Dr Céline BossardDepartment of Pathology, University Hospital, Nantes

celine.bossard@chu-nantes.fr

Subordination of the neoplastic progression to the immune

system

Tumor immunity : an old concept with new clinical applications

• Ehrlich in 1909 proposed this idea :

« tumors are not entirely « self », and immune-mediated recognition of autologous tumor cells could be able to eliminate transformed cells »

• A concept formalized subsequently by Thomas and Burnett:

« the immune surveillance » to refer the recognition and destruction of newly appearing tumor cells which are seen as foreign by the immune system

• But the development of cancer implies

- an imperfect immune surveillance

- mechanisms of tumor immune escape, representing potential new therapeutic targets (ex : anti PD-1, PD-L1 antibodies)

Clinical evidences for tumour immunity

• Spontaneous regression of melanoma associated with an in situ T cell clonal expansion (Ferradini et al, 1993)

• The increased risk of tumour development in immunosuppressed patients (primary or secondary immunodeficiencies) :

- tumours of viral origin : > B-cell lymphoma induce by Epstein Barr Virus, > Kaposi’s sarcoma and HHV8, > carcinoma of the anogenital regions and HPV - tumours with no known viral etiology : > melanoma, sarcoma, lung adenocarcinoma….

• The improved prognosis of tumours containing a high number of tumour-infiltrating lymphocytes (TIL: T cells, NK cells) :

> melanoma (identification of various melanoma-specific Ag) > colon, breast, ovarian adenocarcinomas, head and neck

carcinomas…..

The tumor microenvironment contains more or less immune cells

• Stroma : a complex microenvironnement composed of :

- blood and lymphatic vessels

- an inflammatory milieu consisting of immune cells (of the innate and adaptive immunity) and their secretory products

type, density and location of immune cells varie between each tumour and influence tumour progression differently

Immune cells at the invasive margin of the tumor

In the center, in the stroma

In close contact with tumor cells

Immune cells in close contact with tumour cells (intra-epithelial TIL)

The major effector cell in anti-tumor immunity: the Cytotoxic T Lymphocyte (CTL)

Cell mediated immunity is the major anti tumor mechanism

Prognostic Value of Tumor Infiltrating Lymphocytes in the Vertical Growth Phase of Primary Cutaneous MelanomaClaudio G. Clemente et al, 1996

High number of TIL Low number of TIL

Presence of high number of TIL is a positive prognostic factor

Intratumoral T Cells, Recurrence, and Survival in Epithelial Ovarian CancerLin Zhang et al, 2003, N Eng J Med

CD8 immunostaining : intra-tumoral and peritumoral CD8+ T cells

The presence of intratumoral T cells correlated with delayed recurrence or delayed death

Type, Density, and Location of Immune Cells Within Human Colorectal Tumors Predict Clinical Outcome. J Galon et al, 2006

Patients with a homogeneous increased expression of genes for Th1 adaptive immunity (CD3, CD8, GrB, IFNg) in the tumour have a better prognosis.

Type, Density, and Location of Immune Cells Within Human Colorectal Tumors Predict Clinical Outcome. J Galon et al, 2006

Bossard et al, 2012Int J Cancer

The high density of CD3+ TIL is associated with a better prognosis, whatever their localization

Center of the tumour Invasive margin

CD8+ IEL-TIL

….T cells infiltrate has a prognostic discriminatory power that is superior to the standard TNM staging system….

The immune score as a new possible approach for the cancer staging in colorectal carcinomas

Galon et al, 2012 J Translational Medicine

NK cells : an effector cell of the innate immunity

Intra-epithelial CD244+ NK cells in colorectal adenocarcinoma

C Bossard, 2012, Int J Cancer

• They may provide the first line of defense agains tumor cells

• NK cells can lyse a wide range of human tumors, including some tumors that seem to be nonimmunogenic for T cells

- tumours that fail to express MHC class I Ag cannot be recognized by CTL, but by NK cells that destroy cells without normal expression of MHC class I Ag

• Some studies have demonstrated the favorable prognostic impact of NK cells infiltration in various type of tumors :

- colorectal cancer (Coca et al, Cancer, 1997) - gastric cancer (Ishigami et al, Cancer Lett, 2000)

Tumor antigens• Classified depending on their molecular structure and source• They can induce or not a specific immune response

1 - Products of mutated oncogenes and tumor suppressor genes

• Neoplastic transformation results from genetic alterations, and some of them may lead to the expression of cell surface Ag (with known or unknown function), seen as non-self by the immune system.

