Why CD47 Matters

Cancer cells commandeer a “don’t eat me” signal, called CD47, to escape elimination by our innate immune system’s first responders.

These innate immune cells, called macrophages, respond to “eat me” signals, non-specific signs of danger, from pathogens or abnormal cells, including cancer cells. When a macrophage recognizes a cancer cell through its “eat me” signals, it swallows and digests the cancer cell as a first line of defense. The macrophage then alerts specialized cells in the adaptive branch of our immune system, which include T cells, to specific foreign features, antigens, of that cancer cell. This mobilizes targeted, long-term defenses against the cancer cells.

Cancer cells abuse a “don’t eat me” signal, called CD47

Macrophages respond to threats when “don’t eat me” signals, often found on normal cells to prevent unwanted auto-immune attacks, are outweighed by “eat me” signals commonly found on pathogens or abnormal cells but not on normal cells.

Blocking CD47 “don’t eat me” signals while releasing and boosting “eat me” signals is the core focus of our research to enable the patient’s own immune system to attack and destroy their cancer.

Nearly all types of tumors overexpress CD47. When CD47 binds to its receptor SIRP-alpha on macrophages, it sends a “don’t eat me" signal and thus inhibits destruction by macrophages. Overexpression of CD47 is correlated with poor prognosis in multiple cancers, including acute myeloid leukemia, Non-Hodgkin's lymphoma, ovarian cancer, gastric cancer, and lung cancer.

Forty Seven's 5F9 immunotherapy

The anti-cancer efficacy and specificity of magrolimab (formerly known as 5F9), our antibody versus CD47, involves tipping the balance between the “eat me” and “don’t eat me” signals received by macrophages when they encounter a potential target cell.

Magrolimab Mechanism of Action Explained


Macrophages and Healthy Cells

Macrophages use a signaling pathway to detect abnormal cells for elimination. When macrophages encounter healthy cells, its receptor SIRP-alpha binds to CD47, a "don't eat me" signal, preventing phagocytosis.


Macrophages, Cancer Cells and CD47

When the "eat me" signals found on abnormal cells, including cancer, outweigh the "don't eat me" signals, macrophages will digest them. Some cancers overexpress CD47, allowing them to evade phagocytosis.


Using Magrolimab Against Cancer Cells

Forty Seven's immunotherapy, magrolimab, is an antibody that blocks the CD47 "don't eat me" signal, restoring the macrophages ability to detect and destroy cancer cells. In addition, the Fc region of magrolimab can bind the Fc receptor on macrophages providing an additional phagocytic "eat me" signal.


Combining Magrolimab with Tumor Targeting Antibodies

Combining magrolimab with other immunotherapies such as the anti-CD20 antibody rituximab, can produce an additional "eat me" signal on cancer cells, further stimulating macrophage response.

Healthy cells express CD47 which protects them from macrophages by sending a “don’t eat me” signal though the SIRP-alpha receptor. Cancer cells express signals of abnormality on their surface which send an “eat me” signal to the macrophage but this is neutralized by the “don’t eat me” signal provided by CD47 over-expressed on cancer cells. 

When our antibody, magrolimab, binds CD47 on cancer cells it blocks the interaction with SIRP-alpha on the macrophage eliminating the “don’t eat me” signal, unmasking the “eat me” signals, and also provides an additional “eat me” signal by engaging with the Fc receptors on the macrophage tipping the balance towards phagocytosis. 

Combining magrolimab with a second cancer-targeting antibody, such as rituximab which binds CD20 on Non-Hodgkin's lymphoma cells, tips the balance even further towards phagocytosis by engaging with additional Fc receptors on the macrophage. In contrast, healthy cells are unaffected by magrolimab since they do not express “eat me” signals or targets for cancer-targeting antibodies.

Our Scientific Foundation

Our company was founded by leading scientists at Stanford University who uncovered the fundamental role of CD47 in cancer evasion. Preclinical work performed in the laboratory of our co-founder, Irv Weissman, demonstrated that CD47 blocking antibodies could cause the clearance of tumors in animals as monotherapy and provided the rationale for three strategic approaches to combination therapy with CD47 antibodies.

Our Immunotherapy

Our immunotherapy, magrolimab (formerly known as 5F9), is an antibody that is designed to block the CD47 “don’t eat me” signal, restoring the ability of macrophages to attack and destroy cancer.

