CD7-targeted Antibody-Drug Conjugates: A New Hope for T-Cell Acute Lymphoblastic Leukemia-CAR-T Molecule Discovery Topic-Tekbiotech-Yeast and Phage Display CRO, Expert in Nano-body and Antibody Drug Development

CD7-targeted Antibody-Drug Conjugates: A New Hope for T-Cell Acute Lymphoblastic Leukemia

Currently, the treatment of T-cell acute lymphoblastic leukemia (T-ALL) is primarily based on intensive chemotherapy regimens, which achieve an overall survival rate of approximately 85% in children but less than 50% in adults. Therefore, there is an urgent need for new treatment options in the field of T-ALL. Preclinical studies and clinical trials have shown that inhibitors of two anti-apoptotic proteins in the BCL-2 family—BCL-XL and/or BCL-2—exhibit antileukemic activity against T-ALL. However, the efficacy of BCL-XL inhibitors (BCL-XLi) is compromised by severe target-related thrombocytopenia. Oliveira et al. [1] designed an antibody-drug conjugate (ADC) based on a novel anti-hCD7 monoclonal antibody (mAb), which carries a BCL-XL-selective inhibitor (ADC-CD7-BCL-XLi), thereby circumventing this major limitation. The study demonstrated that ADC-CD7-BCL-XLi effectively kills most T-ALL cell lines. Experiments using patient-derived xenograft (PDX) models from T-ALL patients further demonstrated that: (i) ADC-CD7-BCL-XLi exhibits potent antileukemic activity and is non-toxic to platelets; (ii) ADC-CD7-BCL-XLi exhibits a synergistic effect with the selective BCL-2 antagonist venetoclax, prolonging leukemia remission and mouse survival; (iii) the antileukemic effect of the ADC-CD7-BCL-XLi–venetoclax combination can achieve cure when used in conjunction with chemotherapy. These preclinical data strongly support evaluating the efficacy of ADC-CD7-BCL-XLi in patients with T-ALL and provide new insights for the development of antibody drugs targeting other refractory tumors.

I. Structural Design of ADC-CD7-BCL-XLi:

To avoid the systemic toxicity associated with BCL-XLi administration and selectively target leukemic lymphoblasts, this study engineered an anti-CD7-BCL-XLi antibody-drug conjugate (ADC-CD7-BCL-XLi) (Figure 1). The study employed a dipeptide linker (Mc-Val-Cit-PABC) cleavable by cathepsin M to couple the BCL-XLi inhibitor Payload 11, which exhibits high affinity and reduced cellular permeability, thereby minimizing toxicity.

Figure 1 Structural schematic diagram of ADC-CD7-BCL-XLi

II. ADC-CD7-BCL-XLi Exhibits Apoptotic Activity In Vitro

This study first analyzed the effect of ADC-CD7-BCL-XLi on the survival rates of a series of T-cell acute lymphoblastic leukemia (T-ALL) cell lines. Of the twenty T-ALL cell lines evaluated, fifteen exhibited specific and high sensitivity to ADC-CD7-BCL-XLi (IC?? values ranging from 10 pM to 4 nM; Figure 2a), while four exhibited moderate responsiveness (IC?? values ranging from 50 nM to 215 nM) or poor responsiveness (SUPT11, IC?? > 300 nM; Figure 2a). Importantly, the IC?? values for ADC-CD7-BCL-XLi were significantly lower than those for the unconjugated payload (Figure 2a) and correlated positively with CD7 expression levels (Figure 2b). As expected, both the payload and ADC-CD7-BCL-XLi induced apoptotic cell death in T-ALL cells.

Figure 2 Validation of the in vitro pro-apoptotic activity of ADC-CD7-BCL-XLi

III. Antileukemic Activity of ADC-CD7-BCL-XLi

This study evaluated the antitumor potential of ADC-CD7-BCL-XLi in NSG mice bearing subcutaneous xenografts of the ALL-SIL T-ALL cell line (Figure 3A) and compared its antitumor activity and platelet toxicity with those of the dual BCL-2/BCL-XL inhibitor navitoclax. Tumor-bearing NSG mice were administered either 15 mg/kg of ADC-CD7-BCL-XLi (Figure 3A, blue arrow) or 50 mg/kg of navitoclax (purple arrow), and tumor growth was compared with that of untreated mice (black curve). A single dose of ADC-CD7-BCL-XLi resulted in significant tumor regression, and compared with Navitoclax, its antitumor effect was faster, more profound, and more persistent (Figure 3B). Pharmacokinetic evaluations showed that the half-life of ADC-CD7-BCL-XLi ranged from 12.2 days (2.5 mg/kg) to 14.1 days (15 mg/kg) (Figure 3C), while only trace amounts of free payload were detected in the plasma of the test mice (Figure 3C). Navitoclax exhibited the expected pharmacokinetic characteristics (Figure 2C). Most importantly, thrombocytopenia was observed only in mice treated with navitoclax (Figure 3D, purple bars), whereas ADC-CD7-BCL-XLi did not affect platelet counts in mice (Figure 3D, blue bars).

