Objective:

To develop a scalable platform for expanding and genetically engineering granulocyte-monocyte progenitors (GMPs) for potential CAR-based cancer immunotherapy.

Approach:

• GMP expansion: Researchers developed SCF/2i culture conditions for mouse GMPs and an adapted SCF/2i-IG formulation for human GMPs from cord blood, bone marrow, and mobilized peripheral blood.
• Genetic engineering and testing: Expanded GMPs were engineered using lentiviral delivery or CRISPR-Cas9, then assessed for persistence and antitumor activity in mouse models.
• CAR-Fc design: The team tested a CAR incorporating an immunoglobulin G Fc domain intended to recruit the recipient’s immune cells.

Key Findings:

• Mouse GMPs expanded for more than 50 days, increasing nearly eight orders of magnitude while retaining progenitor identity and differentiation potential.
• Human GMPs from three sources expanded under SCF/2i-IG conditions. Whole-genome sequencing found no detectable increase in somatic mutation burden after 28 days of culture.
• MPO inhibition promoted sustained GMP expansion.
• Human GMP-derived cells persisted for at least 180 days in immunodeficient mice; infused mature macrophages were undetectable within seven days.
• In a mouse model of CD19-positive B-cell acute lymphoblastic leukemia, six of 10 mice treated with CAR-engineered human GMPs survived beyond 80 days, while no untreated controls survived beyond day 38.
• HER2-targeted CAR-GMPs suppressed tumor growth and improved survival in a mouse ovarian cancer model.
• CAR-Fc enhanced antitumor activity in immunocompetent mouse models of lymphoma and breast cancer, including in immunologically mismatched donor-recipient settings.

Interpretation:

The study demonstrates that GMPs can be expanded and engineered while retaining the ability to generate functional immune cells, with antitumor activity shown in mouse models.

Limitations:

• The reported antitumor results are from mouse models.
• Longer-term safety assessments are still needed; the reported mutation analysis covered 28 days of culture.

Conclusion:

The authors present expanded, engineered GMPs as a potential platform for scalable cell-based cancer immunotherapies.

Sources:

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