Study of the adjuvant properties of preparations containing recombinant human granulocyte-macrophage colony stimulating factor

Abstract

The relevance of the search for new vaccine adjuvants is growing along with the increase in the number of current vaccine preparations, especially those developed on the basis of proteins. Some cytokines are known to exert adjuvant properties. The present work is devoted to the study of adjuvant activity of recombinant human granulocyte-macrophage colony stimulating factor (rhGM-CSF) and constructs based on it. Earlier, we developed a technology for isolation and purification of GM-CSF from the E. coli SG20050/p280_2GM producer strain, as well as a technology for conjugating polyglucin:spermidine complexes with rhGM-CSF. Double-stranded RNA was used to obtain molecular constructs on the basis of rhGM-CSF conjugate. To assemble constructs, the ratio of the components was calculated for one dose of the preparation to contain 5-40 mg of rhGM-CSF and 100 mg of double-stranded RNA. The effectiveness of the formation of molecular constructs was evaluated by dsRNA electrophoretic mobility shift in a 1% agarose gel. The effectiveness of the resulting adjuvants was determined in ELISA assays by measuring the titers of specific antibodies in mouse sera against ovalbumin or recombinant receptor-binding domain of the surface S protein of the severe acute respiratory syndrome coronavirus 2 (Delta variant (B.1.617.2). The experiments were carried out in 100 male BALB/c mice weighing 16-18 g. Mice were immunized twice, with a 14-day interval, by intramuscular injection of 200 mL per animal. Recombinant receptor-binding domain of the surface protein of SARS-CoV-2 was administered at a dose of 50 mg/animal, ovalbumin – at two doses – 1 mg or 5 mg/animal. Corresponding antigen was used as a positive control, a saline solution – as a negative control. It was shown that the maximum effect was achieved by immunization with a construct based on double-stranded RNA and rhGM-CSF conjugated to polyglucin-spermidine. The use of a conjugate without double-stranded RNA as an adjuvant also improved humoral response. The use of native rhGM-CSF did not increase the titers of specific antibodies. Thus, it was found that rhGM-CSF being a part of a polysaccharide conjugate or a molecular construct exerted an ability to enhance the humoral immune response to protein antigens.