Background/Aim: Patients with metastasized melanoma have limited treatment options and poor diagnosis. Therefore, the development of treatments requires a new therapeutic approach, of which gene therapy using rAAV vectors can be proposed. The aim of the study was to examine the efficiency of the rAAV vector to transduce mouse melanoma cells both in vitro and in vivo. Materials and Methods: Different rAAV serotypes encoding GFP under the control of both chicken beta-actin and cytomegalovirus promoters were used in the experiments. Intranasal, intraperitoneal, intravenous and intratumoral pathways of administration of rAAV vectors were tested using quantitative-PCR and immunohistochemical staining. Results: The highest transduction efficiency in metastatic cells in vivo was observed 7 days after intranasal administration of a 10 10 gc/0.03 ml dose of rAAV/DJ-CAG. Conclusion: Melanoma gene therapy based on rAAV vectors is a possible treatment option. Melanoma is a tumor that derives from pigment cellsmelanocytes, which develop from the neural tissue of integuments. The most common starting point of melanoma is the skin, but it may also be formed within the mucous membranes of the gastrointestinal tract or in the eyeball. It is a cancer with a high potential for metastasis (1, 2). Despite the progress in anti-cancer treatment, the number of deaths due to metastatic melanoma is still increasing and from the beginning of 2019 circa 7,000 patients in the USA died of it (1). Its aggressiveness causes as much as 90% of deaths among all skin cancers (3). The median survival of patients with melanoma who have distant metastases is shorter than 1 year (4). In the initial stage, the disease is curable, but unfortunately in the advanced stage, when metastasis occurs, it is practically incurable (5). The treatment, which has so far been proposed for the advanced stage, does not provide the desired benefit and the survival of these patients remains unsatisfactory. For instance, the annual survival rate after treatment with targeted therapy for the dual BRAF/MEK mutation is only about 50-60% (4, 6). Therefore, one of the future therapeutic approaches in the treatment of metastatic melanoma can be gene therapy using rAAV vectors, especially with the use of hybrid serotypes, which can achieve high efficiency of gene delivery (7-9). AAV viruses are non-pathogenic, small (approx. 25 nm in diameter) and infect both dividing and non-dividing cells. A distinguishing trait of rAAV is also the occurrence of various serotypes, which are characterized by strong tropism to selected cell types, making them ideal candidates for gene therapy (10). rAAV viruses have become increasingly popular in clinical trials (11, 12). In recent years, two pharmaceutical products using rAAV vectors-Glybera (13) and Luxturna (14) have been registered. Recent studies conducted on hybrid/mosaic serotypes have shown a greater transduction efficiency and are more heterogeneous, both in cellular and tissue specificity (15). The new rAAV vectors are created by a num...