PD-1 Blockade with the Monoclonal Antibody Pembrolizumab (MK-3475) in Patients with Classical Hodgkin Lymphoma after Brentuximab Vedotin Failure: Preliminary Results from a Phase 1b Study (KEYNOTE-013)

The programmed death-1 (PD-1) pathway serves as an immune checkpoint to temporarily dampen immune responses upon chronic antigen stimulation. Normal antigen presenting cells and certain tumor cells express the PD-1 ligands, PD-L1 and PD-L2, which engage PD-1 receptors on activated T cells and induce T-cell exhaustion. PD-1 signaling is a potent mechanism of tumor immune escape and a compelling target for therapy. Antibody-mediated PD-1 blockade has already been successfully exploited as a therapeutic strategy in solid tumors and is currently being evaluated in hematologic malignancies. Classical Hodgkin lymphoma (cHL) may represent a uniquely vulnerable target for PD-1 blockade therapy. This disease is characterized by an extensive inflammatory immune cell infiltrate and a dominant genetic alteration in chromosome 9p24.1 that leads to PDL1 and PDL2 copy gain and associated overexpression of these PD-1 ligands. In cHL, Epstein-Barr virus infection represents an additional mechanism of upregulating PD-1 ligand expression. For these reasons, cHL was included as a cohort of the ongoing, multicenter, open-label, phase 1b clinical trial of the monoclonal antibody pembrolizumab (MK-3475; Merck, Whitehouse Station, NJ) in hematologic malignancies (KEYNOTE-013; ClinicalTrials.gov identifier, NCT01953692).

Eligibility criteria for the cHL arm of KEYNOTE-013 include relapsed or refractory cHL, relapse from or failure to respond to brentuximab vedotin treatment, and adequate performance status and organ function. Patients with autoimmune disease or interstitial lung disease are excluded. Treatment consists of single-agent pembrolizumab 10 mg/kg administered intravenously every 2 weeks until confirmed tumor progression, excessive toxicity, or completion of 2 years of therapy. The main end points of this study are safety, tolerability, and complete remission (CR) rate. The first time point for radiologic restaging is at week 12 (ie, after 6 cycles of treatment).

Herein, we report preliminary results from the 15 patients with cHL who were evaluable for response to pembrolizumab at the 12-week time point. The median patient age was 28 years (range, 21-67), and the median number of prior therapies was 4. By design, all patients previously failed brentuximab vedotin; 67% also failed prior autologous stem cell transplantation. Pembrolizumab was well tolerated. There were no serious adverse events (AEs), and only 1 patient experienced grade 3-5 AEs (grade 3 pain and grade 3 joint swelling, both considered to be unrelated to study drug). Overall, 10 patients experienced ≥1 AE. The most common drug-related AEs were grade 1-2 respiratory events (20%) and thyroid disorders (20%). One patient discontinued study treatment because of an AE (grade 2 pneumonitis), and 3 patients ended therapy after progressive disease (PD). Based on investigator assessment using the Cheson 2007 International Harmonization Project response criteria, 3 patients (20%) had a CR at 12 weeks. Five additional patients (33%) had partial remission as best overall response, for an overall response rate of 53%. Four patients (27%) experienced PD, although all 4 experienced a decrease in their overall tumor burden (Figure 1). In conclusion, pembrolizumab therapy appears to be safe, tolerable, and associated with clinical benefit in patients with heavily pretreated cHL.

Figure 1: Best percentage change from baseline in tumor size for all patients.

Figure 1

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