Cancer Immunotherapy.

CANCER IMMUNOTHERAPY
Amaylia Oehadian
Hematology and Medical Oncology Division , Department of Internal Medicine
Hasan Sadikin Hospital Bandung
The realization that human cancers express cancer-associated antigens has stimulated
research into the development of immunotherapies to mediate the regression of tumor.1
Cancer immunotherapy or biological therapy refers to antitumor treatment utilizing the
actions of natural host-defense mechanisms and/or mammalian-derived substances.2
Research during the past decade has establish immunotherapy as an important anticancer
modality. In fact, tumor immunology is now one of the most active areas of cancer
research and has prompted the development of several novel therapies currently in use,
including cytokine-based therapies, vaccine therapies, and monoclonal antibody therapies.
Understanding the scientific rationale behind tumor immunology will better inform
practitioners about immunotherapies that are currently available or being studied in
ongoing trial.3
This paper will provide a review of immune dysregulation on oncogenesis, followed by
an overview of immunotherapy strategies in cancer.

IMMUNE DYSREGULATION IN ONCOGENESIS
Cancer is 100 times more likely to occur in immunosupressed individuals than those with
normal immune function. Conversely, heightened immune activity has been postulated as

the potential cause of spontaneous tumor regression. On the other hand, development of
some tumors is actually associated with chronic imflammation, such as mucosalassociated lymphoid tumor and immunoproliferative small intestinal disease.3
The first recognition that immune system plays an important role in oncogenesis dated
back to the 1700s, when it was observed that certain cancer patients who acquired and
cleared bacterial infections also experienced remission of their malignancy. In the late
1800s, Dr. Willian B Coley made similar observations about cancer and immune
regulation, ultimately leading to the development and use of early forms of cancer
immunotherapy. Coley noted that some patients with sarcomas had spontaneous tumor
regressions following a bout of erysipelas, a superficial streptococcal skin infection.
Coley deliberately infected some of his inoperable patients with erysipelas to stimulate
tumor regression. He later refined this approach by using heat-killed Streptococcus
pyogenes in combination with heat-killed Serratia marcescens- a mixture that is now
commonly known as “Coley’s toxin”. 2,3
Immune surveillance
The initial findings regarding rejection of transplanted tumors in mice were used to
bolster support for the principle of immune surveillance, originally described in 1956 by
Burnet and Thomas. The concept of immune surveillance postulates that immune system
regularly monitor cells in the body, looking for abnormal antigens expressed by cancer

cells.3 The immune system’s identification of such antigens leads to destruction of the

emergent cancer clone. The immune surveillance principle is supported by 2 primary
lines of clinical evidence :
 The presence of tumor-infiltrating lymphocytes (TILs) within some established
tumors.3
 The increased incidence of several cancers with immunosuprressant therapy.3
Immunoediting : elimination, equilibrium and escape phases of oncogenesis
Recent research has shed additional light on the process of immune surveillance in
oncogenesis. Immunoediting appears to be an important part of this process and consists
of 3 distinct phases : elimination, equilibrium and escape. (Figure 1).3

Figure 1. Immunoediting : elimination, equilibrium, escape.3
BM : bone marrow; iDC : immature dendritic cell; Mj: macrophage, SLN : sentinel lymph node ;
TAM : tumor associated antigens ; TDSFs : tumor derived soluble factors ; TE : effector T cell ;
TiDC : tumor- associated iDC ; Tregs : regulatory T cells.



Elimination phase
The elimination phase of immunoediting relies on the basic principles put forth by
the classic immune surveillance theory, which is that the immune system seeks

out and destroys cells bearing cancer-associated antigens to prevent out growth of
the malignant clone. The elimination of tumor cells involves both innate as well
as adaptive immunity.3

With respect to innate immunity, inflammatory cytokines initially released by
growing tumor cells, macrophages , and stromal cells in the tumor
microenvirontment are recognized by a number of innate immune cells, including
NK cells, NK1.1+ T cells, and  T cells, which in turn produce interferon gamma.
Interferon gamma promotes the kiliing of tumor cells through its effects on
proliferation, angiogenesis and apoptosis. Release of interferon gamma and
interleukin (IL)-12 by both tumor-infiltrating NK cells and macrophages leads to
additional cell killing through activation of cytotoxic mechanisms involving
perforin, tumor necrosis factor-related apoptosis-inducing ligand, as well as
reactive oxygen species.3
Infiltrating dendritics cells, recruited to tumor-draining lymph nodes by NK cells,
can phagocytose necrotic tumor cells, resulting in the presentation of tumorassociated antigens and the priming of naïve T cells. Bringin g in adaptive
immunity processes, antigen-specific cytotoxic CD4+ and CD8+ T lymphocytes
subsequently migrate to the site of the tumor where they identify and kill tumor
cells, producing additional interferon gamma and other cytokines that further
enhance tumor cell killing.3



