Immunotherapy In breast cancer

Intro to immunotherapy

• Immunotherapy harnesses the body's own immune system to fight cancer by activating/enhancing anti-tumour immune responses.

• It has revolutionized treatment for various cancers including breast cancer.

• The immune system plays an important role in controlling tumour growth
  through immune surveillance.

• However, tumours develop mechanisms to evade immune destruction forming an immunosuppressive microenvironment.

Key Immunotherapy Techniques

• Checkpoint Inhibitors: Block inhibitory receptors (PD-1, CTLA-4) and restore anti-
  tumour T cell responses.

• Cancer Vaccines: Stimulate adaptive immune system using tumour-associated
  antigens to develop immunological memory.

• Adoptive Cell Therapy: Engineer/expand tumour-specific T cells outside body and
  infuse them to seek and destroy cancer cells.

• Oncolytic Viruses: Engineered viruses that selectively replicate in and lyse tumour cells, triggering anti-tumour immunity

Mechanisms of Action

• Checkpoint inhibitors remove brakes on immune system, allowing T cells to
  attack cancer cells directly.

• Vaccines educate immune system to recognize and attack tumours expressing targeted antigens.

• ACT and oncolytic viruses work alongside patient's immune cells to shrink
  established tumours.

• Immunotherapy unleashes the power of the immune system offering new
  hope for improved treatment outcomes and long-term remissions for
  breast cancer patients.

Immunotherapy in breast cancer treatment in HER2-positive breast cancer

Role of trastuzumab

1. HER2+ breast cancer accounts for 20% of cases and has poorer prognosis due to more aggressive disease. Trastuzumab targets this high-risk subset.

2. Trastuzumab is a humanized monoclonal antibody immunotherapy that binds to the HER2 receptor protein.

3. It works through dual mechanisms - inhibiting HER2 signalling and activating antibody-dependent cytotoxicity to kill cancer cells.

4. Pivotal clinical trials demonstrated significantly improved response rates, progression-free and overall survival when trastuzumab was added to chemotherapy for HER2+ breast cancer, establishing it as a landmark targeted therapy.

Mechanism of action of trastuzumab

• Trastuzumab binds specifically to the extracellular domain of the HER2 receptor protein. This prevents HER2 from forming heterodimers with other HER receptors such as HER1, HER3 and HER4

• Blocking HER2 dimerization inhibits downstream PI3K-AKT and MAPK signalling pathways crucial for cell proliferation and survival

• Trastuzumab binding also stimulates antibody-dependent cell-mediated
  cytotoxicity (ADCC) where immune cells directly kill the HER2-overexpressing cancer cells

Clinical evidence for trastuzumab in HER2+ beast cancer

• Early studies like the landmark HERceptin Adjuvant (HERA) trial showed 1-year
trastuzumab improved invasive disease-free survival by 50% compared to observation alone after adjuvant chemotherapy
• 5-year follow up of HERA confirmed trastuzumab provided a significant absolute risk reduction in breast cancer recurrence and mortality
• Other large studies confirmed benefit when added to different chemotherapy backbones like taxanes or anthracyclines
• Benefit is seen both in the neoadjuvant (before surgery) and adjuvant (after surgery) settings
• Ongoing research aims to identify predictive biomarkers to stratify who benefits most and understand primary and acquired resistance

Pembrolizumab in PD-L1 expressing triple-negative breast cancer

• Triple-negative breast cancer (TNBC) lacks HER2, ER and PR expression and has a poorer prognosis than other subtypes
• TNBC tumours often express PD-L1 which helps the cancer evade anti-tumour
immune responses
• Pembrolizumab is an anti-PD-1 monoclonal antibody immunotherapy that aims to overcome this immune evasion

