Liquid Biopsy and Lymphoma Monitoring in Clinical Practice

INTRODUCTION Lymphomas represent the fourth most frequent type of cancer, 90% of them arising from B cell lymphocytes. Despite their high prevalence, around 40% remain incurable because of refractoriness to current chemoimmunotherapy or disease relapse after obtaining response (Li et al., 2018; Meng et al., 2020). The cell of origin is a B lymphocyte with a unique B cell receptor (BCR). The BCR is an immunoglobulin composed of two heavy chains (IgH) and two light chains (IgL) whose genes have multiple coding segments that through rearrangement first and further somatic hypermutation in the germinal center, generate a unique sequence that could be used to monitor the treatment response (Seifert et al., 2019; Wang et al., 2020). This project studies the use of next-generation sequencing (NGS) to characterize and monitor such IgH clonality. The use of liquid biopsy samples would provide a minimally invasive method to identify refractory or relapse-risk patients since all of them will have residual tumor cells after treatment. METHODS The sample size of the study was 53 patients with several types of B-cell lymphomas. The IgH gene of the tumor clone was characterized from DNA of tumor samples at diagnosis by NGS and Sanger. The monitoring of this clone was studied by NGS from DNA and circulating tumor nucleic acids (ctNAs) during and after receiving treatment and at different times after clinical response was stablished (CR or PR). Relapse samples were analyzed by NGS and Sanger. RESULTS Characterization of the tumor clone IgH rearrangement is achieved in 45 of the 53 patients with B-cell lymphoma included in the study. As shown in Figure 1, after the two different amplification PCRs results are similar. In contrast, after sequencing the results obtained by Sanger and NGS are very different. In NGS, thanks to the massive amplification prior to sequencing, it is identify the tumor clone in approximately 80% of the samples. It is shown that the effectiveness in characterization is dependent on the origin of the DNA sample, with fresh material samples being the optimal (Figure 1). In monitoring, samples of different origin are used as shown in Figure 2. About 50% of these samples are plasma ctNAs whose average efficiency in the detection of IgH gene rearrangement is 73.3%, with a clear positive correlation between the sensitivity and the toal volume of plasma processed more starting plasma used (2 mL efficiency of 84.09%). Monitoring makes it possible to classify patients into three different groups (Figure 3): patients with complete remission, patients refractory to the different lines of treatment and patients with apparent complete response and subsequent relapse. In patients with complete response, the tumor clone decreases during treatment and at the end of the line it is no longer detectable, nor in subsequent follow-up samples. With respect to refractory patients, it is observed that the tumor clone remains present despite subsequent lines of treatment. Finally, in patients achieving CR with subsequent relapse, the clone can be detected in a small percentage at the end of the treatment schedule and remains present until relapse. A section of patients under treatment is also shown (Figure 3) to demonstrate the application of the study to clinical practice. Two patients with apparent complete response, one of them in complete remission and the other with a high risk of relapse, requiring a more exhaustive follow-up. The monitoring results obtained by flow cytometry are shown being these, in general, concordant. In some cases NGS shows greater sensitivity. CONCLUSION The use of NGS and liquid biopsy samples provides a minimally invasive method to monitor the IgH gene rearrangement of the tumor clone of patients with B-cell lymphomas. In our experience,, patients in remission can be clearly differentiated from those who are refractory or at risk of relapse. facilitating their treatment strategy and clinical decision making. Figure 1 Figure 1. Disclosures Ferrer Lores: Janssen: Membership on an entity's Board of Directors or advisory committees. Terol: BMS: Consultancy; Hospital Clinico Valencia: Current Employment; Roche: Consultancy; Gilead: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Research Funding; Roche: Membership on an entity's Board of Directors or advisory committees, Other: Travel; Janssen: Membership on an entity's Board of Directors or advisory committees, Other: Travel, Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees, Other: Travel; Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Travel.

Clinical Features of Primary Vitreoretinal Lymphoma: A Single-center Study

Background/Aim: This study aimed to demonstrate the clinical outcomes of primary vitreoretinal lymphoma (PVRL). Patients and Methods: Seventeen patients with PVRL who had been treated at Hokkaido University Hospital were enrolled in this study. They were diagnosed based on their cytology, interleukin-10/-6 ratio, and immunoglobulin heavy chain (IgH) gene rearrangement. Results: Diagnostic tests detected cytological malignancy among 14 cases (82.3%), high interleukin-10/-6 ratios among 16 cases (94.1%), and IgH monoclonality in 13 cases (76.5%). Systemic corticosteroids were given to seven (41.2%) patients before their diagnosis of PVRL. Treatments after diagnosis comprised intravitreal methotrexate injection, local radiation, and intravenous chemotherapy for 11, seven, and five cases, respectively. Central nervous system and systemic involvements were observed in nine and one case, respectively, and these complications occurred at 3 to 43 months (mean=16 months) after initial ocular presentation. Conclusion: Many of our patients did not receive any systemic intervention, and almost half of patients with PVRL developed central nervous system involvement during their follow-up period.