Equilibrium phase
Selection pressure produced by the immune system actually promotes the
establishment of less immunogenic tumor variants within the tumor
microenvironment. Because the mutation rate of tumor cells is extremely high,
genetic changes can develop that permit these cells to acquire resistance to
previously establish immune effector cells, thereby enabling them to evade
elimination by the immune system. The equilibrium phases of immunoediting is
characterized by the persistence of tumor cell population. Given that highly
immunogenetic tumor cells are continuously eliminated while resistant tumor
cells are spontaneously generated and gradually maintained, it has been
hypothesized that the equilibrium phase is likely the longest of the 3
immunoediting phases, evolving over the span of several years.3



Escape phase
The escape phase represents the point at which cancer cells are no longer
sufficiently recognized and/or controlled by the immune system to prevent disease

progression. Tumor escape can be achieved through several mechanisms,
including downregulation of various immunoregulatory components :
- Tumor-derived soluble factors
Vascular endothelial growth factor (VEGF) and IL-1-beta alter the tumor
microenvirontment and promotes disease progression. VEGF can block
activation of nuclear facto r-kappa B in hematopoietic cells, thereby
preventing the differentiation and maturation of antigen-presenting
dendritic cells. Tumor cells can also acquire mutations that enable them to
produce high levels of IL-10 and transforming growth factor-beta, wich
further suppress the activity of dendritic cells and T cells.3

-

Alterations in signal transduction
The CD3-zeta chain functions as an important transmembrane signaling
molecule in TILs. Down regulation of zeta chain expression has been
associated with increased levels of IL-10 and transforming growth factorbeta and decreased levels of interferon gamma. Low or absence zeta chain
expression in immune cells impairs the function of TILs and hence
predicts for poor prognosis and unfavorable survival outcomes in cancer
patients.3

-

Immunologic tolerance
In some cases, antigen-expressing tumor cells are ignored by the immune
system because the antigens are masked by surrounding nontumor cells
(eg, immature dendritic cells, fibroblast, endothelial cells) that compete
with mature dendritic cells for antigen binding. As such, these depressed
levels of tumor antigen are not sufficient to produce or sustain a clinically
meaningful cytotoxic T-cell response. As a result, these antigen-presenting
tumors cells are largely ignored by surveillance T cells. Immature
dendritic cells are also capable of stimulating regulatory cells (eg, CD4+
and CD25+ cells), which suppress T-cell activation and further contribute
to immunologic tolerance.3

CURRENT IMMUNOTHERAPY STRATEGIES
Current clinical investigation is being directed at stimulating the immune system via
cytokines, antibodies, and vaccines to improve tumor recognition, thereby allowing an
individual to mount an immune response that can effectively eradicate tumors. It is
important to distinguish between cytokine , antibody , and vaccine therapies :

 The goal of vaccine therapy is to stimulate active antitumor immunity by priming
or expanding immune responses, which can recognize and destroy tumor cells.3
 Cytokines and antibody therapies work indirectly by supplying the necessary tools
directly to effectuate and antitumor response.3
The two main approaches to immunotherapy for cancer are vaccine therapy and celltransfer therapy.1 ( Figure 2)
There are three requirements for an effective immunotherapy for cancer (Figure 2) :
 A sufficient number of avid tumor-reactive lymphocytes must be present in the
tumor bearing host.1
 These lymphocyte must be capable of reaching and extravasating at the site of the
cancer.1
 The lymphocytes at the tumor site must have appropriate effector mechanisms to
destroy cancer cells.1

Figure 2. Two approach in immunotherapy.1

1. Cytokines-based therapies
Cytokines are small signaling molecules essential to mediating immune responses. A
handful of cytokines are currently approved for cancer treatment, the most common of
which are interferon alfa and IL-2 .3,4


