Cancer immunotherapy

History

Immunotherapy began in 1796 when Edward Jenner produced the first vaccine involving immunisation with cowpox to prevent smallpox. Towards the end of the 19th century Emil von Behring and Shibasaburō Kitasato discovered that injecting animals with diphtheria toxin produced blood serum with antitoxins to it.

Paul Ehrlich's research gave rise to the "magic bullet" concept; using antibodies to specifically target a disease. The production of pure monoclonal antibodies for therapeutic use became available in 1975 when Georges J. F. Köhler and Cesar Milstein produced hybridoma technology.

Immune cell therapy for cancer was introduced by Steven Rosenberg and colleagues. In the late 1980s, they reported a low tumor regression rate (2.6–3.3%) in 1205 patients with metastatic cancer who underwent different types of active specific immunotherapy.

In 1987, researchers identified cytotoxic T-lymphocyte antigen 4, or CTLA-4. Allison found that CTLA-4 prevents T cells from attacking tumor cells. He wondered whether blocking CTLA-4 would allow the immune system to make those attacks. In 1996, Allison showed that antibodies against CTLA-4 allowed the immune system to destroy tumors in mice. In 1999, biotech firm Medarex acquired rights to the antibody. In 2010, Bristol-Myers Squibb, who acquired Medarex in 2009, reported that patients with metastatic melanoma lived an average of 10 months on the antibody, versus 6 months without it. It was the first time any treatment had extended life in advanced melanoma in a randomized trial.

In the early 1990s, a biologist discovered a molecule expressed in dying T cells, which he called programmed death 1, or PD-1 and which he recognized as another disabler of T cells. An antibody that targeted PD-1 was developed and by 2008 produced remission in multiple subjects across multiple cancer types. In 2013, clinicians reported that across 300 patients tumors shrunk by about half or more in 31% of those with melanoma, 29% with kidney cancer and 17% with lung cancer.

In 1997 rituximab, the first antibody treatment for cancer, was approved by the FDA for treatment of follicular lymphoma. Since this approval, 11 other antibodies have been approved for cancer; alemtuzumab (2001), ofatumumab (2009) and ipilimumab (2011).

In 2003 cytokines such as interleukin were administered. The adverse effects of intravenously administered cytokines led to the extraction, in vitro expansion against a tumour antigen and reinjection of the cells with appropriate stimulatory cytokines.

However, with both anti–CTLA-4 and anti–PD-1, some tumors continued to grow before vanishing months later. Some patients kept responding after the antibody had been discontinued. Some patients, developed side effects including inflammation of the colon or of the pituitary gland.

The first cell-based immunotherapy cancer vaccine, sipuleucel-T, was approved in 2010 for the treatment of prostate cancer.

After success harvesting T cells from tumors, expanding them in the lab and reinfusing them into patients reduced tumors, in 2010, Steven Rosenberg announced chimeric antigen receptor therapy, or CAR therapy. This technique is a personalized treatment that involves genetically modifying each patient's T cells to target tumor cells. It produced complete remission in a majority of leukemia patients, although some later relapsed.

By mid 2016 the FDA had approved one PD-L1 inhibitor (atezolizumab) and two PD-1 inhibitors (nivolumab and pembrolizumab).

Dendritic cell therapy

Dendritic cell therapy provokes anti-tumor responses by causing dendritic cells to present tumor antigens to lymphocytes, which activates them, priming them to kill other cells that present the antigen. Dendritic cells are components of the immune system called antigen presenting cells (APCs). In cancer treatment they aid cancer antigen targeting. The only approved cellular cancer therapy is sipuleucel-T.

One method of inducing dendritic cells to present tumor antigens is by vaccination with autologous tumor lysates or short peptides (small parts of protein that correspond to the protein antigens on cancer cells). These peptides are often given in combination with adjuvants (highly immunogenic substances) to increase the immune and anti-tumor responses. Other adjuvants include proteins or other chemicals that attract and/or activate dendritic cells, such as granulocyte macrophage colony-stimulating factor (GM-CSF).

Dendritic cells can also be activated in vivo by making tumour cells express GM-CSF. This can be achieved by either genetically engineering tumor cells to produce GM-CSF or by infecting tumor cells with an oncolytic virus that expresses GM-CSF.

Another strategy is to remove dendritic cells from the blood of a patient and activate them outside the body. The dendritic cells are activated in the presence of tumor antigens, which may be a single tumor-specific peptide/protein or a tumor cell lysate (a solution of broken down tumor cells). These cells (with optional adjuvants) are infused and provoke an immune response.

Dendritic cell therapies include the use of antibodies that bind to receptors on the surface of dendritic cells. Antigens can be added to the antibody and can induce the dendritic cells to mature and provide immunity to the tumor. Dendritic cell receptors such as TLR3, TLR7, TLR8 or CD40 have been used as antibody targets.

