自由論題［投稿論文：研究ノート］

Synthetic Tumor Recruited ImmunoCellular Therapy (STRICT)
合成腫瘍リクルート免疫細胞療法
Cherry Yingchi Lu

Second Year, Faculty of Environment and Information Studies, Keio University
Dana-Farber Cancer Institute, Harvard Medical School
Graduate School of Science, The University of Tokyo盧 盈綺慶應義塾大学環境情報学部 2 年
ハーバード大学医学部ダナ・ファーバー癌研究所
東京大学大学院理学系研究科
Correspondence to: cherryyclu@keio.jp

Abstract:

Synthetic Tumor Recruited Immuno-Cellular Therapy (STRICT) enables
tumor-localized therapeutic payload by recruitment and activation of immune cells
to improve existing treatment regiments for metastatic cancer and alleviate triplenegative breast cancer (TNBC).
合成腫瘍リクルート免疫細胞療法（STRICT）は、腫瘍に限局したペイロードの産生を可能にし、免疫細胞の勧誘と活性化により転移性癌の既存の治療レジメンを改善、トリプルネガティブ乳癌（TNBC）の治療に有望な治療法である。

Keywords: breast cancer, cancer immunotherapy, gene circuits
乳がん、がん免疫療法、遺伝子回路

1Introduction
Breast cancer is a disease where cells in the lobules in milk glands or ducts thatconnect the lobules to the nipple undergo uncontrolled division, resulting in theformation of abnormal lumps or masses. In the United States, breast cancer is adisease that most commonly aﬀects women. Approximately one in eight women in
the United States will experience the development of invasive breast cancer during64Synthetic Tumor Recruited Immuno-Cellular Therapy (STRICT)

their lifetime. Among all breast cancer subtypes, triple-negative breast cancer(TNBC) has comparably worse prognosis and often relapses after treatment.
Traditional cancer immunotherapies have demonstrated potential, but significant
challenges persist in treating solid tumors, such as breast cancer. Despite remarkableprogress with multiple novel agents targeting ER+ or HER2+ breast cancers,
treatment is limited to cytotoxic chemotherapy, and few options have developed in
the past decades. The overall response rate of several early-phase clinical trials ofadvanced TNBC therapies was lower than 10%. Due to the low mutation burden ofbreast cancer, it forms hard-to-penetrate tumor masses. It also creates animmunosuppressive tumor microenvironment (TME) that limits immune cell
recruitment, inﬁltration, and activation.
Gene therapies are increasingly applied to deliver payload genes into cancer
cells to trigger anti-tumor immunity. Examples include intra-tumoral injection ofviral vectors1) developed to produce chemokines to enhance immune cell recruitment.
Despite intra-tumoral injection, the possibility for non-specific infection ofsurrounding normal cells remains, and breast cancer patients often do not respond toa single immunotherapy agent such as a checkpoint inhibitor. Therefore, combination
therapies have been used to enhance the response rate. However, combination
therapies generally trigger signiﬁcantly higher systemic toxicity than monotherapy
and are challenging to administer. As the breast cancer microenvironment strongly
inhibits functional immune cell recruitment and activation, chimeric antigen receptor(CAR)-T cells have shown limited eﬃcacy to date. To combat this challenge, we areconstructing Synthetic Tumor Recruited Immuno-Cellular Therapy (STRICT), a
second-generation immunotherapy system to enhance specificity and efficacy.
STRICT utilizes gene circuits that are encoded in viruses and delivered to the target
sites to enable the production of therapeutic payloads for the recruitment andactivation of immune cells.

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2Research Question
STRICT gene circuits are designed to sense the activities of two cancer-

associated transcription factors (TFs) within the cells. These circuits use Booleanlogic computation to determine if the cell is cancerous, and are programmed to detectpre-deﬁned intracellular tumor signatures. Only when the activities of both TFs arehigh, the circuits will trigger tumor-localized combinatorial immunotherapy, while
keeping normal cells from harm. If the cell is considered cancerous, the circuit will
hijack and command the cell, producing an eﬀective tumor-localized combinatorial
immunotherapy. Thus, we leveraged STRICT to induce a more effective tumorlocalized anti-TNBC immunity with less systemic toxicity and evaluatedcombinatorial immunotherapies to overcome TNBC resistance for other challenging
cancer types.
STRICT was validated in TNBC cell lines and primary patient tumors, but not
in normal mammary epithelium in vitro. STRICT will be validated in the whole
mouse body in vivo to minimize any potential oﬀ-target toxicity when administeredsystematically. To achieve maximal delivery and therapeutic output combinations, weexamined STRICTʼs ability to express tumor-localized combinatorial immunotherapy
and its eﬃcacy in triggering an immune response to reduce TNBC cells in vitro andin vivo. We measured T-cell-mediated cytotoxicity and cytokine production in vitro.
We will continue to measure tumor burden and survival benefit and identify theminimal delivery requirement for achieving robust eﬃcacy in vivo.

3Discussion
STRICT may trigger systemic toxicity in advanced metastatic breast cancer

because high-level production of cytokines may result in systemic exposure.
However, we aim to address this challenge by utilizing a small molecule inducible
transcription factor to replace GAD (a fusion protein consisting of the yeast GAL4
DNA-binding domain and the viral VP16 transcriptional activation domain), which
drives output production in STRICT. This will allow ﬁne-tuning of output level by66

Synthetic Tumor Recruited Immuno-Cellular Therapy (STRICT)

adjusting the dosage of small molecule inducers. We will also measure systemic
cytokine levels and signs of systemic toxicity to validate the safety profile.
Furthermore, we are developing composite sensors that identify TNBC-speciﬁc TFs
through screening to enhance the detection of heterogenous TNBC samples.
Additionally, as one-third of invasive breast cancer patients relapse after therapy, we
hope to leverage STRICT to eliminate systemic metastasis and establish long-term
immune memory2) to obviate tumor replacement and morbid systemic chemotherapy.

4Conclusion
We demonstrated that STRICT mediates robust therapeutic eﬃcacy in TNBC invitro, even when only a small fraction of tumor cells was delivered with the circuit.
To further accomplish the clinical translation of STRICT, we continue to build breast
cancer-specific circuits that efficiently detect highly heterogeneous patient tumors,and optimize tumor-targeting efficiency, specificity, and therapeutic output
combinations to encode these circuits into FDA-approved viral vehicles3). We hope toutilize STRICT to achieve maximal anti-tumor immunity, prevent relapse, and elicit arobust host immune response against metastatic TNBC.
Acknowledgements
Y.L. thanks Prof. Ming-Ru, Wu4)-9) from the Dana-Farber Cancer Institute, Harvard Medical
School, Department of Cancer Immunology & Virology for supervising the research andproviding scientiﬁc guidance and analysis. Y.L thanks our collaborators Dr. Antonio Chioccafrom the Brigham and Women Hospital, for expertise and clinical implementation of STRICT10).
This work was supported by the Dana-Farber Cancer Institute and Harvard Medical School.
Y.L. thanks the support of Keio Academic Research Society, Prof. Keisuke Goda fromGraduate School of Science, The University of Tokyo; Prof. Masahiro Sonoshita from theInstitute of Genetic Medicine, Hokkaido University; Prof. Tamiki Komatsuzaki from theGraduate School of Life Science, Hokkaido University; and Asst. Prof. Jorgen Walker Petersonfrom the Graduate School of Science, The University of Tokyo for visiting our research site.

Conflict of interest
There are no potential conﬂicts of interest.

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1)〔受付日 2022. 11. 12〕〔採録日 2023. 2. 8〕68