A process for purifying immunoglobulin, i.e., immunoglobulin G (IgG), from a crude immunoglobulin-containing plasma protein fraction, which process comprises the steps of:
- (a) preparing an aqueous suspension of the crude immunoglobulin-containing plasma protein fraction;
- (b) adding a water soluble, substantially non-denaturating protein precipitant to the said suspension of step (a) in an amount sufficient to cause precipitation of a high proportion of non-immunoglobulin G proteins, aggregated immunoglobulins and particles including potentially infectious particles, without causing substantial precipitation of monomeric immunoglobulin G, thereby forming a mixture of a solid precipitate and a liquid supernatant;
- (c) recovering a clarified immunoglobulin G-containing supernatant from the mixture of step (b);
- (d) applying the clarified immunoglobulin G-containing supernatant of step (c) to an anion exchange resin and subsequently a cation exchange resin;
- (e) washing out protein contaminants and the protein precipitant from the cation exchange resin of step (d) with a buffer having a pH and ionic strength sufficient to remove the contaminants from the resin without causing substantial elution of immunoglobulin G;
- (f) eluting immunoglobulin G from the cation exchange resin of step (e) with a substantially non-denaturating buffer having a pH and ionic strength sufficient to cause efficient elution of the immunoglobulin G, thereby recovering an immunoglobulin G-containing eluate;
- (g) performing a dia/ultrafiltration on the immunoglobulin G-containing eluate of step (f) to concentrate and/or dialyse the eluate, and optionally adding a stabilizing agent, thereby forming a concentrated and/or dialysed and optionally stabilized product;
- (h) adding a virucidal amount of virus-inactivating agent to the product of step (g) resulting in a substantially virus-safe immunoglobulin G-containing solution;
- (i) applying the immunoglobulin G-containing solution of step (h) to an anion exchange resin and subsequently to a cation exchange resin;
- (j) washing the cation exchange resin of step (i) with a buffer having a pH and ionic strength sufficient to wash out protein contaminants and the virus-inactivating agent from the resin without causing substantial elution of immunoglobulin G;
- (k) eluting immunoglobulin G from the cation exchange resin of step (j) with a substantially non-denaturating buffer having a pH and ionic strength sufficient to cause efficient elution of the immunoglobulin G, thereby recovering an immunoglobulin G-containing eluate;
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- (l) subjecting the immunoglobulin G-containing eluate of step (k) to dia/ultrafiltration to lower the ionic strength and concentrate immunoglobulin G of the solution, and adjusting the osmolality by adding a saccharide.