CD80 and CD86 molecules are key costimulatory ligands expressed primarily on the surface of antigen-presenting cells (APCs). However, the presence of these molecules on T cells is currently uncommon and may be associated with various immunopathologies, such as allergic diseases. Literature data demonstrate that the presence of these molecules on T cells can polarize the immune response toward Th2, thereby enhancing inflammation. In our study, we found that all Type 2-dependent diseases we examined (atopic dermatitis, bronchial asthma) were associated with increased CD80 expression by immune cells. One of the modern and effective treatments for these diseases is genetically engineered biological therapy (GEBT). In this study, we found that in patients with severe allergy pathology, GEBT-associated cells exhibit changes in the percentage of cells expressing CD80 and CD86 on both monocytes and T cells.