EP1587543A1

EP1587543A1 - Calcium phosphate ceramics and particles for in vivo and in vitro transfection

Info

Publication number: EP1587543A1
Application number: EP03814492A
Authority: EP
Inventors: Nicole Francine Rouquet; Patrick Pierre Frayssinet
Original assignee: URODELIA
Current assignee: URODELIA
Priority date: 2002-12-27
Filing date: 2003-12-24
Publication date: 2005-10-26
Also published as: FR2849436B1; WO2004060407A1; JP2006514655A; FR2849436A1; BR0317766A; CA2511820A1; AU2003303609A1; US20070048737A1

Abstract

The invention relates to a method of modifying the surface of calcium phosphate ceramics and powders. The inventive method involves maturation in a culture medium, thereby causing epitaxial carbonated apatite growth at the surface of the aforementioned ceramics and powders. The invention also relates to the use of said modified ceramics and powders for in vitro and in vivo cell transfection and for cell culture in a three-dimensional network.

Description

Particles and ceramics of calcium phosphates for transfection in vivo and in vitro

The present invention relates to a method for transfection of DNA attached to the surface of calcium phosphate ceramics with particular characteristics. This method can include a step of preparing the material in a saline solution or a cell culture medium to improve DNA binding and its availability for cell transfection. The invention also relates to the use of powders and ceramics of modified calcium phosphates for the transfection of cells in vitro and in vivo and for the culture of cells transfected in a three-dimensional network.

The transfection of genes into eukaryotic cells is a key step in gene therapy. Several methods can be used with variable yields. They can be used in vitro or in vivo.

For gene therapy purposes, cells can be transfected in vitro and then reinjected into the body or directly transfected into the organs or tissues in which they reside (Evans, CH, Robbins, PD, Possible orthopaedic applications of gene therapy, J Bone Joint Surg, 77-A, 7: 1103-1 1 14)

The different methods used for cell transfection are summarized in the table below:

Method Advantages Disadvantages

DEAE-dextran Simple Transient expression Calcium phosphate Simple Unusable for cells in suspension

Liposomes Simple Relatively unproven Micro-injection Effective Technically difficult Electroporation Good for cells no No co-transfection adherent

Fusion of Good for non-cells Variable results adherent protoplasts Adenovirus High infectivity, production in DNA integrated as an episome, known, infects non-toxic cells, production of non-dividing cells, wide variety of viral proteins host cells

Associated adenoviruses Non-pathogenic, Expression Only supports stable genes, infects short cells, difficult to produce, poorly dividing, large variety of developed host cells

He ès simplex Infects non-dividing cells Toxic, transient expression, no, supports long genes, poorly developed

Infection with Effective Cell type reduced by tropism retrovirus, low coding capacity,

Solids Simple, localized transfection Transient polycationic expression

Chromosome satellite Allows the transfection of genes Long unproven results

Others: polymers Low yields, results in variable form, in vivo use of hydrogel, difficult lipids, polycationic biocompatibility, variable polylysine, polyomithine, histones and other chromosomal proteins, hydrogenated polymers

In the fifteen years since clinical trials of gene therapy began, the results have been generally disappointing for several reasons:

Whatever the vectors used, adenovirus, virus associated with adenovirus (AAV), retrovirus or physico-chemical formulation, the efficiency of gene transfer in the target cells has always been very low (A. Kahn. Ten years of gene therapy: disappointments and hopes. Biofutur 202: 16-21, 2000). The duration of expression of therapeutic transgenes is most of the time short, limited to a few weeks, due an immune reaction which causes the preferential elimination of transduced cells, their intrinsic longevity or the extinction of the DNA sequences or promoters which direct the expression of the inserted genes (Orkin, SH, Motulsky, AG, report and recommendations of the panel to assess the NIH investment in research gene therapy.www.nih.gov/news/panelrep.html).

Finally, certain vectors have shown a toxic effect. Accidents have occurred with the use of adenoviral vectors injected into the body that have resulted in the death of patients in ornithine transcarbamylase treatment trials (Smaglik, P., Investigators ponders what went wrong after gene therapy death. The Scientist 13 [21]: 1 (1999).

Thus, it appears from the analysis of all clinical trials of gene therapy that the strategy of gene transfer would require vectors that are much more efficient, safer and capable of preferentially transfecting the cells on which a therapeutic effect is necessary (Orkin , SH, Motulsky, AG, report and recommendations of the panel to assess the NIH investment in research gene therapy.www.nih.gov/news/panelrep.html).