Sipuleucel-T

Sipuleucel-T (Provenge) is the only approved cancer vaccine. It was approved for treatment of asymptomatic or minimally symptomatic metastatic castrate-resistant prostate cancer in 2010. The treatment consists of removal of antigen-presenting cells from blood by leukapheresis and growing them with the fusion protein PA2024 made from GM-CSF and prostate-specific prostatic acid phosphatase (PAP) and reinfused. This process is repeated three times.

Antibody therapy

Antibodies are a key component of the adaptive immune response, playing a central role in both recognizing foreign antigens and stimulating an immune response. Many immunotherapeutic regimens involve antibodies. Monoclonal antibody technology raises antibodies against specific antigens, such as those present on tumor surfaces.

Conjugation

Two types are used in cancer treatments:

Human/non-human balance

Antibodies are also referred to as murine, chimeric, humanized and human. Murine antibodies are from a different species and carry a risk of immune reaction. Chimeric antibodies attempt to reduce murine antibodies' immunogenicity by replacing part of the antibody with the corresponding human counterpart, known as the constant region. Humanized antibodies are almost completely human; only the complementarity determining regions of the variable regions are derived from murine sources. Human antibodies have completely human DNA.

Antibody-dependent cell-mediated cytotoxicity (ADCC)

Antibody-dependent cell-mediated cytotoxicity (ADCC) requires antibodies to bind to target cell surfaces. Antibodies are formed of a binding region (Fab) and the Fc region that can be detected by immune system cells via their Fc surface receptors. Fc receptors are found on many immune system cells, including natural killer cells. When natural killer cells encounter antibody-coated cells, the latter's Fc regions interact with their Fc receptors, releasing perforin and granzyme B to kill the tumor cell. Examples include Rituximab, Ofatumumab and Alemtuzumab. Antibodies under development have altered Fc regions that have higher affinity for a specific type of Fc receptor, FcγRIIIA, which can dramatically increase effectiveness.

Complement

The complement system includes blood proteins that can cause cell death after an antibody binds to the cell surface (the classical complement pathway, among the ways of complement activation). Generally the system deals with foreign pathogens, but can be activated with therapeutic antibodies in cancer. The system can be triggered if the antibody is chimeric, humanized or human; as long as it contains the IgG1 Fc region. Complement can lead to cell death by activation of the membrane attack complex, known as complement-dependent cytotoxicity; enhancement of antibody-dependent cell-mediated cytotoxicity; and CR3-dependent cellular cytotoxicity. Complement-dependent cytotoxicity occurs when antibodies bind to the cancer cell surface, the C1 complex binds to these antibodies and subsequently protein pores are formed in the cancer cell membrane.

Alemtuzumab

Alemtuzumab (Campeth-1H) is an anti-CD52 humanized IgG1 monoclonal antibody indicated for the treatment of fludarabine-refractory chronic lymphocytic leukemia (CLL), cutaneous T-cell lymphoma, peripheral T-cell lymphoma and T-cell prolymphocytic leukemia. CD52 is found on >95% of peripheral blood lymphocytes (both T-cells and B-cells) and monocytes, but its function in lymphocytes is unknown. It binds to CD52 and initiates its cytotoxic effect by complement fixation and ADCC mechanisms. Due to the antibody target (cells of the immune system) common complications of alemtuzumab therapy are infection, toxicity and myelosuppression.

Ipilimumab

Ipilimumab (Yervoy) is a human IgG1 antibody that binds the surface protein CTLA4. In normal physiology T-cells are activated by two signals: the T-cell receptor binding to an antigen-MHC complex and T-cell surface receptor CD28 binding to CD80 or CD86 proteins. CTLA4 binds to CD80 or CD86, preventing the binding of CD28 to these surface proteins and therefore negatively regulates the activation of T-cells.

Active cytotoxic T-cells are required for the immune system to attack melanoma cells. Normally inhibited active melanoma-specific cytotoxic T-cells can produce an effective anti-tumor response. Ipilumumab can cause a shift in the ratio of regulatory T-cells to cytotoxic T-cells to increase the anti-tumor response. Regulatory T-cells inhibit other T-cells, which may benefit the tumor.

Ofatumumab

Ofatumumab is a second generation human IgG1 antibody that binds to CD20. It is used in the treatment of chronic lymphocytic leukemia (CLL) because the cancerous cells of CLL are usually CD20-expressing B-cells. Unlike rituximab, which binds to a large loop of the CD20 protein, ofatumumab binds to a separate, small loop. This may explain their different characteristics. Compared to rituximab, ofatumumab induces complement-dependent cytotoxicity at a lower dose with less immunogenicity.

