Phase II trial of the regulatory T cell-depleting agent, denileukin diftitox, in patients with unresectable stage IV melanoma

<p>Abstract</p> <p>Background</p> <p>We previously found that administration of an interleukin 2/diphtheria toxin conjugate (DAB/IL2; Denileukin Diftitox; ONTAK) to stage IV melanoma patients depleted CD4⁺CD25^HIFoxp3⁺regulatory T cells and expanded melanoma-specific CD8⁺T cells. The goal of this study was to assess the clinical efficacy of DAB/IL2 in an expanded cohort of stage IV melanoma patients.</p> <p>Methods</p> <p>In a single-center, phase II trial, DAB/IL2 (12 μg/kg; 4 daily doses; 21 day cycles) was administered to 60 unresectable stage IV melanoma patients and response rates were assessed using a combination of 2-[¹⁸F]-fluoro-2-deoxy-glucose (FDG)-positron emission tomography (PET) and computed tomography (CT) imaging.</p> <p>Results</p> <p>After DAB/IL2 administration, 16.7% of the 60 patients had partial responses, 5% stable disease and 15% mixed responses. Importantly, 45.5% of the chemo/immuno-naïve sub-population (11/60 patients) experienced partial responses. One year survival was markedly higher in partial responders (80 ± 11.9%) relative to patients with progressive disease (23.7 ± 6.5%; <it>p </it>value < 0.001) and 40 ± 6.2% of the total DAB/IL2-treated population were alive at 1 year.</p> <p>Conclusions</p> <p>These data support the development of multi-center, randomized trials of DAB/IL2 as a monotherapy and in combination with other immunotherapeutic agents for the treatment of stage IV melanoma.</p> <p>Trial registration</p> <p><a href="http://www.clinicaltrials.gov/ct2/show/NCT00299689">NCT00299689</a></p

Base Composition of Mononucleotide Runs Affects DNA Polymerase Slippage and Removal of Frameshift Intermediates by Mismatch Repair in Saccharomyces cerevisiae

The postreplicative mismatch repair (MMR) system is important for removing mutational intermediates that are generated during DNA replication, especially those that arise as a result of DNA polymerase slippage in simple repeats. Here, we use a forward mutation assay to systematically examine the accumulation of frameshift mutations within mononucleotide runs of variable composition in wild-type and MMR-defective yeast strains. These studies demonstrate that (i) DNA polymerase slippage occurs more often in 10-cytosine/10-guanine (10C/10G) runs than in 10-adenine/10-thymine (10A/10T) runs, (ii) the MMR system removes frameshift intermediates in 10A/10T runs more efficiently than in 10C/10G runs, (iii) the MMR system removes −1 frameshift intermediates more efficiently than +1 intermediates in all 10-nucleotide runs, and (iv) the repair specificities of the Msh2p-Msh3p and Msh2p-Msh6p mismatch recognition complexes with respect to 1-nucleotide insertion/deletion loops vary dramatically as a function of run composition. These observations are relevant to issues of genome stability, with both the rates and types of mutations that accumulate in mononucleotide runs being influenced by the primary sequence of the run as well as by the status of the MMR system

Transient T cell depletion causes regression of melanoma metastases

Abstract Background Cognate immunity against neoplastic cells depends on a balance between effector T cells and regulatory T (Treg) cells. Treg cells prevent immune attack against normal and neoplastic cells by directly suppressing the activation of effector CD4+ and CD8+ T cells. We postulated that a recombinant interleukin 2/diphtheria toxin conjugate (DAB/IL2; Denileukin Diftitox; Ontak) may serve as a useful strategy to deplete Treg cells and break tolerance against neoplastic tumors in humans. Methods We administered DAB/IL2 (12 μg/kg; four daily doses; 21 day cycles) to 16 patients with metastatic melanoma and measured the effects on the peripheral blood concentration of several T cell subsets and on tumor burden. Results We found that DAB/IL2 caused a transient depletion of Treg cells as well as total CD4+ and CD8+ T cells (de novo appearance of melanoma antigen-specific CD8+ T cells in several patients as determined by flow cytometry using tetrameric MART-1, tyrosinase and gp100 peptide/MHC conjugates. Sixteen patients received at least one cycle of DAB/IL2 and five of these patients experienced regressions of melanoma metastases as measured by CT and/or PET imaging. One patient experienced a near complete response with the regression of several hepatic and pulmonary metastases coupled to the de novo appearance of MART-1-specific CD8+ T cells. A single metastatic tumor remained in this patient and, after surgical resection, immunohistochemical analysis revealed MART1+ melanoma cells surrounded by CD8+ T cells. Conclusion Taken together, these data indicate that transient depletion of T cells in cancer patients may disrupt the homeostatic control of cognate immunity and allow for the expansion of effector T cells with specificity against neoplastic cells. Several T cell depleting agents are clinically available and this study provides strong rationale for an examination of their efficacy in cancer patients. Trial registration NCT00299689 (ClinicalTrials.gov Identifier).</p