Phase I/II Clinical Trial of CpG-Activated Whole Cell Vaccine in Mantle Cell Lymphoma (MCL): Results in Safety and Efficacy from Planned Interim Analysis

Introduction

MCL has a poor prognosis. In eligible patients, intensifying frontline, CHOP-like regimens (e.g., cytarabine) as well as high-dose chemotherapy and autologous stem cell transplant (HDT/ASCT) consolidation in first remission have improved progression free survival (PFS) but less so, overall (OS). Preclinical animal models show benefits of adding tumor-specific T-cells to ASCT. CpG (PF-3512676) is a toll-like receptor 9 (TLR9) agonist and an effective vaccine adjuvant that induces costimulatory molecule expression on both antigen-presenting and MCL cells. This phase I/II clinical trial (NCT00490529) adds autologous T-cell transfer, harvested from patients after vaccination with CpG-activated autologous MCL cells – a maneuver termed immunotransplant. This is a planned interim analysis for safety and efficacy triggered by the first 20 patients reaching 1 year post ASCT.

Methods

Prior to therapy, subjects’ tumor cells are collected by biopsy or apheresis and patient-specific vaccine is created by incubating fresh tumor cells with CpG (3 mcg/mL PF-3512676, 72-hr culture), then irradiated and cryopreserved. Patients receive induction chemoimmunotherapy of physician’s choice. Patients achieving at least partial response (PR) then receive 3 subcutaneous autologous tumor vaccinations (1 x 10⁸ cells/dose) mixed with CpG (18 mg) every 4-7 days. Primed T-cells (≥ 1 x 10¹⁰ CD3 cells) were collected by apheresis 2-4 weeks following vaccine 3 and a rituximab (375 mg/m²) B-cell purge. After standard HDT/ASCT (conditioning = BCNU, cyclophosphamide, etoposide), primed T-cells and a 4^th vaccination are given on day+1. A 5^th CpG-MCL vaccination followed 3 months post ASCT. The primary endpoint of this study is freedom from minimal residual disease (MRD) at 1 year post ASCT, measured by presence of patient-specific, malignant B-cell VDJ sequence in peripheral blood (ClonoSeq™, analyzed at a sensitivity of ≥ 1 clone/10,000 leukocytes) – an endpoint previously shown to be highly prognostic. Secondary endpoints include PFS, OS, and immune response to vaccine. 59, transplant-eligible, MCL patients are targeted for accrual in this 2-stage design.

Results

In this interim analysis of 24 patients accrued, 20 have surpassed 1 year post ASCT. All patients had Stage IV disease. Median values included (range): follow-up 43.5 months (11.5-60.1), age 60 years (47-70), and MIPI score 5.9 (5.1-7.8). Vaccine was made from biopsy alone (n=12), apheresis alone (n=9), or both (n=1). Frontline therapy included R-CHOP (n=7), R-hyperCVAD (n=14), alternating R-CHOP/R-DHAP (n=2), and R-EPOCH (n=1). 19 patients achieved complete response while another 3 had PR. All responding patients were vaccinated, able to yield sufficient T-cells for adoptive transfer, and proceeded through standard HDT/ASCT. At 1-year post ASCT, freedom from MRD was 90.5% (n=21). 2 patients did not reach 1-year post ASCT. One died from an ASCT complication (metapneumovirus) while the other relapsed 6 months following ASCT (included in MRD analysis). The most common toxicity due to CpG-MCL vaccine was erythematous rash at injection site (90.9%, n=20, each grade 1). No serious adverse events were seen related to vaccines or adoptive T-cell transfer. All patients had successful hematopoietic recovery, but two were delayed and received backup stem cell infusions with eventual recovery. Though median PFS and OS have not been reached, 3-year PFS and OS at interim analysis are 54.5% and 63.6%, respectively (intention to treat). In this data set, higher expression of co-stimulatory molecules (such as CD40, CD80, and CD86) on a subject’s MCL in response to CpG was associated with freedom from MRD (p=0.02). Post-ASCT, higher peripheral T-cell granzyme and perforin response to ex vivo re-challenge with autologous MCL cells was also associated with freedom from MRD (p=0.01).

Conclusions

The addition of CpG-activated, whole MCL vaccination and autologous, adoptive T-cell transfer to standard therapy appears both feasible and safe. At interim analysis, the 1-year freedom from MRD surpasses rates previously reported in other studies and warrants further investigation. To date, 46 patients have either completed and/or are continuing to undergo study treatment and the study remains open to accrual for patients newly diagnosed with MCL.