Rituximab

Rituximab is a chimeric monoclonal IgG1 antibody specific for CD20, developed from its parent antibody Ibritumomab. As with ibritumomab, rituximab targets CD20, making it effective in treating certain B-cell malignancies. These include aggressive and indolent lymphomas such as diffuse large B-cell lymphoma and follicular lymphoma and leukaemias such as B-cell chronic lymphocytic leukaemia. Although the function of CD20 is relatively unknown, CD20 may be a calcium channel involved in B-cell activation. The antibody's mode of action is primarily through the induction of ADCC and complement-mediated cytotoxicity. Other mechanisms include apoptosis and cellular growth arrest. Rituximab also increases the sensitivity of cancerous B-cells to chemotherapy.

Cytokine therapy

Cytokines are proteins produced by many types of cells present within a tumor. They can modulate immune responses. The tumor often employs them to allow it to grow and reduce the immune response. These immune-modulating effects allow them to be used as drugs to provoke an immune response. Two commonly used cytokines are interferons and interleukins.

Interferon

Interferons are produced by the immune system. They are usually involved in anti-viral response, but also have use for cancer. The fall in three groups: type I (IFNα and IFNβ), type II (IFNγ) and type III (IFNλ). IFNα has been approved for use in hairy-cell leukaemia, AIDS-related Kaposi's sarcoma, follicular lymphoma, chronic myeloid leukaemia and melanoma. Type I and II IFNs have been researched extensively and although both types promote anti-tumor immune system effects, only type I IFNs have been shown to be clinically effective. IFNλ shows promise for its anti-tumor effects in animal models.

Unlike type I IFNs, Interferon gamma is not approved yet for the treatment of any cancer.However, improved survival was observed when Interferon gamma was administrated to patients with bladder carcinoma and melanoma cancers. The most promising result was achieved in patients with stage 2 and 3 of ovarian carcinoma.The in vitro study of IFN-gamma in cancer cells is more extensive and results indicate anti-proliferative activity of IFN-gamma leading to the growth inhibition or cell death, generally induced by apoptosis but sometimes by autophagy.

Interleukin

Interleukins have an array of immune system effects. Interleukin-2 is used in the treatment of malignant melanoma and renal cell carcinoma. In normal physiology it promotes both effector T cells and T-regulatory cells, but its exact mechanism of action is unknown.

Polysaccharide-K

Japan's Ministry of Health, Labour and Welfare approved the use of polysaccharide-K extracted from the mushroom, Coriolus versicolor, in the 1980s, to stimulate the immune systems of patients undergoing chemotherapy. It is a dietary supplement in the US and other jurisdictions.

Adoptive T-cell therapy

Adoptive T-cell therapy is a form of passive immunization by the transfusion of T-cells (adoptive cell transfer). They are found in blood and tissue and usually activate when they find foreign pathogens. Specifically they activate when the T-cell's surface receptors encounter cells that display parts of foreign proteins on their surface antigens. These can be either infected cells, or antigen presenting cells (APCs). They are found in normal tissue and in tumor tissue, where they are known as tumor infiltrating lymphocytes (TILs). They are activated by the presence of APCs such as dendritic cells that present tumor antigens. Although these cells can attack the tumor, the environment within the tumor is highly immunosuppressive, preventing immune-mediated tumour death.

Multiple ways of producing and obtaining tumour targeted T-cells have been developed. T-cells specific to a tumor antigen can be removed from a tumor sample (TILs) or filtered from blood. Subsequent activation and culturing is performed ex vivo, with the results reinfused. Activation can take place through gene therapy, or by exposing the T cells to tumor antigens. Although research has made major advances in this form of therapy, no adoptive T-cell therapy is as yet approved.

As of 2014, multiple ACT clinical trials were underway.

Another approach is adoptive transfer of haploidentical γδ T cells or NK cells from a healthy donor. The major advantage of this approach is that these cells do not cause GVHD. The disadvantage is frequently impaired function of the transferred cells.

Anti-CD47 antibodies

Anti-CD47 antibodies, which block the protein CD47 from telling the cancer host's immune system not to attack it, have been shown to eliminate or inhibit the growth of multiple cancers and tumors in laboratory tests on cells and mice. CD47 is present on many cancer cells and on many healthy cells. After the cancer cells have been engulfed by macrophages, the host immune system's CD8+ T Cells become mobilized against the tumor and attack it. Another alternative to Anti-CD47 is to use Polypurine reverse Hoogsteen oligonucleotides (PPRHs), a silencing tool formed by DNA hairpins, as shown in MCF-7 breast cancer cells.

