Polypeptide delivery system

Abstract

An expression construct is disclosed which is useful for delivering an exogenous polypeptide (e.g. a growth hormone such as somatotropin) to a host. In one application of the invention, the expression construct is introduced into a non-host recombinant cell encapsulated in a semi-permeable membrane for implantation into the host. The semi-permeable membrane inhibits immune surveillance and cell rejection events so that non-host, highly expressing, recombinant cells can be used.

1 . An expression cassette including a sequence encoding an insulin secretory signal operably linked to a heterologous sequence encoding a mature form of a polypeptide which is normally secreted.  
     
     
         2 . An expression cassette according to  claim 1 , wherein the insulin secretory signal has the amino acid sequence shown as SEQ ID NO:1.  
     
     
         3 . An expression cassette according to  claim 1 , wherein the insulin secretory signal is a modified insulin secretory signal which has one or more amino acid modifications of the amino acid sequence shown as SEQ ID NO:1 and has substantially the same biological activity as an insulin secretory signal having the amino acid sequence shown as SEQ ID NO:1.  
     
     
         4 . An expression cassette according to any one of  claims 1  to  3 , wherein the heterologous sequence encodes a polypeptide selected from hormones, cytokines, receptor agonists, receptor antagonists, pheromones, and enzymes.  
     
     
         5 . An expression cassette according to  claim 4 , wherein the heterologous sequence encodes a cytokine.  
     
     
         6 . A vector including an expression cassette according to  claim 1 .  
     
     
         7 . A recombinant cell which includes an expression cassette according to  claim 1 .  
     
     
         8 . A recombinant cell according to  claim 7 , wherein the cell is a bacterial, yeast, insect or mammalian cell.  
     
     
         9 . A recombinant cell according to  claim 8 , wherein the cell is a mammalian cell.  
     
     
         10 . A mammalian cell according to  claim 9 , wherein the cell is a rat myoblast (L6) cell.  
     
     
         11 . A method of producing a polypeptide which includes culturing a recombinant cell of  claim 7  under conditions enabling the expression and secretion of the polypeptide and optionally isolating the polypeptide.  
     
     
         12 . A capsule for implantation in a host, the capsule including a semi-permeable membrane encapsulating recombinant cells according to  claim 9 .  
     
     
         13 . A capsule according to  claim 12 , wherein the semi-permeable membrane is an alginate-poly-L-lysine-alginate (APA) membrane.  
     
     
         14 . A method of administering a polypeptide to a host, wherein said method includes administering to the host an expression cassette according to  claim 1 .  
     
     
         15 . A method of administering a polypeptide to a host, wherein the method includes implanting in the host a capsule according to  claim 12 .  
     
     
         16 . A method according to  claim 15 , wherein the host is an animal or human.  
     
     
         17 . A method according to  claim 16 , wherein the host is a livestock animal.  
     
     
         18 . A method according to  claim 17 , wherein the livestock animal is a pig.