United States Patent:  6,048,524

Assignee:  Transkaryotic Therapies, Inc. (Cambridge, MA)

Filed:  May 22, 1995

The present invention relates to transfected primary and secondary somatic cells of vertebrate origin, particularly mammalian origin, transfected with exogenous genetic material (DNA) which encodes erythropoietin or an insulinotropin [e.g., derivatives of glucagon-like peptide 1(GLP-1)], methods by which primary and secondary cells are transfected to include exogenous genetic material encoding erythropoietin or an insulinotropin, methods of producing clonal cell strains or heterogenous cell strains which express eruthropoietin or an insulinotropin, methods of gene therapy in which the transfected primary or secondary cells are used, the methods of producing antibodies using the transfected primary or secondary cells.

SUMMARY OF THE INVENTION

The present invention relates to transfected primary and secondary somatic cells of vertebrate origin, particularly mammalian origin, transfected with exogenous genetic material (DNA or RNA) which encodes a clinically useful product, such as erythropoietin (EPO) or insulinotropin [e.g. derivatives of glucagon-like peptide 1 (GLP-1) such as GLP(7-37), GLP(7-36), GLP-1(7-35) and GLP-1(7-34) as well as their carboxy-terminal amidated derivatives produced by in vivo amidating enzymes and derivatives which have amino acid alterations or other alterations which result in substantially the same biological activity or stability in the blood as that of a truncated GLP-1 or enhanced biological activity or stability], methods by which primary and secondary cells are transfected to include exogenous genetic material encoding EPO or insulinotropin, methods of producing clonal cell strains or heterogenous cell strains which express exogenous genetic material encoding EPO or insulinotropin, a method of providing EPO or insulinotropin in physiologically useful quantitites to an individual in need thereof, through the use of transfected cells of the present invention or by direct injection of DNA encoding EPO into an individual; and methods of producing antibodies against the encoded product using the transfected primary or secondary cells. Transfected cells containing EPO-encoding exogenous genetic material express EPO and, thus, are useful for preventing or treating conditions in which EPO production and/or utilization are inadequate or compromised, such as in any condition or disease in which there is anemia. Similarly, transfected cells containing insulinotropin-encoding exogenous genetic material express insulinotropin and, thus, are useful for treating individuals in whom insulin secretion, sensitivity or function is compromised (e.g., individuals with insulin-dependent or non-insulin dependent diabetes).

The present invention includes primary and secondary somatic cells, such as fibroblasts, keratinocytes, epithelial cells, endothelial cells, glial cells, neural cells formed elements of the blood, muscle cells, other somatic cells which can be cultured and somatic cell precursors, which have been transfected with exogenous DNA encoding EPO or exogenous DNA encoding insulinotropin. The exogenous DNA is stably integrated into the cell genome or is expressed in the cells episomally. The exogenous DNA encoding EPO is introduced into cells operatively linked with additional DNA sequences sufficient for expression of EPO in transfected cells. The exogenous DNA encoding EPO is preferably DNA encoding human EPO but, in some instances, can be DNA encoding mammalian EPO of non-human origin. EPO produced by the cells is secreted from the cells and, thus, made available for preventing or treating a condition or disease (e.g., anemia) in which EPO production and/or utilization is less than normal or inadequate for maintaining a suitable level of RBCs. Cells produced by the present method can be introduced into an animal, such as a human, in need of EPO and EPO produced in the cells is secreted into the systemic circulation. As a result, EPO is made available for prevention or treatment of a condition in which EPO production and/or utilization is less than normal or inadequate to maintain a suitable level of RBCs in the individual. Similarly, exogenous DNA encoding insulinotropin is introduced into cells operatively linked with additional DNA sequences sufficient for expression of insulinotropin in transfected cells. The encoded insulinotropin is made available to prevent or treat a condition in which insulin production or function is compromised or glucagon release from the pancreas is to be inhibited.

