Eradicating micrometastases with immune checkpoint blockade: Strike while the iron is hot.

Immune checkpoint blockade (ICB) is transforming treatment for many cancers. While ICB alone initially demonstrated efficacy in patients with metastatic melanoma, it has expanded to other types and to earlier-stage cancers. We describe ICB history, mechanisms underlying variation in response, and how ICB is being integrated into adjuvant and neoadjuvant treatment approaches.

Consistent antibody response against ganglioside GD2 induced in patients with melanoma by a GD2 lactone-keyhole limpet hemocyanin conjugate vaccine plus immunological adjuvant QS-21.

PURPOSE: Melanomas, sarcomas, and neuroblastomas abundantly express the ganglioside GD2 on the cell surface where it is susceptible to immune attack by antibodies. Overexpression of GD2 on these tumors is striking, as is the frequency of clinical responses after treatment of neuroblastoma with monoclonal antibodies against GD2. In addition, preclinical models have demonstrated the ability of a GD2-keyhole limpet hemocyanin (KLH) conjugate vaccine to induce antibodies that eliminate micrometastases. However, vaccination of patients with GD2-KLH has previously failed to induce a consistent relevant antibody response. We test here whether the use of GD2 lactone-KLH can overcome the low immunogenicity of GD2-KLH. EXPERIMENTAL DESIGN: Eighteen patients with melanoma were vaccinated s.c. in the adjuvant setting on weeks 0, 1, 2, 3, 10, and 24. Groups of 6 patients were entered at three dose levels (3, 10, or 30 micro g) of GD2 lactone (GD2L) in vaccines containing GD2L-KLH plus the immunological adjuvant QS-21. Blood was drawn at regular intervals to assess the antibody response. RESULTS: The vaccine was well tolerated. The majority of patients in all three dose levels produced anti-GD2 antibodies detectable by ELISA assay. Specificity for GD2 was also confirmed by immune thin-layer chromatography. Although there was no statistical difference in terms of titers between the three groups, patients at the 30- micro g dose level had higher titers and longer lasting antibody responses overall by ELISA (median IgM/IgG peak titer 1:640/1:80) and generated the strongest cell surface reactivity by fluorescence-activated cell sorting (median IgM peak percentage positive cells/mean fluorescence intensity for pre- and postvaccination sera is 10%/63 and 70%/135). Patients vaccinated with the 30- micro g GD2 dose also had the most potent complement dependent cytotoxicity using human complement, with 5 of 6 patients showing strong cell surface reactivity by fluorescence-activated cell sorting and >30% cytotoxicity by chromium release with a serum dilution of 1/100. CONCLUSIONS: GD2L-KLH conjugate vaccine plus adjuvant QS-21 induces antibodies against GD2 that bind to the cell surface and induce complement-dependent cytotoxicity in the majority of patients with melanoma.

DNA vaccines: an active immunization strategy for prostate cancer.

Immunotherapy is currently being investigated as a treatment for patients with asymptomatic, recurrent prostate cancer manifested only by a rising prostate-specific antigen (PSA) level. Several different approaches to active immunization against antigens found on cancer cells have been explored. Immunization with DNA overcomes many of the obstacles noted in previous studies. Injection of plasmid DNA encoding a xenogeneic differentiation antigen (prostate-specific membrane antigen [PSMA]) is a potent means to induce antibody and T-cell responses to these otherwise poorly immunogenic self proteins. Use of the xenogeneic DNA (ie, human PSMA DNA injected into mouse) has been shown to be an absolute requirement to overcome immunologic tolerance. We are currently conducting a phase I trial of human and mouse PSMA DNA vaccines in patients with recurrent prostate cancer, based on preclinical experiments described below.

Phase I trial of high dose paracetamol and carmustine in patients with metastatic melanoma.

Reduced glutathione (GSH) production by tumour cells has been proposed as a mechanism for resistance to alkylating agents. High levels of paracetamol can deplete intracellular GSH. We conducted a phase I trial of high dose paracetamol and carmustine (BCNU) in patients with advanced malignant melanoma to determine the optimal biological dose and the maximum tolerated dose (MTD) with the goal of increasing sensitivity to BCNU by GSH depletion. Groups of three to five patients received escalating doses of paracetamol (10, 15 or 20 g/m(2)) every 3 weeks. Every other cycle, BCNU (10 mg/m(2)) was given 6.5 h after administration of paracetamol and 45 min before a 20 h infusion of N-acetylcysteine. Once the MTD for paracetamol had been determined, the dose of BCNU was sequentially escalated in subsequent cohorts to 150 mg/m(2). GSH levels were measured in peripheral blood mononuclear cells (PBMCs) and, when available, in tumour biopsies. The MTD of paracetamol was 15 g/m(2). The dose of BCNU was safely escalated to 150 mg/m(2). The most common toxicity was grade II nausea/vomiting. At 15 g/m(2), peak paracetamol levels (median 253 microg/ml) were reached between 1 and 4 h. No changes in GSH levels in PBMCs were seen. There were two partial responses, including a dramatic decrease in hepatic metastases. Treatment of melanoma patients with paracetamol (15 g/m(2)) every 3 weeks and BCNU (150 mg/m(2)) every 6 weeks is safe. The observation of two partial responses has led to a phase II study to evaluate treatment with high dose paracetamol alone or in combination with BCNU.