Veeramani, Suresh

Abstract Background: The soluble form of the low affinity Interleukin 2 receptor alpha subunit (sCD25) is often elevated and correlates with inferior outcome in cancers, including follicular B lymphoma (FL). We recently reported a novel RNA aptamer-based assay designated as the LIRECAP assay (for Ligand-Receptor Complex-binding Aptamers) that allows for specific measurement of the fraction of CD25 occupied by IL2 in a biospecimen. The LIRECAP assay demonstrated that the fraction of sCD25 that circulates as an IL2-sCD25 complex varies considerably in B cell lymphoma patients (from 10% to 96% occupancy of sCD25 by IL2) and that this fractional occupancy was significantly higher in FL compared to diffuse large B cell lymphoma (Cancer Immunol Res. 2019. 7: 1511-1522). The prognostic significance of IL2-occupied and unoccupied sCD25 fractions is not known and the current studies were designed to study their effect on FL outcome. Methods: Determining total, unoccupied and IL2-occupied sCD25 levels: Using the LIRECAP assay, we evaluated the fractional IL2 occupancy of sCD25 in pretherapy serum samples from FL patients who were subsequently treated with standard chemoimmunotherapy. In addition, total sCD25 was determined by a commercially available Luminex assay kit. Levels of total sCD25, unoccupied sCD25, IL2-occupied sCD25 and ratios of unoccupied to IL2-occupied sCD25 were then calculated for each sample. Patients were followed for 24 months following therapy to determine whether they achieved or failed to achieve event-free survival (EFS 24) (N=10 per group). Results: Unoccupied sCD25 levels correlates with poor prognosis: Total sCD25 and IL2-occupied sCD25 levels did not correlate with EFS24 (p=0.085 and 0.404, respectively). However, levels of unoccupied sCD25 and the ratio of unoccupied to IL2-occupied sCD25 were significantly higher in patients who failed to achieve EFS24 (p=0.048 both). Conclusions and significance: Unoccupied sCD25, but not IL2-occupied sCD25, in FL patient serum correlates with poor outcome. This could, in part, be due to the ability of IL2-occupied sCD25, but not unoccupied sCD25, to induce Tregs, as we have reported previously. A higher Treg infiltration has also been shown to correlate with a better FL outcome. Taken together, these data suggest that unoccupied sCD25 can serve as an independent prognostic marker in FL. Further analysis in a larger cohort of patients, and assessment of the biological effects of unoccupied and IL2-occupied sCD25 is ongoing. Citation Format: Suresh Veeramani, Sue E. Blackwell, Paula Banuelos, Zhi-Zhang Yang, Stephen M. Ansell, George J. Weiner. Unoccupied and IL2-occupied soluble CD25 have distinct prognostic effects in follicular lymphoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4333.

Abstract Ligand–receptor complexes play a central role in mediating a range of processes in immunology and cancer biology. The ability to directly quantify the fraction of receptors occupied by a ligand in a given biospecimen, as opposed to assessing the concentration of ligand and receptor separately, could provide an additional and valuable clinical and research tool for assessing whether receptors are occupied by a ligand. To address this need, a biomarker platform was developed to quantify the fraction of receptors occupied by a ligand using pairs of RNA aptamers, where one aptamer binds preferentially to the unoccupied receptor and the other to the ligand–receptor complex. Bound aptamer was quantified using RT-qPCR colorimetric probes specific for each aptamer. The binding ratio of aptamer correlated with the fraction of receptors occupied by a ligand. This assay, termed as LIRECAP (LIgand–REceptor Complex-binding APtamer) assay, was used to determine the fraction of soluble CD25 occupied by IL2 in the serum from subjects with B-cell lymphoma. No correlation was found between the type of lymphoma and total soluble CD25 or IL2 independently. In contrast, the fraction of soluble CD25 occupied by IL2 was significantly higher in follicular lymphoma patient serum compared with diffuse large B-cell lymphoma patient serum. We conclude that this technology has the potential to serve as a high-throughput biomarker platform to quantify the fraction of receptors occupied by a ligand.

Chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL) patients with purine analog refractory disease or TP53 dysfunction still have limited treatment options and poor survival. Alemtuzumab‐containing chemoimmunotherapy regimens can be effective but frequently cause serious infections. We report a Phase II trial testing the efficacy and tolerability of a short‐duration regimen combining pentostatin, alemtuzumab, and low‐dose high‐frequency rituximab designed to decrease the risk of treatment‐associated infections and to limit the loss of CD20 expression by CLL cells. The study enrolled 39 patients with progressive CLL that was either relapsed/refractory (n = 36) or previously untreated with 17p13 deletion (17p13−) (n = 3). Thirteen (33%) patients had both 17p13− and TP53 mutations predicted to be dysfunctional, and eight patients had purine analog refractory CLL without TP53 dysfunction. Twenty‐six (67%) patients completed therapy, with only five (13%) patients having treatment‐limiting toxicity and no treatment‐related deaths. Twenty‐two (56%) patients responded to treatment, with 11 (28%) complete responses (four with incomplete bone marrow recovery). Median progression‐free survival was 7.2 months, time to next treatment was 9.1 months, and overall survival was 34.1 months. The majority of deaths (82%) were caused by progressive disease, including transformed diffuse large B‐cell lymphoma (n = 6). Correlative studies showed that low‐dose rituximab activates complement and natural killer cells without a profound and sustained decrease in expression of CD20 by circulating CLL cells. We conclude that pentostatin, alemtuzumab, and low‐dose high‐frequency rituximab is a tolerable and effective therapy for CLL and that low‐dose rituximab therapy can activate innate immune cytotoxic mechanisms without substantially decreasing CD20 expression. Am. J. Hematol. 89:757–765, 2014. © 2014 Wiley Periodicals, Inc.