It is for this reason that polycationic polymer vectors have been developed. These vectors are solids and can adsorb DNA in various forms, in particular, in the form of a plasmid. They have the particularity to transfect the cells which come into contact with them with a variable yield. They have been used in vivo to transfect loose connective tissue cells involved in bone healing to accelerate bone healing (S. Goldstein and J. Bonadio. In vivo gene transfer methods for wound healing. The Regent of the University of Michigan Anonymous, United States: (5,962,427): 1-3, 1999. gene therapy. A61K 48/00. 514/44). The calcium phosphate and DNA co-precipitates have been used for many years to transfect cells in vitro (ET Schenbom and V. Goiffon. Calcium phosphate transfection of mammalian cultured cells. Edited by MJ Tymms, Totowa, NJ: Humana Press Inc, 2000, pp. 135-144; W. Song and DK Lahiri. Efficient transfection of DNA by mixing cells in suspension with calcium phosphate. Nucleic Acid Research 23 (\ l): 3609-36l l, 1995; Y.- W. Yang and J.-C. Yang. Calcium phosphate as a carrier gene: electron microscopy. Biomaterials 18: 213-217, 1997).

They are obtained by pouring a solution of calcium chloride into the medium in order to supersaturate it in calcium and to precipitate a calcium phosphate in which DNA molecules are included. These composite particles are then phagocytosed by cells which integrate the plasmid in different ways and express the genes which are transported.

However, these coprecipitates have a major drawback. They are very difficult to use in vivo because it is difficult to obtain supersaturation in an open system. On the other hand, they cannot allow localized transfections in space.

Calcium phosphate ceramics are materials obtained by sintering a slip containing suspended particles of calcium phosphate. These are assemblies of grains linked by grain boundaries (Frayssinet, P., Fages, J., Bonel, G., Rouquet, N., Biotechnology, material sciences and bone repair. European Journal of Orthopedic Surgery & Traumatology (1998 ) 8: 17-25).

These materials have a particular biocompatibility with bone tissue, which makes them particularly useful as bone reconstruction material or as a vector of osteogenic cells (P., Frayssinet, JL Trouillet, N. Rouquet, E. Azimus, A. Autefage ( 1993), Osseointegration of macroporous calcium phosphate ceramics having a different chemical composition. Biomaterials, 14, 6: 423-429). In the context of the invention, we have developed calcium phosphate powders and ceramics capable of transfecting cells both in vivo and in vitro, in particular mesenchymal cells. The chemical composition of these ceramics can vary because several salts of orthophosphoric acid can enter their composition, in particular, tricalcium phosphate, hydroxyapatite which is the phase of synthesis closest to the mineral phase of bone tissue, and octocalcium phosphate. These ceramics have another particularity, they have very variable surface properties according to different parameters such as, among others, the mode of synthesis of the powder, the firing temperature, or the presence of various trace elements. These different factors influence in particular the surface charge, the zeta potential and the substitution capacities in the calcium phosphate mesh. Phosphocalcic ceramics also have the particularity of having epitaxial growths of carbonated apatite on their surface once implanted in the organism or immersed in a saline medium of composition comparable to the extracellular liquid (M. Heughebaert, RZ LeGeros, M. Gineste, and A. Guilhem. Hydroxyapatite (HA) ceramics implanted in non-bone-forming sites. Physico-chemical characterization. J Biomed Mat Res 22: 257-268, 1988). It is to these crystal growths that the biocompatibility properties of these materials have been attributed.

The adsorption properties of calcium phosphates with respect to nucleic acids have been used in chromatography on HA columns to separate and purify DNA or certain RNAs. It is essential to understand that, for an equal chemical composition, all the hydroxyapatite powders used in chromatography do not have the same separating power of nucleic acids (A. Eon-Duval, Purification of plasmid DNA by hydroxyapatite chromatography, Abstract of 2 ⁿ conference on hydroxyapatite. San Francisco March 2001). The interactions between organic molecules and hydroxyapatite depend on the surface properties of this ore (MJ Gorbunoff, Protein chromatography on hydroxyapatite columns. Methods in Enzymology, vol 182, Académie Press Inc 1985: 329-339), which may vary from batch to batch.

