designed to overcome blockages to T cell activity mediated by immune checkpoints.
Work by reactivating TILs (tumour infiltrating lymphocytes), particularly CD8+ cytotoxic T cells. CTLA-4 Checkpoint Inhibitors: Anti-CTLA-4 mAbs are designed to augment T cell activation by blocking inhibitor receptors such as CTLA-45.
Checkpoint inhibitors against PD-1 and its ligand PD-L1 release PD-1 pathway-mediated inhibition of T cell activation.
What was Allison’s research?
Allison’s discoveries built on the work of French immunologists from the 1980s who were studying T cells, components of the immune system that attack cells that the body recognizes as foreign. They identified a key receptor on the surface of T cells that they called cytotoxic T-lymphocyte antigen 4, or CTLA-4. Allison and others found that the receptor puts the brakes on T cells, preventing them from launching full out immune attacks. Other groups hoped to use the receptor to help treat autoimmune disease in which the immune system’s brakes aren’t strong enough. But Allison had a different idea. Cancer develops when the body’s immune system fails to attack tumour cells, even though they are growing out of control; Allison wondered whether blocking the blocker—the CTLA-4 molecule—would set the immune system free to destroy cancer. This was a new concept, to target the body’s system of immunosuppression as a tool to help defeat tumours. In 1996, Allison published a paper in Science showing that antibodies against CTLA-4 erased tumours in mice.
Pharmaceutical companies initially shied away from cancer immunotherapy, wary of possible side effects and also of an approach so different from the standard treatments of surgery, radiation, or chemotherapy. So the job of getting anti–CTLA-4 into people fell to a small biotechnology company, Medarex, in Princeton, New Jersey. It acquired rights to the antibody in 1999 and were the first to use it as a drug.
What was Honjo’s research?
Honjo, meanwhile, in the early 1990s discovered a molecule expressed in dying T cells, which he called programmed death 1, or PD-1; he recognized PD-1 as another brake on T cells. Initially, “I didn’t realize there was a connection to cancer,” Honjo said at today’s press conference. Later, however, he and others performed key experiments showing that the molecule could be a target in cancer therapies. The first clinical trials using PD-1 were even more dramatic than those with CTLA-4. Several patients with metastatic cancer were apparently cured. And side effects seemed milder than those observed with CTLA-4 therapies.
