To explore the potential of anti-programmed cell death ligand 1 (PD-L1) immunotherapy in giant congenital melanocytic nevus (GCMN) treatment.

GCMN cells were divided into four groups: GCMN group (GCMN cells alone), unactivated peripheral blood mononuclear cells (PBMC)+GCMN group (GCMN cells with unstimulated PBMCs), activated PBMC+GCMN group (GCMN cells with CD3/CD28 antibody-stimulated PBMCs), and activated PBMC+GCMN+PD-L1 inhibitor group (the activated PBMC +GCMN group treated with 10 μg·mL^-1 PD-L1 inhibitor atezolizumab). After 72 hours of culture, cell cytotoxicity and confluence were assessed. Cell viability was measured using the cell counting kit (CCK-8) assay, and apoptosis was evaluated via flow cytometry. Additionally, a humanized immune system was established in C-NKG severely immunodeficient mice by intraperitoneal injection of human PBMCs. A GCMN patient-derived xenograft (PDX) model was constructed in these humanized mice, divided into two groups: control group [phosphate buffer saline (PBS)] and experimental group (intraperitoneal injection of 10 mg·kg^-1 atezolizumab), administered every 3 days for 2 weeks, to evaluate in vivo efficacy.

Cell confluence rates for the GCMN, unactivated PBMC+GCMN, activated PBMC+GCMN, and activated PBMC+GCMN+PD-L1 inhibitor groups were (93.14±3.25)%, (85.29±2.40)%, (68.29±3.68)% and (22.55±4.28)%, respectively. Cell viability rates were (100.00±1.48)%, (80.35±2.60)%, (52.17±2.37)% and (15.61±1.82)%, respectively. Apoptotic cell proportions were (0.64±0.14)%, (9.32±0.91)%, (19.29±3.98)% and (28.43±0.33)%, respectively. Compared to the GCMN group, the activated PBMC+GCMN+PD-L1 inhibitor group showed statistically significant differences in all measured parameters (all P<0.05). In GCMN-PDX model, dermal cell density in experimental group and control group were (580±183) and (3 658±532) cells·mm^-2, respectively. And the difference of the above index between the two groups was statistically significant (all P<0.05).

This study demonstrates that PD-L1 inhibitors effectively target GCMN cells by activating the immune system, offering a promising new strategy for the clinical treatment of GCMN.