SLAMF7: Activating Natural Killer Cells for Potent Anti-Cancer Responses

SLAMF7, also known as Signaling Lymphocytic Activation Molecule F7, is a surface receptor found on natural killer (NK) cells, T cells, plasma cells, and certain immune-regulatory cells. This receptor plays a crucial role in modulating immune responses, particularly by enhancing the cytotoxic activity of NK cells, which are a critical part of the body’s first line of defense against tumors. The SLAMF7 receptor, also referred to as CD319, has garnered significant attention as a target for cancer immunotherapy due to its ability to activate NK cells and facilitate tumor destruction.

In cancers such as multiple myeloma and solid tumors, SLAMF7 expression is often upregulated, making it a promising target for therapeutic intervention. Agents like the monoclonal antibody Hu19 are designed to enhance NK cell-mediated killing of cancer cells by engaging SLAMF7, leading to improved immune responses against tumors. This article explores the biology of SLAMF7, its role in cancer immunity, and the therapeutic potential of targeting SLAMF7 in cancer treatment.

SLAMF7 is a member of the SLAM family of receptors, which are expressed on various immune cells and play a key role in modulating cell signaling and immune activation. One of SLAMF7's primary functions is to activate NK cells, the innate immune cells responsible for detecting and destroying abnormal or infected cells, including cancer cells. SLAMF7 mediates NK cell activation through both homophilic interactions (SLAMF7 binding to itself on other immune cells) and heterophilic interactions with immune signaling molecules, thus enhancing immune surveillance.

The SLAMF7 receptor triggers immune signaling cascades when engaged, promoting NK cell activation, cytotoxic activity, and cytokine production. This results in the increased ability of NK cells to recognize and destroy tumor cells, making SLAMF7 a powerful lever in cancer immunotherapy.

SLAMF7 primarily signals through EAT-2, an adaptor protein that is expressed in NK cells and myeloid cells. Upon engagement of SLAMF7, EAT-2 is recruited to the receptor, initiating a signaling cascade that activates cytotoxic pathways in NK cells. This activation promotes:

• Degranulation of cytotoxic molecules (e.g., perforin and granzymes) to kill target cells.
• Production of pro-inflammatory cytokines like IFN-γ, which enhances the overall anti-tumor immune response.
• Antibody-dependent cellular cytotoxicity (ADCC), whereby NK cells recognize and kill antibody-coated tumor cells.

SLAMF7 signaling is critical not only for NK cell activation but also for immune coordination in the tumor microenvironment, enhancing the recruitment and activation of other immune cells.

SLAMF7 is overexpressed in several types of cancer, particularly in multiple myeloma, where it is highly expressed on plasma cells. In addition to multiple myeloma, SLAMF7 is also found on certain subsets of NK cells, making it an ideal target for immunotherapy in cancers where the immune system is compromised. The broad expression of SLAMF7 in tumor-associated immune cells and plasma cells allows therapies targeting this receptor to have a direct impact on both the cancer cells and the immune microenvironment. 

Cancer cells often develop mechanisms to evade immune destruction, such as downregulating surface markers that NK cells recognize. SLAMF7-targeted therapies help to overcome these immune evasion strategies by enhancing NK cell activation directly at the tumor site. SLAMF7 signaling boosts the natural killing capacity of NK cells and supports antibody-dependent cellular cytotoxicity (ADCC), which is crucial in cancers where traditional immune responses have been compromised.

In addition, SLAMF7-targeted therapies can reduce the immunosuppressive signals within the tumor microenvironment, making the cancer cells more vulnerable to immune attack.

Hu19 is a fully humanized monoclonal antibody that binds specifically to SLAMF7 on NK cells and myeloma cells, enhancing immune-mediated tumor destruction. The mechanism of action of Hu19 can be summarized as follows:

1. Engagement of SLAMF7: Hu19 binds to SLAMF7 receptors on NK cells, activating them and enhancing their cytotoxic function.
2. Direct tumor targeting: By binding to SLAMF7 on tumor cells, such as myeloma cells, Hu19 promotes their recognition by NK cells.
3. Facilitation of ADCC: Hu19-coated cancer cells are more efficiently targeted by NK cells through ADCC, leading to rapid tumor cell lysis.
4. Enhancement of cytokine production: NK cells activated by SLAMF7 produce higher levels of
   IFN-γ and TNF-α, which contribute to an inflammatory response against the tumor.

Hu19 and other SLAMF7-targeting agents have shown remarkable efficacy in the treatment of multiple myeloma, particularly in patients who are refractory to standard therapies. Clinical trials investigating the use of Hu19 in combination with other immunotherapies or standard chemotherapeutics have demonstrated enhanced tumor reduction and improved survival rates.

