Module 2: Tumor Immunology (Week 2)
LECTURE 11: IMMUNE ESCAPE MECHANISMS Monday, 8/10/2018
Lessons from HPV-related cervical cancer:
3rd most common cancer type in women worldwide
Cervical cancer: HPV infects basal layer replicates spread of HPV
after top-most cell layer dies off (spreading requires episomal structures
unattached to the genome for mobilization)
Not all HPV-infected cells grow into malignant cluster (effective
immune clearance); only 10 subtypes are considered carcinogenic
Preventive vaccination: mainly for HPV-16 & HPV-18 peptides elicit
immune response against HPV-infected cells & induce immune clearance
(47% remission rate in vulvar intraepithelial neoplasia cases)
Early stage has high 5-year survival rate (80%), but low survival of
advanced/metastatic cervical cancer
Most dangerous viral protein: E6 & E7
Able to escape immune regulation by downregulation of HLA class
1/MIC A and switching to non-classical HLA
Immune response to cancer cells
a. Priming adaptive response: DC
vaccine, cancer-antigen-based
vaccine
b. Effector adaptive response: T-cell
adoptive transfer, checkpoint
inhibition
Adoptive transfer: isolate T cell from
patient activation/enhancement ex vivo
reintroduce to patient
CP inhibition: loosen brakes for CD8+ T cell
proliferation
Circumventing immune elimination by inducing immunosuppression: release of inhibitory molecules (TGF beta,
IL-10, VEGF, IDO, PGE-2, etc), upregulation of T cell inhibitory receptors (PD-1, CTLA-4, TIM-3, etc), loss of T
cell activating receptors (HLA), recruitment of suppressive immune cells (Treg & MDSC)
, Module 2: Tumor Immunology (Week 2)
Cascade of immune activation
Antigen taken up by APC presented by MHC II to Th cell (also releasing co-stimulatory cytokines) Th
activation Th memory cells releasing IL-2 affect production of cytotoxic T cell
T cell can also be activated by presentation of antigen by MHC I direct cytotoxicity to altered cell
Immune escape mechanism
Increasing levels of Treg (marker: FOXP3), damaged HLA (no killing by NK cell), lack of MHC presentation in
APC no activation of T cells, loss of MHC/MIC A no detection by cytotoxic T cell
Means of immune evasion:
a. Cytokines production
b. T cell inhibitory receptors
c. Loss of activating receptor (no HLA)
T cells do not recognize tumor
cells as foreign & no cytotoxicity
Backup mechanism: low HLA
expression on cell surface detected
by NK cells cell destruction
Wrong HLA expression (like in most
tumor) = NK cell does not sense as
target, no cell destruction
d. High amount of suppressive cells (T
reg, MDSC)
, Module 2: Tumor Immunology (Week 2)
HLA Class I
HLA: classical (HLA-A, etc), non-classical (HLA-G, HLA-E); HLA-A & HLA-G have cross-reactivity to HCA-2
marker
Mechanism of HLA activity
Oligopeptide (e.g. TAA) transported into
ER by TAP form complex with other
proteins presentation to HLA + surface
migration through Golgi complex T cell
recognition + response
HLA complex require stabilization by several
molecules (calnexin, calreticulin, tapasin, etc)
in order to be able to bind to the antigen &
carry the antigen to the cell surface
Functional HLA: stable, peptide-bound structure has 2 A alleles, 2 B alleles, 2 C alleles; induction of T cell
cytotoxicity requires all alleles to be intact, if one allele is lost/wrong: reduced T cell recognition & no
cytotoxicity
HLA alterations in cancer
In cancer cells: altered HLA
expression total loss,
loci/alleleic loss, haplotype loss,
compound phenotype T cell
can’t be activated
In cervical cancer: 50% cases
express reduced HLA, 20% no HLA
expression
In cervical Ca cases with weak
HLA expression (IHC staining):
worse prognosis than no HLA
expression
Normal cervix: MIC A(+), HLA-G(-)
, Module 2: Tumor Immunology (Week 2)
Genetic aberrations causing HLA alterations (examination method: allele-specific FACS):
a. Beta-2m loss: total loss of HLA
b. LOH: haplotype loss of HLA
c. Certain genetic mutations: alleleic loss of HLA
HLA analysis
HLA alterations in cervical cancer
Cervical cancer express MIC A & non-classical HLA-E: can bind to NKG2A receptor on NK cell activation or
inhibition (depending on the skewing of activating/inhibiting signals); normally functions as a brake to immune
reaction, activating effects depend on the presence of other T cell receptors
More aberrations of HLA expression in metastatic tumor (addition of other classic HLA loss/HLA-B & HLA-C)
Escape mechanisms = escaping T cell detection (HLA-A loss) + escaping NK cell detection (HLA-G upregulation)
Chemotactic cytokines by cervical cancer cells
CCL2: attract immune cells to tumor site more CCL2 = higher T cell infiltration
Increased CCL2 production by tumor cells more leaky vessels extravasation of immune cells homing to
tumor site; however, CCL2 expression by tumor cells is sometimes followed by differentiation of macrophages
into TAM (more suppressive, marker: CD68)
