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Aim evaluation of specific T-cell immunity against SARS-CoV-2 in primary and secondary response to virus antigens by screening method., Materials and Methods: Patients were tested 11.5 months after COVID-19 and 610 months before and after vaccination. Healthy volunteers were screened before, 26 times during the vaccination course, and 68 months after revaccination with the Sputnik V vaccine. IgG and IgM antibodies to SARS-CoV-2 were detected by ELISA using commercially available kits (Vector-Best, Russia). Antigenic (AG) activation of T cells in the fraction of bloods mononuclear cells was assessed by IFN- production after AG stimulation in the wells of plates from ELISA kits intended for detection of antibodies against SARS-CoV-2. Data were processed by MS Excel and Statistica 10.0 software., Results: AG-specific T cells were detected in 88.5% of vaccinated healthy volunteers, half of whom were found to have T cells appearing earlier than antibodies to AG. After 6-8 months, the level of AG activation decreases. Following the revaccination, the level of AG activation of memory T cells in vitro increases within six months in 76.9100.0% of vaccinated subjects. On the contrary, after COVID-19, 86.7% of individuals had in their blood the AG-specific T cells with high activity at the time of vaccination. The activity of T cells recognizing the RBD domain of the SARS-CoV-2 S protein and the proportion of individuals who had these cells in their blood increased after the vaccination of reconvalescents., Conclusion: T-cell immunity against SARS-CoV-2 antigens has been shown to persist for 6 months after illness. In vaccinated individuals without history of COVID-19, such duration of the preservation of AG-specific T cells in blood was only achieved after the revaccination.

Introduction: The development of the COVID-19 pandemic has stimulated the scientific research aimed at studying of the mechanisms of formation the immunity against SARS-CoV-2. Currently, there is a need to develop a domestic simple and cost-effective specific method suitable for monitoring of T-cell response against SARS-CoV-2 in reconvalescents and vaccinated individuals., Aim: Development of a screening method for evaluation specific T-cell immunity against SARS-CoV-2., Materials and Methods: Total 40 individuals who had mild to moderate COVID-19 and 20 healthy volunteers who did not have a history of this disease were examined. The presence and levels of IgG and IgM antibodies to SARS-CoV-2 were identified in participants sera by ELISA using the diagnostic kits from JSC Vector-Best (Novosibirsk, Russian Federation). Antigenic stimulation of mononuclear cells was carried out on commercial plates with adsorbed whole-virion inactivated SARS-CoV-2 antigen (State Research Center of Virology and Biotechnology VECTOR Novosibirsk, Russian Federation). The concentration of IFN- was measured in ELISA using the test systems from JSC Vector-Best (Novosibirsk, Russian Federation). The immunophenotyping of lymphocytes was performed on a flow cytometer Cytomics FC500 (Beckman Coulter, USA). Statistical data processing was carried out using the Microsoft Excel and STATISTICA 10 software package., Results: Stimulation of mononuclear cells isolated from the peripheral blood with whole-virion inactivated SARS-CoV-2 antigen fixed at the bottom of the wells of a polystyrene plate showed a significantly higher median response in terms of IFN- production in 40 people who had history of COVID-19 compared to 20 healthy blood donors (172.1 [34.3575.1] pg/ml versus 15.4 [6.925.8] pg/ml, p 0.0001). There was no difference in median IFN- levels in supernatants collected from unstimulated mononuclear cells from COVID-19 reconvalescents and healthy donors (2.7 [0.411.4] pg/ml versus 0.8 [0.023.3] pg/ml, p 0.05). The overall sensitivity and specificity of this method were 73% (95% CI 5888%) and 100% (95% CI 100100%), respectively, at a cut-off of 50 pg/ml., Conclusion: The developed method for assessment of the cellular immune response to SARS-CoV-2 can be used as a screening method for monitoring the T-cell response in a population against a new coronavirus infection in recovered people.

The aim of the study was to develop some approaches to evaluate the basic parameters of the humoral and cellular immune response to a bacteriophage, taking into account the multifactorial aspects of its interaction with both the pathogen and the macroorganism. The necessary reagents were obtained and a line of diagnostic ELISA test systems was designed to allow semi-quantitative assessment of the anti-bacteriophage IgG-antibody level in serum or other biological human fluids, as well as in preparations obtained from human blood. The need for neutralization reaction to determine the effect of detected antibodies on phage activity against a target bacterium has been proven. Testing the approaches used in the investigation of patients' blood sera showed that antibodies to bacteriophages synthesized during phage therapy are not always neutralizing. Also approaches have been developed to evaluate cell immunity reactions to bacteriophage namely to identify T-lymphocytes (T-helpers and cytotoxic lymphocytes) that can be activated in the presence of the phage under study (by expressing the early activation marker (CD69) and by the ability to produce IFNγ). Approbation of the technique in the study of lymphcytes in patients during phage therapy showed the presence of activated cells by both the CD69 expression and IFNγ production, the dynamics of which depended on the timing and frequency of therapy. The appearance of neutralizing anti-phage antibodies and corresponding activated T-lymphocytes should be taken into account in phage therapy, the effectiveness of which can directly depend not only on the activity of the phage against the target bacterium, but also on the response of the patient's immune system to the bacteriophage., Competing Interests: The authors declare no conflict of interest.