Hu19 is also being explored in combination with checkpoint inhibitors like anti-PD-1 to further boost the immune response. By overcoming multiple layers of immune evasion, this combination strategy could be especially effective in solid tumors that are resistant to conventional treatments.

In addition to multiple myeloma, SLAMF7-targeted therapies hold promise in other hematologic malignancies, such as non-Hodgkin’s lymphoma and chronic lymphocytic leukemia (CLL). In these cancers, SLAMF7 is expressed on immune cells that support the growth and survival of malignant cells. Targeting SLAMF7 in this context disrupts the tumor microenvironment and enhances the anti-cancer activity of NK cells.

Recent studies have also explored the potential of SLAMF7-targeting agents in solid tumors. Although SLAMF7 expression is less common in solid tumors compared to hematologic malignancies, its expression in the tumor microenvironment—especially on NK cells, macrophages, and dendritic cells—makes it a viable target for enhancing immune responses in these cancers. By activating immune cells within the tumor microenvironment, SLAMF7 therapies can promote better infiltration and activity of effector cells, leading to improved tumor clearance.

As with other immune-targeting therapies, SLAMF7 antibodies like Hu19 can lead to immune-related toxicities. The activation of NK cells and other immune cells can sometimes result in off-target effects, such as:

• Cytokine release syndrome (CRS), characterized by fever, fatigue, and inflammation.
• Hematologic toxicity, including anemia or thrombocytopenia, due to overactivation of immune
  cells in the bone marrow.

To minimize these risks, ongoing clinical trials are exploring optimal dosing strategies and combination regimens that balance efficacy with safety.

Some patients may develop resistance to SLAMF7-targeted therapies, either due to downregulation of SLAMF7 expression on tumor cells or compensatory immune-suppressive pathways in the tumor microenvironment. Combination therapies with checkpoint inhibitors, cytokine treatments (e.g., IL-15), or other immune-activating agents could help to overcome these resistance mechanisms and enhance the overall effectiveness of SLAMF7-targeted therapies.

As research continues to uncover the role of SLAMF7 in different cancers, expanding the use of SLAMF7-targeted therapies beyond multiple myeloma and hematologic cancers is a promising direction. Future studies will likely focus on:

• Identifying biomarkers that predict which patients will respond best to SLAMF7-targeted therapies.
• Exploring combination strategies that target other immune checkpoint receptors or co-stimulatory pathways.
• Investigating SLAMF7 expression in other solid tumors and rare malignancies to broaden the clinical application of SLAMF7-targeted agents like Hu19.

SLAMF7 is a powerful activator of NK cell function, making it a valuable target in cancer immunotherapy. Therapies like Hu19 leverage the SLAMF7 pathway to enhance NK cell-mediated tumor clearance, offering new hope for patients with cancers such as multiple myeloma and solid tumors. As research continues to advance, SLAMF7-targeted therapies are poised to become an integral part of cancer treatment, either as monotherapies or in combination with other immune-modulating agents. With ongoing clinical trials and promising results, SLAMF7 represents a crucial frontier in the fight against cancer.

1. Bouchon, A., et al., 2001. SLAM family receptors activate NK cell-mediated cytotoxicity through a SAP-dependent mechanism. Nature Immunology, 2(10), pp.918-924.


2. Veillette, A., et al., 2012. SLAM family receptors and SAP-related adaptors: matters arising. Trends in Immunology, 33(7), pp.386-393.


3. Pardoll, D.M., 2012. The blockade of immune checkpoints in cancer immunotherapy. Nature Reviews Cancer, 12(4), pp.252-264.


4. Maciocia, P.M., et al., 2017. Anti-SLAMF7 antibody elotuzumab enhances T-cell mediated anti-myeloma immunity via SLAMF7 expression on immune effector cells. Blood, 129(6), pp.987-998.


5. Richardson, P.G., et al., 2015. Elotuzumab incombination with lenalidomide and dexamethasone for relapsed multiple myeloma. New England Journal of Medicine, 373(7), pp.621-631.


6. Glouch, K., et al., 2019. SLAMF7 as a novel therapeutic target in non-Hodgkin’s lymphoma. Haematologica, 104(3), pp.477-482.


7. Paiva, B., et al., 2016. Elotuzumab in multiple myeloma: targeting SLAMF7. OncoTargets and Therapy, 9, pp.45-53.


8. Brown, J.R., et al., 2018. SLAMF7 as an immunotherapeutic target in solid tumors: opportunities and challenges. Frontiers in Immunology, 9, pp.2104.