Antibody-dependent difference in biodistribution of monoclonal antibodies in animal models and humans

Screening and characterization of the scFv for chimeric antigen receptor T cells targeting CEA-positive carcinoma

Introduction

Chimeric antigen receptor T (CAR-T) cell therapy presents a promising treatment option for various cancers, including solid tumors. Carcinoembryonic antigen (CEA) is an attractive target due to its high expression in many tumors, particularly gastrointestinal cancers, while limited expression in normal adult tissues. In our previous clinical study, we reported a 70% disease control rate with no severe side effects using a humanized CEA-targeting CAR-T cell. However, the selection of the appropriate single-chain variable fragment (scFv) significantly affects the therapeutic efficacy of CAR-T cells by defining their specific behavior towards the target antigen. Therefore, this study aimed to identify the optimal scFv and investigate its biological functions to further optimize the therapeutic potential of CAR-T cells targeting CEA-positive carcinoma.

Methods

We screened four reported humanized or fully human anti-CEA antibodies (M5A, hMN-14, BW431/26, and C2-45), and inserted them into a 3rd-generation CAR structure. We purified the scFvs and measured the affinity. We monitored CAR-T cell phenotype and scFv binding stability to CEA antigen through flow cytometry. We performed repeated CEA antigen stimulation assays to compare the proliferation potential and response of the four CAR-T cells, then further evaluated the anti-tumor efficacy of CAR-T cells ex vivo and in vivo.

Results

M5A and hMN-14 CARs displayed higher affinity and more stable CEA binding ability than BW431/26 and C2-45 CARs. During CAR-T cell production culture, hMN-14 CAR-T cells exhibit a larger proportion of memory-like T cells, while M5A CAR-T cells showed a more differentiated phenotype, suggesting a greater tonic signal of M5A scFv. M5A, hMN-14, and BW431/26 CAR-T cells exhibited effective tumor cell lysis and IFN-γ release when cocultured with CEA-positive tumor cells in vitro, correlating with the abundance of CEA expression in target cells. While C2-45 resulted in almost no tumor lysis or IFN-γ release. In a repeat CEA antigen stimulation assay, M5A showed the best cell proliferation and cytokine secretion levels. In a mouse xenograft model, M5A CAR-T cells displayed better antitumor efficacy without preconditioning.

Discussion

Our findings suggest that scFvs derived from different antibodies have distinctive characteristics, and stable expression and appropriate affinity are critical for robust antitumor efficacy. This study highlights the importance of selecting an optimal scFv in CAR-T cell design for effective CEA-targeted therapy. The identified optimal scFv, M5A, could be potentially applied in future clinical trials of CAR-T cell therapy targeting CEA-positive carcinoma.

Potential of three-step pretargeting radioimmunotherapy using biotinylated bevacizumab and succinylated streptavidin in triple-negative breast cancer xenograft

OBJECTIVE

Pretargeting radioimmunotherapy (PRIT) is a promising approach that can reduce long-time retention of blood radioactivity and consequently reduce hematotoxicity. Among the PRIT strategies, the combination of biotin-conjugated mAb and radiolabeled streptavidin (StAv) is a simple and convenient method because of its ease of preparation. This study performed three-step (3-step) PRIT using the sequential injection of (1) biotinylated bevacizumab (Bt-BV), (2) avidin, and (3) radiolabeled StAv for the treatment of triple-negative breast cancer (TNBC).

METHODS

Four biodistribution studies were performed using ¹¹¹In in tumor-bearing mice to optimize each step of our PRIT methods. Further, a therapeutic study was performed with optimized 3-step PRIT using ⁹⁰Y-labeled StAv.

RESULTS

Based on the biodistribution studies, the protein dose of Bt-BV and avidin was optimized to 100 μg and 10 molar equivalent of BV, respectively. Succinylation of StAv significantly decreased the kidney accumulation level (with succinylation (6.96 ± 0.91) vs without succinylation (20.60 ± 1.47) at 1 h after injection, p < 0.0001) with little effect on the tumor accumulation level. In the therapeutic study, tumor growth was significantly suppressed in treatment groups with optimized 3-step PRIT using ⁹⁰Y-labeled succinylated StAv compared to that of the no-treatment group (p < 0.05).

CONCLUSIONS

The 3-step PRIT strategy of this study achieved fast blood clearance and low kidney uptake with little effect on the tumor accumulation level, and a certain degree of therapeutic effect was consequently observed. These results indicated that the pretargeting treatment of the current study may be effective for human TNBC treatment.

90Y-Labeled Anti-ROBO1 Monoclonal Antibody Exhibits Antitumor Activity against Small Cell Lung Cancer Xenografts

INTRODUCTION

ROBO1 is a membrane protein that contributes to tumor metastasis and angiogenesis. We previously reported that 90Y-labeled anti-ROBO1 monoclonal antibody (90Y-anti-ROBO1 IgG) showed an antitumor effect against ROBO1-positive tumors. In this study, we performed a biodistribution study and radioimmunotherapy (RIT) against ROBO1-positive small cell lung cancer (SCLC) models.

METHODS

For the biodistribution study, 111In-labeled anti-ROBO1 monoclonal antibody (111In-anti-ROBO1 IgG) was injected into ROBO1-positive SCLC xenograft mice via the tail vein. To evaluate antitumor effects, an RIT study was performed, and SCLC xenograft mice were treated with 90Y-anti-ROBO1 IgG. Tumor volume and body weight were periodically measured throughout the experiments. The tumors and organs of mice were then collected, and a pathological analysis was carried out.

RESULTS

As a result of the biodistribution study, we observed tumor uptake of 111In-anti-ROBO1 IgG. The liver, kidney, spleen, and lung showed comparably high accumulation of 111In-labeled anti-ROBO1. In the RIT study, 90Y-anti-ROBO1 IgG significantly reduced tumor volume compared with baseline. Pathological analyses of tumors revealed coagulation necrosis and fatal degeneration of tumor cells, significant reduction in the number of Ki-67-positive cells, and an increase in the number of apoptotic cells. A transient reduction of hematopoietic cells was observed in the spleen, sternum, and femur.

CONCLUSIONS

These results suggest that RIT with 90Y-anti-ROBO1 IgG is a promising treatment for ROBO1-positive SCLC.

Novel mouse model for carcinoembryonic antigen-based therapy

Many novel cancer therapies, including immunotherapy and gene therapy, are specifically targeted to tumor-associated molecules, among which carcinoembryonic antigen (CEA) represents a popular example. Discrepancies between preclinical experimental data in animal models and clinical outcome in terms of therapeutic response and toxicity, however, often arise. Preclinical testing can be compromised by the lack of CEA and other closely related human CEA family members in rodents, which lack analogous genes for most human CEA family members. Here, we report the construction of a transgenic mouse with a 187-kb human bacterial artificial chromosome (CEABAC) that contains part of the human CEA family gene cluster including complete human CEA (CEACAM5), CEACAM3, CEACAM6, and CEACAM7 genes. The spatiotemporal expression pattern of these genes in the CEABAC mice was found to be remarkably similar to that of humans. This novel mouse will ensure better assessment than previously utilized models for the preclinical testing of CEA-targeted therapies and perhaps allow the testing of CEACAM6, which is overexpressed in many solid tumors and leukemias, as a therapeutic target. Moreover, expression of CEA family genes in gastrointestinal, breast, hematopoietic, urogenital, and respiratory systems could facilitate other clinical applications, such as the development of therapeutic agents against Neisseria gonorrhoeae infections, which use CEA family members as major receptors.