FIELD: medicine.SUBSTANCE: group of inventions refers to medicine, namely to immunology, and can be used to produce immunostimulating polypeptide derivative of transcription transactivation (Tat). Immunostimulating polypeptide derivative of the transactional transactivation agent has an amino acid sequence comprising the following sequence: (i) a transcription factor domain sequence of human immunodeficiency virus (HIV) (TAT) protein or monkey immunodeficiency virus, having the amino acid sequence SEQ ID NO: 96, 97 or 98, (ii) a sequence of a cysteine-rich domain from monkey immunodeficiency virus, HIV or defensin, having more than 85 % sequence identity to the amino acid sequence of one of SEQ ID NO: 124–132, and (iii) a sequence of the C-terminal domain of the HIV protein Tat or the immunodeficiency virus of monkeys, having more than 85 % sequence identity to the amino acid sequence of one of SEQ ID NO: 133–150, wherein the polypeptide derivative Tat is not one of SEQ ID NO: 2, 3 or 4. Group of inventions also involves the use of Tat for inhibiting suppression of an antitumour immune response in a patient with cancer, for treating an expressing PD-L1 tumour.EFFECT: using the given group of inventions enables to overcome the PD-1/PD-L1 signal transmission pathway in PD-L1-expressing mammary gland cancer by administering the polypeptide derivative of Tat, and also reverses the immunosuppression periodically occurring during the progression of cancer, and restores immunoreactivity.19 cl, 5 ex, 4 tbl, 14 dwgГруппа изобретений относится к медицине, а именно к иммунологии, и можжет быть использована для получения иммуностимулирующего полипептидного производного трансактиватора транскрипции (Tat). Иммуностимулирующее полипептидное производное трансактиватора транскрипции имеет аминокислотную последовательность, содержащую в следующем порядке: (i) последовательность домена транскрипционного фактора из белка Tat вируса иммунодефицита человека (ВИЧ) или вируса иммунодефицит
