Introduction:

In low-resource populations, vaccinations against preventable infectious diseases, e.g., malaria and HIV, are logistically problematic. “Living pharmacies” using encapsulated cell technology may prove to be an efficacious, cost-effective, widely applicable and durable means of vaccine delivery to address this global health issue. Here, we report a proof-of-concept in vivo study, establishing that cells - when encapsulated within a device of clinically feasible size - survive and produce IgG antibody at therapeutically meaningful plasma levels for 3+ months. This approach is clinically scalable; with future device optimization it could be utilized for outpatient subcutaneous insertion by trocar. Once inserted, we postulate delivery of a therapeutic dose for one year or longer, eliminating the need for repeated costly patient treatments every few months.

Methods:

ADC26.2 cells engineered to produce humanized IgG antibody against HIV were provided by Dr. Omid Veiseh, Rice University. Cell-loaded devices of three different footprints (3.0cm2, 1.5cm2, and 0.5cm2) were implanted subcutaneously into male Crl:NIH-Foxn1rnu nude rats. Loaded cell numbers were scaled to footprint area.  Blood samples were collected weekly for three months and the plasma analyzed for human IgG by ELISA (Abcam Human IgG ELISA). Explanted devices and surrounding tissue were formalin-fixed and paraffin-embedded, sectioned, and stained for histological evaluation of cell survival, transgression of cells from the device, extent of neovascularization, presence of human IgG, and evidence of host fibrosis and immune response.

Results:

When loaded at the same density (i.e., 15 million cells in 3.0 cm2 devices), steady state IgG plasma concentrations during the 3rd month post-implantation were proportional to device footprint (Mean + SEM): 0.5 cm2 =  9.6+1.0; 1.5 cm2 = 25.03+0.35; 3.0 cm2 = 55.4+ 4.03 µg/mL. Histological evaluation with Ku80 staining showed that encapsulated cells were retained within the device; no human nuclei were identified in the host tissues surrounding it (n=12). Excellent vascularization was present in the outer membrane of the device as early as 35 days post-implantation and increased over time. No fibrotic capsular formation or inflammatory response was identified.

Conclusion:

IgG production was proportional to device footprint; the highest IgG concentrations were with the 3.0cm2 device loaded with 15 million cells. The level of IgG production by the current device and cell line approaches that needed therapeutically. Extensive neovascularization penetrating the vascularizing membrane was key to a productive cell pharmacy. Further refinements of device design and cell engineering will be needed to achieve the clinical goal of an easily implantable (microchip-like) efficacious cell pharmacy.