Updated Results of a Phase 1/2a, Dose Escalation Study of Pvx-410 Multi-Peptide Cancer Vaccine in Patients with Smoldering Multiple Myeloma (SMM)

Methods: As reported previously, PVX-410 Multi-Peptide Vaccine (OncoPep, Inc.) is being developed for the treatment of SMM. PVX-410 consists of 4 human leukocyte antigen-A2 (HLA-A2), synthetic 9-mer peptides from unique regions of 3 multiple myeloma (MM)-associated antigens (XBP1 US_184-192; XBP1 SP_367-375; CD138_260-268; and CS1_239-247) emulsified in Montanide^® ISA-720 VG (Seppic). Adults with SMM at high risk of progression to active MM and were HLA-A2-positive were eligible. The primary objective of this study was to determine the tolerability of PVX-410, initially as monotherapy. Immune response and change in M protein and free light chain ratio (FLC) were also assessed. PVX-410 alone was safe and immunogenic in the initial 12 patients treated, with all 12 having positive immune response to at least 1peptide, as determined by interferon-gamma enzyme-linked immunosorbent spot (Elispot) and tetramer assays. Given its immunomodulatory properties, it was hypothesized that co-administration of lenalidomide (len; Celgene Corporation) would enhance the T cell-mediated immune response induced by PVX-410. Accordingly, the tolerability, immunogenicity, and anti-MM activity of PVX-410+len was then investigated.

Results in the PVX-410 alone cohort were previously reported. In the PVX-410+len cohort, patients received a dose of PVX-410, 0.8mg (0.2mg/peptide / 0.8mg total dose) subcutaneously plus 0.5 mL (1mg) Hiltonol^® (poly-ICLC; Oncovir, Inc.) intramuscularly every 2 weeks for a total of 6 doses with 3 standard cycles of len (25 mg orally) on Days 1-21 every 28 days, without dexamethasone. Patients are followed for 12months post-treatment. Blood samples for immune response evaluation are collected at Week 0 (Baseline; pre-dose), 2, 4, and 8 during treatment and at Months 1, 3, 6, 9, and 12 post-treatment. Disease response is assessed at the same time points, except Weeks 0 and 2, using International Myeloma Working Group and modified European Group for Blood and Bone Marrow Transplant criteria.

Results: Overall, 22 patients have been enrolled, with ages ranging from 39 to 82 years. Ten patients were enrolled in the PVX-410+len cohort, with 9 evaluable for response. All 10 patients received at least 1 cycle of len; 8 received all 3 cycles; 1 received 1 cycle before discontinuing due to a deviation; and 1 completed 2 cycles as of the cutoff date. One patient had 7 of 21 planned doses held due to neutropenia related to lenalidomide, but resumed the next cycle at a reduced dose (from 25 mg to 20 mg).

Immunogenicity data with PVX-410+len and PVX-410 alone, as determined via intracellular cytokine staining and tetramer analysis, will be presented.

With PVX-410 alone, 5 patients, 2 of 3 with the low-dose of 0.4 mg (0.1mg/peptide) and 3 of 9 at the target-dose (0.2 mg/peptide), experienced progression to active disease within 9 months post-treatment, and 7 had stable disease (SD) at the last follow up visit in the 12 month follow up period. With PVX-410+len, 5 patients have experienced partial or minimal responses and 3 have experienced SD. Durability of response is assessed through the 12-month study period; 1 patient has progressed to active myeloma during this time.

PVX-410 was well-tolerated alone and with len. Most adverse events (AEs) have been ≤Grade 2 and non-serious. AEs seen more frequently with PVX-410+len versus PVX-410 alone are expected with len and include hematologic abnormalities (neutropenia, anemia, thrombocytopenia), gastrointestinal disorders (nausea, diarrhea, constipation), skin and cutaneous disorders (rash, pruritus), and myalgia. There was 1serious AE in the combination cohort (pneumonia), considered possibly related to len and unrelated to PVX-410.

Conclusions: Six doses of PVX-410 were well tolerated in 22 patients with SMM. Additional AEs seen with PVX-410+len versus PVX-410 alone were expected with the addition of len to the treatment regimen. An immune response to the vaccine was seen in all patients treated with PVX-410 alone and is expected to be enhanced with PVX-410+len; these data will be presented. Based on the promising findings to date, an evaluation of PVX-410 in combination with an antibody to the programmed cell-death-1-ligand complex (PD1/PDL1) is planned to begin in 2015.