The aim of the present invention is to provide a method of acquiring immunological tolerance to a foreign DNA or its expression product whereby the foreign DNA such as a vector carrying a foreign gene incorporated thereinto or its expression product can be recognized not as non-self but as self; a method of sustaining a gene therapeutic effect whereby a rejection to a foreign DNA such as a vector carrying a foreign gene incorporated thereinto or its expression product can be avoided; and a non-human animal which has acquired immunological tolerance to a foreign DNA such as a vector carrying a foreign gene incorporated thereinto or its expression product. Fetal immature T lymphocytes transferred with a foreign DNA, such as a foreign gene-incorporated viral vector, are introduced into thymus and said foreign DNA is expressed in the thymus organ. The methods of transferring said foreign DNA into a fetal immature T lymphocyte include, for example, co-cultivating the fetal immature T lymphocytes with viral vector-infected virus producer cells.

Description of the Invention

TECHNICAL FIELD

The present invention relates to a method of acquiring immunological tolerance, by fetal immature T lymphocyte-mediated DNA transfer into thymus, to a foreign DNA such as a viral vector-derived component and/or its expression product, a method of sustaining a gene therapeutic effect whereby a rejection raised in gene therapy to a foreign DNA and/or its expression product can be avoided, and a non-human animal such as a mouse or the like that has acquired immunological tolerance to a foreign DNA such as a viral vector-derived component and/or its expression product.

BACKGROUND OF THE INVENTION

A living organism generally does not display immune response to a self-composing antigen. This is called natural or innate immunological tolerance. On the other hand, even if an antigen is originally heterogeneous to a living organism, it may not react to the immune response which is displayed on dosing of the antigen, depending on when it is dosed (especially at viviparous period and neonatal period), how it is dosed (for example using immunosuppressant), and in what form it is dosed (e.g. a denatured substance is removed before dosing protein antigen). This is called acquired tolerance. Immune response is generally thought as celullar or humoral response to a non-self on having distinguished self from others (non-self). Self and non-self is distinguished by an antigen receptor located on the lymphocyte surface. When a substance is recognized as being non-self, lymphocytes proliferate to demonstrate cytotoxity or produce antibody to the substance. However, at the primary recognition stage by lymphocytes, a step is necessary in which a foreign substance (non-self) is incorporated into dendritic cells or macrophages, and is then presented in a way as to be recognized by T lymphocytes. Thus the self/non-self recognition is thought to occur at the interaction level of dendritic cells or macrophages, and T lymphocytes.

Meanwhile, gene therapy, in which a foreign gene, obtained from such as recombinant DNA experiments is transferred into a patient's somatic cell in order to treat the patient's gene disease, through the gene function, has now been applied to various gene diseases such as cancer, immunodeficiency, cardiovascular diseases, or the like. But what prevents gene therapy most from being brought in practice is the immune responsiveness to a component of a vector (a vehicle for gene transfer) used for gene transfer, as mentioned above. In other words, the technique of gene transfer into cells has almost been completed, but the problem remains in that a vector should be used anyway for gene transfer. The known gene transfer methods using a vector involve viral vector methods using various kinds of virus systems such as retrovirus, adenovirus, lentivirus and the like; liposome methods in which a membrane encompassing DNA is fused with the cell; microinjection methods wherein a gene is transferred directly into the cell; and a method using Sendai virus (HVJ) which shows high affinity with the cell, wherein the size of inserting DNA will not be restricted (J. Biol. Chem. 264, 12126-12129, 1989, J. Biol. Chem. 266, 3361-3364, 1991, Bioche. Biophys. Res. Commun. 186, 129-134, 1992, Circ. Res. 73, 898-905, 1993, Science 243, 375-378, 1989, J. Clin. Invest 94, 978-984, 1994).

In any of the above mentioned gene transfer techniques, a transfer vector is foreign to human body, thus immune response is caused to the vector component resulting in the rejection of the vector by the living body sooner or later (generally within two weeks to a month). In case of viral vector, for example, a vector component is expressed as a protein in the infected cell, which protein subsequently is expressed as a peptide on the cell surface. The vector-derived peptide is then recognized by T lymphocytes that consequently kill the infected cell so that the vector (virus) is rejected. Thus the present gene therapy has succeeded in gene transfer itself, but a defect still remains that a long-sustaining effect has not successfully been attained.

