CD40 ligand(Amgen, Inc.)

Vaccination with idiotype (Id) protein‐pulsed dendritic cells (DCs) has been explored in multiple myeloma and the results have been disappointing. To improve the efficacy of DC vaccination in myeloma, we investigated the use of Id‐ and keyhole limpet haemocyanin (KLH)‐pulsed, CD40 ligand‐matured DCs administered intranodally. Nine patients with smouldering or stable myeloma without treatment were enrolled and DC vaccines were administered at weekly intervals for a total of four doses. Following vaccination, all patients mounted Id‐specific γ‐interferon T‐cell response. Interleukin‐4 response was elicited in two, and skin delayed‐type hypersensitivity reaction occurred in seven patients. More importantly, Id‐specific cytotoxic T‐cell responses were also detected in five patients. Most if not all patients mounted a positive T‐cell response to KLH following vaccination. At 1‐year follow‐up, six of the nine patients had stable disease, while three patients had slowly progressive disease even during the vaccination period. At 5‐year follow‐up, four of the six patients continued with stable disease. No major side effects were noted. In summary, intranodal administration of Id‐pulsed CD40 ligand‐matured DCs was able to induce Id‐specific T and B‐cell responses in patients. Current efforts are geared towards breaking tumour‐mediated immune suppression and improving clinical efficacy of this immunotherapy.

Stimulation of the CD40 receptor using an agonistic anti-CD40 antibody can slow the growth of AB1 tumors. Stimulation of the GITR receptor may also have antitumor activity by countering the immunosuppressive effects of regulatory CD4 T cells. Similarly, agonists for Toll-Like Receptors (TLR) such as CpG oligodeoxynucleotides (TLR9 agonist) have activity against AB1 tumors. Combinations of CpG with CD40 ligand and polyinosinic-polycytidylic acid (poly(I:C), TLR3 agonist) may be even stronger than CpG alone. The synergistic effects of these combinations have been tested in other tumor types but not in mesothelioma.

Established AB1 mesothelioma tumors were injected with either plasmid DNA encoding a novel 4-trimer form of murine CD40 ligand (pSP-D-CD40L), GITR ligand (GITRL), or control plasmid DNA. In addition, CpG with or without poly(I:C) was also injected intratumorally.

Plasmid injections of pSP-D-CD40L or pSP-D-GITRL, had no significant antitumor effect, possibly reflecting the difficulty of administering DNA injections into this very dense tissue. However, the injection of CpG with or without poly(I:C) strongly suppressed tumor growth and led to long-term tumor-free survival. The response to a triple combination of pSP-D-CD40L + CpG + poly(I:C) was demonstrated by an increase in intratumoral CD8 T cells and a dramatic increase in F4/80 macrophages.

Intratumoral injections of plasmid DNAs encoding highly active forms of either CD40 ligand or GITR ligand had no significant antitumor effects in this model, although improved DNA delivery techniques could possibly improve this strategy. In contrast, intratumoral CpG injections had significant antitumor effects and there were indications that CpG plus poly(I:C) was even more effective. Taken together, these data confirm previous reports that immune stimulants, especially CpG TLR9 agonists, have potential as a treatment for mesothelioma.