These are my notes taken from the Cancer Vaccine Conference in Boston in 2003. I've been working on it from time to time; hoping to make the notes more readable and useful. Time to let it go, warts and all. ~ Karl
Background notes on cancer immunotherapy.
The goal of immunotherapy is to enable specialized immune cells to recognize and destroy cancer cells. The potential benefits of this immune activation against cancer are: (1) The activity will have high specificity - that is will have minimal impact on normal cells. (2) It can result, potentially, in long term
surveillance that might change the natural course of the disease - stabilize the disease without treatment for example. (3) It may cure some fraction of patients if it results in removing tumors that survived a previous standard treatment, or slow down the progression of same - increasing remission time (time to progression).
One promising approach to educating the immune system about cancer targets is to inject tumor antigens into or just beneath the skin. These are called cancer vaccines. The goal is not to prevent cancer, but to induce *active immunity* in order to rid the body of existing cancer cells.
active immunity is an acquired immunity in which the immune system comes to recognize an antigen as foreign and generates an attack on the invading pathogen or abnormal cell that expresses the antigen (a unique protein signature). The goal of cancer vaccines is to induce active immunity against unique proteins specific to the tumor cells.
Here the immune system "learns" about the identity of part of the tumor and "remembers" this information in order to produce a sustained attack and long-term surveillance against the cancer cells.
Tumor Targets may be Tumor Associated Antigens (TAA) or Tumor Associated Receptors (TAR)
Antigens are molecules that are recognized by the immune system as not belonging in the body (not
self). Tumor antigens are peptide sequences (fragments of proteins) that make a
tumor distinct from normal cells.
It's encouraging that the search for tumor antigens is becoming industrialized and automated, and thus more efficient.
Some types of tumor antigens:
- Differentiation antigens,
- Mutated tumor antigens,
- Over expressed antigens,
- Viral antigens
Some technologies to identify and utilize TAAs are:
- DNA chips to identify tumor-specific genes,
- Autologous cell therapy: to expand tumor infiltrating t-cells that have identified
multiple tumor antigens naturally,
- Cross priming TAAs with Dendritic cells. (Forcing the immune system to process tumor antigens)
Tumors may also express unique receptors based on normal or abnormal gene
expression. Examples of normal receptors:
- CD20, CD22, CD19 expression on mature b-cells
Potential settings for immunotherapy, such as cancer vaccines, are numerous. And as the safety profile of vaccines becomes established, the settings in which it can be tried will increase, such as:
* Frontline early stage disease - taking advantage of immune competence, and in some cases minimal disease state.
* Following treatment - taking advantage of minimal disease state; consolidating the
* During treatment - taking advantage of antigen fallout and diminishing tumor burden; consolidating the treatment response.
Idiotype as Tumor Associated Antigen (TAA):
On the surface of lymphocytes is a molecule called the idiotype. It's a receptor that's specific to an antigen (bacteria, virus, etc.) that this lymphocyte is designed to recognize and produce antibody to destroy.
The goal of Idiotype vaccine treatment is to "teach" the immune system to identify this receptor as foreign.
(NOTE: I speculate that the so-called "cancer stem cell" could not be for b-cell lymphomas, because the idiotype is an acquired normal or controlled mutation that creates a binding site for an antigen at a late stage of development of the cell. If lymphomas came from cancer stem cells, I don't see how all idiotypes could be the same in the malignant cells.)
Idiotype is a desirable target for cancer therapy because it is clonally expressed on each malignant cell. That is it has specificity. It is not highly immunogenic, however, and so the protein sequence of the idiotype is coupled with KLH in order to induce immune cells to process the idiotype proteins.
Note: The idiotype has multiple targets or epitopes - the mimimal structural unit of an antigen that are recognizable for antibodies and lymphocyte antigenic receptors.
Antigen presenting cells, such as dendritic cells, are key to the processing and education of the immune system attack. A reason to give gm-csf (Leukine) along with vaccine is to recruit antigen presenting cells to the injection site, and to help this type of cells to mature.