Interferon alfa
Interferon alfa was first isolated on 1970 from white blood cells in a search for
agent that interfere with viral infection-hence its name.3 Interferon alfa functions
on a number of levels including :
- upregulation of genes encoding for the major histocompatibility complex
class I molecules, tumor antigens , and adhesion molecules.3
- Promotes the activity of B cells, T cells , macrophages and dendritic cells
- Increases the expression of Fc receptors.3
Interferon alfa is currently used for the treatment of malignant melanoma,
follicular lymphoma, hairy-cell leukemia, Philadephia-positive chronic
myelogenous leukemia, condyloma acuminate, and AIDS-related Kaposi’s
sarcoma.3



Interleukin-2
Interleukin-2, a T-cell growth factor, is currently approved for the treatment of
renal cell carcinoma and malignant melanoma. In metastatic renal cell cancer,
response rates approaching 23% have been reported, and these responses have

been durable for up to 24 months.3



Sargramostim
Sargramostim , a recombinant human granulocyte macrophage–colony
stimulating factor (rhGM—CSF) has been shown to induce the differentiaion of
myeloid dendritic cells that promote the development of T-helper type 1 (cellular)
immune responses. Sargramostim has been used to augment the activity of
rituximab in patients with follicular lymphoma and to induce autologous
antitumor immunity in patients with hormone-refractory prostate cancer. The
addition of sargramostim to standard vaccines may increase effectiveness by
recruiting dendritic cells to the site of vaccination.5

2. Monoclonal antibody therapies
Since their initial clinical development in the late 1970s, monoclonal antibodies directed
against antigens expressed on cancer cells have proven to be one of the most promising
classes of immunomodulatory agents. Monoclonal antibodies function by :
 Directly disrupting cancer cell activity through their affinity for relevant
antigens.4,6

 Enhancing the immune response againts cancer cell through antibody-dependent
cell-mediated or complement-dependent cytotoxicity.4,6
To enhance the efficacy of these agents, some investigators have developed strategies
in which cytotoxic therapy is delivered directly to tumor cells via tumor-antigenspecific antibodies linked to toxins (eg, gemtuzumab ozogamicin) or radioisotopes
(eg, tositumomab-I 131, ibritumomab tiuxetan).3

To date, a total of 9 monoclonal antibodies have been approved for a variety of
therapeutic indications (table 1)
Table 1. Currently approved monoclonal antibody therapies for cancer.3
Drug

Target

Type

Type of cancer

Year of
FDA
approval

1997

Rituximab

CD20

Chimeric

Non-Hodgkin’s lymphoma

Traztuzumab

ErbB2/HER2

Humanized

Breast cancer

1998

Gemtuzumab
ozogamicin

CD33

Humanized

Acute myeloid leukemia

2000

Alemtuzumab

CD52

Humanized

Chronic lymphocytic
leukemia

2001

Ibritumomab
tiuxetan

CD20

Murine,
radiolabeled
with ytrium 90

Non-hodgkin lymphoma

2003

TositumomabI131

CD20

Murine,
radiolabeled
with iodine 131

Non-hodgkin lymphoma

2004

Cetuximab

EGFR

Chimeric

Colorectal ca, head and
neck ca

2004

Bevacizumab

VEGF

Humanized

Colorectal ca, non-smallcell lung ca

2004

Panitumomab

EGFR

Human

Colorectal cancer

2005

EGFR : epidermal growth factor receptor; HER2 : human epidermal growth factor receptor-2;
VEGF : vascular endothelial growth factor

Cytotoxic T lymphocyte antigen 4 (CTLA-4)
CD4+ T cells play key role in the adaptive immune response to foreign antigens. T cell
activation depends on a 2-step signaling process :
 The first signal is delivered through antigen recognition by the T-cell receptor.3
 A second or costimulatory signal is also required for optimal activation of T cells.
CD28 ligation by B7 is a potent mediator of positive costimulation. By contrast,
B7 ligation of CTLA-4, a homolog of CD28, acts as a critical for many immune
responses.3
CTLA-4 , a key negative regulator of T-cell responses, can restrict the antitumor immune
response.7

