Vaccines and other positive things

•Vaccine design• Current vaccines• Developing new approaches

•Cancer vaccines• Possible role of the immune system in

suppressing cancer• Ways being explored to target immunity to

tumors

Parham Chapter 12

• Attenuated organism: live, but non-pathogenicGive good CD8 T cell responses because they lead to intracellular protein synthesis. Some risk of reversion or pathogenesis in immunodeficient people.

• Killed whole organism: heat, chemical fixation. Does not elicit as good CD8 response. Inactivated whole bacteria can cause unwanted inflammation.

• Vectored vaccines: putting new genes in attenuated organism (such as vaccinia)Still experimental, but works well in animals. Safety concerns.

• Subunit vaccine: specific protein of microorganism Safe, can be effective. Problems of poor CD8 responses and low natural adjuvancy.

• Conjugate: Specific portion of microorganism (Often carbohydrate) linked to carrier protein. This is the basis of recent vaccines for infants for Haemophilus influenzae (bacterial menigitis) and pneumococci.

• DNA vaccines: introduce plasmid DNA directly into host cells.Relatively cheap, specific, and targets CD8 cells. Technical problem of getting DNA into host cells (Gene gun). Some safety concerns. Activates Tlr9.

• Modern adjuvants (Tlr agonists), cytokinesCpG DNA (TLR9 agonist). Cytokines that boost growth or numbers of dendritic cells (GM-CSF), T cell responses (IL2). Target best APCs.

Types of vaccine approaches to common pathogens

Toxoids +killed bacteria

Killed (Salk)or attenuated

(Sabin)

Attenuated viruses

Conjugates

Subunit vaccine

Attenuated virus

Major currently used vaccines

(Toxoid is an enzymatically inactive, but antigenically intact toxin)

Efficacyantibody attenuated> killed> subunit> DNAcytotoxic T cells attenuated> DNA> killed> subunit

Safety subunit> killed> DNA> attenuated(biological)

Toxicity attenuated> killed> DNA> subunit(inflammation)

Tradeoffs in vaccine design

Figure 12-7

Anthrax Killed bacteria

The principle behind the smallpox vaccine

Figure 12-2 part 1 of 2Generation of the attenuated rubella vaccine

A reverse genetic approach to

generate attenuated viruses for

immunization

Neonates make poor antibody responses to T cell independent type 2 antigens. These are antigens that are polymeric and lack T cell epitopes. Conjugate vaccines overcome this limitation and promote class switching to IgG, which is longer lasting and more protective.

It is not clear why these antigens are not tolerogenic to B cells.

Possibly, they stimulate innate receptors in B cell such as Tlrs.

Conjugate vaccines provide a peptide

that stimulates CD4 T cells to antigens

that lack good determinants, such

as bacterial capsular polysaccharides.

Stimulates a good IgG antibody response to

the carbohydrate

Naked DNA vaccine works for influenza virus (experimental)

DNA is injected into muscle cells, which express the genes on the plasmid (when they have appropriate eukaryotic promoters and enhancers). This can promote a good CD8 T cell response and antibody.

Another approach to get antigenic peptides presented through the MHC class I pathway

Figure 12-5 part 2 of 2

Hepatitis B pathogenesis is similar: the virus is more prevalent, but somewhat less carcinogenic. However, there is an effective HepB vaccine. HepB cannot be grown in tissue culture. The surface antigen HBsAg is expressed as a recombinant protein, purified and used as an immunogen.

Hepatitis B vaccine was the first recombinant vaccine, and also the first anti-cancer immunization.

There is no vaccine for hepatitis C

Together Hepatitis B and C account for 85% of liver cancer

15% of cancers

are caused

by viruses

95% carrier rate

0.1-15% carrier rate

Can the immune system be harnessed to eliminate tumors?

• There is some evidence that the immune system provides cancer resistance.

• Spontaneously arising cancers have antigens that can be used to generate a meaningful and specific immune response.

• Cancers are not intrinsically resistant to the immune system, though they may evade the immune system.

• Cancer immunity may be achieved by boosting a preexisting, weak immune response.

• Antibodies to tumors are being used clinically to eradicate certain cancers.

Cancer formation involves accumulation of transforming mutations.

Some of these mutated oncogenes can be the targets of immunological responses.

Tumors can typically be transferred between genetically identical

mice.

BALB/c

BALB/c

BALB/c

Tumor cells

BALB/c

preimmunize (for example, with dead tumor cells)

BALB/c

Experimental evidence that tumors can be immunogenic

time

time

Resistance to tumor

Tumor donor Recipients:

Figure 12-46

Mutation(e.g. oncogene)

Embryonic gene expression Overexpression

Ways that tumor specific antigens

can arise

Figure 12-52

CD8 T cells can be raised

against tumors.

Tumors can express specific

antigens that might be

targeted by the immune system.

Many tumors reexpress embryonic antigens that are no longer expressed by the adult.

There is evidence for antibodies and some T cell responses to these antigens even in cancer patients.

Do tumors represent escape variants that are invisible to the immune system?

What is the tumor incidence in immunodeficient individuals?

in AIDS

T cell deficient humans get more cancers, but mainly virally induced ones or lymphoid tumors

A herpes virus

Though still controversial, there is evidence that immunodeficient mice have a higher

tumor incidence.