It has been proven that the distribution of charges on the surface of the solid and its hydration capacities have an important influence on the adsorption of organic molecules on its surface (Norde, W., Lyklema, J., (1991) Why proteins prefer interfaces. J Biomed Sci Polymer Edn 2, 183-202 (1991)). Likewise, the ionic strength and the pH of the solvent for organic molecules must be taken into account.

If the protein in solution and the solid have an opposite charge, they attract each other. At least if the charge of the protein and that of the surface of the solid roughly compensate for each other. If the charges do not compensate, this results in an accumulation of charges in the contact region causing a high electrostatic potential, energetically unfavorable for adsorption. A similar situation is observed when the surface of the solid and the organic molecule have the same sign. However, in many cases, adsorption can still be done in some cases thanks to the incorporation of ions of the solution at the interface of the adsorbed layer which prevents charge accumulation.

Hydrophobia has an influence on adsorption because it participates in the distribution of charges, in particular in organic molecules which have a tertiary and quaternary structure. The hydrophobicity of a surface (molecule or solid) can promote adsorption.

The distribution of the charges as well as the hydration capacities of the apatites are advantageous properties because they can have a positive or negative surface charge and can be hydrophilic or hydrophobic. In addition, the substitutions in the mesh can be numerous, the functional groups on the surface can vary. We have developed hydroxyapatite-based calcium phosphate powders capable of fixing DNA in various forms and delivering it to isolated cells or in the body for transfection purposes. These powders can be injected in suspension in a liquid or a gel. They can also be deposited with a curette or else serve as a transfecting vector for cells cultivated in a three-dimensional network. They have particular physicochemical properties in order to possess these transfection properties. A series of experiments was carried out to judge the transfection of cells isolated or not with a plasmid carrying the galactosidase gene which can be demonstrated by histochemistry. The powder is a particularly well adapted form to be able to transfect both isolated cells or tissues both in vitro and in vivo. These powders allow the internalization of DNA as well as its protection from intracytoplasmic nucleases and its transfer into the nucleus.

The mechanism involved in the attachment of DNA (organic molecule of negative charge) to the surface of hydroxyapatite particles may be:

• Electrostatic adsorption when the material is positively charged

• Coprecipitation of the DNA molecules in the carbonate apatite layer appearing by epitaxial growth on the surface of these materials and resulting from complex dissolution / reprecipitation processes taking place on the surface in media supersaturated with calcium and phosphorus.

• An ion exchange between the interfacial phase and the solution

Once the DNA is fixed on the material, it must enter the cell. The composition and surface characteristics are also important for the degradation of the material in a biological medium and the emission of transfecting particles. We know that HA ceramics degrade at grain boundaries and that the apatite layer carbonate appearing on the surface of the material by epitaxial growth has a different solubility from the material itself.

On the other hand, not all calcium phosphates can transfect cells. The DCPD for example or certain forms of HA or TCP have shown their inability to do so. Their cytotoxicity is certainly responsible for this.

On the contrary, the modification of the surface of powders and ceramics by maturation in a culture medium resulting in an epitaxial growth of carbonate apatite improves the labeling yield.

Description

Thus, in a first aspect, the present invention relates to a process for creating a mineral-DNA composite characterized in that it comprises a step consisting of an incubation in a saline or culture medium unsaturated with calcium and phosphorus in the presence of the DNA molecule. This method makes it possible to obtain a DNA fixation on the surface of the ceramic by adsorption on a ceramic surface modified by epitaxial growth or else by co-precipitation on the surface of the material. These particles of calcium phosphates are immersed in a saline medium or a culture medium of the type of cell culture media commonly used in biotechnology, in particular DMEM, for approximately a few minutes, for example

1, 5, 10 or 30 minutes at least at about 12, 24, 48 hours, a few days or more at a temperature ranging from 15 to 50 ° C, preferably about 37 ° C. The aim is to have the formation of a layer of carbonated apatite on the surface before or during contact with the plasmids.

In a particular embodiment, the method mentioned above is carried out before contacting with the nucleic acids, in particular plasmids. alternatively, this step causing epitaxial growth of carbonated apatite to the surface of said powders and ceramics is produced in a medium containing the nucleic acids. In this mode, the surface modification and the fixation of the nucleic acids are carried out simultaneously.

Preferably, the powders and ceramics are immersed in a DMEM culture medium for 48 hours at 37 ° C. before or simultaneously with the fixation of the nucleic acids.

