Abstract 4333: Unoccupied and IL2-occupied soluble CD25 have distinct prognostic effects in follicular lymphoma
Authors: Veeramani Suresh , Blackwell Sue E. , Banuelos Paula , Yang Zhi-Zhang , Ansell Stephen M. , Weiner George J. 
Published: September 2020

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.