Methods: Ten patients with multiple myeloma who were up to 6 months after high dose chemotherapy with autologous stem cell support, were enrolled. Subcutaneous vaccinations with IO103 with the adjuvant Montanide ISA 51 was given up to fifteen times during 1 year. Safety was assessed by the common toxicity criteria for adverse events (CTCAE). Immunogenicity of the vaccine was evaluated using IFNg enzyme linked immunospot and intracellular cytokine staining on blood and skin infiltrating lymphocytes from sites of delayed-type hypersensitivity. The clinical course was described.
Results: All adverse reactions to the PD-L1 vaccine were below CTCAE grade 3, and most were grade 1–2 injection site reactions. The total rate of adverse events was as expected for the population. All patients exhibited peptide specific immune responses in peripheral blood mononuclear cells and in skin-infiltrating lymphocytes after a delayedtype hypersensitivity test. The clinical course was as expected for the population. Three of 10 patients had improvements of responses which coincided with the vaccinations.
Conclusion: Vaccination against PD-L1 was associated with low toxicity and high immunogenicity. This study has prompted the initiation of later phase trials to assess the vaccines efficacy.
Clinical Trial Registration: clinicaltrials.org, identifier NCT03042793.