In a complementary aspect, the invention relates to a method for fixing DNA in plasmid form to the surface of powder or ceramic of calcium phosphates, characterized in that it comprises a step a) consisting in hydration of the powder of calcium phosphate or calcium phosphate ceramic in a solution of phosphate buffer unsaturated with calcium and phosphate and a step b) consisting of immersion of the products obtained in step a) in a solution of unsaturated phosphate buffer in calcium and phosphate containing a single or double stranded DNA for variable durations from a few minutes to several hours, c) obtaining particles of calcium phosphates comprising DNA molecules attached to its surface.

Preferably, the solution of step a) and b) comprises a 0.12 M phosphate buffer (pH 6.8). The immersion is carried out for at least 1, 5, 10 or 30 minutes up to approximately 12, 24, or 48 hours at a temperature ranging from 15 to 50 ° C, preferably approximately 37 ° C. In addition, the calcium phosphate particles are kept immersed in a culture medium of the cell culture medium type, for about a few minutes to a few days, and at a temperature ranging from 15 to 50 ° C., preferably approximately 37 °. vs.

Thus, in this process, the hydration preferably resides in an immersion of the calcium phosphate powder or the calcium phosphate ceramic in a solution simulating the extracellular fluids intended to produce growth. epitaxial of carbonated apatite on the surface of said powders and ceramics. As such, step b) is carried out by means of a medium simulating extracellular fluids or a medium of the type of cell culture media containing nucleic acids, said medium being non-denaturing for DNA and not saturated with calcium. and phosphate. This medium causes epitaxial growth of carbonated apatite on the surface of said powders and ceramics.

Steps a) and b) can be carried out simultaneously or successively. Thus, the invention can be implemented with a solution containing a single or double stranded DNA for variable durations from a few minutes to several hours to approximately

37 ° C.

Advantageously, this method makes it possible to fix the DNA at physiological pH on calcium phosphate particles under conditions which are not denaturing for the DNA molecule. The ceramics can be porous or dense ceramics.

In another aspect, the invention relates to a method for transfecting isolated cells, cultured in a monolayer or in three dimensions, consisting in bringing the cells to be transfected into contact with the particles obtained by the method described above for periods of time. a few hours to a few weeks. This method can also be implemented to transfect cells contained in a cultured tissue fragment. The particles obtained mentioned above is particularly useful for the preparation of a medicament for in vivo transfection of cells contained in a tissue or in an organ.

In another aspect, the invention relates to powders and ceramics of calcium phosphates capable of being obtained from the process described above, characterized in that they can support an epitaxial growth of apatite carbonated on their surface under non-denaturing conditions, in particular in an unsaturated and non-denaturing saline solution for biological macromolecules. The invention also relates to these powders and ceramics of calcium phosphates further comprising the nucleic acids attached to their surface.

These products are particularly effective for the transfection of cells in vitro and in vivo.

Advantageously, the powders and ceramics obtained have at least one of the properties described below before the surface modification:

- Nature of groups charged at the surface: PO ₄ ^" , OH ^" , Ca ^

- basic surface pH

- Negative electrokinetic potential

- Hydrophobic - particle size between 0-200 μm, in particular between 80-125 μm and 0-25 μm.

Preferably, the products of the invention comprise all of the characteristics described above.

In addition, the powders and ceramics of calcium phosphates mentioned above may comprise a core composed of another polymeric material, ceramic or metallic, preferably magnetic.

The invention also relates to the particles formed on the basis of calcium phosphate powders described above, said particles being included in an inorganic or polymeric matrix, in particular in cements of calcium phosphate or sulphate. In another aspect, the invention relates to a ceramic coating of joint prostheses having the characteristics of the ceramic defined above.

The invention also relates to the use of said calcium phosphate powders and ceramics loaded with DNA at their surface as a support for cell culture, in particular for the three-dimensional network culture of cells transfected by the support and for the transfection of cells in vitro. and in vivo.

The following examples are given by way of illustration. They constitute preferred embodiments of the invention.

Example 1: Characteristic of the powders used

Type P15: spherical powder with a specific surface 0.62 m ² / g. They were calcined at 1180 ° C and their particle size is between 80-125 μm.

Type PI: powder of any shape with a specific surface 56.84 m ² / g, non-calcined (raw) with a particle size between 0-25 μm.

