[Screening of antiviral activity of samples from chaga Inonotus obliquus and humic acid from brown coal on Vero cell culture against ectromelia virus (Poxviridae: Orthopoxvirus; ECTV)].

INTRODUCTION: The mouse-specific orthopoxvirus, ectromelia virus, is one of the best models that can be used to study key issues of pathogenesis, prevention, and treatment of smallpox, and to develop measures to increase virulence, transmissibility, or the ability to overcome vaccine immunity. The aim of the work is to screen the antiviral activity of samples from Inonotus obliquus chaga and humic acid from brown coal in vitro against ectromelia virus. MATERIALS AND METHODS: We used ectromelia virus, strain K-1 (reg. No V-142), obtained from the State Collection of Pathogens of Viral Infections and Rickettsioses of the State Scientific Center of Virology and Biotechnology "Vector"; Vero Е6 cell culture (No 70) from the Collection of cell cultures of the State Scientific Center of Virology and Biotechnology "Vector". Nine samples from chaga I. obliquus and humic acid from brown coal were used to evaluate the changes in the infectivity of the ectromelia virus on cell culture using 2 schemes of application of drugs and virus (preventive and therapeutic schemes), and to assess their cytotoxicity and antiviral activity. RESULTS: 50% cytotoxic concentration, 50% virus-inhibiting concentrations and selectivity index were determined for all samples. The studied samples were shown to be non-toxic to the monolayer of Vero cell culture in a dilution of 300 and more micrograms/ml, while demonstrated high antiviral activity against strain K-1 of ectromelia virus in two application schemes - preventive and curative. CONCLUSION: All samples tested for ectromelia virus in vitro can be considered promising for further development of drugs against diseases caused by orthopoxviruses.

[Mutations in the A34R gene increase the immunogenicity of vaccinia virus]. / Мутации в гене A34R, приводящие к увеличению иммуногенности вируса осповакцины.

Vaccination is the most simple and reliable approach of protection to virus infections. The most effective agents are live vaccines, usually low-virulence organisms for humans and closely related to pathogenic viruses or attenuated as a result of mutations/deletions in the genome of pathogenic virus. Smallpox vaccination with live vaccinia virus (VACV) closely related to smallpox virus played a key role in the success of the global smallpox eradication program carried out under the World Health Organization auspices. As a result of the WHO decision as of 1980 to stop smallpox vaccination, humankind has lost immunity not only to smallpox, but also to other zoonotic, orthopoxviruscaused human infections. This new situation allows orthopoxviruses to circulate in the human population and, as a consequence, to alter several established concepts of the ecology and range of sensitive hosts for various orthopoxvirus species. Classic VACV-based live vaccine for vaccination against orthopoxvirus infections is out of the question, because it can cause severe side effects. Therefore, the development of new safe vaccines against orthopoxviral infections of humans and animals is an important problem. VACV attenuation by modern approaches carried out by targeted inactivation of certain virus genes and usually leads to a decrease in the effectiveness of VACV in vivo propagation. As a result, it can cause a diminishing of the immune response after administration of attenuated virus to patients at standard doses. The gene for thymidine kinase is frequently used for insertion/inactivation of foreign genes and it causes virus attenuation. In this research, the effect of the introduction of two point mutations into the A34R gene of attenuated strain LIVP-GFP (ТК-), which increase the yield of extracellular enveloped virions (EEV), on the pathogenicity and immunogenicity of VACV LIVP-GFP-A34R administered intranasally to laboratory mice were studied. It was shown that increase in EEV production by recombinant strain VACV LIVP-GFP-A34R does not change the attenuated phenotype characteristic of the parental strain LIVP-GFP, but causes a significantly larger production of VACV-specific antibodies.

The Influence of an Elevated Production of Extracellular Enveloped Virions of the Vaccinia Virus on Its Properties in Infected Mice.

The modern approach to developing attenuated smallpox vaccines usually consists in targeted inactivation of vaccinia virus (VACV) virulence genes. In this work, we studied how an elevated production of extracellular enveloped virions (EEVs) and the route of mouse infection can influence the virulence and immunogenicity of VACV. The research subject was the LIVP strain, which is used in Russia for smallpox vaccination. Two point mutations causing an elevated production of EEVs compared with the parental LIVP strain were inserted into the sequence of the VACV A34R gene. The created mutant LIVP-A34R strain showed lower neurovirulence in an intracerebral injection test and elevated antibody production in the intradermal injection method. This VACV variant can be a promising platform for developing an attenuated, highly immunogenic vaccine against smallpox and other orthopoxvirus infections. It can also be used as a vector for designing live-attenuated recombinant polyvalent vaccines against various infectious diseases.