图3 ADC-CD7-BCL-XLi的抗白血病作用及血小板毒性验证.png

Figure 3 Validation of the antileukemic activity and platelet toxicity of ADC-CD7-BCL-XLi

ADC-CD7-BCL-XLi and venetoclax act synergistically to inhibit leukemic cell proliferation

Subsequently, the study explored the potential synergistic effects of combining ADC-CD7-BCL-XLi with the BCL-2-selective inhibitor venetoclax. To validate this phenomenon in vivo, mice with T-ALL#2 xenografts were treated with either solvent, a single dose of ADC-CD7-BCL-XLi, venetoclax, or a combination of ADC-CD7-BCL-XLi and venetoclax. Leukemia burden and leukemia cell apoptosis were analyzed at 12, 36, and 60 hours post-treatment. As shown in Figure 4, ADC-CD7-BCL-XLi reduced the leukemia burden in the blood, bone marrow, and spleen over time; this effect was significantly enhanced when combined with venetoclax, whereas venetoclax alone had only a minimal effect. This is associated with a synergistic effect on apoptosis induction (Figure 4D), which was detectable as early as 12 hours post-treatment and remained observable at 60 hours, by which time leukemic cells were virtually undetectable in the mice. To investigate whether this antileukemic effect could translate into improved survival in mice, leukemic mice carrying two independent T-ALL patient-derived models (T-ALL#2 and #3) were treated with a solvent control (black curve), Iso-BCL-XLi + venetoclax (dark gray curve), naked CD7 antibody (alone, light gray solid line; or in combination with venetoclax, light gray dashed line), and ADC-CD7-BCL-XLi (alone, blue curve; or in combination with venetoclax, pink curve) (see Figure 4E for a schematic diagram). As shown in Figure 4F, compared with the control group, monotherapy with ADC-CD7-BCL-XLi significantly delayed leukemia progression, whereas the antileukemic effect of venetoclax was negligible. Notably, compared with ADC-CD7-BCL-XLi alone, the dual administration of ADC-CD7-BCL-XLi and venetoclax significantly inhibited leukemic cell proliferation and substantially prolonged the time to relapse (Figure 4F). Furthermore, this combination therapy improved survival outcomes: mice that received allogeneic transplants of T-ALL #2 and T-ALL #3 survived for up to 140 days, whereas in the group treated with ADC-CD7-BCL-XLi alone, T-ALL #2 mice survived for 83 days and T-ALL #3 mice survived for 102 days (Figure 4G).

图4 ADC-CD7-BCL-XLi与维奈托克协同作用验证.png

Figure 4 Validation of the synergistic effect of ADC-CD7-BCL-XLi and venetoclax

IV.Summary:

This study demonstrated that an antibody-drug conjugate (ADC) based on a novel anti-hCD7 monoclonal antibody (mAb)—namely, ADC-CD7-BCL-XLi—can effectively kill most T-ALL cell lines and exhibits potent antileukemic activity in PDX models, with no toxicity to platelets. It exhibits a synergistic effect with the selective BCL-2 antagonist venetoclax, prolonging remission duration and survival in mice; the antileukemic effect of the combination with venetoclax can achieve a cure when used in conjunction with chemotherapy. These preclinical data provide guidance for future evaluation of ADC-CD7-BCL-XLi in T-ALL patients and offer new insights for the development of antibody-drug conjugates targeting other refractory tumors.

About TekBio:

TekBio (Tianjin) Co., Ltd. has established a comprehensive platform for the development of targeted antibody drugs based on phage display and yeast display technologies. The company is committed to providing scientists worldwide with high-quality, one-stop ADC drug development and druggability assessment services, including the discovery of candidate sequences for targeted antibody drugs, antibody humanization, antibody affinity maturation, ADC design and synthesis, cell-binding validation, cytotoxicity validation, and animal model validation, providing robust support for drug R&D targeting refractory tumors and diseases associated with “undruggable” targets.

References:

[1] Oliveira, M.L., Nuantang, K., Huré, G. et al. A novel CD7-directed antibody-drug conjugate targeting BCL-XL with potent anti-leukemic activity in T-cell acute lymphoblastic leukemia. Leukemia (2026).

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