The particle size study of the powders used shows that the spherical powders (PI 5) have a well-defined particle size section whereas those of any shape (PI) have much larger particle size sections with many fine particles. The zero charge pH varies with the calcination temperature of the powders. The zeta potential of the PI powder measured in demineralized water is -27.5 mV and the surface pH is 9.08.

Depending on the sintering temperature of the powder, the zero charge pH is variable but much lower than the physiological pH. This means that whatever the sintering temperature, the electrokinetic potential of the powders, at neutral pH, is negative.

Examination by scanning microscopy of the spherical powders shows that they consist of grains assembled by grain boundaries. There are surface irregularities on some of the faces of the high magnification grains.

Example 2 Method of Attaching DNA to the Vector

The vector can be used in two different ways:

Method A: It can be incubated directly with the plasmid in a phosphate buffer solution. It is then kept incubated therein for several hours while its surface is modified by epitaxial growth of carbonated apatite. The fixing can then be done by coprecipitation on the surface of the material. Method B: It can also be put in the presence of a saline solution for several days in order to modify the surface. Once this is balanced, the material is then put into the solution containing the plasmid. DNA binding is assumed to take place on the surface of the modified material. Fixation of the plasmid on the surface of the native particles (method A):

Double stranded DNA has a marked affinity for HA when dissolved in low concentrations of phosphate buffer. They are eluted in higher concentrations of phosphate buffer. 1 m of powder surface was placed in the Petri dishes, ie 1.61 gr for type A and 0.017 g for type B.

• Hydration of HA powder (2ml / g) in 10ml of 0.12M phosphate buffer at pH 6.8. Heating 15 to 30 min at 100 ° C. • Let stand at room temperature and take out the tampon. Resuspend in 5 to 10 ml of 0.12 M phosphate buffer at pH 6.8 at 60 ° C, decant and resuspend in 5 ml of the same buffer at 60 ° C.

• Add the nucleic acid sample in 1 ml of 0.12 M phosphate buffer at pH 6.8 at 40 ° C (elution of double-stranded nucleic acids can be done by washing the HA 8 to 10 times with 0.5 ml of phosphate buffer (0.4M)).

Attachment of the plasmid to the surface of the particles modified by epitaxial growth (method B):

• The particles were incubated at 37 ° C in DMEM culture medium for 48 hours.

• They are washed in a 0.12M phosphate buffer solution at pH 6.8

• The nucleic acid sample is added in 1 ml of 0.12 M phosphate buffer at pH 6.8 at 40 ° C

EXAMPLE 3 Transfection of Cells in Vitro

Three lines were used:

• Rabbit growth cartilage • Rabbit periosteum

• Rat calvaria cells

They are obtained by digesting the collagen matrix in a collagenase solution followed by centrifugation.

3.1 Material with unmodified surface

The amount of powder (type B) has always been the same: 10 mg.

During the transfection the cells were not at confluence. The cells were transfected on D0 and the first histochemical evaluation of the expression of galoctosidase was made on D4, D21, D30. At D4:

All lines have marking areas. In wells transfected with particles, the labeled cells are grouped around the particles, although some are far from it. This distance can be explained by the fact that the particles emit debris with a high specific surface. They are seen under a microscope in the middle of groups of labeled cells. Growth cartilage cells: in absolute value, the series was the most marked. At D21 As regards the cartilage cells, the number of transfected cells is large. The cells of rat calvarias are strongly positive. At D30

The cells have a relative contact inhibition, they are almost three-dimensional and rounded. Most of the cells in the three groups are positive. The number of positive cells and the previous growth rate seem to indicate that the plasmids are transmitted from one cell to another or that the release of DNA particles spreads over time, the percentage of positive cells would have been very weak otherwise. It is also possible that the releases of transfecting particles are progressive. The cells preferentially labeled are those in contact with the particles. Percentage of cells labeled according to the lines used:

3.2 Material with surface modified by epitaxial growth

From the earliest times of culture, most cells are labeled.

3.2.1 Transfection on either side of a hemipermeable membrane

The grains were placed in contact with the cells, either separated from them by a porous membrane (0.2 μm) made of polycarbonate separating them from the cell mat. Cell labeling with galactosidase is evaluated by histochemistry on D4. Cells in direct contact with the particles are sporadically labeled. Cells that are not in contact with the particles (separated by the membrane) are also labeled. There are therefore transfecting particles smaller than 0.2 μm in size passing through the pores of the polycarbonate membrane.

