Immunotherapy for Cancer

Immunotherapy for Cancer (by Shaunak Raole, Replico)

Immunotherapy, also referred to as biological therapy, is done to treat a disease either by activation/enhancement or suppression of the immune system. When the immune system is amplified, it is called activation immunotherapy, and when it is suppressed, it is called suppression immunotherapy.

Inactive immunotherapy, the immune response against cancer is triggered and in passive immunotherapy, immunity molecules are administered to patients who can not produce them on their own.

A lot of potential has been seen in immunotherapy, especially against cancer.

Immunotherapies have been designed to eliminate a tumour by reviving, initiating or supplementing the in vivo anti-tumour immune response. They can also neutralize the inhibitory pathways.

There are many classes of immunotherapy:

Monoclonal Antibodies against Tumour Cells

The immune system produces antibodies when it senses a threat. These antibodies are proteins that interact with antigens and lead to an immune response. Monoclonal antibodies are produced in labs and boost the natural antibodies or defend against foreign threats.

The mAbs can be unmodified or they can be conjugated with some agent to improve their efficacy. For example, potent toxins, chemical agents, chemotherapy drugs, or radioactive particles can be conjugated with a mAb which then can be delivered to the target site/cell. These are also called “guided missile therapies”. In this, the toxic agents are specifically delivered to the tumour cells. The normal tissues are spared.

Certain reagents known as immunotoxins have been synthesised. This is done by coupling the inhibitor chain of a toxin like Diptheria toxin to an antibody against a tumour-specific or tumour associated antigen.

Some tumours express significantly high levels of growth factors which can be promising targets for anti-tumour mAbs. As an example, in 25% to 30% of women having metastatic breast cancer, there is a genetic alteration of tumour cells which leads to increased expression of human epidermal-growth-factor-like receptor 2 (HER2), encoded by the neu gene, and is present in trace amounts in normal adults. Thus, a humanized mAb against HER2 has been successfully used to treat breast cancers in which HER2 is expressed. Normal cells aren’t damaged in the process.

Bispecific monoclonal antibodies (BsmAb) are antibodies that bind with two proteins at once, and some can bind to both cancer cells and an immune system cell, which facilitates the immune response against cancer.

Approximately 12 different monoclonal antibodies have been approved for treating cancer.

Checkpoint Inhibitors

This is the most thoroughly investigated class of immunotherapy, in which the two most common strategies are: PD-1/PD-L1 blockade and CTLA4 inhibition. Certain immune checkpoints are responsible for maintaining appropriate immune responses and protecting healthy tissues from immune attacks. So these are basically molecules present on specific immune cells and need to be either activated or inactivated for the immune response to get elicited.

When T cells activate in response to inflammation, PD-1, a checkpoint protein, is expressed by them which allows them to recognize abnormal and cancerous cells. It also prevents the T cells from attacking other cells in the body. The prevention occurs when the cells express PD-L1 protein. This is because if PD-1 binds to PD-L1, T cells are stopped from attacking any cell. The tumour cells express PD-L1 which binds to PD-1 and renders T-cells inactive. If we use mAbs that target PD-1 or PD-L1, this interaction can be blocked and tumour cells can be killed.

Some drugs which target PD-1/PD-1 inhibitors: Pembrolizumab (Keytruda), Nivolumab (Opdivo), cemiplimab (Libtayo). Drugs that target PD-L1 (PD-L1 inhibitors) are Atezolizumab (Tecentriq), Avelumab (Bavencio), Durvalumab (Imfinzi).

CTLA-4 (cytotoxic T-lymphocyte-associated protein 4), which is a co-inhibitory molecule regulates the degree of T-cell activity and is another immune checkpoint. T cell activity gets inhibited by the interaction between CTLA4 and its ligands, CD80 and CD86.  This can promote tumour progression. Hence if we are able to block that interaction, T cells can remain active and recognize and kill the tumour cells. Unfortunately, the exact mechanism of the CTLA4 blockade is unknown and the various antibodies which target CTLA4 have different properties. For example, some anti-CTLA4 antibodies inhibit checkpoint functionality and also deplete regulatory T cells. Ipilimumab (Yervoy) is a CTLA4 targeting mAb.

The mAbs which target these checkpoints have been FDA-approved for the treating malignant cancers like melanoma, non-small cell lung cancer, RCC, Hodgkin lymphoma, Merkel cell carcinoma, head and neck cancer and carcinoma of the bladder

Cytokines

IFN α therapies were approved in 1986, hence cytokines were the first class of clinically applied immunotherapy. Cytokines are injected and directly stimulate the growth and activity of immune cells.

