# FAK signaling suppression by OCT4-ITGA6 mediates the effectively removal of residual pluripotent stem cells and enhances application safety

## TL;DR

This study introduces a method to safely remove leftover stem cells after differentiation, reducing the risk of tumor formation in regenerative therapies.

## Contribution

A novel strategy using BSS(Ca-Mg-) to selectively detach residual pluripotent stem cells while preserving differentiated cells.

## Key findings

- BSS(Ca-Mg-) treatment effectively removes PSCs without affecting iDCs in co-culture systems.
- BSS(Ca-Mg-) treatment prevents teratoma formation in immunodeficient mice.
- OCT4 and ITGA6 form a feedback loop suppressing FAK signaling in PSCs.

## Abstract

Rationale: Pluripotent stem cells (PSCs) serve as a critical source of seed cells for regenerative therapies due to their unlimited proliferative capacity and ability to differentiate into all three germ layers. Despite their potential, the risk of teratoma formation caused by residual PSCs within differentiated cell populations poses a significant barrier to clinical applications. This study aims to develop a novel strategy to selectively remove residual PSCs while preserving the safety and functionality of PSC-derived differentiated cells (iDCs).

Methods: The calcium- and magnesium-free balanced salt solution (BSS(Ca-Mg-)) was employed to selectively target PSCs in a co-culture system comprising PSCs and four types of iDCs. The effect of BSS(Ca-Mg-) treatment on teratoma formation was evaluated in immunodeficient mice following cell transplantation. Comparative analysis and gene knockdown experiments were conducted to explore the molecular mechanisms underlying the differential response of PSCs and iDCs to BSS(Ca-Mg-), focusing on FAK signaling and its interaction with OCT4 and ITGA6.

Results: The BSS(Ca-Mg-) treatment effectively induced the detachment of PSCs in the co-culture system without disrupting iDC adhesion. In vivo experiments confirmed that cells treated with BSS(Ca-Mg-) did not form teratomas upon implantation into immunodeficient mice. Mechanistic studies revealed that PSCs exhibit lower activation of FAK signaling compared to iDCs, contributing to their selective detachment. Additionally, OCT4 and ITGA6 were found to maintain each other's protein expression, forming a feedback loop that suppressed FAK signaling, while FAK suppression further enhanced OCT4 expression.

Conclusions: The study presents a safe, effective, and cost-efficient method for the selective removal of residual PSCs. This approach enhances existing safety measures for iDC applications, improving the clinical feasibility of iDC-based cell therapies.