3.2.2 Transfection of cells in a three-dimensional network

The cell lines described above are suspended in the culture medium. The bed is placed at the bottom of a culture dish. The suspension is used to seed a bed of microbeads (1.5-2 10 ⁵ cells / 0.05 g of beads) carrying plasmids carrying the galactosidase gene. The bed is placed at the bottom of a culture dish. The cells are cultured for 10 to 15 days. The formation of a three-dimensional cellular layer bridging and agglomerating the beads is obtained. This layer also contains an abundant collagen matrix. On the date of observation, the cells form a three-dimensional network bridging the different particles and assembling them. Light microscopy reveals that the cells in the particle cluster are labeled with galactosidase.

3.2.3 Transfection of cells in tissue cultures

Material used for marking: Type A: spherical powder with a specific surface 0.62 m ² / g. They were calcined at 1180 ° C and their particle size is 80-125 μm. The amount of powder is a few tens of particles per box (PI 5).

A few beads were placed in contact with the bone fragments after being incubated without pre-immersion (method A).

The bone fragments come from femurs, tibias and calvaria of 3-day-old newborn rats. The bony parts were cleaned of adjoining soft tissue. The long bones were cut into three pieces: 2 epiphyses and the diaphysis. The calvarias were cut into small fragments of 2 to 3 mm per side. These different fragments were deposited on the surface of a 3% agar gel in DMEM. The culture medium (DMEM + SVF) was then added so that the fragments were exposed at the liquid-air interface.

The beads were kept in contact with the tissues for 2 to 30 days, date on which the galactosidase activity of the cells is demonstrated before making histological sections.

At 2 days of contact, sporadic marking areas are identifiable. The marking is done remotely and in contact with the HA beads. It also takes place in contact with these same balls. At 30 days, all of the bone fragments turned blue macroscopically (figure

1).

FIG. 1 represents a macro photograph of a culture of bone tissue in the presence of transfecting powder for 30 days. The bone fragment is completely blue due to transfection of the cells with the galactosidase vector plasmid. In reflection optical microscopy, it is not possible to see an area which is not marked. The beads are stuck in a matrix marked by the reaction to galactosidase.

The sections of the various samples of cultivated bone tissue 30 d show that the bone cells (osteoblasts, chondroblasts, perichondral cells, periosteal cells, osteoclasts) are marked (FIG. 2 is a histological section of the same tissue showing that all the cells have been transfected with galoctosidase X 30). The cells of the hematopoietic lines are not labeled. It should be noted that:

• All bone cells are labeled

• They are so regardless of the distance from the cells to the balls.

3.2.4 In vivo transfection A group of 10 4-week-old NZW maize rabbits is randomly selected. These rabbits are divided into two groups: Lot A and Lot B. One rabbit from each group serves as a control.

The operating area is located on the mandible on the left side behind the mandibular incisors. It should be noted that a preliminary study made it possible to select this site in which the bone is most abundant. Powder type PI 5 was used. DNA was fixed by method A.

After laying sterile drapes and disinfecting the skin and mucosa, an intraoral buccal incision is made using a scalpel. A full flap thickness is removed to access the mandibular bone area at the base of the incisors. A 3mm drill bit is used to systematize the bone break-in. The bone defect produced is of the order of 2 mm in depth. The bone flap is removed using a bone chisel. The biomaterial is aspirated using a 5 ml syringe and deposited in the bone defect so that it fills it. Light pressure is used with sterile gauze to hold the biomaterial in place. The repositioned flap is then sutured

Two witnesses undergo a second contralateral operation without removing any biomaterial. The rabbits were killed at 3 and 6 weeks of age. The mandibles were removed, fixed in ethanol and included in hydroxyethylmethacrylate. 5 μm thick sections were made and the galactosidase activity highlighted

• At 3 weeks: In the control sites:

Histological sections show a spongy bone with few trabeculae, the pores of which are occupied by very loose stromal tissue. There are osteoclastic-looking multinucleated cells on the surface of the trabeculae. These cells are all marked by the reaction to galactosidase. Likewise, all monocytes are also labeled. These are the only cells that are marked. In the sites located:

The sections passing through the calcium phosphate beads show that the beads are included in a relatively dense connective tissue with numerous multinucleated cells on their surface. All cells, fibroblastic or multinucleated, are labeled with galactosidase.