In summary, the goal of idiotype vaccine trick immune cells into creating anti-idiotype antibodies, which would bind only to tumor cells, which could induce cell death and attract effector cell killing in a way that Rituxan does to all mature b-cells. The idiotype vaccine may induce the body to produce antibody against the idiotype. It may also induce t-cells to attack tumor cells that express the the idiotype.
=Basic approaches to cancer vaccines:
* First identify and isolate antigens specific to the tumor,
* Deliver antigens present on tumor cells into the body in ways that induce
the immune system to recognize and attack cancer cells.
* Add adjuvants to increase immune effects and attention to tumor antigens
(Make them more immunogenic or reduce tolerance)
* Add additional therapies to offset evasion or protection tactics by cancer
cells (Agents that turn off or kill regulatory t-cells, for example.)
* Add treatments to decrease tumor burden and increase antigen fallout,
without compromising immunity. Tumor Associated Antigens in dying cells
could enhance immune response in some circumstances.
* Alter the immune profile to favor anti-cancer immune effector cell action.
An immune profile is the predominance of types of immune cells and what
they are expressing as signals. They have been categorized as Th1 and Th2, but this is probably an oversimplification. More below.
* Alter the expression of cancer cells so that they become more visible to
the immune system. For example, virally infecting b-cell lymphomas could
change how these cells look to the immune system, making them more immunogenic (capable of evoking an immune response).
Immune system components (a very brief summary)
* Dendritic cells - specialized antigen presenting cells (APCs) that engulf,
package, and then present foreign antigens to immune cells (such as CTLs) in
order to prime the immune system to attack cells that contain the antigen,
such as a cancer cell.
* Immune profile - a state in which signals (cytokines such as IL-2, IL-6,
INF, etc) may or may not favor maturation and activation of immune cell
recognition and killing of cancer cells. These profiles have been characterized as Th1 and TH2, with TH1 being generally considered the better
environment for immune action against cancer cells. One example: Only
Th1-matured dendritic cells are resistant to killing by the immune cells
(CTLs) they present antigens to. Translation: If the environment is favorable (Th1), dendritic cells can present tumor antigens to immune cells
without being killed by the immune cells. Here I imagine a cop giving the
scent of a criminal to a dog, and the dog attacking the cop because he has
NOTE: the inflammatory signals appear to be important to immune rejection of cancers. Other factors include duration of
exposure to antigens, and the presence of danger signals (such as
* Effector cells - a functional name which means those immune cells
(lymphocytes) which produce the end effect -- i.e., killing cancer cells.
Consider that immune cells are highly adaptable and will change expression
and function in response to stimulus in the host environment. Perhaps, not
unlike minute men, during the American revolutionary war, who changed from
farmers to soldiers when an alarm was sounded. Unlike minute men, activated
immune cells can also expand in number to meet a challenge, and than reduce in
number when the threat has resolved.
Note: lymphoma might be thought of as a"
disease that marks a failure of lymphocytes to turn off the expand and attack response.)
* Memory T-cells are antigen-specific CD8 T cells. The are not antigen naive. Memory t-cells are regulated by IL-15 and IL-2. The activation of these cells may be key to sustaining an immune response against tumor antigens induced by cancer vaccines.
And the immune profile also influences memory t-cell function: "This
division (of memory t-cells) requires interleukin-15 and is markedly
increased by inhibition of interleukin-2 (IL-2). Therefore, the numbers of
CD8+ memory T cells in animals are controlled by a balance between IL-15 and
IL-2." PMID: 10784451
"While naive lymphocytes appear to randomly access peripheral lymphoid
tissues during re-circulation, memory lymphocytes selectively return to the
tissues where they first were stimulated by antigen." http://www.geocities.com/artnscience/ly-traffic.html
* Humoral Immunity - One of two primary arms of the immune system that
describes B cell activity against disease. B-cells start in the bone marrow
and mature to become antibody producing cells, specific to a immune target.
For example, a cancer vaccine might induce this arm of the immune system to
produce antibodies against a tumor-specific antigen.
* Cellular Immunity - One of two primary arms of the immune system that
describes T cell activity against disease.
* Complement system - consists of inactive circulating glycoproteins that
can be sequentially activated by antigen-antibody (IgG or IgM) complexes or
bacterial products to enhance inflammation or to attack cellular membranes.
