After a Week, Efgartigimod Lets 38% of Patients With ITP Reach Platelet Counts to Avoid Bleeding

Efgartigimod, already approved as Vyvgart to treat myasthenia gravis, allowed a third of patients with immune thrombocytopenia (ITP) to quickly achieve platelet levels that signal an ability to avoid sudden bleeding events in a randomized clinical trial, with other results showing sustained responses compared with placebo.

Results of the phase 3 study, ADVANCE-IV, were presented Sunday in a plenary session at the 64th American Society of Hematology Annual Meeting and Exposition in New Orleans, Louisiana.

Both the study’s lead author, Catherine M. Broome, MD, associate professor of medicine, Georgetown University, and Douglas B. Cines, MD, professor of medicine and pathology, University of Pennsylvania, who introduced the abstract, said patients with chronic ITP experience low platelet counts brought on by immunoglobulin G (IgG) platelet autoantibodies. IgG bind to platelets, which causes their clearance and limits their production. Besides bleeding risk, patients experience fatigue and poor quality of life, Broome said, and current therapies are linked to comorbidities and don’t work long enough.

“There is a need for better ITP therapy, which is why we embarked on this trial,” Broome said. The new approach to blocking the effects of IgG involves the neonatal Fc receptor (FcRn). Although its name is derived from its discovery for its ability to transport IgG from mother to fetus, Cines explained, “FcRn is also widely expressed in other cell types, including endothelial cells, where it helps regulate the lifespan of IgG.”

As Broome explained in a press briefing prior to the session, “When native IgG is bound to the neonatal FC receptor, it is protected from lysosomal degradation.” Thus, disrupting the how IgG binds to FcRn would interfere with its effect platelets. This knowledge is behind the mechanism of efgartigimod.

Study design. Broome outlined the trial’s design, which randomized 131 participants 2:1 to receive 10 mg/kg of efgartigimod or placebo along with entry-level doses of background therapy, such as corticosteroids, for 24 weeks. All patients had chronic or persistent ITP; at screening, all had received at least 2 prior ITP therapies or 1 prior and 1 concurrent treatment, along with 2 platelet counts of less than <30×109/L, which Broome explained is the point at which patients can expect to avoid sudden bleeding.

During the study, all patients received treatment intravenously weekly but could switch to biweekly after week 4 if their platelet levels increased sufficiently. The primary end point was the proportion of chronic ITP patients with a sustained platelet response of ≥50×109/L in at least 4 of 6 visits between weeks 19 and 24 without intervening events, such as rescue therapy after week 12.

Key secondary end points were:

• disease control, which was measured by the number of with platelets at ≥50×109/L in the chronic ITP population,
• proportion of participants in the overall population (chronic and persistent) with sustained platelet response,
• incidence of bleeding events, and
• a durable, sustained platelet response, as measured by platelets at ≥50×109/L in at least 6 of 8 visits between weeks 17 and 24 in the overall population.

Results. Among the patients, the median time since di agnosis was 4.57 years and 67% had at least 3 prior treatments. Broome reported that the study met its primary end point, as sustained platelet response was achieved in more efgartigimod patients, 21.8% (17/78) vs 5.0% (2/40), P = 0.0316.

Efgartigimod achieved all platelet-related secondary end points. The mean number of weeks of disease control was 6.1 for the group taking the study drug, compared with 1.5 for placebo. This translated into 44% of the efgartigimod group achieving sustained response for at least 5 to 9 weeks, compared with 12% for placebo; 28% for at least 10 to 14 weeks (0% placebo), and 17% for at least 15 to 19 weeks (0% placebo).

Sustained platelet count response was achieved by 25.6% in the efgartigimod group (22/86), compared with 6.7% for the placebo group (3/45).

Broome explained that although the group taking efgartigimod beat the placebo group on the next secondary end point—number of visits with World Health Organization bleeding score ≥ 1—it did not reach statistical significance. However, the group taking efgartigimod bested the placebo group on durable platelet count as well, 22.1% vs 6.7%.

Of note, the study drug worked quickly with 38% of patients in the efgartigimod group achieving the <30×109/L platelet level by week 1, compared with 11% of the placebo group.

In the press briefing, Broome said the drug produced no new safety signals, and she noted that 90% of the patients who took part in ADVANCE IV moved forward to an open-label extension study, “which will give us an opportunity to evaluate durability of response, as well as safety.”

“Most adverse events were mild to moderate,” she said. “The results of this study showed us that we have some flexibility in dosing with both weekly and every other week administration.”

Argenx is the maker of efgartigimod.

Reference

Broome CM, McDonald V, Miyakawa Y, et al. Efficacy and safety of intravenous efgartigimod in adults with primary immune thrombocytopenia: results of a phase 3, multicenter, double-blinded, placebo-controlled, randomized clinical trial (ADVANCE-IV). Presented at: 64th American Society of Hematology Annual Meeting and Exposition; New Orleans, Louisiana; December 10-13, 2022; Abstract 3.