Further, there are methods of acquiring immunological tolerance such as a method inducing immunological tolerance to mammal animals by not making them intake a fat-soluble component or a substance including fat-soluble component simultaneously with the antigen (Japanese Laid-Open Patent Application No. 9-194393). Also a method is known which uses a pharmaceutical preparation having a medicament as its effective component which has no substantial pharmacological effect when orally dosed, meanwhile showing the effect when injected, which effect, however, diminishes when injected repeatedly. Said pharmaceutical preparation is composed of a preparation for oral dose including the medicament with enough dose/unit to induce oral immunological tolerance and a preparation for injection including the medicament that is to be administrated after the oral immunological tolerance has been induced (Japanese Laid-Open Patent Application No. 10-298101). Furthermore there is a method which uses an artificial organ in order to establish immunological tolerance in the recipient. Said artificial organ is prepared by removing an organ from an animal showing specific immunological tolerance to the recipient. Thus peripheral immune mechanism composed of lymphocytes or the like of the transplanted organ will not attack human histocompatibility complex when transplanted to the recipient, which results in good survival of the transplanted organ (Japanese Laid-Open Patent Application No. 9-187470).

THE PROBLEM TO BE SOLVED BY THE INVENTION

The report (Cell 86, 243-251, 1996) describes a method of direct gene transfer mediated by retrovirus in FTOC (fetal thymus organ culture) and the role of MAP kinases in T lymphocyte development. Up to the present attempts have been made to transfer genes into thymus, which turned out to be so inefficient even when normal animals were used. These attempts displayed poor effect in suppressing a rejection caused by the existing T lymphocytes and it was not useful in practice (FASEB. J. 6, 2853-2858, 1992, Ann. Surg. 222, 229-242, 1995, J. Clin. Invest. 98, 2640-2647, 1996).

The present inventors performed transdermal or intraperitoneal injection to a mouse, an individual model animal which is to undergo gene therapy, with pGD-GFP, a combination of GFP (green fluorescent protein) gene and retroviral vector (pGD). They have found that the mouse displayed immune response to the vector component, which results in the diminishment of the viral vector carrying GFP gene within 2 weeks or a month. They have also found out that no immune response was observed when using immunodeficiency mouse deficient of T lymphocytes. This is because of T lymphocyte-mediated cellular immune response, that is T lymphocytes recognized a vector gene, which is useful for gene disease therapy, or its expression product as non-self and eliminated it.

The subject of the present invention involves providing: a method of acquiring immunological tolerance to a foreign DNA such as a vector carrying a foreign gene incorporated thereinto or its expression product, wherein a foreign DNA, such as a vector carrying a foreign gene useful for gene disease therapy, or its expression product is recognized as "self" and not as "non-self"; a method of sustaining a gene therapeutic effect whereby a rejection to a foreign DNA, such as a foreign gene-incorporated vector or its expression product can be avoided; and a non-human animal which has acquired immunological tolerance to a foreign DNA such as a foreign gene-incorporated vector or its expression product.

DISCLOSURE OF THE INVENTION

The present inventors have made a keen study on the method of avoiding immune response to a vector for gene transfer by re-educating the in vivo T lymphocyte system so as to in vivo T lymphocytes recognize the component of viral vector for gene transfer as "self", not as "non-self". They have found out the following through their study. With their gene transfer technique into fetal immature T lymphocyte in thymus (J. Immunol. 161, 2888-2894, 1998, Immunity 9, 565-574, 1998), a pGD-GFP gene was transferred into a mouse fetal immature T lymphocyte, which gene-transferred cell was purified through fluorescent staining using the GFP expression. Then a normal mouse was exposed to a low radiation to transiently suppress T lymphocytes of the mouse, subsequently the gene-transferred fetal immature T lymphocytes were introduced into its thymus. When the normal mouse had recovered from the radiation, it was transdermally or intraperitoneally injected with pGD-GFP retrovirus. As an effect of pre-treatment of fetal immature T lymphocytes, the expression of gene-transferred GFP in the mouse was sustained for a long period. This means anti-vector immune response was avoided and sustaining gene therapy could be conducted, and thus the present invention was completed.

Immune response to a foreign substance other than the vector component was kept normal in the above experiment. Therefore, it is made clear that the mouse immune system is not damaged as a whole, that the specific immunonogical tolerance to a vector for gene therapy is induced, and that a vector for gene transfer in other organs can be expressed without any problem right in fetal immature T lymphocytes. With this method, a gene can be transferred efficiently into thymus, a central organ for self/non-self recognition, by mediation of fetal immature T lymphocytes. This leads to an efficient expression of the vector component in thymus organ, wherefrom the efficient self-tolerance of T lymphocytes is established.