Primary and secondary cells transfected by the subject method can be seen to fall into three types or categories: 1) cells which do not, as obtained, produce and/or secrete the encoded protein (e.g., EPO, insulinotropin; 2) cells which produce and/or secrete the encoded protein (e.g., EPO, insulinotropin) but in lower quantities than normal (in quantities less than the physiologically normal lower level) or in defective form, and 3) cells which make the encoded protein (e.g., EPO or insulinotropin) at physiologically normal levels, but are to be augmented or enhanced in their production and/or secretion of the encoded protein.

Exogenous DNA encoding EPO is introduced into primary or secondary cells by a variety of techniques. For example, a construct which includes exogenous DNA encoding EPO and additional DNA sequences necessary for expression of EPO in recipient cells is introduced into primary or secondary cells by electroporation, microinjection, or other means (e.g., calcium phosphate precipitation, modified calcium phosphate precipitation, polybrene precipitation, microprojectile bombardment, liposome fusion, receptor-mediated DNA delivery). Alternatively, a vector, such as retroviral vector, which includes exogenous DNA encoding EPO can be used, and cells can be genetically modified as a result of infection with the vector. Similarly, exogenous DNA encoding insulinotropin is introduced into primary of secondary cells using one of a variety of methods.

In addition to exogenous DNA encoding EPO or insulinotropin, transfected primary and secondary cells may optionally contain DNA encoding a selectable marker, which is expressed and confers upon recipient cells a selectable phenotype, such as antibiotic resistance, resistance to a cytotoxic agent, nutritional prototrophy or expression of a surface protein. Its presence makes it possible to identify and select cells containing the exogenous DNA. A variety of selectable marker genes can be used, such as neo, gpt, dhfr, ada, pac, hyg, mdr and hisD.

Transfected cells of the present invention are useful, as populations of transfected primary cells, transfected clonal cell strains, transfected heterogenous cell strains, and as cell mixtures in which at least one representative cell of one of the three preceding categories of transfected cells is present, as a delivery system for treating an individual with a condition or disease which responds to delivery of EPO (e.g. anemia) or for preventing the development of such a condition or disease. In the method of the present invention of providing EPO, transfected primary cells, clonal cell strains, or heterogenous cell strains, are administered to an individual in need of EPO, in sufficient quantity and by an appropriate route, to deliver EPO to the systemic circulation at a physiologically relevant level. In a similar manner, transfected cells of the present invention providing insulinotropin are useful as populations of transfected primary cells, transfected clonal cell strains, transfected heterogenous cell strains, and as cell mixtures, as a delivery system for treating an individual in whom insulin production, secretion or function is comprised or for inhibiting (totally or partially) glucagon secretion from the pancreas. A physiologically relevant level is one which either approximates the level at which the product is normally produced in the body or results in improvement of an abnormal or undesirable condition.

Clonal cell strains of transfected secondary cells (referred to as transfected clonal cell strains) expressing exogenous DNA encoding EPO (and, optionally, including a selectable marker gene) are produced by the method of the present invention. The present method includes the steps of: 1) providing a population of primary cells, obtained from the individual to whom the transfected primary cells will be administered or from another source; 2) introducing into the primary cells or into secondary cells derived from primary cells a DNA construct which includes exogenous DNA encoding EPO and additional DNA sequences necessary for expression of EPO, thus producing transfected primary or secondary cells; 3) maintaining transfected primary or secondary cells under conditions appropriate for their propagation; 4) identifying a transfected primary or secondary cell; and 5) producing a colony from the transfected primary or secondary cell identified in (4) by maintaining it under appropriate culture conditions and for sufficient time for its propagation, thereby producing a cell strain derived from the (founder) cell identified in (4). In one embodiment of the method, exogenous DNA encoding EPO is introduced into genomic DNA by homologous recombination between DNA sequences present in the DNA construct used to transfect the recipient cells and the recipient cell's genomic DNA. Clonal cell strains of transfected secondary cells expressing exogenous DNA encoding insulinotropin (and, optionally, including a selectable marker gene) are also produced by the present method.