Anti-GD2 antibodies

Carbohydrate antigens on the surface of cells can be used as targets for immunotherapy. GD2 is a ganglioside found on the surface of many types of cancer cell including neuroblastoma, retinoblastoma, melanoma, small cell lung cancer, brain tumors, osteosarcoma, rhabdomyosarcoma, Ewing’s sarcoma, liposarcoma, fibrosarcoma, leiomyosarcoma and other soft tissue sarcomas. It is not usually expressed on the surface of normal tissues, making it a good target for immunotherapy. As of 2014, clinical trials were underway.

Immune checkpoints

Immune checkpoints affect immune system functioning. Immune checkpoints can be stimulatory or inhibitory. Tumors can use these checkpoints to protect themselves from immune system attacks. Checkpoint therapy can block inhibitory checkpoints, restoring immune system function. One ligand-receptor interaction under investigation is the interaction between the transmembrane programmed cell death 1 protein (PDCD1, PD-1; also known as CD279) and its ligand, PD-1 ligand 1 (PD-L1, CD274). PD-L1 on the cell surface binds to PD1 on an immune cell surface, which inhibits immune cell activity. Among PD-L1 functions is a key regulatory role on T cell activities. It appears that (cancer-mediated) upregulation of PD-L1 on the cell surface may inhibit T cells that might otherwise attack. Antibodies that bind to either PD-1 or PD-L1 and therefore block the interaction may allow the T-cells to attack the tumor.

CTLA-4 blockade

The first checkpoint antibody approved by the FDA was ipilimumab, approved in 2011 for treatment of melanoma. It blocks the immune checkpoint molecule CTLA-4. Clinical trials have also shown some benefits of anti-CTLA-4 therapy on lung cancer or pancreatic cancer, specifically in combination with other drugs. In on-going trials the combination of CTLA-4 blockade with PD-1 or PD-L1 inhibitors is tested on different types of cancer.

However, patients treated with check-point blockade (specifically CTLA-4 blocking antibodies), or a combination of check-point blocking antibodies, are at high risk of suffering from immune-related adverse events such as dermatologic, gastrointestinal, endocrine, or hepatic autoimmune reactions. These are most likely due to the breadth of the induced T-cell activation when anti-CTLA-4 antibodies are administered by injection in the blood stream.

Using a mouse model of bladder cancer, researchers have found that a local injection of a low dose anti-CTLA-4 in the tumour area had the same tumour inhibiting capacity as when the antibody was delivered in the blood. At the same time the levels of circulating antibodies were lower, suggesting that local administration of the anti-CTLA-4 therapy might result in fewer adverse events.

PD-1 inhibitors

Initial clinical trial results with IgG4 PD1 antibody Nivolumab were published in 2010. It was approved in 2014. Nivolumab is approved to treat melanoma, lung cancer, kidney cancer and Hodgkin's lymphoma. A 2016 clinical trial for non-small cell lung cancer failed to meet its primary endpoint.

Pembrolizumab is another PD1 inhibitor that was approved by the FDA in 2014. Keytruda (Pembrolizumab) is approved to treat melanoma and lung cancer.

Antibody BGB-A317 is a PD-1 inhibitor (designed to not bind Fc gamma receptor I) in early clinical trials.

PD-L1 inhibitors

In May 2016, PD-L1 inhibitor atezolizumab was approved for treating bladder cancer.

Anti-PD-L1 antibodies currently in development include avelumab and durvalumab, in addition to an affimer biotherapeutic.

Other

Other modes of enhancing [adoptive] immuno-therapy include targeting so-called intrinsic checkpoint blockades e.g. CISH.

Polysaccharides

Certain compounds found in mushrooms, primarily polysaccharides, can up-regulate the immune system and may have anti-cancer properties. For example, beta-glucans such as lentinan have been shown in laboratory studies to stimulate macrophage, NK cells, T cells and immune system cytokines and have been investigated in clinical trials as immunologic adjuvants.

Agaricus subrufescens, (often mistakenly called Agaricus blazei), Lentinula edodes (shitake mushroom), Grifola frondosa and Hericium erinaceus are fungi that produce beta-glucans and have been tested for anti-cancer potential.

Neoantigens

Many tumors express mutations. These mutations potentially create new targetable antigens (neoantigens) for use in T cell immunotherapy. The presence of CD8+ T cells in cancer lesions, as identified using RNA sequencing data, is higher in tumors with a high mutational burden. The level of transcripts associated with cytolytic activity of natural killer cells and T cells positively correlates with mutational load in many human tumors. In non–small cell lung cancer patients treated with lambrolizumab, mutational load shows a strong correlation with clinical response. In melanoma patients treated with ipilimumab, long-term benefit is also associated with a higher mutational load, although less significantly. The predicted MHC binding neoantigens in patients with a long-term clinical benefit were enriched for a series of tetrapeptide motifs that were not found in tumors of patients with no or minimal clinical benefit. However, human neoantigens identified in other studies do not show the bias toward tetrapeptide signatures.