• Tumor-specific Ag (p53, RAS, BRAF, b-catenin, and many others not related to the transformed phenotype as in MSI tumors….) not expressed by normal cells

• Shared by many different tumors

• Recognized as non-self proteins by the immune system

• These self-mutant proteins can induce specific CTL, but these CTL don’t elicit a protective response

• The product of an unmutated oncogene is overexpressed in a subset a breast cancers : HER2/NEU oncogene

• Can be assessed by immunohistochemistry and/or FISH

• The target of a monoclonal antibody : Trastuzumab (Herceptin)

2 - Overexpressed or aberrantly expressed normal proteins

• Structurally normal protein overexpressed in tumor cells = normal self-Ag

- ex : tyrosinase in melanoma cell (expressed at a low level only in normal melanocyte)

> T cells in patients with melanoma recognize peptides derived from tyrosinase

> development of tyrosinase vaccine (clinical trials ongoing)

• Cancer-testis antigen: Ag only expressed in testis but without antigenic expression at the cell surface (no MHC class I expression by sperm !), but with deregulated expression in tumor cells

> A tumor-specific Ag

ex : the MAGE family of genes (Melanoma Antigen Gene); MAGE Ag are found in melanoma, lung, liver, stomach…..

> several MAGE Ag are used in tumor vaccine trials

Tumor antigen produced by oncogenic viruses

• Somes virus are associated with cancers (HPV and cervix, HBV, HCV and hepatocarcinoma, EBV and lymphomas….)

• Produced proteins are recognized as foreign and induced a strong CTL response (DNA viruses +++)

> vaccines against HPV Ags are effective to prevent cervical cancer +++

Oncofetal/embryonic antigens

• Ag only expressed during the embryogenesis but not in normal adult tissues

ex : CEA (carcinoembryonic Ag in colon cancer) and α foetoprotein in liver cancer

> used as serum markers of cancer

Altered cell surface glycolipids or glycoproteins

• Most human tumors expressed higher than normal levels and/or altered forms of glycolipids or glycoproteins

• Can be used as diagnostic markers and/or targets for therapy

• These molecules include gangliosides, mucins, bloog group Ag

ex : CA-125, CA 19-9, MUC-1

Cell type-specific differentiation antigens

• Differentiation Ag are specific molecules expressed in particular lineages or at a differentiation stage of various cell types = normal self Ag

• Tumor cell can express a differentiation Ag normaly expressed by the normal cell counterpart

• They do not induce immune response

> use for identifying the tissue of origin for a morphologically undifferentiated tumor (IHC)

> use as a target for immunotherapy : anti-CD20 antibody (Rituximab) used in B-cell lymphomas expressing CD20 as normal B lymphocytes

How do tumor cells escape from the immune system in immunocompetent hosts?

The immune evasion by tumor

Dendritic cell T cells Tumor cell

MHC TCR

B7

B7

CD28

CTLA-4

Inhibitory signal

Activation signal

Peripheral tissueLymph node

TCR MHC class I

Negative regulation

From Ribas A in N Eng J Med, 2012:366;26

PD-1

Several escape mechanisms have been proposed

X

XPD-L1PD-L2

✔

TGFb

CD94

HLA-E/β2m –HLA-E/β2m +

P=0.02

Overexpression of HLA-E/β2m by tumour cells in CRC is associated with a high number of inhibitory

CD94/NKG2 +IEL-TIL, and with a poor prognosis

HLA-E

NK cell and CTL

Tumour cell

β2M

LYSIS

Bossard et al, Int J Cancer, 2012

Conclusion

• Type, density and location of immune cells within a tumour can predict the prognosis in some tumours

> proposition of an « immune score » for the classification of cancer

• Host immune cells have essential roles in regulating tumour growth in the tumour microenvironment.

• Host immune cells provide a great opportunity for therapeutic and preventive interventions

> need to boost the effective and specific anti-tumor immune response, and to inhibit the mechanisms of tumor immune evasion