Pygenic acid A, a small-molecule PD-1/SHP-2 inhibitor, enhances efficacy of therapeutic melanoma vaccines and prophylactic influenza vaccines.

Overcoming immunosuppressive tumor microenvironments remains a critical challenge in advanced vaccine development. Here, we evaluated Pygenic acid A (PA), an intracellular small-molecule inhibitor targeting the PD-1/SHP-2 axis, as a novel vaccine adjuvant. The adjuvant efficacy of PA was systematically assessed in two murine models: a therapeutic B16-F10 melanoma lung metastasis model and a prophylactic lethal H1N1 influenza virus challenge model. In the melanoma metastasis model, PA potentiated the anti-tumor effect of the mTRP2 vaccine, markedly inhibiting pulmonary metastatic lesions and prolonging the survival of tumor-bearing mice. Mechanistically, PA robustly boosted the intratumoral infiltration of functional T cells, thereby reversing local tumor immunosuppression. In the influenza vaccination model, consistent immunostimulatory effects were observed: the PA-adjuvanted hemagglutinin (HA) vaccine effectively elicited broad-spectrum cross-neutralizing antibody responses and provided complete protection against lethal heterologous influenza virus challenge. Further mechanistic investigations demonstrated that PA specifically promoted the differentiation of T follicular helper (Tfh) cells and the expansion of germinal center (GC) B cells in draining lymph nodes, while triggering a robust Th1-type cellular immune response dominated by IFN-γ secretion. Furthermore, in vivo safety assessments verified that PA intervention induced no obvious systemic inflammation, hematological abnormalities, or visceral organ injury, indicating a favorable safety profile. Collectively, these results demonstrate that PA serves as a potent and safe intracellular checkpoint-targeting adjuvant capable of potentiating both cellular immunity and cross-protective humoral immunity, holding great translational promise for the development of advanced cancer vaccines and broad-spectrum influenza vaccines.