Active and passive immunotherapy: vaccines and antibodies

Authors

  • Egbert Oosterwijk,

    1. Department of Urology, Radboud University Nijmegen Medical Centre, Nijmegen, the Netherlands, Department of Radiology, University of Pennsylvania and Hospital of the University of Pennsylvania, Philadelphia, PA, and
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  • Chaitanya Divgi,

    1. Department of Urology, Radboud University Nijmegen Medical Centre, Nijmegen, the Netherlands, Department of Radiology, University of Pennsylvania and Hospital of the University of Pennsylvania, Philadelphia, PA, and
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  • Neil H. Bander

    Corresponding author
    1. Department of Urology, New York Presbyterian Hospital-Weill Medical College of Cornell University, NY, NY, USA
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Neil H. Bander, Bernard and Josephine Chaus Professor of Urological Oncology, Department of Urology, New York Presbyterian Hospital-Weill Medical College of Cornell University, 1300 York Ave, NY, NY 10021, USA.
e-mail: nhbander@med.cornell.edu

Abbreviations
mAb

monoclonal antibody

VEGF

vascular endothelial growth factor

CAIX

carbonic anhydrase IX

VHL

von Hippel–Lindau

RIT

radioimmunotherapy

ADCC

antibody-dependent cellular cytotoxicity

DC

dendritic cell

HSP

heat-shock protein.

INTRODUCTION

Elsewhere in this volume, McDermott and Rini briefly outline the rationale for immunological approaches in RCC. In addition, they summarize the data on cytokine therapy. In this section we briefly review the current status of antibody and vaccine approaches to the treatment of RCC.

MONOCLONAL ANTIBODIES (mABS)

Clinical experience with mAbs in RCC is basically restricted to bevacizumab and G250, recognizing vascular endothelial growth factor (VEGF) [1], and carbonic anhydrase IX (CAIX) [2], respectively. Bevacizumab is a humanized mAb against VEGF that binds and neutralizes all of the major isoforms of VEGF-A. Therapeutic inhibition of VEGF for the treatment of RCC is based on the knowledge that VEGF is over-expressed in RCC. The molecular basis of this over-expression lies in loss of heterozygosity of the von Hippel–Lindau (VHL) tumour-suppressor gene and somatic inactivation of the remaining VHL allele [3]. The resulting VHL gene silencing leads to the induction of hypoxia-regulated genes including VEGF. In a randomized phase II trial, 116 patients with metastatic, refractory clear cell RCC were randomized to placebo, low-dose (3 mg/kg) or high-dose (10 mg/kg) bevacizumab given i.v. every 2 weeks [4]. Patients with disease progression on placebo crossed over to receive low- dose bevacizumab. The time to progression of disease and the response rate were primary endpoints, and survival was a secondary endpoint. There was a significant prolongation of the time to progression of disease in the high-dose-antibody group (4.8 vs 2.5 months). The study was inadequately powered to show a significant difference in overall survival between the groups. The Cancer and Leukaemia Group B is currently conducting a phase III trial randomizing patients with untreated, metastatic clear cell RCC to interferon-α alone vs interferon-α plus bevacizumab [5].

Clinical efforts with mAb G250 in RCC have focused on radioimmunotherapy (RIT) and naked-antibody therapy. This mAb was initially identified by differential immunohistochemical screening as a mAb recognizing a RCC-associated antigen, absent in normal kidney and homogeneously expressed in most tumour RCC, most notably clear cell RCC [6]. In 2000, the G250 antigen was molecularly identified and shown to be CAIX [2]. Transcriptional regulation studies revealed a strict dependence of G250 expression on hypoxia-inducible factor-1α, i.e. the molecular basis of CAIX expression is also VHL-related [7]. After chimerization of the antibody, various phase I and phase II trials were conducted. The rationale of G250-directed therapy obviously differs from that for bevacizumab; the latter leads to VEGF depletion and consequently to diminished neovascularization, whereas G250 treatment targets RCC cells directly. Initially, clinical trials with G250 focused on RIT with 131I-labelled G250 in patients with progressive metastatic RCC [8] (Fig. 1). The absolute and relative amount of tumour-targeted mAb was significantly higher than that of any other mAb in any solid tumour. In biopsy-based studies, the G250 accumulation was up to 0.5% of the injected dose/g tumour [9]. The reasons for this higher uptake than for mAb uptake in other tumour systems are unknown. Although it is tempting to speculate that the dense vasculature of clear cell RCC is the cause of this phenomenon, the perfusion rate of these tumours is low, and interstitial fluid pressures in RCC are very high, both unfavourable for high mAb accrual.