In one embodiment of the present method of producing a clonal population of transfected secondary cells, a cell suspension containing primary or secondary cells is combined with exogenous DNA encoding EPO and DNA encoding a selectable marker, such as the bacterial neo gene. The two DNA sequences are present on the same DNA construct or on two separate DNA constructs. The resulting combination is subjected to electroporation, generally at 250-300 volts with a capacitance of 960 .mu.Farads and an appropriate time constant (e.g., 14 to 20 msec) for cells to take up the DNA construct. In an alternative embodiment, microinjection is used to introduce the DNA construct containing EPO-encoding DNA into primary or secondary cells. In either embodiment, introduction of the exogenous DNA results in production of transfected primary or secondary cells. Using the same approach, electroporation or microinjection is used to produce a clonal population of transfected secondary cells containing exogenous DNA encoding insulinotropin alone, or insulinotropin and a selectable marker.

In the method of producing heterogenous cell strains of the present invention, the same steps are carried out as described for production of a clonal cell strain, except that a single transfected primary or secondary cell is not isolated and used as the founder cell. Instead, two or more transfected primary or secondary cells are cultured to produce a heterogenous cell strain.

The subject invention also relates to a method of producing antibodies specific for EPO. In the method, transfected primary or secondary cells expressing EPO are introduced into an animal recipient (e.g., rabbit, mouse, pig, dog, cat, goat, guinea pig, sheep, non-human primate). The animal recipient produces antibodies against the EPO expressed, which may be th entire EPO protein antigen or a peptide encoded by a fragment of the intact EPO gene. Polyclonal sera is obtained from the animals. It is also possible to produce monoclonal antibodies through the use of transfected primary or secondary cells. Splenocytes are removed from an animal recipient of transfected primary or secondary cells expressing EPO. The splenocytes are fused with myeloma cells, using known methods, such as that of Koprowski et al. (U.S. Pat. No. 4,172,124) or Kohler et al., (Nature 256: 495-497 (1975)) to produce hybridoma cells which produce the desired anti-EPO monoclonal antibody. The polyclonal antisera and monoclonal antibodies produced can be used for the same purposes (e.g., diagnostic, preventive, or therapeutic purposes) as antibodies produced by other methods. Similarly, antibodies specific for insulinotropin can be produced by the method of the present invention.

The present invention is particularly advantageous in treating anemia and other conditions in which EPO production, utilization or both is compromised in that it: 1) makes it possible for one gene therapy treatment, when necessary, to last a patient's lifetime; 2) allows precise dosing (the patient's cells continuously determine and deliver the optimal dose of EPO based on physiologic demands, and the stably transfected cell strains can be characterized extensively in vitro prior to implantation, leading to accurate predictions of long term function in vivo); 3) is simple to apply in treating patients; 4) eliminates issues concerning patient compliance (periodic administration of EPO is no longer necessary); and 5) reduces treatment costs (since the therapeutic protein is synthesized by the patient's own cells, investment in costly protein production and purification facilities is unnecessary).

Claim 1 of 9 Claims

1. A method of expressing erythropoietin in a mammal, comprising the steps of:

a) obtaining a source of primary cells from a mammal;

b) transfecting primary cells obtained in (a) with a DNA construct comprising exogenous DNA encoding erythropoietin and additional DNA sequences sufficient for expression of the exogenous DNA in the primary cells, thereby producing transfected primary cells which express the exogenous DNA encoding erythropoietin;

c) culturing a transfected primary cell produced in (b), which expresses the exogenous DNA encoding erythropoietin, under conditions appropriate for propagating the transfected primary cell which expresses the exogenous DNA encoding erythropoietin, thereby producing a clonal cell strain of transfected secondary cells from the transfected primary cell;

d) culturing the clonal cell strain of transfected secondary cells produced in (c) under conditions appropriate for and sufficient time for the clonal cell strain of transfected secondary cells to undergo a sufficient number of doublings to provide a sufficient number of transfected secondary cells to produce erythropoietin; and

e) introducing transfected secondary cells produced in (d) into a mammal of the same species as the mammal from which the primary cells were obtained in sufficient number to express erythropoietin in the mammal.

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