Engineered Bcor mutations lead to acute leukemia of progenitor B-1 lymphocyte origin in a sensitized background

Approximately 10% of NUP98-PHF23 (NP23) mice develop an aggressive acute lymphoblastic leukemia of B-1 lymphocyte progenitor origin (pro-B1 ALL), accompanied by somatic frameshift mutations of the BCL6 interacting corepressor (Bcor) gene, most commonly within a 9-bp “hotspot” in Bcor exon 8. To determine whether experimentally engineered Bcor mutations would lead to pro-B1 ALL, we used clustered, regularly interspaced, short palindromic repeats–associated protein 9 to introduce a Bcor frameshift mutation into NP23 hematopoietic stem and progenitor cells through the use of Bcor small guide RNAs (Bcor sgRNAs). Recipient mice transplanted with NP23 bone marrow or fetal liver cells that had been transduced with a Bcor sgRNA developed pro-B1 ALL, characterized by a B-1 progenitor immunophenotype, clonal Igh gene rearrangement, and Bcor indel mutation, whereas control recipients did not. Similar to a subset of human B-cell precursor ALL, the murine pro-B1 ALL had acquired somatic mutations in Jak kinase genes. JAK inhibitors (ruxolitinib and tofacitinib) inhibited the growth of pro-B1 ALL cell lines established from Bcor sgRNA/NP23 recipients at clinically achievable concentrations (100 nM). Our results demonstrate that Bcor mutations collaborate with NP23 to induce pro-B1 ALL, and that JAK inhibitors are potential therapies for pro-B1 ALL.

Establishment of Induced Pluripotent Stem Cells from Lymph Node B Cells and Induction of Aid Expression in Their Differentiation into Hematopoietic Stem Cells

Induced pluripotent stem cells (iPSCs) have been established from a variety of somatic cells not only for regenerative medicine but also for studies of the pathogenesis of inherited genetic diseases or neoplasms. In iPSCs established from T cells, the rearrangement of the T cell receptor (TCR) of the established T cell-derived iPSCs (TiPSCs) took over that of the original T cells. If B cell-derived iPSCs (BiPSCs) could be similarly established from mature B cells or plasma cells, the rearrangement of the B cell receptor (BCR) of the BiPSCs would take over that of the original B cell. BiPSCs were recently established from peripheral blood B cells by the simultaneous transfection of Yamanaka factors (Oct3/4, Sox2, Klf4, c-Myc) together with ectopic expression of the myeloid transcription factor CCAAT/enhancer-binding-protein-α (C/EBPα) using a Sendai virus vector (Bueno C, et al. Leukemia 2016). We were able to also establish BiPSCs with immunoglobulin heavy chain (IgH) gene rearrangement from normal B cells purified from lymph nodes using a method different from the above. The main points of our method are consecutive transfection of a high concentration of Yamanaka factors into B cells, which were pre-stimulated with IL-21 and CD40L, using a retrovirus vector, and centrifugations of the cells after their activation by IL-4, IL-2, and CD40-ligand (CD40L) on a retronectin coated plate. We further established doxycycline-controlled (Tet-off system) activation-induced cytidine deaminase (AID)-induced BiPSCs (BiPSCs-A). AID is an enzyme that initiates somatic hypermutation (SHM) and class-switch recombination (CSR) in B cells. We hypothesized that the origin of a myeloma cell is a reprogrammed mature B cell, in which reciprocal chromosome translocation occurs by double stranded breakage (DSB) of DNA induced by AID activation in the nonproductive (nonfunctional) allele of chromosome 14. First, we did not detect an increase in dicentric chromosome (DIC) formation, which is evidence of DSB of DNA, in the BiPSCs-A. We next analyzed the ability of these BiPSCs to differentiate into hematopoietic stem cells (HSCs). Both the parental BiPSCs and BiPSCs-A were capable of differentiating into HSCs as judged by confirmation of CD34 expression and colony-formation of macrophages, granulocytes, and erythrocytes from CD34-positive cells. However, these cells were negative for CD38, CD43, and CD45; we therefore think that these CD34+/CD38-/CD43-/CD45- cells might be hematoendothelial cells as Maxim proposed previously (Vodyanik MA, et al. Blood 2006). Furthermore, both BiPSCs with induced AID expression and BiPSCs without induced AID expression were capable of differentiating into HSCs. Based on the findings regarding the differentiation of BiPSCs-A into HSCs and their retention of the IgH gene rearrangement, there is a possibility that the induction of AID expression might induce chromosomal translocations in the process of differentiation of these BiPSCs into HSCs and further into B cells in experiments using mouse. Thus these BiPSCs might be useful in elucidating the tumor origin of abnormal B cells in B cell tumor formation. These cells might be especially useful in understanding multiple myeloma, which is thought to originate from germinal center (GC) or post-GC B cells and has a productive (functional) allele with IgH gene rearrangement that produces M-protein, and another nonproductive (nonfunctional) allele of chromosome 14. Disclosures No relevant conflicts of interest to declare.

CNOT3 contributes to early B cell development by controlling Igh rearrangement and p53 mRNA stability

The CCR4–NOT deadenylase complex plays crucial roles in mRNA decay and translational repression induced by poly(A) tail shortening. Although the in vitro activities of each component of this complex have been well characterized, its in vivo role in immune cells remains unclear. Here we show that mice lacking the CNOT3 subunit of this complex, specifically in B cells, have a developmental block at the pro- to pre–B cell transition. CNOT3 regulated generation of germline transcripts in the VH region of the immunoglobulin heavy chain (Igh) locus, compaction of the locus, and subsequent Igh gene rearrangement and destabilized tumor suppressor p53 mRNA. The developmental defect in the absence of CNOT3 could be partially rescued by ablation of p53 or introduction of a pre-rearranged Igh transgene. Thus, our data suggest that the CCR4–NOT complex regulates B cell differentiation by controlling Igh rearrangement and destabilizing p53 mRNA.