Using the Ground Squirrel (Marmota bobak) as an Animal Model to Assess Monkeypox Drug Efficacy.

In experiments to study the sensitivity of ground squirrels (Marmota bobak) to monkeypox virus (MPXV) at intranasal challenge, expressed pox-like clinical symptoms (hyperthermia, lymphadenitis, skin rash all over the body and mucous membranes and others) were observed 7-9 days post-infection. The 50% infective dose (ID50 ) of MPXV for these marmots determined by the presence of clinical signs of the disease was 2.2 log10 PFU. Some diseased marmots (about 40%) died 13-22 days post-infection, and the mortality rate was weakly dependent on MPXV infective dose. Lungs with trachea were primary target organs of marmots challenged intranasally (with ~30 ID50 ). The pathogen got to secondary target organs of the animals mainly via the lymphatic way (with replication in bifurcation lymph nodes). Lungs with trachea, nasal mucosa and skin were the organs where the maximum MPXV amounts accumulated in these animals. Evidences of the pathogen presence and replication were revealed in these and subcutaneously infected marmots in the traditional primary target cells for MPXV (macrophages and respiratory tract epitheliocytes), as well as in some other cells (endotheliocytes, plasmocytes, fibroblasts, reticular and smooth muscle cells). Our use of this animal species to assess the antiviral efficacy of some drugs demonstrated the agreement of the obtained results with those described in scientific literature, which opens up the prospects of using marmots as animal models for monkeypox to develop therapeutic and preventive anti-smallpox drugs.

[EVALUATION OF THE HUMAN SENSITIVITY TO SMALLPOX VIRUS BY THE PRIMARY CULTURES OF THE MONOCYTE-MACROPHAGES].

Studies of the primary cultures of granulocytes, mononuclear, and monocyte-macrophage cells derived from human blood were performed using variola virus (VARV) in the doses of 0.001-0.021 PFU/cell (plaques-forming units per cell). Positive dynamics of the virus accumulation was observed only in the monocyte-macrophages with maximum values of virus concentration (5.0-5.5 Ig PFU/ml) mainly within six days after the infection. The fact of VARV replication in the monocyte-macrophages was confirmed by the data of electron microscopy. At the same time, virus vaccines when tested in doses 3.3 and 4.2 Ig PFU/ml did not show the ability to reproduce in these human cells. The people sensitivity to VARV as assessed from the data obtained on human monocyte-macrophages corresponded to -1 PFU (taking into account the smooth interaction of the virus in the body to the cells of this type), which is consistent to previously found theoretical data on the virus sensitivity. The human susceptibility to VARV assessed experimentally can be used to predict the adequacy of developed smallpox models (in vivo) based on susceptible animals. This is necessary for reliable assessment of the efficiency of development of drugs for treatment and prophylaxis of the smallpox.

[THE USE OF THE MODEL MOUSE ICR--VARIOLA VIRUS FOR EVALUATION OF ANTIVIRAL DRUG EFFICACY].

Mice of the ICR outbred population were infected intranasally (i/n) with the variola virus (VARV, strain Ind-3a). Clinical signs of the disease did not appear even at the maximum possible dose of the virus 5.2 lg PFU/head (plaque-forming units per head). In this case, 50% infective dose (ID50) of VARV estimated by the presence or absence of the virus in the lungs three days after infection (p.i.) was equal to 2.7 ± 0.4 lg PFU/head. Taking into account the 10% application of the virus in the lungs during the intranasal infection of the mice, it was adequate to 1.7 lg PFU/lungs. This indicates a high infectivity of the VARV for mice comparable to its infectivity for humans. After the i/n infection of mice with the VARV at a dose 30 ID50/ head the highest concentration of the virus detected in the lungs (4.9 ± 0.0 lg PFU/ml of homogenate) and in nasal cavity tissues (4.8 ± 0.0 lg PFU/ml) were observed. The pathomorphological changes in the respiratory organs of the mice infected with the VARV appeared at 3-5 days p.i., and the VARV reproduction noted in the epithelial cells and macrophages were noticed. When the preparations ST-246 and NIOCH-14 were administered orally at a dose of 60 µg/g of mouse weight up to one day before infection, after 2 hours, 1 and 2 days p.i., the VARV reproduction in the lungs after 3 days p.i. decreased by an order of magnitude. Thus, outbred ICR mice infected with the VARV can be used as a laboratory model of the smallpox when evaluating the therapeutic and prophylactic efficacy of the antismallpox drugs.