Because costimulatory molecule interactions are critical for many immune responses, a
greater understanding of CTLA-4 function may promise development of
immunotherapies where enhancement or inhibition of the immune responses is clinically
beneficial. Monoclonal antibodies that exert their antitumor effects indirectly via the
immune system are currently being investigated in clinical trial. As of June 2007, there
are 2 fully human anti-CTLA-4 monoclonal antibodies in advanced clinical trials :
tremelimubab and ipilimumab.3,7
Ipilimumab (MDX-101) is a fully human monoclonal antibody, that overcomes CTLA-4mediated T-cell suppression to enhance the immune response against tumors.7 Preclinical
and early clinical studies of patients with advanced melanoma show that ipilimimab
promotes antitumor activity as monotherapy and in combination with treatments such as
chemotherapy, vaccines, or cytokines.3,7
3. Vaccine therapies
In cancer therapy, potential use of vaccine include passive or adoptive immunotherapy
and active specific immunotherapy. With passive immunotherapy, the goal is to enhance
and/or stimulate the immune system using exogenous cytokines, antibodies, immune cells,
or growth factors. With active specific immunotherapy, a specific tumor-associated
antigen elicits and endogenous immune or antitumor response.6
The goal of therapeutic vaccines in the treatment of cancer is to prime and expand the
host’s immune system to identify and destroy tumor cells. Over the past few decades,
many clinical trials have tested a variety of cancer vaccines. Although the number of
patients achieving objective responses has been small, these studies have always
identified a consistent subgroup of patients who achieve significant clinical benefit from
such therapies.3 The variety of vaccine approaches has included :
 Antigen peptides to known major histocompatibility complex motifs.3
 Viral vectors.3
 Whole cell vaccines.3
 Dendritic cell caccines.3
 Anti-idiotype vaccine.3
Despite encouraging phase I and II study results, no therapeutic cancer vaccine has been
approved by FDA. Only a few therapeutic vaccine strategies have progressed to phase III
testing.3


Viral vectors vaccine
Viral vectors vaccines are created by cloning the genes encoding tumor antigens
into vector backbones derived from poxviruses or adenoviruses.3 A list of
antigens that have served as targets for viral vector vaccines is given in table 2.

Table 2. Tumor antigens targeted by viral vector vaccines.3
Carcinoma-associated antigens
 Carcinoembryonic antigen
 Prostate-specific antigen
 Mucin-1
 Prostatic acid phosphatase
Melanoma-associated antigens
 Melanoma antigen gene family
 Melanoma antigen recognized by T cells
Viral antigen
 Human papillomavirus

The concept of using replication viruses as anticancer agents is not a new one, but
the ability to genetically modifiy this viruses into increasingly potent and tumorspecific vectors is a recent phenomenon. The paradoxical roles of the immune
response are addressed with respect to oncolytic viral therapy, as it, on one hand,
impedes the spread of viral infection, and on the other, augment tumor cell
destruction through the recruitment of T cells “vaccinated” against tumor antigen.
The most commonly used oncolytic viruses are adenoviruses, herpes simplex
viruses, vaccinia viruses, reovirus and Newcastle disease viruses.8 Oncolytic
viruses mediate the destruction of tumor cells by several potential mechanisms
(table 3)
Table 3. Mechanism of antitumoral efficacy of oncolytic viruses.8
Mechanism
Direct cell lysis due to viral replication

Example
Adenoviruses
Herpesviruses

Direct cytotoxicity of viral protein

Adenovirus E4ORF4

Induction of antitumoral immunity
 Nonspecific (eg. TNF)
 Specific (eg. CTL response)

Adenovirus (EIA)
Herpes simpleks virus

Sensitization to chemotherapy and radiotherapy

Adenovirus (EIA)

Transgene expression
Adenovitus (AdTK RC)
Herpes simpleks virus (rRp450)
Vaccinia virus (GM-CSF)



Dendritic cell vaccines
Dendritic cell vaccines are one of the most prominent vaccine strategies being
tested for stimulating a tumor-specific immune response. These vaccines are
typically created by culturing the patient’s own dendritic cells in the presence of
tumor peptides and immunogenic adjuvants. Several dendritic vaccine strategies
have focused on treating individuals with metastatic melanoma.3

Conclusions
Immunoediting appears to be an important part of immune surveilance in oncogenesis
and consists of 3 distinct phase : elimination, equilibrium and escape. Anticancer
immune therapies consist of cytokines, monoclonal antibodies and vaccines. The best
use of these agents may involve combination therapies with multiple immunologically
active agents as well as other treatment modalities including chemotherapy or radiation
therapy. In this way, immune therapies may be better able to identify and eradicate tumor
cells through the induction of programmed cell death as well as by disrupting the tumor
microenvirontment and halting angiogenesis while maintaining and stimulating antitumor
immune acitivity.
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