# In Situ Engineering of Tumor Cells as Self‐Sustaining cDC1 Programming Factories for Effective Cancer Immunotherapy

## TL;DR

This paper introduces a new method to reprogram tumor cells to boost immune responses by creating self-sustaining factories that produce immune-boosting signals.

## Contribution

A novel extracellular vesicle platform is developed to engineer tumor cells into in situ cDC1 programming factories for enhanced cancer immunotherapy.

## Key findings

- The engineered EV platform promotes recruitment, differentiation, and activation of cDC1s within the tumor microenvironment.
- The approach significantly inhibits tumor growth and prevents metastasis and recurrence through immune memory.
- The EV platform disrupts VEGF–NRP1 interaction to prevent cDC1 exhaustion.

## Abstract

Conventional type 1 dendritic cells (cDC1s) play a crucial role in initiating and regulating antitumor immunity. However, the insufficient infiltration and dysfunctional state of these cells within the tumor microenvironment hinder antitumor immune response. A tumor‐derived extracellular vesicle (EV), termed AS16‐EL@MPLA/p‐FX, is designed to engineer tumor cells into cDC1 programming factories. The EV lumen carries a plasmid encoding XCL1 and FLT3L. Leveraging the prolonged circulation time and homotypic targeting properties of tumor‐derived EV, AS16‐EL@MPLA/p‐FX demonstrates enhanced tumor‐selective accumulation and efficient cellular internalization. Following uptake, tumor cells are reprogrammed into in situ cytokine factories that continuously secrete XCL1 and FLT3L, which effectively recruit and differentiate cDC1s within the tumor microenvironment. Simultaneously, MPLA embedded in the EV membrane is released locally and activates the newly accumulated cDC1s through the TLR4 pathway. Furthermore, an AS16 peptide is tethered to the EV surface via a matrix metalloproteinase‐2–cleavable linker. The enzymatic release of AS16 disrupts the VEGF–NRP1 interaction, preventing cDC1 exhaustion. The engineered EV, AS16‐EL@MPLA/p‐FX, exhibited remarkable tumor‐targeting capabilities, promoting the recruitment, differentiation, and activation of cDC1s. This innovative approach not only significantly inhibited tumor growth but also triggered a robust immune memory response, safeguarding against tumor metastasis and recurrence.

The fused EV platform AS16‐EL@MPLA/p‐FX reprograms tumor cells into cytokine‐producing factories that continuously secrete XCL1 and FLT3L to recruit and differentiate cDC1s, while embedded MPLA activates them through TLR4 signaling and AS16 prevents their exhaustion, thereby enhancing antitumor immunity and establishing durable immune memory against tumor progression, metastasis, and recurrence.