The Possibility of Using the ICR Mouse as an Animal Model to Assess Antimonkeypox Drug Efficacy.

As a result of the conducted experimental studies on intranasal challenge of ICR mice, rabbits and miniature pigs (even in the maximum variant) with the doses of 4.0-5.5 lg PFU of monkeypox virus (MPXV), some clinical signs such as purulent conjunctivitis, blepharitis and ruffled fur were found only in mice. The 50% infective dose (C ID50 ) of MPXV for these animals estimated by the presence of external clinical signs was 4.8 lg PFU, and L ID50 estimated by the virus presence in the lungs of mice 7 days post-infection taking into account its 10% application in the animal respiratory tract was 1.4 lg PFU. When studying the dynamics of MPXV propagation in mice challenged intranasally with 25 L ID50 of MPXV, the maximum pathogen accumulation was revealed in nasal cavity, lungs and brain: 5.7 ± 0.1, 5.5 ± 0.1 and 5.3 ± 0.3 lg PFU/ml, respectively. The pathomorphological examination of these animals revealed the presence and replication of the pathogen in the traditional primary target cells for MPXV (mononuclear phagocyte system cells and respiratory tract epitheliocytes) as well as in some other types of cells (endothelial cells, reticular cells, connective tissue cells). Our use of these animals to assess the antiviral efficacy of some drugs demonstrated the agreement of the results (a significant positive effect of NIOCH-14 and ST-246) with those described in scientific literature, which opens up the prospects of using ICR mice as animal models for monkeypox to develop preventive antismallpox drugs.

[Evaluation of therapeutic-prophylactic effectiveness of chemical compound NIOC-14 against ectromelia virus in vivo].

AIM: Study pharmacodynamic parameters of anti-viral effectiveness of a chemical compound NIOC-14 in experiments in mice infected with ectromelia virus (EV). MATERIALS AND METHODS: EV (K-1 strain) was obtained from the State Collection of Viral Infections and Rickettsioses Causative Agents of the State Scientific Centre of Virology and Biotechnology "Vector". Outbred ICR mice were intranasally infected with EV at a dose of 10 LD50 per animal (10 x 50% lethal doses/animal) and per orally received NIOC-14 or ST-246 as a positive control. Chemical compound NIOC-14 (7-[N'-(4-trifluoromethylbenzoyl)-hidrazincarbonyl]-tricyclo[3.2.2.0(2,4)]non-8-en-6-carbonic acid) was synthesized in Novosibirsk Institute of Organic Chemistry (NIOC). Anti-pox preparation ST-246, developed by SIGA Technologies Inc. (USA), was synthesized in NIOC using the technique described by the authors. RESULTS: 50% effective doses against EV in vivo were shown not to differ significantly between the preparations NIOC-14 (3.59 µg/g mouse mass) and ST-246 (5.08 µg/g mouse mass). During determination of therapeutic window, administration of NIOC-14 to mice 1 day or 1 hour before EV infection, as well as 1, 2 and 4 days after EV infection and then for 9 days was found to ensure 100% animal survival. Administration of NIOC-14 as well as ST-246 resulted in the decrease relative to control of EV titers in lungs, nasal cavity, brains, liver, spleen, kidneys and pancreas. CONCLUSION: Anti-viral effectiveness of NIOC-14 against EV in vivo was thus comparable by all the studied pharmacodynamic parameters with anti-viral activity of anti-pox-virus preparation ST-246.

[Development of the disease in marmot at the intranasal infection with the monkeypox virus].