Inject carcinogen*

Wild type

Immunodeficient mutant mouse

Measure tumor incidence and

survival

*Methylcholanthrene (MCA) is typically used

-/-

+/+

One way that the role of the immune system in cancer resistance has been measured

Kaplan, D.H. et al. (1998) Proc. Natl. Acad. Sci. USA 95, 7556-7561

IFN--insensitive mice demonstrate an increased susceptibility to development of spontaneous and chemically induced tumors

Methycholanthrene induced tumors

Spontaneous tumors in

mice with the p53 tumor suppressor

mutation

Age (weeks)

Perforin and IFN- deficiency appear to permit increased spontaneous tumors in mice.

Perforin deficient

No tumors during time

of study

Dunn et al 2002

Nature Immunology

Though still controversial, there

is evidence that immunodeficient

mice have a higher tumor incidence.

The resistance appears to include both adaptive and innate immunity.

Tumors often lose MHC class I expression, suggesting that they are selected to avoid immune recognition

There is also evidence of avoidance of the NK response.

The evidence that there may be an immune response to tumors, albeit ultimately ineffective, has prompted many

studies to see if immunization can be used to cure tumors.

Problems:

• Chemotherapy can suppress the immune system.

• Tumors generate variants that could escape the immune system.

• Tumors may carry few or low levels of tumor specific antigens.

• Must avoid generating unwanted immune autoreactivity to normal tissues.

• The adjuvants available for use in humans are limited to two: alum and squalene/oil emulsion.

Experimental approaches to tumor therapy by immunization

• Find tumor specific antigens using antitumor CD8 T cells or antibodies.

• Make tumors more immunogenic by mixing them with adjuvants or forcing them to express cytokines or costimulatory molecules.

• Reverse the natural processes that limit immune reactions. (Blocking CTLA4, eliminating CD25+CD4+ suppressor cells)

• Dendritic cell loading with specific antigen or whole tumor cells and stimulation with specific adjuvants in cell culture prior to reintroduction to host.

How one would like tumor vaccines to work

Figure 12-49

Immunization with peptides from tumor specific antigen MAGE-1 and MAGE-3

The problem of immunological escape tumor mutants

The notion of prophylactic cancer vaccines

• Hepatitis B vaccine proves that this approach can work.

• People infected with human papilloma virus may avoid cervical cancer by specific immunization. A vaccine has been developed against HPV16, which is involved in about 50% of these tumors.

• Some cancer predisposing genes have been identified. For example certain alleles of BRCA1 and 2 are associated with hereditary breast cancer. Immunization of these people prior to evidence of cancer might provide protection.

• Advantages: immune response would be most likely to eliminate tumors at an early, preclinical stage. Memory could be established before tumor arises.

Could cancer vaccines cause autoimmunity?

Some types of tumor are well suited to an immunization approach. Melanomas are derived from melanocytes, pigment cells. These tumors are highly metastatic making them difficult to eliminate surgically. Melanocytes are not required for survival. Anti-melanocyte response after cancer vaccine immunization can lead to vitiligo (destruction of normal pigment cells leading to white blotching).

This normally pure black mouse rejected a melanoma when treated with anti-CTLA4 (to block the downregulation of T cell responses) and GM-CSF (to increase dendritic cells), but then began to eliminate normal melanocytes.

• Vaccines for infectious diseases balance the importance of antibody and CD8 T cell responses with the mode of protection and side effects of inflammation. Safety is a major concern that prevents the use of most adjuvants and limits the use of certain types of vaccines, such as attenuated microbes.

• Cancer vaccines present different challenges and opportunities. Faced with life threatening disease, the possibility of using more powerful adjuvants and vaccines that may lead to autoreactivity are less of a limitation than in prophylactic vaccines. Major limitations involve the identification of robust antigens the elicit a strong, high affinity T cell response. Other barriers include the problem of chemotherapy induced immunosuppression and mutational escape of immune recognition by the tumors.

Concepts

•Thank you to the teaching fellows!•Lauren•Laura•Hart •Matt •Adam

•Thanks to you students for not whining!

Review session: Saturday 4-6 Here

Please prepare questions to ask us

Better yet, email your questions in advance to meAlso, feel free to suggest questions for the exam

Final March 18th 3-6PM Here (York 2722)

Topics to be on test

Comprehensive with added emphasis on last 4 lectures

•Functions and major products of different immune cell types•CD8, CD4 (Th1 vs 2), regulatory T cells, B, macrophage, DC, NK, mast cells, eosinophils, neutrophils

•Key receptors on different cells•BCR, TCR, FcR,FcR, complement receptors

•Antigen receptor genes and proteins•Lymphocyte development: purpose and differentiation steps•Structure, function and genetics of MHC•Antigen processing, how and where MHC is loaded with cargo•T cell activation and costimulation, adjuvant action•Ways to artificially improve or suppress immunity•Hypersensitivity types and their cellular and molecular basis•Autoimmunity: causes and natural barriers to autoimmunity•HIV: modes of escape and resistance•Transplantation: barriers, challenges and therapies