The present invention, therefore, relates to a method of acquiring immunological tolerance to a foreign DNA and/or its expression product characterized in that the foreign DNA is transferred into thymus mediated by fetal immature T lymphocytes; a method of acquiring immunological tolerance to a foreign DNA and/or its expression product, characterized in that a foreign-DNA-transferred fetal immature T lymphocyte is introduced into thymus and said foreign DNA is expressed in thymus organ; a method of acquiring immunological tolerance to a foreign DNA and/or its expression product, characterized in that the foreign DNA is DNA which at least comprises a gene coding for a substance causing allergic diseases or a substance causing auto-immune diseases; a method of acquiring immunological tolerance to a foreign DNA and/or its expression product, characterized in that the foreign DNA is DNA which at least comprises a gene coding for a peptide therapeutic medicament; a method of acquiring immunological tolerance to a foreign DNA and/or its expression product, characterized in that the foreign DNA is DNA which at least comprises a vector; a method of acquiring immunological tolerance to a foreign DNA and/or its expression product, characterized in that the vector is a viral vector for transferring a foreign gene; and a method of acquiring immunological tolerance to a foreign DNA and/or its expression product, characterized in that the viral vector is a vector derived from retrovirus, adenovirus, or lentivirus.

The present invention further relates to a method of sustaining a gene therapeutic effect characterized in that a foreign DNA in gene therapy is transferred into thymus mediated by fetal immature T lymphocytes; a method of sustaining a gene therapeutic effect, characterized in that immune response caused by a foreign DNA and/or its expression product is avoided by introducing a foreign-DNA-transferred fetal immature T lymphocyte in gene therapy into thymus, and by expressing a foreign DNA in thymus organ; a method of sustaining a gene therapeutic effect, characterized in that the foreign DNA is DNA which at least comprises a vector; a method of sustaining a gene therapeutic effect characterized in that the vector is a viral vector for transferring a foreign gene; and a method of sustaining a gene therapeutic effect characterized in that the viral vector is a vector derived from retrovirus, adenovirus, or lentivirus.

The present invention still further relates to a non-human animal that has acquired immunological tolerance to a foreign DNA and/or its expression product characterized in that the foreign DNA is transferred into thymus mediated by fetal immature T lymphocytes; a non-human animal that has acquired immunological tolerance to a foreign DNA and/or its expression product, characterized in that a foreign-DNA-transferred fetal immature T lymphocyte is introduced into thymus and said foreign DNA is expressed in thymus organ; a non-human animal that has acquired immunological tolerance to a foreign DNA and/or its expression product, characterized in that the foreign DNA is DNA which at least comprises a vector; a non-human animal that has acquired immunological tolerance to a foreign DNA and/or its expression product characterized in that the vector is a viral vector for transferring a foreign gene; a non-human animal that has acquired immunological tolerance to a foreign DNA and/or its expression product characterized in that the viral vector is a vector derived from retrovirus, adenovirus, or lentivirus; a non-human animal that has acquired immunological tolerance to a foreign DNA and/or its expression product, characterized in that the non-human animal belongs to rodents; and a non-human animal that has acquired immunological tolerance to a foreign DNA and/or its expression product characterized in that the non-human animal which belongs to rodents is a mouse.

THE BEST MODE FOR CARRYING OUT THE INVENTION

The method of the present invention for acquiring immunological tolerance to a foreign DNA and/or its expression product is characterized in that a foreign DNA is transferred into thymus mediated by fetal immature T lymphocytes. It is in particular characterized in that a fetal immature T lymphocyte, that has been transferred a foreign DNA, is introduced into thymus and said foreign DNA is expressed in thymus organ.

A foreign DNA of the present invention means DNA that does not originally exist in an animal which is to acquire immunological tolerance, wherein a translation product of the DNA is recognized as non-self to the animal. Also, a foreign gene of the present invention means a gene that does not originally exist in an animal which is to acquire immunological tolerance, wherein a translation product of the gene is recognized as non-self to the animal. As said foreign DNAs, such as a foreign gene, a vector, a vector incorporated with a gene of the interest, and the like are specifically exemplified. Also, the followings are enumerated as examples of foreign genes; such as genes coding for at least substances causing allergic or auto-immune diseases, especially genes coding for a substance causing serious allergic disease and a substance causing auto-immune diseases such as MBP (myelin basic protein) molecule that causes chronic rheumatoid arthritis (RA) or the like; and genes coding for at least a peptide anti-cancer agent, a peptide pharmaceutical medicament for diabetes, or the like. Further, a viral vector for such as transferring the above-mentioned foreign gene, a plasmid vector, a pharge vector, a yeast artificial chromosome (YAC) vector or the like are exemplified as vectors. Among these, viral vectors, especially viral vectors derived from such as retrovirus, adenovirus, or lentivirus are preferable in that they show considerably high transformation efficiency when infected as virus particle. When using one of these viral vectors, it is preferable to infect a host cell with the viral vector and to use it as a virus producer cell.

