T-Cell Monoclonality As Assessed By TCR-Sequencing: A Potential Biomarker of Response in Patients with MDS with Autoimmune Cytopenias Treated with IVIG
Authors: Feld Jonathan , Houldsworth Jane , Reddy Asha , Mai Zinnia , Hussein Shafinaz , Navada Shyamala C. , Silverman Lewis R. , Mehrotra Meenakshi 
Published: February 2021

Background:
We have previously reported 75% of patients (pts) achieved clinical responses to treatment with intravenous immunoglobulin (IVIG) in pts with myelodysplastic syndromes (MDS) that exhibit autoimmune cytopenias in the context of T-cell clonality. T-cell clonality was previously determined via peripheral blood (PB) gel-based testing of T-cell receptor (TCR) beta (TRB) and/or gamma (TRG) gene rearrangements or flow cytometry. IVIG was shown to be variably effective in normalizing hemolytic parameters and cytopenias (Feld et al, Blood 2019). Since next generation sequencing of TRG and TRB (TCR-seq) offers better resolution as to the identity of T-cell clones, we reassessed T-cell clonality in a subset of our cohort and longitudinally evaluated the persistence of clones with IVIG treatment.
Methods:
Among 27 pts who were previously treated with IVIG +/- steroids, we processed the PB of 9 pts who had serial samples of leftover DNA available for TCR-Seq analysis (7 had samples available prior to treatment). Clinical responses were per MDS IWG 2006 criteria, whereas hemolytic responses were established by either a complete normalization or a mild response if there was &gt;50% improvement in hemolytic parameters from baseline. TCR-Seq was performed on 100ng DNA using the Lymphotrack® TRG and TRB Assays on Illumina® MiSeq platform according to manufacturer's instructions (Invivoscribe, Inc.). Using the LymphoTrackMiseq2.4.3 software T-cell clonality was interpreted as monoclonal (MC), oligoclonal, small clone(s) of uncertain significance (SCUS) or polyclonal (PC), based on percent total merged clonal reads and polyclonal background.
Results:
Baseline characteristics of our 9 pt cohort included 8 males and 1 female, a median age of 70 years (range 45-82), and a median duration of treatment with IVIG of 23 months. Six pts received steroids in addition to IVIG. Diagnosis included 8 pts with MDS and one with large granular lymphocytic (LGL) leukemia. Of the MDS pts measurable by IPSS criteria, 6 were Int-1 and one was low risk.
Expanded lymphocyte populations were detected in 7 pts by PB flow cytometry and all pts exhibited T-cell clonality by gel-based assessment. All were TRB positive (+) and 7 were TRG+ by PCR. In 3 pts, 4 serial samples were available for TCR-seq; 4 pts had 3 samples available and 2 had only 2 serial samples. Samples were collected over a period of 5 months up to 4-5 years.
With the better resolution afforded by TCR-Seq, 3 pts exhibited only PC populations of T-cells for TRG and TRB at all time points, and 1 pt exhibited SCUS in 1 of 3 samplings for TRG. Of the four pts, only one had an erythroid response; importantly, this sample was tested after treatment. One pt had a normalization in their bilirubin, otherwise only mild responses in hemolytic parameters were noted in the remaining 3 PC pts. Median duration of treatment was 1.5 months.
Five pts had a MC TRB and/or TRG population by TCR-Seq. Two pts had MC TRG, two had MC TRG & TRB, and one had MC TRB populations. Four of the 5 pts had hematologic improvement (HI): 1 had an erythroid and platelet response, 2 had an erythroid response, and 1 had a platelet response. More significant hemolytic responses were also observed in 3/5 pts, with a mild response in the 2 remaining pts. Only 1 TCR-Seq+ pt had no HI, and this pt had a monoclonal population detected by TCR-Seq after finishing IVIG treatment. Median duration of treatment was 45 months. For all these cases, the same clonal sequences were found across all samples up to 4-5 years. Of 4 evaluable patients, 3 had reductions in their clonal read percentage burden over their treatment period.
Conclusions:
TCR-Seq of the TRG and TRB genes affords better resolution of T-cell clones and permits tracking of clones over time. On a further subgroup analysis of 9 pts from our cohort of IVIG-treated pts, we found that pts who exhibited monoclonality as established by TCR-Seq were more likely to respond to IVIG, with more significant erythroid and hemolytic responses, associated with a consequential (45+ months) longer treatment duration. Thus, TCR-Seq appears to be a superior option to PCR-based TCR gene rearrangement assays to reliably identify T cell clones in pts with MDS, and may be a useful biomarker to prospectively identify a subset of pts that can respond to IVIG. Further studies are ongoing to test this hypothesis.

Disclosures
Navada: Onconova Therapeutics Inc: Research Funding. Silverman:Onconova Therapeutics Inc: Patents & Royalties, Research Funding; Medimmune: Research Funding; Celgene: Research Funding.