Cancer immunotherapy harnessed an individual's immune system to detect and destroy tumor cells. [[1], [2], [3]] The blooming of immune checkpoints therapy has been witnessed in provoking systemic responses against tumors, while unitary therapeutic modality was incapable to reverse immunosuppression. [4,5] Reprogramming the immunosuppressive tumor microenvironment (TME) to enhanced tumor immunogenicity and obtain sufficient T cell infiltration has been considered as attractive strategies to induce integrated immune responses. [[6], [7], [8]] Chemokines, as noncellular mediators, play a critical role to establish and maintain the TME. [[9], [10], [11]] CXCR4, overexpressed in a variety of tumor membranes, and its cognate ligand CXCL12 produced by cancer-associated fibroblast (CAF), are closely related to tumor growth and invasion. [[12], [13], [14]] CXCR4/CXCL12 signaling axis modulates the immune microenvironment by suppressing the intratumoral accumulation of T cells. [[15], [16], [17]] AMD3100, a small-molecule CXCR4 antagonist has shown encouraging anti-tumor effect in improving tumor apoptosis, inducing T cell infiltration and selectively decreasing regulatory T cells. [[18], [19], [20]] Much effort has been directed towards developing CXCR4 antagonists that regulate the immune process to enhance anti–PD-L1 immunotherapy. [[21], [22], [23]] CXCR4 antagonists has the defects of easy degradation and non-targeting, so it is urgent to find safe and effective vehicles in vivo. [24,25]

Nano-scaled vehicles based delivery systems are widely investigated in tumor therapy owing to their merits on longer blood circulation time, tumor targetability and low cytotoxicity. [26,27] Nano-encapsulation of CXCR4 antagonists can enhance its physiological stability and improve the delivery efficiency to tumor site. [[28], [29], [30], [31], [32]] However, traditional nanocarriers are easily internalized by tumor cells, resulting in low drug concentration and short residence time of CXCR4 antagonists on cell surface, followed by poor blocking efficiency. [[33], [34], [35]] The “in vivo self-assembly” strategy, showed an assembly/aggregation induced retention (AIR) effect, may provide opportunities to meet this challenge. [[36], [37], [38]] Designing by the characteristic of TME to construct reassembled nanomaterials in vivo may improve their biological performance in tumor diagnostics. [[39], [40], [41]] We previously presented enzyme-responsive polymer–peptide conjugates (PPCs) to achieve re-assembly in the tumor region, realized long-term accumulation and enhanced PD-L1 blocking efficiency. [42] Inspired by AIR effect, we hypothesize a cytomembrane-located morphology transformation platform to obtain improved CXCR4 antagonists concentration on cell surface and enhanced the biological function.

Herein, we propose a specifically CXCR4/CXCL12 disrupting strategy to modulate immune response and enhance anti–PD-L1 immunotherapy with CXCR4 antagonists (AMD3100) grafted polymer-peptide conjugates (PPCs). The PPCs are composed of (i) an acryl chitosan backbone, (ii) a pH-cleavable acylhydrazone bond with a poly (ethylene glycol) (PEG, Mw: 2 kDa) terminal, (iii) P: a PD-L1 antagonist (DPPA-1, NYSKPTDRQYHF) and AMD3100 were linked to acryl chitosan via secondary amine group. The resultant PPCs can self-assemble into spherical nanostructures. After reaching the tumor, the nanoparticles rapidly responded to the weakly acidic pH in TME and transformed into nanofibers, increasing DPPA-1 and AMD3100 exposure and prolonging retention time (Scheme 1). The reassembled nanofibers intertwine around tumor cells, which is beneficial to the long-term combined blockade of PD-L1 and CXCR4, and then induce activation cytotoxic T lymphocytes (CTLs) and overcome immune exclusion. Indocyanine green (ICG), a photosensitizer, is chosen to convert near-infrared light energy into heat energy to cause ICD and increase the sensitivity of tumor cells to CTL killing (Scheme 2). In addition, the prolonged CXCR4 and PD-L1 combined blockade synergized with photothermal therapy (PTT) shows obvious distal effects and inhibits tumor metastasis so as to remarkably expand the benefit of immunotherapy.