Rationale for Using Pembrolizumab in PD-L1+ TNBC
• PD-1 is an inhibitory receptor commonly expressed on tumour-infiltrating
lymphocytes that downregulates immunity
• When its ligand PD-L1 binds to PD-1, it sends an inhibitory signal that stops T-cells from killing cancer cells
• Pembrolizumab blocks this interaction, lifting the brakes on anti-tumour T-cells
within PD-L1+ TNBC tumours

Clinical Trial Results
• The Phase 1b KEYNOTE-012 trial tested pembrolizumab monotherapy in patients with advanced PD-L1+ TNBC
• The objective response rate was 18.5% with median response duration of 7.5 months
• The responses were durable with 80% ongoing at 32-40 weeks
• The managed side effects were consistent with other anti-PD-1 antibodies

The current ongoing Studies that are available are larger Phase 2 trials which assess pembrolizumab in combination with chemotherapy in advanced TNBC
Adjuvant studies are evaluating pembrolizumab after standard chemo to prevent
recurrence in early TNBC

Exploring pembrolizumab's success in treating metastatic breast cancer
• Metastatic breast cancer remains largely incurable with chemotherapy and
endocrine therapies
• Harnessing the immune system through checkpoint inhibitors represents a novel treatment approach
• The rationale for Checkpoint Inhibition in Metastatic Breast Cancer shows that the expression of PD-L1 is seen in up to 40% of metastatic breast cancers, which acts as an immune resistance mechanism
• Pembrolizumab blocks the PD-1/PD-L1 axis, releasing the brakes on anti-tumour T-cell responses
Clinical Trial Results
The multicohort KEYNOTE-012 trial evaluated pembrolizumab monotherapy in metastatic breast cancer. For PD-L1+ patients, overall response rate was 18.5% with median duration of response of 7.5 months
Responses were seen across all breast cancer subtypes regardless of hormone receptor or HER2 status
Ongoing Combination Studies include combining pembrolizumab with chemotherapy or other targeted agents may improve responses and trials that pair anti-PD-1/PD-L1 drugs with immunotherapy like tumour vaccines also
underway.

Trastuzumab Mechanism of Action
The HER2 gene is a receptor tyrosine kinase that activates growth signalling when bound by other HER ligands
• In breast cancer, HER2 is often overexpressed leading to hyperactive
downstream signalling and the chief pathways among these are PI3K-AKT and MAPK, which stimulate cell proliferation and inhibits apoptosis

How Trastuzumab Works
• Trastuzumab is a humanized monoclonal antibody targeted against the extracellular domain of HER2
• It binds tightly to HER2 with high specificity and affinity, preventing receptor dimerization (dimerization is the process of joining two identical or similar molecular entities by bonds)
• This blocks HER2 from heterodimerizing with other HER family members such as HER1, HER3, HER4
Effects on Signalling and Protein Trafficking:
• By inhibiting dimerization, trastuzumab prevents downstream PI3K-AKT and MAPK cascade activation
• It also induces internalization of HER2 receptors, taking them out of play at the cell surface
• This decreases levels of activated signalling proteins and blocks transmission of growth signals

Immune-Mediated Effects
• In addition to direct inhibition, trastuzumab activates antibody-dependent cell
cytotoxicity (ADCC) and acts as a bridge linking HER2+ cancer cells to natural killer cells of the immune system
• NK cells then directly lyse and eliminate HER2-expressing breast tumour cells
coated with trastuzumab
Consequence for Breast Cancer Cells
• The dual blockade of key oncogenic signalling and targeted immune killing
explains trastuzumab's potency
• It inhibits HER2-driven proliferation and survival advantages conferred to breast cancer cells

Review of nivolumab's efficacy in breast cancer through targeting the PD-1 pathway
• Nivolumab is a fully human IgG4 PD-1 immune checkpoint inhibitor antibody
• By blocking the PD-1 receptor, nivolumab aims to reverse T-cell exhaustion and boost anti-tumour immunity
Rationale for Targeting PD-1 in Breast Cancer
• PD-1 pathway activation inhibits T-cell effector function against cancer cells
• Increased tumour-infiltrating lymphocytes in breast cancer express PD-1,
impairing their function
• Nivolumab hopes to reinvigorate these T-cells to better attack breast
cancer cells

