Preparation of substances with encapsulated cells

#This invention relates to a method of producing biological materials of the type generated by cells.

#Advances in cellular biology have shown that the cells of various higher organisms produce small quantities of substances having significant potential or demonstrable utility for the treatment or diagnosis of disease. Examples of such substances abound in the literature and include various biological response modifiers such as hormones, interferons, and lymphokines, as well as other substances such as antibodies used in diagnostic testing. Cell cultures of microbial origin have long been used to produce large quantities of antibiotics.

#Especially in cell cultures derived from higher animals, there is an ever present danger of bacterial or other contamination. Also, in most instances the quantities of the substance of interest produced by cell cultures are very small and collect in the culture medium which contains a complex mixture of serum proteins and other substances. This make isolation and purification of the substance of interest difficult.

#These and other objects and features of the invention will be apparent from the following description and from the drawing wherein

#FIG. 1 is a schematic diagram illustrating the concept of the invention and

#FIG. 2 is a graph showing the results of the experiment described in example 5.

#The broad concept of the invention is to interpose a semipermeable membrane about individual cells or groups of cells so as to provide a microenvironment for the cells complete with the cell culture medium and separated by the membrane from an external aqueous medium. Cells of mammalian origin typically require for ongoing health and viability the presence of serum proteins, a portion of which have a molecular weight in excess of about 65,000-150,000 daltons. In the prior art technique of unencapsulated cell culturing, materials of interest secreted from the cells are dispersed in the culture medium and mixed with both high and low molecular weight components. Since the quantities of cell-produced products are typically rather small, isolation of the substance of interest becomes an arduous purification task. Furthermore, mammalian cell cultures are notoriously sensitive to contamination by bacterial or other sources. This necessitates that culturing be conducted using various techniques to maintain sterility and often that antibiotics be included in the medium.

#According to the practice of this invention, the foregoing difficulties are alleviated by encapsulating the cells of the culture within semipermeable membranes having a selected limit of permeability generally no greater than about 200,000 daltons, that is, the membrane contains pores which allow substances having a maximum molecular weight at or below the upper permeability limit to traverse the membrane whereas substances of molecular weight above the upper permeability limit are precluded from traversing the membrane. This allows one to encapsulate cells together with a culture medium containing all components needed for ongoing viability, metabolism, and even mitosis, and then to suspend the so encapsulated cells in a culture medium which contains lower molecular weight substances consumed by the cells but which need not include the required high molecular weight substances.

#Typically, cells from higher organisms do not ingest high molecular weight serum proteins and the like, but rather require them in close proximity for ongoing normal biological responses. Salts, amino acids and other lower molecular weight factors which are ingested or metabolized by the cells pass freely through the membrane and may be replenished as needed by simple change of the culture medium external to the capsules. Secreted products of cell metabolism having a molecular weight below the upper limit of membrane permeability collect in the extracapsular medium, where, because of the absence in the medium of the high molecular weight materials, harvesting and isolation of the metabolic products of interest are simplified. Harvesting of products of interest having a molecular weight above the upper permeability limit is also aided in that such products collect within the capsules and are not dispersed in the extracapsular volume.