Preventing cancer from suppressing the innate immune system is an emerging field in oncology, and magrolimab is among the first in a new class of innate immune checkpoint inhibitors. We are investigating magrolimab in multiple Phase 1 and Phase 2 trials in various cancers, including non-Hodgkin’s lymphoma, colorectal cancer, ovarian cancer and acute myeloid leukemia as both monotherapy and in combination with approved therapies.

Combination with Our Immunotherapy

We believe combining our magrolimab immunotherapy with existing cancer therapies can further enhance macrophages' ability to recognize cancer cells and can mobilize potent adaptive immune responses to eliminate cancer.

Cancer Targeting Antibodies

Targeted Antibodies. Therapeutic antibodies that target specific cancers can produce strong “eat me” signals on cancer cells, stimulating macrophage recognition and response. For example, many B cell lymphomas, including follicular lymphoma and diffuse large B-cell lymphoma, express CD20 on the cell surface and some solid tumors, including colorectal cancer, express EGFR. We are conducting clinical trials in collaboration with Genentech and Eli Lilly to test magrolimab in combination with the anti-CD20 antibody rituximab and the anti-EGFR antibody cetuximab.

T Cell Checkpoint Inhibitors. In a similar way that CD47 on cancer cells suppresses macrophages, some cancer cells can suppress T cell attacks by expressing immune checkpoint proteins such as PD-L1. This can reduce the potency of the specific anti-cancer T cell responses that macrophages mobilize after ingesting cancer cells. Combining our magrolimab immunotherapy with T cell checkpoint inhibitors may help maximize the T cell response induced by macrophages.

T Cell Checkpoint Inhibitors

We are collaborating with Merck KGaA and Genentech to test magrolimab in combination with the PD-L1 checkpoint inhibitors avelumab and atezolizumab in clinical trials for ovarian cancer, acute myeloid leukemia, and urothelial (bladder) cancer. Additionally, preclinical studies suggest the binding of a PD-L1 checkpoint inhibitor to cancer cells provides an “eat me” signal on cancer cells that can further stimulate macrophage responses and can combine multiple mechanisms of action in one combination.

We believe our magrolimab immunotherapy will work in concert with existing therapies to enhance the potency of both innate and adaptive immune responses against cancer.


Anti-CD47 Antibody
Solid Tumors:
Anti-SIRPα Antibody
Anti-cKIT Antibody
HSC Transplantation

*Expansion arm of ongoing NHL: magrolimab + Rituximab trial


Posters and Presentations

The First-in-Class Anti-CD47 Antibody Hu5F9-G4 is Well Tolerated and Active Alone or with Azacitidine in AML and MDS Patients: Initial Phase 1b Results
Congress of The European Hematology Association (EHA) | June 2019

Activity of the first-in-class anti-CD47 antibody Hu5F9-G4 with rituximab in relapsed/refractory Non-Hodgkin’s lymphoma: interim Phase 1b/2 results
Congress of The European Hematology Association (EHA) | June 2019

The First-in-Class Anti-CD47 Antibody Hu5F9-G4 is Well Tolerated and Active Alone or with Azacitidine in AML and MDS Patients: Initial Phase 1b Results
American Society of Clinical Oncology Annual Meeting (ASCO) | June 2019

RBC-Specific CD47 Pruning Confers Protection and Underlies the Transient Anemia in 5F9 Anti-CD47 Treatment
The American Society of Hematology Annual Meeting (ASH) | December 2018

Combination Treatment with 5F9 and Azacitidine Enhances Phagocytic Elimination of Acute Myeloid Leukemia
The American Society of Hematology Annual Meeting (ASH) | December 2018

Initial Phase 1 Results of the First-in-Class Anti-CD47 Antibody Hu5F9-G4 in Relapsed/Refractory Acute Myeloid Leukemia Patients
Congress of The European Hematology Association (EHA) | June 2018

A First-in-class, First-in-human Phase 1 Pharmacokinetic (PK) and Pharmacodynamic (PD) Study of Hu5F9-G4 (5F9), an Anti-CD47 Monoclonal Antibody (mAb), in Patients with Advanced Solid Tumors
American Society of Clinical Oncology Annual Meeting (ASCO) | June 2018

Activity of the first-in-class anti-CD47 antibody Hu5F9-G4 with rituximab in relapsed/refractory non-Hodgkin's lymphoma: initial Phase 1b results
American Society of Clinical Oncology Annual Meeting (ASCO) | June 2018

Pharmacokinetics of Hu5F9-G4, a first-in-class anti-CD47 antibody, in patients with solid tumors and lymphomas
American Society of Clinical Oncology Annual Meeting (ASCO) | June 2018