In experimental study the sensitivity of the Marmota bobak species to the monkeypox virus (MPXV) with the intranasal (i/n) infection was tested. It was demonstrated that 50% of the infective dose (ID50) of the MPXV on external clinical signs of the disease was 2.2 Ig plaque forming units (PFU). The percentage of the marmot mortality is slightly dependent on the infecting dose of the MPXV, therefore it is not possible to correctly determine the value of 50 % fatal dose (FD50) for these animals. The most pronounced external clinical signs of the disease were obtained in the marmots: pox-like skin rash throughout the surface of the body and mucous membranes, purulent discharge from the nose, lymphadenitis, discoordination, tremor of the extremities, fever, increased aggression, and ruffled fur. In the course of experiments intended to determine the dynamics of the accumulation of the MPXV in various organs, tissues, and blood serum of marmot infected i/n with dose of 3.7 Ig PFU, it was found that the trachea, lungs, and the bifurcation lymph nodes are the primary target organs. The trachea, lungs, nasal mucosa membrane, and skin are the organs with maximal virus replication recorded at 5, 7, 9, and 12 days after the infection. The transfer of the MPXV into the secondary target organs (nasal mucosa membrane, brain, spleen, duodenum, adrenal glands, and skin) was carried out in marmots with lymphogenic and hematogenic ways of the dissemination of the infection.

[A comparative study of the antiviral activity of chemical compounds concerning the orthopoxviruses experiments in vivo].

In the experiments using intranasal (i/n) infection of mice with the ectromelia virus (EV) in a dose 10 LD50/head (10 x 50% lethal doselhead) or with the monkaypox virus (MPXV) in a dose 10 ID50/head (10 x 50% infective dose/ head) it was demonstrated that the antiviral efficiency of chemical compounds - the condensed derivatives of pyrrolidin-2,5-dion, as well as their predecessors and the nearest analogues, synthesized in Novosibirsk Institute of Organic Chemistry of the Siberian Branch of the Russian Academy of Sciences (NIOCH SB RAS) was observed. As a positive control we used the antipoxvirus chemical preparation ST-246 available from SIGA Technologies Inc. (USA), synthesized in NIOCH SB RAS by the technique suggested by the authors. It was demonstrated that the compound NIOCH-14 (7-[N'-(4-Trifluoromethylbenzoil)-hydrazidecarbonil]-tricyclo[3.2.2.02,4]non-8-en-6-carbonic acid) possessed comparable with ST-246 antiviral activity concerning EV and MPXV on all indicators used. Therefore, at infection of mice with EV (strain K-1) and peroral administration of NIOCH-14 and ST-246 in a dose 50 mkg/g of mouse weight (12-14 g) within 10 days the survival rate and average life expectancy of mice authentically exceeded the control levels. EV titers in lungs through 6 days after infection in the same groups were lower than in the control. In addition to that, after 7 days of infection of mice with MPXV (strain V79-1-005) and daily peroral administration of NIOCH-14 and ST-246 in a dose 60 mkg/g of mouse weight (9-11 g) authentic decrease in a part of infected animals and MPXV titers in lungs was observed.

[Efficacy of combined administration of ridostin and oseltamivir (tamiflu) for therapy and prophylaxis of experimental infection induced by influenza virus A (H5N1) in mice].

AIM: Study of possibility of treatment-prophylaxis effect increase during combined administration of ridostin and tamiflu in experiments in mice infected with highly pathogenic influenza virus strain A/chicken/Kurgan/05/2005 (H5N1). MATERIALS AND METHODS: Balb/c line mice infected intranasally with influenza virus at 100 and 10 LD50 doses received ridostin and tamiflu as monopreparation or the combined variant before or after the infection. The mice were observed for 16 days, lethality rate, protection coefficient and average life span were evaluated. Virus concentration in lungs was determined by using titration in MDCK cell line. RESULTS: Combined administration ofridostin and tamiflu after the infection increased survivability of the animals when compared with the control group, and reduced influenza virus concentration in lungs. CONCLUSION: Treatment effect during combined administration of ridostin and tamiflu after influenza virus infection increased.

[Evaluation of immunogenicity and safety of 2 immunizations with allantoic intranasal live influenza vaccine Ultragrivac].