Figure 1.

A. Anterior and posterior whole-body images in a patient with metastatic RCC, treated with 131I-G250 (2220 MBq/m2). B. Single-photon emission CT of the abdomen showing targeting to the viable liver lesion and in the large renal primary. The central necrotic portion in the renal primary does not accumulate radioactivity.

RIT studies with single high-dose 131I-G250 [10], rapid fractionated-dose 131I-G250 [11] (Fig. 2), and sequential high-dose 131I-G250 [12] have resulted in only occasional therapeutic responses. This was despite dosimetric analyses suggesting that tumour-sterilizing levels are achievable. Even two sequential high-dose treatments with 131I-G250 did not result in objective responses, but in stabilization of previously progressive disease in a few patients [12]. RCC is known as a radiotherapy-resistant tumour and possibly even higher radiation doses are necessary to realise tumour-sterilizing levels. RIT with G250 was accompanied by bone marrow toxicity, similar to mAb RIT in other tumour types. Current G250 RIT efforts are directed to lutetium-177- and yttrium-90-labelled G250. It is hypothesized that the use of more powerful radionuclides that are also better retained in the tumour cells might lead to clinical responses. Animal experiments showed the superiority of 177Lu- and 90Y-labelled G250 over 131I-G250 [13]. Importantly, there was stabilization of previously progressive disease in almost all patients treated with 177Lu-G250, although the maximum tolerable dose has not been achieved. Dosimetric analyses of the first patients treated with 177Lu-G250 suggested that indeed tumour-sterilizing levels might be achieved. Figure 3 shows targeting of 177Lu-G250 in a patient with metastatic RCC.

Figure 2.

Sequential images in a patient with metastatic RCC treated with fractionated 131I-cG250. The whole-body images were obtained 2–3 days after each infusion.

Figure 3.

Targeting of 177Lu-DOTA-cG250 in metastatic RCC.

Apart from RIT, G250 has also been tested in a non-randomized phase II trial at 50 mg/week for 12 weeks. This protein dose is of a completely different magnitude than the doses used for bevacizumab, which was chosen on the basis of VEGF neutralization. For G250 the protein dose was chosen such that the minimum trough level was >1 µg/mL blood, a concentration that showed appreciable antibody-dependent cellular cytotoxicity (ADCC) in vitro. Thirty-six patients were entered and 10 showed stable disease and received extended treatment [14]. The median survival after treatment started was 15 months, but the non-randomized character of this trial precluded the conclusion that G250 modulated metastatic RCC. In the subsequent trial, G250 (20 mg/week for 11 weeks) was combined with interleukin-2 in a low-dose pulsing schedule, based on in vitro studies that had firmly established that G250 ADCC could be enhanced by interleukin-2. Again, with three partial responses and five patients with disease stabilization at ≥ 24 weeks, and a mean survival of 22 months, the data suggested that G250 might influence the natural course of metastatic RCC [15]. Surprisingly, ADCC and clinical outcome did not appear to correlate in either trial. Notably, as for all non-randomized phase 1 and phase 2 clinical trials, it is difficult to accurately predict the effect on survival. Based on the collective evidence, treatment with unmodified mAb G250 is currently being investigated in an adjuvant setting in high-risk patients with RCC, in a randomized, international phase 3 trial.