Interferons (IFN-α, -β, and -ϒ), Interleukins (IL-2, -4, -6, and -12) and granulocyte-macrophage colony-stimulating factor (GM-CSF) are the three main types of cytokines used for immunotherapy. The immune cells normally produce interferons as a response against microbial pathogens. Interferons elicit an immune response by inducing the maturation of macrophages, NK cells, lymphocytes and dendritic cells. Angiogenesis in the extracellular tumour space can also be inhibited by interferon activation.

The activity and growth of CD4+ T cells and CD8+ T cells, along with NK cells, can be stimulated by Interleukins, mainly Interleukin 2. Activated myeloid cells produce IL-15 as a membrane-bound heterodimer (IL-15Rα associated) such that it is trans-presented to NK cells and T cells express IL-2/IL-15Rβ and the common ϒ chain receptor. IL-15 has critical importance for the ontogeny of NK cells and CD8+ T cells. It induces proliferation, cytotoxic action and release of other cytokines like IFN-gamma from these cells, which indicates its role in potentiating immune response.

GM-CSF is responsible for improving immune response by promoting T cell homeostasis (which improves T-cell survival) and by supporting dendritic cell differentiation in order for these cells to express tumour specific antigens.

Granulocyte colony-stimulating factor (G-CSF) and GM-CSF have both been used to augment and accelerate granulocyte recovery after chemotherapy, however, GM-CSF is more pro-inflammatory.

Along with these cytokines, certain agonists are being investigated which activate immune cells via intracellular mechanisms. As an example, TGFβ receptor type 1 (TGFβR1) inhibitors like SD-208 restore functions of T cells and bring an improvement in the immune response. APCs are directly activated by the small molecule agonists of TLR7/TLR8 to promote antitumour activity. STING (Stimulator of interferon genes) agonists induce pro-inflammatory cytokine production and other types I interferon responses.

Engineered T cells: chimeric antigen receptor T and T cell receptor T cells.

 In this approach, T cells are collected from the patient’s blood and are genetically modified/engineered such that they express CARs (chimeric antigen receptors) which are specific against certain antigens present on the tumour cells. The patient is re-administered with these engineered T cells. These CAR T cells recognize the targeted antigen present on tumour cells which induces tumour cell death.

The extracellular domain of CAR contains the antigen-binding moiety along with a spacer. The antigen-binding moieties can either be an scFv (single-chain fragment variable) which is derived from antibodies, or a human Fab fragment taken from phage display libraries, or nature ligands that engage their cognate receptor.

The scFv is a fragment derived from mouse mAbs humanized mAbs or human mAbs and is responsible for the recognition and binding to the tumour associated antigens (TAAs) which are expressed in the tumour cell surface.

Along with unprocessed antigens, these receptors can also recognize carbohydrate and glycolipid structures present on the tumour cell surfaces. Antigen presentation via MHC is bypassed. The CAR T-cells (CD4+ and CD8+) are recruited for redirected recognition of target cell, and CAR mediated tumour elimination uses at least two pathways in executing cytolysis, for example, perforin and granzyme exocytosis. Death receptor signalling via Fas/Fas-ligand or TNF/TNF-receptor can also take part to some extent.

These CAR T cells retain their activity for over 10 years after injection, hence this can be called a one-time therapy. These cells are bring clinically tested for haematological as well as solid cancers.

Engineered TCR T cells are currently undergoing clinical trials for haematological and solid cancers. The TCRs interact with tumour-associated intracellular antigens which are presented by MHCs. The antigenic target can be shared antigens like cancer-testis antigens, or patient-specific neoantigens arising from tumour mutations. Contrary to MHC independent CAR T Cells, the TCR T cells need to be MHC matched with the patient.

As of now, researchers are developing novel delivery technologies for overcoming toxicities associated with CAR T Cells and TCR T cells, and to increase their applicability for solid tumours.

Co-stimulatory receptor agonists

Certain agonistic antibodies can be designed to bind specifically to receptors present on T cell surfaces and trigger intracellular signalling pathways which induce T cell growth, survival and effector functions against tumour cells. The most common of these receptors are the co-stimulatory receptors (namely CD28) and many members of the tumour necrosis factor receptor (TNFR) family like 4-1BB (also called TNFRSF0 or CD137), OX40 (also called TNFRSF4) and glucocorticoid-induced TNFR-related protein (GITR) which are expressed on APCs surfaces. The binding of ligands to these co-stimulatory receptors trigger intracellular cell signalling which in turn promotes T cell growth and anticancer activity.

Since agonistic antibodies are at the early development stage, there aren’t any approved by the FDA. However, several have reached clinical trials. 

Cancer Vaccines

Also called therapeutic vaccines, they are given to people already suffering from cancer in order to increase the body’s natural defence. They either prevent cancer from recurring, or they destroy remnant cancer cells (from other treatments). They can also stop a tumour from spreading.