Fetal immature T lymphocytes of the present invention means T lymphocytes before they develop to mature T lymphocytes that express antigen receptors and functional co-receptors CD4/CD8, etc. It can be obtained, for instance, by fractioning/purifying from mature thymus lymphocytes, or from thymus lobes of embryonic day (ED) 14 to 18. Thymus lobes of embryonic day (ED) 14 to 15 exist at the upper heart such that left and right lobes exist individually. Thymus lobes at this stage is preferred to use in that they, being transparent spheres, are easy to be distinguished from peripheral organs and they do not allow mature T lymphocytes to immix.

As the methods of transferring a foreign DNA of the present invention into fetal immature T lymphocytes, the gene transfer technique (J. Immunol. 161, 2888-2894, 1998, Immunity 9, 565-574, 1998) developed by the present inventors is exemplified as a preferable one in that a foreign DNA-transferred cell can be differentiated/matured in thymus organ, an educational organ for T lymphocytes. Said technique involves a method wherein fetal immature T lymphocytes and virus producer cells are co-cultured; the gene-transferred fetal immature T lymphocytes are separated by forward and side scatter benefiting from their smaller size and lower density than those of virus producer cells; and fetal immature T lymphocytes having viability are separated/purified by fluorescence-activated cell sorter. The technique also involves a method that is carried out by separating/purifying the gene-transferred fetal immature T lymphocytes through distinguishing from fibroblast-derived virus producer cells by sorting GFP.sup.+CD45.sup.+ cells with flow cytometry cell sorter by using an antibody, which is stained, to hematopoietic cell marker CD45.

Immunological tolerance to an expression product of a foreign DNA of the present invention can be acquired, for instance, by the following procedures. A vector is transferred into a fetal immature T lymphocyte obtained by the methods described above, wherein the vector is incorporated with a gene of interest such as said foreign gene etc. The vector-transferred fetal immature T lymphocyte is then introduced into thymus by direct or intravenous injection into thymus followed by the expression of the foreign DNA in thymus organ, where, at the same time, immune response that was developed by the foreign DNA can be avoided

The method of sustaining gene therapy effect is characterized in transfer of a foreign DNA of gene therapy into thymus by mediation of fetal immature T lymphocytes. Especially it is characterized in that immune response caused by a foreign DNA and/or its expression product can be avoided for a long time, i.e. more than a month, through introducing fetal immature T lymphocytes transferred with foreign DNA of gene therapy into thymus, thereby said foreign DNA is expressed in thymus organ. The sustenance of gene therapy effect will be attained when a foreign DNA useful for gene therapy is used as a foreign DNA in a method of acquiring immunological tolerance to the above-mentioned foreign DNA and/or its expression product.

A non-human animal of the present invention that have acquired immunological tolerance to a foreign DNA and/or its expression product is characterized in that the foreign DNA is transferred into thymus mediated by fetal immature T lymphocytes. Especially it is characterized in that an fetal immature T lymphocyte transferred with a foreign DNA is introduced into thymus, thereby said foreign DNA is expressed in thymus organ. As these non-human animals, non-human mammals such as mice, rats, rabbits or the like can be exemplified, among them, mice are most preferable because of the easiness in breeding or using them, and so on. The present invention is now demonstrated in more detail with the embodiments where a non-human animal is a mouse, but the technical scope of the invention is not limited to these embodiments.

Claim 1 of 6 Claims

1. A non-human animal that has acquired immunological tolerance to a foreign DNA and/or its expression product produced by a method comprising: providing a fetal immature T lymphocyte transfected with the foreign DNA, irradiating a host mammal in order to transiently suppress T lymphocytes, and introducing the transfected fetal immature T lymphocyte into thymus of the host mammal, and subsequently expressing said foreign DNA in thymus organ during differentiation and maturation of the immature T lymphocyte in the thymus organ to reconstitute the immune system.

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