Immutep SA, a biopharmaceutical company developing immunostimulatory factors for the treatment of cancer and chronic infectious diseases and immunomodulatory therapeutic antibodies for the treatment of cancer or autoimmune disease, informed the publication of a clinical research paper that its lead product, IMP321, given with first-line paclitaxel achieved clinical benefit in 90 per cent of metastatic breast carcinoma (MBC) patients. Correlations were observed with both the patients' monocyte (i.e. the primary target cell for IMP321) count before treatment and the degree of activation of monocytes during treatment.

The study was an open-label fixed-dose-escalation trial carried out in three cancer centers in the Paris region. The lead center was the René Huguenin Cancer Centre in Saint Cloud. The other centers were Tenon Hospital and the Georges Pompidou European Hospital in Paris. The immuno-monitoring was done by Immutep at its labs near Paris.

MBC patients were administered one dose of IMP321 every two weeks for a total of 24 weeks (12 injections). The repeated single doses were administered the day after chemotherapy at day two and day 16 of the 28-day cycles of paclitaxel (six cycles). Blood samples were taken 13 days after the sixth and the twelfth IMP321 injections to determine sustained APC, NK and memory CD8 T cell responses. Thirty patients received IMP321 in three cohorts (doses: 0.25, 1.25 and 6.25 mg).

IMP321 induced both a sustained increase in the number and activation of APC (monocytes and dendritic cells) and an increase in the percentage of NK and long-lived cytotoxic effector-memory CD8 T cells. Clinical benefit was observed for 90 per cent of patients with only three progressors in six months. Also, the objective tumor response rate of 50 per cent compared favorably to the 25 per cent rate reported in the historical control group.

IMP321 is a recombinant soluble LAG-3Ig fusion protein that binds to MHC class II with high avidity and mediates APC and then antigen-experienced memory CD8+ T cell activation. Further evidence of the mechanism of action came from the analysis of tumor regression during the second three months compared to the first three months. Under chemo alone, most tumor regression takes place during the early period and less during the later period. Using IMP321, however, investigators observed enhanced tumor regression in the later period as well; late responses are characteristic of a cancer immunotherapy effect.

“We now have the results required to go forward to a pivotal trial,” said Frédéric Triebel, scientific and medical director, Immutep. He said that this form of chemo-immunotherapy should be applicable to many chemotherapies. For example, it is now being tested in the US in association with gemcitabine in pancreatic cancer.