When the sections move away from the beads, there are fewer marked cells, however the tissue structures which have not been disturbed by the operating procedure give interesting information. The fibroblasts of the dental ligaments are marked. There are islets of fibroblast-like cells marked in the tissue stromal pores between trabeculae. In some cases, it even seems that cells of the osteoblastic line are also labeled.

• 6 weeks: Macroscopically, there is a marking around the HA grains. The sections show positive stromal cells, the cells of the dental ligaments as well as the odontoblasts express the gene.

Claims

1. Method for attaching DNA in plasmid form to the surface of calcium phosphate powder or ceramic, characterized in that it comprises a step a) consisting in hydration of the calcium phosphate powder or of the ceramic of calcium phosphate in a solution of phosphate buffer unsaturated with calcium and phosphate and a step b) consisting of immersion of the products obtained in step a) in a solution of phosphate buffer unsaturated with calcium and phosphate containing a simple DNA or double strand for variable durations from a few minutes to several hours, c) obtaining calcium phosphate particles comprising DNA molecules attached to its surface.

2. Method according to claim 1, characterized in that the solution of step a) and b) comprises a 0.12 M phosphate buffer (pH 6.8).

3. Method according to claim 1, characterized in that the immersion is carried out for at least 1, 5, 10 or 30 minutes up to approximately 12, 24, or 48 hours at a temperature ranging from 15 to 50 ° C, preferably about 37 ° C.

4. Method according to claim 1, characterized in that the calcium phosphate particles are kept immersed in a culture medium of the type of cell culture media.

5. Method according to claim 4, characterized in that the particles of calcium phosphates are immersed for about a few minutes to a few days.

6. Method according to one of claims 4 and 5, characterized in that the particles of calcium phosphates are immersed at a temperature ranging from 15 to 50 ° C, preferably about 37 ° C.

7. Method according to one of claims 1 to 6, characterized in that step b) is carried out by means of a medium simulating extracellular fluids or a medium of the type of cell culture media containing nucleic acids, said medium being non-denaturing for DNA and not saturated with calcium and phosphate; causing epitaxial growth of carbonated apatite on the surface of said powders and ceramics.

8. Method according to one of claims 1 and 7, characterized in that steps a) and b) are carried out simultaneously or successively.

9. Use of the method according to one of claims 7 and 8 to fix the DNA under physiological pH conditions on calcium phosphate particles.

10. Method for transfecting isolated cells, cultured in a monolayer or in three dimensions, consisting in bringing the cells to be transfected into contact with the particles obtained by the method according to one of claims 1 to 8 for periods of a few hours to a few weeks.

1 1. A method for transfecting cells contained in a cultured tissue fragment consisting in bringing the cells to be transfected into contact with the particles obtained by the method according to one of claims 1 to 8 for periods of a few hours to a few weeks.

12. Use of the particles obtained by the method according to one of claims 1 to 8 for the preparation of a medicament for transfecting in vivo cells contained in a tissue or in an organ.

13. Calcium phosphate powders and ceramics capable of being obtained from the process according to one of claims 1 to 8, characterized in that they support an epitaxial growth of carbonated apatite on their surface under non-denaturing conditions .

14. Calcium phosphate powders and ceramics according to claim 13 further comprising nucleic acids attached to their surface.

15. Calcium phosphate powders and ceramics according to either of Claims 13 and 14, characterized in that they have at least one of the following properties:

- Nature of groups charged on the surface: PO ₄ ^"" , OH ^" , Ca ^{" 1 "1"}

- basic surface pH

- Negative electrokinetic potential - Hydrophobic

- particle size between 0-200 μm, in particular between 80-125 μm and 0-25 μm.

16. Calcium phosphate powders and ceramics according to one of claims 13 to 15 characterized in that they further comprise a core composed of another polymeric, ceramic or metallic material, preferably magnetic.

17. Particles formed based on calcium phosphate powders according to one of claims 13 to 16 included in a mineral or polymeric matrix in particular in cements of phosphate or calcium sulphate.

18. Use of powders and ceramics of calcium phosphates according to one of claims 13 to 16 for the transfection of cells in vitro

19. Use of the powders and ceramics of calcium phosphates according to one of claims 13 to 16 for the manufacture of a medicament for the transfection of cells in vivo.

20. Use of the powders and ceramics of calcium phosphates according to one of claims 13 to 16 for the culture of cells transfected in three dimensions with the formation of a cellular and extracellular matrix aggregating the particles.