VACCINATION STRATEGIES

Dendritic cell (DC) vaccination against cancer is a relatively recent immunotherapeutic approach. It has now become feasible to reproducibly generate DC from peripheral monocytes in substantial numbers, and in all, 183 patients with metastatic RCC were treated with DC vaccination in 15 phase I/II clinical trials [16,17]. Due to the novelty of this technology and lack of knowledge about the best vaccine preparation, administration route, or treatment schedule, the value of DC vaccination remains unclear. Tumour lysates, and peptides combined with DCs of different maturation state, have been tested in these trials. In all, 77 (38%) patients had a clinical response, with four complete and eight partial responses, and 61 with disease stabilization, whereas four had a mixed response. Unfortunately, the clinical effects were not long-lasting. As expected, DC vaccination resulted in (peptide/tumour)-specific immune responses, albeit in a subset of patients. Surprisingly, these were not always associated with a clinical response. In some patients, there was epitope spreading, i.e. T cell responses to antigens not used for vaccination. Thus, it is clear that DC vaccination can induce (tumour)-specific T cell responses, but improvements such as depletion of regulatory T cell subsets, or alternative loading, are necessary.

Alternatively, patients have been vaccinated with peptides. Uemura et al.[18] reported on a group of 23 patients with RCC vaccinated with CAXI-derived peptides. With three partial responses and six with stable disease, the clinical response rate (39%) was similar to that in DC vaccination trials. Again, these results should be viewed with caution because it is uncertain that this clinical response rate is significantly above the background variability observed in any unrandomized patient cohort.

Finally, vaccination with autologous heat-shock protein (HSP)-peptide (Oncophage®) complexes produced from each patient’s tumour have been investigated in a large group of patients with early-stage RCC (stage I, II high-grade, and stage III T1, T2 and T3a low-grade). Harvesting HSP-peptide complexes from the patient’s tumour is reported to provide a sample of the tumour’s antigens. Surgically removed tumour tissue is processed to capture the HSP-peptides, which are then purified and used to immunize the patient. A phase 3 randomized, international trial was completed, with preliminary release of the data by the sponsor in early 2006. The protocol entered patients with ‘high-risk’, fully resected disease. Patients were randomized to receive nephrectomy plus Oncophage vs nephrectomy alone. The primary endpoint was recurrence-free survival, with overall survival being the secondary endpoint. Although the data have not yet been published in peer- reviewed form, the preliminary data were released by the sponsor. Of the 728 patients entered, data review indicated that 124 (17%) were ineligible as they had disease present at baseline (http://www.antigenics.com/news/2006/0607.phtml). When the 604 eligible patients were analysed, the improvement in recurrence-free survival was not statistically different between the arms. Overall survival at the time of the data limit (January 2006) was worse for the vaccine-treated arm, with 31 deaths (10.3%), vs 22 in the control arm (7.2%). The overall survival data was said to be immature at the time of data release. An ad hoc analysis of 361 ‘better prognosis’ patients revealed improved recurrence-free survival with a hazard ratio of 0.567 (P = 0.018) or a 43% improvement in recurrence-free survival vs patients in the observation arm. The possibility that this vaccine might benefit patients with a better prognosis is hypothesis-generating, as it comes from an unplanned subset analysis of the data. Clearly, to prove this point, the sponsor must conduct a prospectively designed trial to address this specific question. No such plans have yet been announced by the sponsor.

CONCLUSIONS

Antibody therapy has shown clinical benefit in many tumour types. In RCC, an antibody to VEGF has shown benefit in progression-free survival and is currently being tested in a phase 3 randomized trial. G250, an antibody to a RCC-related antigen, is also being evaluated in a phase 3 trial. To date, clinical benefit from therapeutic cancer vaccines has not yet been validated, but interest and effort remains at a high level.

CONFLICT OF INTEREST

None declared.

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