The Complement system consists of the classical and alternative pathways
that converge to activate the membrane attack complex.
* Major Histocompatibility Complex (MHC) - genes that encode (recipes) for cell surface molecules that start and regulate specific immune responses
to T-cell dependent antigens. MHC encodes cell surface protein molecules
that bind antigenic peptides, which are recognized by T cells.
You might think of MHC as a quality control and education system of the
immune system. (Not to worry, many find this area difficult to
grasp, including me.)
There are three classes of these molecules.
- MHC class I molecules are found on all nucleated somatic cells and aid in
presenting endogenously (from self) synthesized antigens
- MHC class II molecules are found principally on antigen processing/presenting cells (i.e., macrophages, B cells) and are involved in
presenting processed exogenous (outside self) protein antigens.
- MHC class III region contains a heterogeneous (varied) group of genes that
encode for some components of the complement system, heat shock proteins,
tumor necrosis factor-alpha, and tumor necrosis factor-beta.
=Role of MHC in T Cell Development:
One major job of MHC molecules is to present antigens to T cells. Lymphocytes in the thymus are exposed to various endogenous (self) proteins,
particularly the products of MHC. Some nascent T cells that have specificity
towards self MHC molecules are eliminated (negative selection), while
remaining T cells become "educated" to recognize foreign antigenic peptides
that are associated with self MHC (positive selection).
Thus, antigen recognition by T cells becomes "MHC restricted," that is, the
mature T cell recognizes its specific antigen only if that antigen is
presented by the correct MHC molecule.
Two kinds of MHC genes, class I and class II are involved in the development
of T cells. In the course of selective adaptation, T cells learn to recognize foreign antigens in association with protein products of either
MHC class I or II genes.
MHC class I-restricted T cells express CD8 molecules that bind to the
invariant portion of MHC class I, whereas MHC class II-restricted T cells
express the CD4 molecule that binds to MHC class II molecule. Thus, mature T lymphocytes leaving the thymus are either CD4+
or CD8+ (single positive) and express CD3 and TcR molecules.
* Administration of vaccine (boosters) When the primary immune response
decreases. To expand memory cells. (T-cells cycle in a week.)
What doses? How many doses of vaccines (that present tumor antigens) are optimal?
(Most expert opinion seems to be that the more vaccine the better. )
* Blocking immune negative regulation: One strategy is to overcome CTLA4
Blockade > MDX-010 - reactivation of memory immune responses. This may
depend on prior successful induction of immunity against a tumor antigen.
There is risk of autoimmune disease, but this risk might be transient.
* Anti-CD25 antibodies may help to turn off regulatory t-cell suppression
(CD25 is a marker for NHL progression)
* Cell death: which way of inducing cell death is best to induce immunity?
By necrosis or by apoptosis. (cyroablation?) (RIT?)
* Chemo and vaccines: Chemo does not eliminate memory cells. Low dose
chemo (cytoxan) being explored with vaccines. Cytoxan also seems to
selectively kill regulatory t-cells which might free the immune system
to attack residual cancer cells (theory).
Serpins may be expressed by tumor to escape immunity: Cow pox increases serpins expression in infected cells protects against CTL killing. Research is needed to find ways to downregulate serpin expression
=Expansion of CTLs: Many approaches under investigation. For example:
Isolate tumor infiltrating cells; then expand in cultures using various
cytokines. Redeliver to patients. Isolate CD8 T cells, then use in vitro
(outside the body) stimulation with peptide loaded dendritic cells.
= Isolated, MODIFY, and Expand CTLS: We already see CTLS modified to attack mature b-cells in clinical trials for lymphoma. For example, following Rituxan which binds to and kills mature b-cells, investigators can administer CTLs modified to attack cd19 cells in a one-two punch approach.
* How long do these cells persist? Is there a danger of autoimmune disease if
the tumor antigen is a receptor on normal mature b-cells? Do these cells
migrate to the right places?
=DC (dendritic cell) based vaccines: Dendritophages® (dendritic cells
issued from the patient's white blood cells) loaded in vitro with specific tumor antigens derived from cancer cell
extracts, also known as lysates. The lysates are not extracted from the
patient's own tumor cells but rather from a tumor cell line.
