Spontaneously immortalized porcine cells support scalable cultured pork production in serum-free suspension

Technical Summary: Spontaneously Immortalized Porcine Cells for Scalable Cultured Pork Production

Problem Statement
The commercialization of cultured meat faces persistent bottlenecks in cell-line development, specifically the need for cell sources that support serum-free suspension culture without genetic modification. Primary cells (e.g., muscle stem cells) suffer from limited proliferative capacity and senescence during extended passaging, while genetically immortalized lines raise regulatory and safety concerns regarding genomic stability. Furthermore, existing porcine cell lines often require animal-derived serum or adherent culture conditions, which are difficult to scale efficiently. There is a critical need for a spontaneously immortalized, serum-free, suspension-adapted porcine cell line that can be produced at industrial scales with high medium efficiency.

Methodology
The researchers established a porcine muscle-derived cell line starting from a satellite-cell-enriched primary culture obtained from a 1-week-old pig. The process involved:

1. Adaptation: Cells were transitioned from adherent monolayers (P1–P8) to microcarrier culture (P9), and subsequently adapted to serum-free suspension culture under orbital agitation without genetic modification.
2. Characterization: The team employed longitudinal single-cell RNA sequencing (scRNA-seq) across nine stages to track transcriptional state transitions. They also conducted bulk RNA-seq, immunofluorescence staining, and qPCR to assess lineage markers (myogenic vs. adipogenic).
3. Safety Assessment: The cell line underwent rigorous safety testing, including microbiological screening (bacteria, fungi, mycoplasma, porcine viruses), DNA damage recovery assays (γH2AX foci), soft agar colony formation assays, and in vivo tumorigenicity studies in nude mice.
4. Bioprocess Engineering: Three production strategies were compared in 50-liter bioreactors: fed-batch, cell-retention perfusion, and semi-continuous culture. The optimal process was then scaled up to a 2,000-liter bioreactor.
5. Product Integration: Harvested biomass was incorporated into a hybrid spring roll formulation and analyzed using electronic nose and tongue technologies to assess sensory compatibility.

Key Results

• Spontaneous Immortalization: The adapted cell line (designated SD300) achieved over 255 population doublings by day 300 without genetic modification. The adaptation process involved two proliferative bottlenecks, after which the population doubling time stabilized between 18 and 26 hours.
• Cell State Remodeling: scRNA-seq revealed a distinct trajectory: the initial myogenic state (98% at P5) declined rapidly, giving way to a mesenchymal stromal-like state, and finally stabilizing as an adipogenic-like state (99% by SD38). The cells retained high proliferative capacity but lost myogenic differentiation potential (no myotube formation) while acquiring inducible adipogenic potential (lipid accumulation upon induction).
• Safety Profile: The SD300 cells were confirmed to be of porcine origin and free of adventitious agents. They demonstrated robust DNA damage recovery and showed no evidence of tumorigenicity in soft agar assays or in vivo mouse models, distinguishing them from the HeLa positive control.
• Process Efficiency: In 50-liter comparisons, semi-continuous culture proved superior to fed-batch and perfusion regarding medium efficiency. It achieved the lowest dry-medium-to-wet-biomass ratio (0.77 kg/kg) and sustained harvesting without culture restart.
• Scale-Up: In a 2,000-liter bioreactor, the semi-continuous process yielded 97.18 kg of wet biomass over 22 days with a medium conversion ratio of 0.63 kg dry medium per kg wet biomass. The biomass contained approximately 59.56% protein and 10.24% fat (dry basis).
• Cost and Application: At current medium prices ($9.41/L), the medium cost contribution was $283.23/kg. The authors project this could drop to $18.96/kg if medium prices reach $0.63/L (as seen in large-scale chicken production). The biomass was successfully integrated into a spring roll, showing improved richness and umami profiles compared to controls in electronic tongue analysis.

Significance and Claims
The paper claims to provide a validated, non-transgenic porcine cell source and an experimentally evaluated semi-continuous process for the scalable production of cultured pork biomass. The authors emphasize that the SD300 line offers a solution to the "serum-free suspension" bottleneck, enabling large-scale production (demonstrated in a 2,000-liter vessel) without the regulatory complexities of genetic modification.

The study highlights that while the cells have lost myogenic competence, their adipogenic-primed state allows for the production of lipid-rich biomass suitable for hybrid food products. The authors present the medium conversion ratio of 0.63:1 as a significant efficiency metric, noting it is numerically lower than the feed conversion ratio of conventional pigs, though they caution that direct comparisons are limited by differences in input materials. The work establishes a foundation for reducing production costs through process optimization and medium price reductions, positioning this cell line as a viable candidate for industrial cultured meat manufacturing.