Next-Generation Sequencing Minimal Residual Disease of Mantle Cell Lymphoma in Autologous Stem Cell Grafts and Its Implication on Tumor Recurrence
Authors: Wang Yu-Hung , Chuang Yi-Kuang , Yang Yu-Hsuan , Yu Shan-Chi , Yang Yi-Tsung , Ko Bor-Sheng , Yao Ming , Huang Tai-Chung , Tang Jih-Luh 
Published: November 2020

Background & Purpose
The clinical course of mantle cell lymphoma (MCL) is often inflicted with tumor recurrence even though front-line autologous stem cell transplantation (ASCT) is the current standard of care. To elucidate the mechanism of post-transplant recurrence, this study aimed to interrogate the minimal residual disease (MRD) of MCL in the autologous grafts.
Materials & Methods
Paired samples of 17 MCL patients' lymphoma diagnostic FFPE specimens were analyzed in parallel with their harvested autologous stem cell grafts. Extracted genomic DNA was subjected to LymphoTrackⓇ Dx IGH/IGK assay coupled with Illumina MiSeq sequencer to characterize the post-recombination immunoglobulin VDJ sequences. Positivity of MRD was defined for any identical sequences identified both in the diagnostic FFPE and in the autologous graft DNA. As the control for recombined VDJ protein motif analysis, diagnostic FFPE samples from 23 patients with diffuse large B cell lymphoma (DLBCL) were analyzed with the same platform.
Results
Of the 17 patients undertaking autologous stem cell harvest, 11 patients achieved complete response and 6 were in partial response before stem cell harvest. Sixteen of these actually underwent transplantation while one died of disease before transplantation. MRD was detected via next-generation sequencing (NGS) in 5 patients' autologous grafts with variable MRD loads and recombined VDJ stereotypes (Table 1). VH3-21 was the most prominent stereotype (41%), followed by VH4-59 (14%). The median somatic hypermutation rate was 0.88% (range 0 - 5.17%). Interestingly, a 46-amino-acid domain in recombined VDJ sequences, which was hydroxyl and amine group-rich, differed between MCL and DLBCL: hydrophilic amino acids were enriched in 6 positions of this domain in MCL (p&lt;0.05). Among the five patients who had MRD in autologous grafts, the median MRD read number was 12,764 reads (range 89 - 33,554) with the median read depth of 195,865 reads (range 94,820 - 396,894). The MRD loads in the autologous grafts were inversely correlated with post-harvest PFS (Figure 1a and 1b). As for post-ASCT outcomes, patients with MRD had a trend toward worse PFS and OS than those without MRD (medians, 10 months vs 27 months, and 25 months vs 66.8 months, respectively). In subgroup analysis, a higher load of NGS-MRD (&gt;1%) correlated with shorter post-ASCT PFS and OS than those without MRD (medians, 1.9 months vs 27 months (p=0.024) in Figure 1c, and 11.9 months vs 66.8 months (p=0.001) in Figure 1d, respectively).
Conclusions
Identification of MRD in autologous grafts by deep-sequencing VDJ recombination helped stratify MCL patients' post-ASCT outcomes. Higher MRD loads correlated with inferior post-ASCT PFS and OS. The implication of recombined VDJ stereotypes and their impact on ASCT outcomes warrants further investigation.

Disclosures
Ko: Roche: Honoraria.