There are various types of cancer vaccines. They include tumour cell lysate, dendritic cells, nucleic acids (like mRNA) or neo-antigens. The most commonly studied class of cell-based cancer vaccines are dendritic vaccines. They are made up of dendritic cells which are collected from patients and are engineered such that they express tumour associated antigens and hence directly activate T cells to attack tumour cells. Sipuleucel-T is the first Dendritic Cell-based cancer vaccine for asymptomatic/minimally symptomatic metastatic castration-resistant prostate cancer. It induces an immune response to a common self prostate tumour antigen, prostatic acid phosphatase (PAP). The DCS is isolated from prostate cancer patients. Next, they are stimulated in vitro using a fusion protein that consists of PAP and GM-CSF. The expanded autologous APCs are then re-infused into the patient yielding an increased survival of just over 4 months.

Nucleic acid therapeutics (DNA and RNA based vaccines) are good alternatives to conventional vaccines. They rely on intracellular delivery of exogenous nucleic acids into the target cells. APCs take up DNA or mRNA, which are translated for inducing antigen expression. T cells, after being presented with the targeted antigens, are then activated against tumour cells that express antigen of interest. DNA vaccines are sometimes unsuccessful due to nuclear delivery barriers and immunogenicity; hence mRNA cancer vaccines are developed.

Neoantigen vaccines have the ability to boost immune responses against cancer cells. Neoantigens are specific to tumours and arise from somatic DNA alterations in cancer cells. The biggest advantage of these is that they are only present on cancer cells, hence off-target adverse effects are absent. Neoantigen vaccines are ideal for treating heterogenous cancers as the vaccines can encompass an unlimited number of neoantigens.

Oncolytic virus therapy

In this, viruses are modified in the laboratory such that they infect and kill specific tumour cells. The procedure is as follows:

•  The virus is genetically modified and injected into the tumour.
•  It reaches the cancer cells and makes a copy of itself.
•  The cancer cells are disrupted and die.

·       Once the cells die, the immune system is stimulated to attack any cancer cells in the body having similar proteins as the dead cells. When the infected cancer cells are destroyed by oncolysis, they release virions that help in destroying the remaining tumour.

This oncolytic virus does not affect any healthy cells. Since it does not depend on any specific antigen expression patterns, it is considered as superior immunotherapy. Some features which make it the ideal candidate for treating diverse malignancies are:

·      -They enhance the recruitment of tumour-infiltrating lymphocytes (TILs).
-Reprogramming of immunosuppressive tumour microenvironment (TME).
-Boost systemic anti-tumour immunity.

The viruses have two kinds of interactions with the immune system.

1.     Immunity as an obstacle

The immune system naturally attempts to deactivate any virus. Hence, immunosuppression by chemotherapy and inhibition of the complement system has to be done. Since antibody generation cannot be avoided, the viral vector can be coated with polyethene glycol to shield it from antibodies. The viruses can also be hidden inside macrophages, as they automatically migrate towards areas of tissue destruction and where oxygen levels are low. Such sites are characteristic of cancer growth.

2.     Immunity as an ally

The infection of the virus can attract the attention of the immune system to the tumour and can help in the generation of useful and long-lasting antitumour immunity. This can also allow the production of a personalized cancer vaccine. Some immunogenic oncolytic viruses, after infecting the tumour cells, can elicit an anti-tumour immune response. This is especially true in the case of viruses delivering cytokines or other immune-stimulating factors. Imlygic is an attenuated herpes simplex virus that has been engineered genetically to replicate preferentially within tumour cells and generate antigens that can trigger an immune response.

Genetically unmodified ECHO-7 strain enterovirus RIGVIR was the first oncolytic virus to be approved by a national regulatory agency for treating melanoma.

Using Immunotherapy for other conditions

·       Guillain-Barre syndrome is a common cause of acute neuromuscular weakness and paralysis around the world. Intravenous immunoglobulin (IVIg) and plasma exchange (PE) are methods of immunotherapy for GBS.

·       Food Allergy is a serious pathological cascade of immune responses to molecules or molecular fragments. Oral immunotherapy can be used to redirect the atopic immune responses to food allergy patients, as the patients ingest small and gradually increasing allergen doses over some months, triggering safer immune responses against these antigens.

·       Covid 19 has become a global threat and deaths keep increasing every day. An immunotherapeutic agent can be developed which targets the neutralizing epitopes in the RBD of the virus. This is called immunofocusing.         

by Shaunak Raole

https://replicoo.blogspot.com/2021/07/toll-like-receptors.html

https://replicoo.blogspot.com/2021/06/microbial-bioinformatics-game-changing.html

https://replicoo.blogspot.com/2021/07/spyder-python-install.html