AIM: Evaluate reactogenicity, safety and immunogenicity in phase 2 clinical trials of 2 immunization schedules with Ultragrivac--an allantoic intranasal life influenza vaccine based on A/17/ duck/Potsdam/86/92 [17/H5] reassortant strain. MATERIALS AND METHODS: 4 groups of volunteers participated in the study: group 1--40 individuals were vaccinated twice with a 10 day interval; group 2--40 individuals were vaccinated twice with a 21 day interval; group 3 (control)--10 individuals received placebo twice with a 10 day interval; group 4 (control)--10 individuals received placebo twice with a 21 day interval. Local (secretory IgA), cellular and humoral immune response were evaluated. Humoral immunity was evaluated by the intensity of increase of geometric mean antibody titers against 2 influenza virus strains A/17/duck/Potsdam/86/92 [17/H5] and A/chicken/Suzdalka/Nov-1 1/2005 (H5N1), and by the level of significant (4 times or more) antibody seroconversions after the vaccination. RESULTS: After the use of Ultragrivac the level of secretory IgA in the nasal cavity of vaccinated volunteers in the groups with revaccination intervals of 10 and 21 days increased significantly. The second immunization with 10 or 21 day intervals significantly increased postvaccinal humoral immune response. Humoral immune response induction after 2 vaccinations with 10 day interval was no less effective than with 21 day interval. CONCLUSION: Ultragrivac allantoic intranasal live influenza vaccine is areactogenic, harmless for vaccinated individuals, safe for those around, and has immunogenic properties against not only homologous virus A(H5N2), but also against influenza strain A(H5N1).

[In vitro and in vivo efficacy of Ingavirin against strains of pandemic influenza virus A(H1N1/09)v].

AIM: To study efficacy of Ingavirin in vitro and in vivo against strains of pandemic influenza virus A(H1N1/09)v and influenza virus A(H5N1) and A(H3N2). MATERIALS AND METHODS: Changes in hemagglutinating and cytopathic activity of influenza virus strains A(H1N1/09)v, A(H5N1) and A(H3N2) during their incubation in the presence of Ingavirin or Remantadin on MDCK cell culture were studied. In mice infected by influenza strains A(H1N1/09)v and A(H3N2) and orally treated with Ingavirin, Tamiflu or Remantadin virus titers in lungs were measured. RESULTS: There was decrease in hemagglutinating and cytopathic activity of influenza virus strains after incubation with Ingavirin in vitro. Ingavirin effectively inhibited reproduction of influenza virus strains A(H1N1/09)v and A(H3N2) in lungs of infected mice. Titers of these strains in lung homogenates decreased when Ingavirin was orally administered to infected mice. CONCLUSION: Strains of influenza virus A(H1N1/09)v were susceptible to Ingavirin and Tamiflu but resistant to Remantadin. Reference strains of A(H5N1) and A(H3N2) were susceptible to Ingavirin, Tamiflu and Remantadin.

[Study of efficacy of anaferon pediatric in mice infected by pandemic influenza virus A(H1N1/09)v].

AIM: To study efficacy of anaferon pediatric in mice infected by pandemic influenza virus A(H1N1/09)v. MATERIALS AND METHODS: Influenza virus strain A/California/07/2009 (H1N1)v was used. Three groups of BALB/c mice intranasally inoculated with influenza virus were studied. First group received solution of Anaferon pediatric during 5 days before and 8 days after inoculation, 2nd group received Tamiflu during 5 days after inoculation. Distilled water was administered orally to mice from control group. RESULTS: It was shown that Anaferon pediatric used as preventive and treatment agent in mice intranasally inoculated with 100% infectious dose of influenza virus strain A/ California/07/2009 (H1N1)v had antiviral effect, which expressed in 10-fold decreased reproduction of influenza virus in lungs of infected mice compared to control group measured 4, 6, and 8 days after inoculation. CONCLUSION: Use of anaferon pediatric before and after inoculation with influenza virus A(H1N1/09)v was not less effective than use of Tamiflu after inoculation.

[Study of antiviral activity of extracts obtained from basidial fungi against influenza viruses of different subtypes in experiments in vitro and in vivo].

AIM: To study antiviral activity of extracts obtained from basidial fungi against influenza viruses of different subtypes. MATERIALS AND METHODS: Antiviral activity of extracts obtained from basidial fungi against influenza virus A/chicken/Kurgan/05/2005 (H5N1) was determined in in vitro experiments. Changes in infectiousness of pandemic influenza virus A/Moscow/226/2009 (HIN1)v caused by extracts of basidial fungi was studied in experiments in vitro and in vivo. RESULTS: Seventy water extracts of basidial fungi were studied, of which 10 were able to inhibit infectiousness of influenza virus strain A/ chicken/Kurgan/05/2005 (H5N1) in MDCK cell culture. Also, several studied extracts decreased infectiousness of pandemic influenza virus strain A/ Moscow/226/2009 (H1N1)v in MDCK cells and inhibit its reproduction in lungs of infected mice. CONCLUSION: High antiviral activity of extracts obtained from basidial fungi against influenza viruses opens perspectives for development of drugs with preventive and treatment effects.

