Purpose: Historically, in vitro study of human plasma cells (PCs) has been greatly limited by their short survival (48-72 hrs). Therefore, systems that maintain viability of bone marrow PCs (BMPCs) are needed to aid in identification of PC targeted therapies. Development of a model system that enables in vitro study of human PCs would greatly enhance our understanding of PC biology.

Methods: Patient BM PCs, obtained before and during carfilzomib desensitization, were co-cultured in transwells with BMSCs and BMSC culture media to determine the effects on PC viability in the presence or absence of different drugs or drug combinations.

Results: At 72 hours, in vitro survival of normal human PCs was only 20%. However, their relative survival was increased to >85% when PCs were co-cultured with BMSC or BMSC media in a transwell system that precluded direct cell-cell contact. BMSCs or BMSC culture media increased PC survival to ~70% at 15 days. Studies were then performed to assess the effects of individual proteasome inhibitors (PIs) on PC survival. Patient PCs co-cultured with BMSC culture media were relatively resistant to the constitutive PIs carfilzomib, bortezomib and ixazomib. However, PCs that survived in vivo carfilzomib desensitization therapy were relatively sensitive to an immunoproteasome-specific inhibitor, ONX-0914. Importantly, combination treatment with both a constitutive and immunoproteasome inhibitor synergistically reduced PC viability in the transwell system.

Conclusions: This novel system enhances the in vitro survival of human PCs isolated from HLA-sensitized patients and extends PC viability to allow for the in vitro testing of drugs, alone or in combination, to determine their effects on PC survival. The model system provides a powerful tool to screen for pharmacologics that most effectively reduce PC survival and that can then be used as personalized medicines for desensitization therapy. Finally, we have made the unexpected observation that combination of a constitutive and immunoproteasome inhibitor further reduced PC survival.

CITATION INFORMATION: Driscoll J, Tremblay S, Knechtle S, Woodle E. A Novel 3-Dimensional Culture System Enables In Vitro Study of Human Bone Marrow Plasma Cells. Am J Transplant. 2017;17 (suppl 3).

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