* Still labor intensive, expensive. Production is key.
The above points to the potential importance of culturing NHL tumor cells
lines so that perhaps, universal antigen targets for NHL can be identified
and utilized for vaccine therapies.
=Blood monocyte-derived antigen presenting cells, which have the characteristics of mature dendritic cells.
=IDM's Dendritophages® loaded in vitro with tumor antigens and then
reinjected to the patient to stimulate an immune response to a particular
disease-related antigen. Dendritophages are engineered from monocyte-derived
dendritic cells, the most powerful natural adjuvant existing today.
These are cyto-therapeutic agents - activated macrophages (immune cells)
derived from the patients own monocytes (immune cells), coupled or not with
antibodies. Goal is to eliminate tumors.
=Phase I/II For CLL: IDM-4 - MAK + monoclonal anti-CD20 antibody
Exosomes - Novel alternative to DC type. Tumor peptide-pulsed DC-derived exosomes prime
specific cytotoxic T lymphocytes
=Heat Shock Protein (HSP) - based vaccines. For NHL?
"HSPs are a family of proteins that exist within all cells. Inside the
cell, they act as "chaperones," helping newborn proteins fold into shape and
helping existing proteins survive environmental stress. HSPs are also
believed to play a role in the presentation of pieces of proteins (peptides)
on the cell surface to help the immune system recognize diseased cells.
Because HSPs are normally found inside cells, their presence outside the
cell serves a s powerful signal to the immune system that something is
wrong. Very sick cells often undergo necrosis, a messy type of cell death in
which the cell breaks open, spilling out its contents. The immune system's
dendritic cells then pick up the HSPs, which are associated with the
peptides they had been chaperoning within the cell. Once inside the dendritic cells, the peptide that is recognized as foreign - such as that
from an infected or cancerous cell - is called an antigen and has the
potential to trigger an immune response." - Antigenics literature.
Autologous HSP vaccines (from the patient) HSP -based vaccines are derived
by patient tumors removed by surgery. HSP - peptide complexes are then
extracted and purified. This vaccine product then contains normal and
abnormal peptides specific to the patients tumor and packaged in ways (in
HSP) to induce an immune response against an array of abnormal proteins
specific to the patient's tumor. The normal proteins appear to be ignored
by the immune system. To date, no autoimmune disease has been observed in
animals or humans.
Pathogen-specific HSP vaccines. This type of vaccine works like the above
but the antigen is derived from a pathogen, such as a virus, that has been
identified in the target cells. It's being investigated to treat viral
disease, but a cancer with a clonally integrated virus could potentially be
treated with this approach as well.
KLH - can you have too much?
Alternatives to injection? A patch?
Novel Immune Enhancers
DTH - test to measure general immune competence. Immuno-monitoring research and development program to precisely monitor the
effects of Cell Drugs on the patient. The patient's immune response is
tracked and evaluated during the course of treatment, as well as after
treatment is complete. This helps allow clinicians to rapidly and accurately
evaluate their patient's immune status, and modify therapy if needed to improve patient care.
Opsonokines: Novel approach.
Peptide-based vaccines (targeting viral sequences in cancers)
Viral antigens can be the basis of vaccines for cancers that are viral in
origin. The peptide-based vaccine for refractory HCV-associated cervical
cancer. This cancer is caused by the virus and is clonally integrated in all
malignant cells for this cancer. The work is being done at Tufts University,
but it's not associated with a commercial body, (or disclosed) as far as I
With this study they co-culture recombinant HPV protein (viral protein) with
human HLA-A*0201 dendritic cells to induce CTL against cancer cells containing the virus. They had a least one dramatic recovery of a patient,
but most patients have not benefited much. But, in each case the patients
had advanced and aggressive disease at the beginning of treatment.
I believe that this approach could apply to any cancer that clonally integrates a particular virus, be it EBV, or SV40. A difference
would be in the peptide sequence used (the protein specific to the virus).
The approach for cervical cancer also requires "priori knowledge of the
peptides specific for each HLA phenotype." I'm still struggling to understand what this means.
Snap freezing of tumor cells at biopsies must be made routine. Patients can
advance the science and their chances of benefiting from emerging therapies
by asking for this.