Antiviral activity of Anaferon (pediatric formulation) in mice infected with pandemic influenza virus A(H1N1/09).

Anaferon (pediatric formulation) administered in the therapeutic-and-prophylactic regimen to mice receiving intranasally 100% infecting dose of A/California/07/2009(H1N1)v influenza virus exhibited an antiviral effect and 10-fold reduced the production of influenza virus in the lungs of infected mice on days 4, 6, and 8 after infection compared to the control (distilled water). The efficiency of Anaferon (pediatric formulation) administered before and after infection with A/California/07/2009(H1N1)v influenza virus was not inferior to the use of Tamiflu after infection.

[In vivo efficacy of Ingavirin against pandemic A (H1N1/09)v influenza virus].

Ingavirin was shown to be efficient in inhibition of the pandemic influenza virus strains A/California/04/2009 (H1N1)v, A/California/07/2009 (H1N1)v, A/Moscow/225/2009 (H1N1)v and A/Moscow/226/2009 (H1N1)v. as well as the influenza virus strain A/Aichi/2/68 (H3N2) in the lungs of the infected mice. After oral administration of Ingavirin the titers of the influenza virus strains in the lung homogenates lowered.

[In vitro efficacy of Ingavirin against the pandemic influenza virus A(H1N1/09)v].

Ingavirin was shown to be efficient in inhibition of the influenza virus strains A/California/04/2009 (H1N1)v, A/California/07/2009 (H1N1)v, A/Moscow/225/2009 (H1N1)v and A/Moscow/226/2009 (H1N1)v, as well as the strains A/Chicken/Kurgan/05/2005 (H5N1) and A/Aichi/2/68 (H3N2) in the MDCK cell culture. The hemagglutinin and cytopathic activity of the influenza virus strains decreased at entering Ingavirin in vitro.

[Results of clinical trials on reactogenicity, safety, and immunogenicity of influenza allantoic intranasal live vaccine "Ultragrivac" (type A/H5N2)].

Results of phase II of a clinical trial of the influenza allantoic intranasal live vaccine "Ultragrivac" (type A/H5N2) are presented. The vaccine was developed based on strain /17/Duck/Potsdam/86/92 H5N2 [17/H5] - reassortant of two viruses, /Leningrad/134/17/57 (H2N2) and /Duck/Potsdam/1402-86 (H5N2), obtained from the Virology Department, St. Petersburg Institute of Experimental Medicine.Two schemes of immunization (with revaccination on days 10 and 21) were used. Evaluation of vaccine immunogenicity included determination of local, cellular and humoral immunity. A significant rise in the level of secretory IgA in the nasal cavity of vaccinated volunteers (with revaccination on days 10 and 21) was documented after application of the vaccine. The postvaccination humoral immune response was estimated from the level of significant (4-fold and more) antibody seroconversions, geometric mean titers of antibodies to two strains of influenza virus /17/Duck/Potsdam/86/92 H5N2 [17/H5] and /Chicken/Suzdalka/Nov-11/2005 (H5N1), and their incremental rate. Results of measurement of antibody titers in hemagglutination-inhibition assay are presented, with two antigens being used to analyse all serum samples from volunteers twice vaccinated with influenza vaccine "Ultragrivac" at 10 and 21 day intervals. Result of phase II of this clinical study show that influenza allantoic intranasal live vaccine "Ultragrivac" is nonreactogenic and safe for both vaccinated and surrounding individuals. Moreover, it is sufficiently immunogenic with respect not only to homologous virus A(H5N2) but also to the A(H5N1) strain.

Comparative analysis of reproduction of influenza virus strains in cell lines perspective for the creation of cultural vaccines grown on nutrient medium on the basis of rise flour protein hydrolysate.

We studied vaccine strains of influenza viruses A and B during their culturing in MDCK and Vero cells grown in Eagle's MEM medium and in a medium on the basis of enzyme hydrolysate of rise flour proteins with reduced (2%) content of fetal calf serum. Optimal conditions for cell culturing and reproduction of influenza virus strains in these cells were studied. Culturing of vaccine strains of influenza viruses in MDCK and Vero cells grown in nutrient media on the basis of rise flour protein hydrolysate yielded high infection titers, which suggests that this medium can be used for the development of cultural influenza vaccine.