drug discov today moghimi sm, symonds p, murray jc, hunter ac, debska g and prednisone hair szewczyk a a twostage polyethyleniminemediated cytotoxicity implications for gene transfertherapy mol ther gbadamosi jk, hunter ac and moghimi sm pegylation of microspheres generates a heterogeneous population of particles with differential surface characteristics and biological performance febs lett genetic vaccines a role for liposomes gregory gregoriadis, prednisone hair andrew bacon, brenda mccormack and peter laing introduction prevention of microbial infections by the use of vaccines is a preferred alternative to treatment vaccines have been applied successfully, for example, in prednisone hair the eradication of smallpox as well as against tetanus, diphtheria, whooping cough, polio and measles, prednisone hair thus preventing millions of deaths each year however, vaccines made of attenuated organisms, which mimick natural infections usually without the disease, can be potentially unsafe for instance, there is a prednisone hair risk of reversion during replication of live viruses or even mutation to a more pathogenic state furthermore, with immunocompromised individuals, some of the attenuated viruses may still provoke disease on the other hand, with killed virus vaccines, their extracellular localization and subsequent phagocytosis by professional antigen prednisone hair presenting cells apc or antigenspecific � cells, lead to mhcii class restricted presentation and to prednisone hair t helper cell and humoural immunity however, they do not elicit significant cytotoxic t cell prednisone hair ctl responses moreover, subunit vaccines produced from biological fluids may not be entirely free of infectious prednisone hair agents even with subunit and peptide vaccines produced recombinantly or synthetically and thus considered safe, immune responses are weak and often not of the appropriate kind the great variety of prednisone hair immunological adjuvants that are now available go a long way in rendering subunit and peptide prednisone hair vaccines stronger and more efficient however, more than seventy years after the introduction of aluminium prednisone hair salts as an adjuvant, only two other adjuvants, liposomes and mf, have been approved for use prednisone hair in humans thus, inspite of considerable progress, the road to the ideal vaccine appears as prednisone hair elusive as ever, until recently recent developments have led to a novel and exciting concept, namely de novo production bactrim temporary remission in rheumatoid arthritis of the required vaccine antigen by the hosts cells in vivo, prednisone hair which promises to revolutionize vaccination especially where vaccines are either ineffective or unavailable the concept prednisone hair entails the direct injection of antigenencoding plasmid dna which, on uptake by cells, localizes to some extent into the nucleus where it transfects the cells episomally the produced antigen is recognized prednisone hair as foreign by the host and is thus subjected to pathways similar to those observed for antigens of internalized viruses but without their disadvantages, leading to protective humoural and cell prednisone hair mediated immunity a series of publications since first established the ability of plasmid dna to prednisone hair induce an immune antibody response to the encoded foreign protein in experiments with dna encoding influenza prednisone hair nucleoprotein, immunity was both humoural and cellmediated, and also protective in mice challenged with the prednisone hair virus, this was the first demonstration of an experimental dna vaccine another observation was the prednisone hair induction of humoural and cellmediated immunity against hiv using plasmids encoding the hiv rev and env proteins similar results were obtained with a gene for the hepatitis � surface antigen prednisone hair hbsag dna immunization was also found to apply in cancer treatment for instance, injection of plasmids encoding tumor antigens promoted immune responses, which were protective in an animal model the concept of dna immunization has now been adopted by vaccinologists worldwide using an ever increasing number prednisone hair of plasmids encoding immunogens from bacterial, viral and parasitic pathogens, and a variety of tumors, in many of these studies, genetic immunization has led to the protection of animals from prednisone hair infection a number of clinical trials for the therapy of, or prophylaxis against, a variety of prednisone hair infections are in progress the dna vaccine a plasmid dna vaccine is usually supercoiled and consists of the gene encoding the vaccine antigen the section of the target pathogen which elicits protective immunity, a promoter sequence which is often derived from cytomegalovirus cmv or rous prednisone hair sarcoma virus rsv, an mrna stability polyadenylation region at the end of the insert, and prednisone hair the plasminogen activator gene which controls the secretion of the recombinant product in addition, there are prednisone hair an origin of replication for the amplification of the plasmid in bacteria, and a gene for antibiotic resistance to select the transformed bacteria immunization procedures with dna vaccines are carried out by the intramuscular and, to a lesser extent, the intraepidermal route other routes include prednisone hair the oral, nasal, vaginal, intravenous, intraperitoneal and subcutaneous routes, intramuscular