Clinical Trial Results
• The single-arm, Phase 1/2 CheckMate-028 trial evaluated nivolumab in advanced,
refractory breast cancer
• Objective response rate was 9.5% with a disease control rate of 27.6% and similar safety
to other tumours
• Genomic analyses found higher ORR in patients with increased tumour mutational
burden
Ongoing Combination Studies
• Trials underway adding nivolumab to chemotherapy, hormonal therapy or other
immunotherapy
• Novel combinations may provide synergistic benefit and push response rates higher

Future Directions
• Identifying predictive biomarkers to select optimal patients remains crucial
• Earlier application as adjuvant or neoadjuvant therapy also under investigation
• Nivolumab demonstrated promising initial efficacy in pretreated breast
cancer, warranting further trials
• Combinatorial approaches may fully realize the potential of PD-1/PD-L1
blockade in this disease

Basic mechanism of action of immune checkpoint inhibitors
• The immune system has built-in checkpoints to prevent excessive immune activation
against normal tissues
• These checks include receptors like CTLA-4 and PD-1 expressed on T-cells
• Cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) competes with co-stimulatory
molecule CD28
• CTLA-4 binding inhibits T-cell activation and proliferation at early stages of immune
response
• Ipilimumab blocks CTLA-4, removing the brakes early in an immune reaction

PD-1 Pathway Inhibition:
• Programmed cell death protein 1 (PD-1) is mainly expressed by activated T-
cells
• Its ligands PD-L1 and PD-L2 are often expressed on tumour and immune
cells
• PD-1 ligation transmits inhibitory signals that dampen T-cell effector
function
• Nivolumab/pembrolizumab disrupt this signal, preventing T-cell exhaustion

Effects on Anti-Tumour Immunity:
• By inhibiting CTLA-4 and/or PD-1, immune checkpoints are released
• This boosts the quantity and quality of anti-tumour T-cell responses
• Primed T-cells are no longer suppressed and can better migrate, proliferate and kill
tumour cells
Clinical Impact
• Tumours formerly escaping immune destruction face attacks from reinvigorated T-cells
• Checkpoint blockade has revolutionized cancer treatment across various solid and liquid
tumours
• Durable responses emerge from modulation of the natural anti-cancer immune capacity

Explanation of CAR-T cell therapy
What are CAR-T Cells?
• Chimeric antigen receptor T (CAR-T) cells - Patient's own T
cells engineered with a chimeric antigen receptor
How CAR-T Cells Work
• T cells are collected from a patient through leukapheresis then the genes for an artificial CAR are inserted
• The CAR allows T cells to recognise a specific antigen on tumour cells independent of MHC
• Once reinfused, CAR-T cells can target and kill cancer cells expressing the antigen

Components of CAR
• An extracellular domain anchors to the target antigen
• A transmembrane domain anchors the receptor to the T cell
• An intracellular domain provides co-stimulation and activates T cell functions upon binding
target
Significance in Cancer Immunotherapy
• CAR-T cells redirect the potent killing ability of T cells to eliminate cancers
• They show dramatic responses in some hematologic cancers resistant to other therapies
• Potential to treat both liquid and solid tumours that express unique antigens
Explanation of CAR-T cell therapy

Challenges and Applications
• Safety concerns include cytokine release syndrome and neurotoxicity from high activation
• Identifying targets specific to cancer cells vs normal tissues is crucial
• Ongoing research optimizes design, targets, and combination with other agents
• CAR-T cell therapy harnesses the immune system's precision to provide a potentially curative approach
• While still developing, it represents a breakthrough in immunotherapy that may transform cancer treatment

