Possibilities and prospects of using biofluorescent proteins at the stage of preclinical evaluation of live vaccines, using the example of the <i>Yersinia pestis</i> vaccine strain EV NIIEG pTURBOGFP-B

Introduction. Currently, studies aimed at finding the most informative and optimized method for assessing the survival rate of the plague microbe vaccine strain in the body of animals vaccinated against plague are relevant. Aim — to evaluate the feasibility of using biofluorescent proteins using the example of the Yersinia pestis vaccine strain EV NIIEG pTurboGFP-B (EVGFP) in combination regimens with immunomodulators at the stage of preclinical evaluation of live vaccines. Materials and methods. Guinea pigs were immunized with EVGFP grown at 28ºC and 37ºC (EVGFP28 and EVGFP37, respectively), in combination with immunomodulators (azoximer bromide, AB, and human recombinant interferon gamma, HRI). Results. Fluorescence microscopy revealed seeding (up to 600 m.c. in one field of view) with EVGFP cells at the site of culture introduction in all experimental groups on the 1st day. In vivo flow cytometry showed that on the 1st day in all experimental groups the phagocytic index (PI) averaged 94.5%, with a subsequent decrease by the 4th day by an average of 4.4 times (21.2%). On the 4th day of the study in the EVGFP37+AB group the PI exceeded the similar indicator in the EVGFP37 group by 1.8 times. On the contrary, in the EVGFP28+HRI group the PI decreased by 2.2 times relative to the similar indicator in the EVGFP28 group. In addition, in the EVGFP37+AB and EVGFP37+HRI groups, on day 4, the PI was 2 times higher than in the EVGFP28+AB and EVGFP28+HRI groups, respectively. In the EVGFP37 group, the phagocytic number was on average 1.5 times higher than in the EVGFP28 group. Conclusion. The obtained data confirm the dependence of the outcome of in vivo interaction of the plague microbe with spleen phagocytes on the temperature of bacterial growth, as well as on the presence of AB and HRI. The use of biofluorescent proteins, as shown by the example of the EVGFP strain and the flow cytometry method, expands the possibilities for assessing live plague vaccines in preclinical studies.