injection of dna vaccines leads prednisone hair to such types of immunity as ctl, this was unexpected because antigen presentation requires the function prednisone hair of professional apc however, myocytes which were shown to take up the plasmid only to prednisone hair a small extent and with only a fraction of cells participating in the uptake, are not professional apcs although myocytes carry mhc class i molecules and can present endogenously produced prednisone hair viral peptides to the cd cells to induce ctls, they do so inefficiently as they prednisone hair lack vital costimulatory molecules eg the b molecule it is thus difficult to accept that antigen presentation, leading to a ctl response, occurs via myocytes instead, it was reported that ctl prednisone hair responses occur as a result of the transfer of antigenic material between the myocytes and prednisone hair professional apc to some extent in parallel, it could also be that plasmid secreted by prednisone hair the myocytes or as such, is taken up directly by apc infiltrating the injected site such apc would include dendritic cells which will express and present peptides to cd cells following prednisone hair transport to the lymph nodes or spleen on the other hand, cd cells may be prednisone hair activated by apcs via mhc class ii presentation of antigen secreted by the myocytes or prednisone hair released from them after their destruction via a tc response and captured by the cells such events would lead to both cellular th and humoural th immunity indeed, it has been shown that dendritic cells are the essential apc involved in immune responses elicited by intramuscularly prednisone hair given dna vaccines dna vaccination via liposomes vaccination with naked dna by the intramuscular route is dependent on the ability of myocytes to take up the plasmid however, some of prednisone hair the dna may also be engulfed by apc infiltrating the site of injection, or in prednisone hair the lymph nodes following migration of the dna to the lymphatics the extent of dna prednisone hair degradation by extracellular deoxyribonucleases is unknown, but depending on the time of its residence interstitially, degradation could be considerable therefore, approaches that protect dna from the extracellular nucleases and promote dna prednisone hair uptake by cells more efficiently, or target it to apc, should contribute to the optimal prednisone hair design of dna vaccines it has been suggested that as apc are a preferred alternative to muscle cells for dna vaccine uptake and expression, liposomes known to be taken up prednisone hair avidly by apc infiltrating the site of injection or in the lymphatics, an event that has prednisone hair been implicated in their immunoadjuvant activity would be a suitable means of delivery of entrapped prednisone hair dna to such cells liposomes would also protect their dna content from deoxyrubonuclease attack moreover, the structural versatility of the system would ensure that its tranfection efficiency is further improved by the judicial choice of its structural characteristics or by the coentrapment of cytokine genes, prednisone hair other adjuvants eg immunostimulatory sequences, or indeed protein antigens see later together with the plasmid vaccine prednisone hair as a number of injectable liposomebased drug formulations, including vaccines against hepatitis a and influenza, have been already licensed for clinical use, acceptance of the system clinically would be less prednisone hair problematic than with other systems that are still at an experimental stage procedure for the prednisone hair entrapment of plasmid dna into liposomes ready to use mlv, =nm dna, antigen or both entrapped over entrapment yield a variety, of plasmid dnas have been quantitatively entrapped into liposomes by a mild dehydrationrehydration procedure the procedure fig consists of mixing preformed small unilamellar vesicles suv prednisone hair with a solution of the dna destined for entrapment, freezedrying of the mixture, followed by controlled rehydration of the formed powder, and centrifugation to remove non entrapped material formed liposomes are multilamellar however, when an appropriate amount of sucrose is added to can zyrtec make my child emotional the suv and dna mixture prior to dehydration, the resulting liposomes are much smaller about nm in diameter as prednisone hair expectcd, dna incorporation values, were higher up to of the amount used when a cationic prednisone hair lipid was present in the bilayers no apparent relationship was observed between amount of dna prednisone hair used g and the values of incorporation for the compositions and lipid mass used, the prednisone hair possibility that dna was not entrapped within the bilayers of cationic liposomes, but was rather complexed with their surface as suggested by the high fig entrapment of dna andor protein into prednisone hair cationic liposomes the procedure entails mixing up empty suv with the solutes destined for entrapment prednisone hair and subsequent dehydration on rehydration, most of the solutes is recovered entrapped within the generated prednisone hair multilamellar liposomes liposomes suv = rim dna, antigen or both naked d laaxea dna q m complexed d � naked d complexed d fig gel electrophoresis of a mixture of prednisone hair cationic suv and prccmv hbs before com plexed dna and after entrapped dna dehydrationrehydration of the mixture !?