ML7710 for photoimmunotherapy against regulatory T cells in tumors

Customer case

The Laboratory of Molecular Theranostics is a major research section of the Molecular Imaging Program at National Cancer Institute (NCI) and is led by Dr. Hisataka Kobayashi. The groundbreaking research includes the development of imaging and theranostic probes, which can aid in cancer detection and treatment. Dr. Kobayashi has invented near-infrared photoimmunotherapy (NIR-PIT) with IRDye700DX, which has been commercialized by Rakuten Medical and was approved in Japan in 2020 and is currently in FDA-designated fast-track global Phase 3 trials for inoperable Head & Neck cancer.

Dr. Hisataka Kobayashi M.D., PhD


Dr. Peter L. Choyke M.D., PhD



Modulight products: ML7710 (multiple channels on 689 nm, 2 W)

Laser use: High-throughput in vivo illumination to study photoimmunotherapy of cancer targeted against various molecular targets including EGFR, HER2, CTLA-4, and CD25. Multi-channel ML7710 laser system was used to illuminate multiple test subjects in parallel enabling controlled and high-throughput in vivo experiments.

Link to the study:



Body’s immune system detects and destroys abnormal cells and prevents the growth of cancers as part of its normal function. However, cancers often develop strategies to evade or suppress immune system so that they can continue growing without being destroyed. Cancer immunotherapies, such as immune checkpoint inhibition or CAR T cell therapy, help the patient’s own immune system to fight these cancers. Immunotherapies have achieved dramatic clinical success during the past decade and resulted in lasting remissions even in cancer patients that were previously considered terminally ill.

One key immunotherapy strategy is to eliminate immune suppressor cells such as regulatory T cells (Tregs) from the tumors. Typically a large number of Tregs infiltrate cancers and their presence correlates with a poor prognosis. These cells prevent tumor-infiltrating killer T cells from destroying the tumor and depletion of Tregs might result in tumor regression through activation and amplification of killer T cells. CD25 is a highly expressed target molecule on the surface of Tregs and could be targeted with immunotherapy to selectively eliminate these cells.

Near-infrared photoimmunotherapy (PIT) is a novel type of immunotherapy that utilizes photoabsorber IRDye700DX conjugated to tumor cell-targeting antibody. The photoactive component is then activated with near-infrared (NIR) light at 689 nm to induce the therapeutic response. This therapy modality has been shown to be effective in directly targeting cancer cells while targeting tumor microenvironment such as Tregs could be applicable to many different tumor types and become a versatile cancer therapy.


Motivation for the study

This study is aimed to design an effective CD25-targeted photoimmunotherapy strategy against tumor-infiltrated Tregs for cancer treatment. However, the problem with using antibody (IgG) against CD25, also known as IL-2 receptor α-chain, is that it can also block interleukin-2 (IL-2) cytokine from binding to killer T cells which is needed for their proliferation and survival. This might undesirably decrease antitumor immune response. Therefore, solution was to use antibody fragments that have much faster clearance from the circulation and this way less opportunity to suppress activated killer T cells once the Tregs have been depleted. The efficacy of photoimmunotherapy was in this study compared between using full IgG antibody and F(ab’)2 antibody fragments for CD25-targeting.




The above schematics are reproduced from the original publication.



Tumor-bearing mice were randomized into 4 groups: 1) no treatment (control), 2) anti-CD25 full IgG antibody (no light activation), 3) anti-CD25 F(ab’)2 fragment, and 4) anti-CD25 full IgG antibody. NIR light using ML7710 (689 nm, 150 mW/cm2, 50 J/cm2) was administered to group 3 and 4 mice on day 1 (PIT). Tumor volumes were monitored for 21 days and survival of mice for up to 80 days.

Photoimmunotherapy was also studied in mice with bilateral tumors to evaluate the ability of killer T cells to migrate and attack similar type of tumors elsewhere in the body after photoimmunotherapy (abscopal effect). The left-hand-side tumor (NIR- tumor) was covered with aluminum foil and only the right-hand-side tumor (NIR+ tumor) received 50J/cm2 689 nm light using ML7710 multi-channel laser system. The amount of tumor-infiltrating killer T cells was also determined with multiplex immunohistochemical analysis 7 days after 689 nm light exposure.



Tumor growth was significantly inhibited in mice receiving photoimmunotherapy, while anti-CD25 IgG without light activation did not affect tumor growth (Figure 1). Photoimmunotherapy with F(ab)2 antibody fragments resulted in significantly better tumor growth suppression than full IgG antibody. Mice treated with F(ab’)2 photoimmunotherapy also survived much longer than mice receiving IgG: over 50% of these mice were still alive after 80 days (Figure 2).


Figure 1. Tumor growth compared between the study groups.


Figure 2. Survival of mice compared between the study groups.


In mice with bilateral tumors, growth of untreated tumors was significantly more inhibited in mice treated with F(ab’)2 photoimmunotherapy compared to mice treated with full IgG antibody (Figure 3). These mice also survived significantly longer than mice treated with full antibody, over 40% of mice being alive after 60 days. Also higher amount of tumor-infiltrating killer T cells were detected from the tumors in the F(ab’)2 group than in the IgG group, supporting the higher photoimmunotherapy efficacy in untreated tumors of the F(ab’)2 group.


Figure 3. Tumor growth compared in mice with bilateral tumors, one tumor receiving light (NIR+) and other one not (NIR-).

Figure 4. Survival of mice with bilateral tumors after photoimmunotherapy with F(ab’)2 or full IgG antibody.


Graphs from the original publication. Reproduced with permission from the contact author of the publication.



Anti-CD25 targeted photoimmunotherapy against tumor-infiltrating Treg cells demonstrated superior efficacy in vivo when F(ab’)2 antibody fragments were used compared to full IgG antibody. The therapeutic effect was also not limited to the immediate treated site but was able to effectively eradicate tumors elsewhere in the body. This systemic effect is mediated by killer T cells, which were found in much higher numbers in tumors treated with F(ab’)2 since this antibody fragment with faster clearance does not block the crucial IL2 binding to killer T cells. In future, efficacy might be further increased by combining this tumor microenvironment-targeted strategy with conventional photoimmunotherapy that directly targets the cancer cells.


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Related Publications

The Effect of Antibody Fragments on CD25 Targeted Regulatory T Cell Near-Infrared Photoimmunotherapy
Ryuhei Okada, Yasuhiro Maruoka, Aki Furusawa, Fuyuki Inagaki, Tadanobu Nagaya, Daiki Fujimura, Peter L. Choyke, Hisataka Kobayashi
Bioconjug Chem, 2019, 30 (10)




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