Evaluation of the primary role of monoclonal antibodies in cancer immunotherapy focusing on their mechanism of action
• Role of Monoclonal Antibodies
• Monoclonal antibodies are engineered versions of immune system proteins able to precisely target molecular markers on cancer cells
Mechanisms of Action
• Direct Blockade - Binding to targets like HER2 receptors interferes with downstream oncogenic signalling
• Opsonization - Coating tumour cells allows for antibody-dependent cellular cytotoxicity via NK cells and macrophages
• Immune Cell Recruitment - Effector functions stimulate an inflammatory response and attract immune cells to the tumour
• Co-stimulation - Increasing supportive signals or blocking inhibitory receptors licenses T cell anti-tumour activity

Key Applications in Cancer Immunotherapy
• Delivery of Radioisotopes/Chemotherapy - Conjugating agents directly delivers drugs to cancer tissue sparing healthy cells
• Checkpoint Inhibition - Anti-CTLA-4, PD-1, PD-L1 antibodies harness pre-existing immunity by removing brakes from T cells
• Targeted Delivery - CAR-T cells armed with tumour antigen recognition via recombinant monoclonal antibodies
Benefits
• Highly specific targeting limits off-tumour toxicities compared to traditional therapies
• Persistence allows for durable clinical responses through sustained immune modulation
• Combination with other modalities increases potency by attacking tumours through multiple avenues

The primary goal of immune checkpoint inhibitors in cancer treatment is to restore and enhance the body's natural anti-tumour immune response
• Cancers have developed mechanisms to evade immune destruction, such as overexpressing immune checkpoint proteins like CTLA-4 and PD-1.
• These checkpoint proteins act as "brakes" that inhibit T cell activation and antitumor activity when they bind to ligands on tumours cells.
• Checkpoint inhibitors are monoclonal antibodies that block these inhibitory checkpoint interactions between T cells and cancer cells.
• By disrupting checkpoints, the goal is to "release the brakes" on T cells and empower them to better recognise tumours as foreign threats.
• Uninhibited by checkpoint signals, T cells can proliferate robustly at tumour sites and launch
more effective attacks on cancer via their cytotoxic and cytokine releasing functions.
• This aims to turn a "cold" immunosuppressive tumour microenvironment back into a "hot" inflamed one that drives a potent immunotherapeutic response.
• The ultimate goal is durable regression or even cure of cancers by restoring and enhancing the body's natural antitumor defences, rather than directly killing cancer cells like chemotherapy.
• By unleashing pre-existing anti-tumour immunity, checkpoint inhibitors offer a potentially self-sustaining treatment paradigm.
• The overarching objective is reinvigorating and optimizing the immune system's intrinsic ability to eliminate cancers on its own.

Explanation of tumour-infiltrating
lymphocyte (TIL) therapy
• TIL therapy involves extracting T cells from a patient's own tumour tissue that are actively
infiltrating the tumour microenvironment.
• These TILs have already demonstrated an ability to recognise tumour antigens and traffic to
tumour sites.
• The TILs are then expanded ex vivo by activating and stimulating them with IL-2 and anti-
CD3/CD28 antibodies in culture over 2-4 weeks.
• This amplification process increases the number of TILs, especially those specifically
targeting the patient's tumour.
• The expanded population of tumour-reactive TILs are then infused back into the patient to
induce an antitumour immune response.
• TIL therapy has shown durable responses in metastatic melanoma when combined with
lymphodepletion to remove regulatory T cells.

• It aims to harness the immune system's intrinsic ability to generate tumour-specific T cell
clones within tumours.
• Identifying novel tumour antigens recognised by TILs also helps develop more targeted
immunotherapies.
• Current research optimises TIL culture methods and explores combining with checkpoint
inhibitors or adoptive NK cell therapy.
• TIL therapy isolates, amplifies and redeploys a patient's pre-existing tumour-specific T
cells to induce potent, personalised antitumour immunity.