Despite recent advances in therapy, such as stem cell transplantation and new drugs including proteosome inhibitors, multiple myeloma (MM) remains incurable for most patients. Immune therapy using dendritic cell (DC) vaccination to generate anti-myeloma cytotoxic T cell (CTL) responses targeting residual disease is a promising, potentially curative strategy that would be compatible with other therapies. Blood DC isolated using the monoclonal antibody (mAb) CMRF-56, can induce CTL responses (

J. Immunotherapy
). We have established the ability of CMRF-56 blood DC to migrate in vitro and induce CTL responses to MM antigens and developed clinical scale production of the CMRF-56 blood DC preparations. Migration of CMRF-56 blood DC toward a CCL21 gradient was significantly improved by addition of granulocyte macrophage colony stimulating factor (GM-CSF) and prostaglandin E2 (PGE2) (n=5, p<0.05) and exceeded that of activated MoDC. Activation of CMRF-56 blood DC with GM-CSF also optimal for induction mature phenotype (n=4, p<0.05), survival of blood DC after 48 hours culture (n=3, p<0.01), and generation of CTL (n=5, p<0.05). Addition of PGE2 made no significant difference to CTL induction. GM-CSF activated CMRF-56 blood DC loaded with U266 lysate induced polyclonal anti-myeloma CTL responses capable of 38–61% specific lysis of U266 cells in a 51Cr release assay. To determine specificity, we examined the CTL specific for known MM tumour antigens and could identify CTL recognising Muc1 and HM1.24 HLA-A*201 epitopes in 3/3 donors tested. CMRF-56 blood DC derived from both healthy and MM donors were pulsed with HLA-A*201 restricted peptides derived from MM tumour antigens including Muc1 and HM1.24/BST2, along with novel antigens such as cancer testis antigen (CT)-7 (MAGE-C1) and B cell maturation antigen (BCMA). Results from healthy donors have shown that CTL specific for all above mentioned antigens can be induced with 4/8 responding to HM1.24, 2/8 to Muc1, 4/8 to CT7 and 1/6 to BCMA and these CTL lysed U266 cells specifically. In parallel, we have developed and validated clinical scale production of CMRF-56 blood DC preparations using clinical grade biotinylated CMRF-56 mAb and the CliniMACS system. On average over 100 million CMRF-56 blood DC were recovered from immunoselected apheresis products from both healthy (n=10) and MM donors (n=4) with average blood DC purities of 31% and 42% respectively. These results indicate that CMRF-56 blood DC can be produced on a clinical scale, can migrate toward secondary lymphoid chemokine CCL21 in vitro and can induce anti-myeloma CTL responses to both known and novel MM antigens. These data supports the use of CMRF-56 blood DC preparations loaded with peptide antigen as a potential anti-myeloma vaccine for patients with minimal residual disease.

Author notes

Disclosure: No relevant conflicts of interest to declare.