Reinforcing cancer immunotherapy with engineered porous hollow mycobacterium tuberculosis loaded with tumor neoantigens

Background: Enhancing antigen cross-presentation is essential for the development of a tumor neoantigen vaccine. One approach is to stimulate antigen-presenting cells (APCs) to uptake neoantigens. Mycobacterium tuberculosis (MTb) contains pathogen-associated molecular patterns (PAMPs) recognized by APCs and adhesion molecules that facilitate MTb invasion of APCs. Therefore, we suggest using MTb as a carrier to enhance APC phagocytosis of neoantigens, thereby promoting antigen cross-presentation.

Methods: The successful preparation of the MTb carrier (phMTb) was confirmed through electron and confocal microscopy. Fluorescence microscopy was used to detect PAMPs and adhesion molecules on phMTb as well as to observe its role in aiding dendritic cells (DCs) in antigen uptake into endosomes or lysosomes. Flow cytometry was used to assess the retention of PAMPs and adhesion molecules on phMTb, investigate antigen uptake by DCs, evaluate their activation and maturation status, examine the presentation of tumor neoantigens, and analyze immune cells in draining lymph nodes and tumor tissues. The efficacy of phMTb vaccine formulations in combination with anti-programmed cell death protein 1 (PD-1) antibody therapy was assessed using the MC38 mouse tumor models. Adverse effects were evaluated through H&E staining of major organs, assessment of reproductive capability and detection of biochemical indices.

Results: The engineered porous hollow phMTb carrier successfully encapsulated model tumor neoantigens, with or without the Adjuvant CpG. The phMTb retained PAMPs and adhesion molecules on its surface, similar to the parental MTb, thereby enhancing DC uptake of phMTb and its formulations containing tumor neoantigens and CpG. Vaccines formulated with phMTb facilitated DC maturation, activation, cross-presentation of tumor neoantigens, and promoted migration of phMTb-laden DCs to lymph nodes, enhancing effector and memory CD8⁺ T lymphocyte function. In murine tumor models, immunization with phMTb-formulated neoantigen vaccines elicited a robust tumor-specific cytotoxic T lymphocyte immune response with minimal adverse effects. Additionally, vaccination with phMTb-formulated neoantigen vaccines effectively reversed the tumor's immune-suppressive microenvironment. Concurrent administration of the PD-1 antibody with the phMTb-formulated neoantigen vaccine exhibited significant synergistic therapeutic effects.

Conclusions: The results of our study highlight the potential clinical translation of personalized tumor neoantigen vaccines using the phMTb carrier.

Adjuvant; Immune Checkpoint Inhibitor; Immunotherapy; Major histocompatibility complex - MHC; Vaccine.