IGH::CD274 (PD‐L1) rearrangement in diffuse large B cell lymphoma and its therapeutic implication

Abstract Diffuse large B cell lymphoma (DLBCL) expresses abundant programmed death ligand 1 (PD‐L1), which shields tumor cells from immune attacks through the PD‐L1/PD‐1 signaling axis. The mechanism of PD‐L1 overexpression includes the deletion of the 3′end of PD‐L1, which increases its mRNA stability, and the gain or amplification of PD‐L1. Previous studies found two cases of DLBCL carrying an IGH::PD‐L1 by whole genome sequencing. We describe two more such cases by a targeted DNA next‐generation sequencing (NGS) capable of detecting IGH rearrangements, leading to PD‐L1 overexpression. DLBCL with PD‐L1 overexpression is often resistant to R‐CHOP (rituximab, cyclophosphamide, doxorubicin hydrochloride, vincristine and prednisolone). Our patients responded to a combination of R‐CHOP and a PD‐1 inhibitor.

whole genome sequencing. We describe two more such cases by a targeted DNA next-generation sequencing (NGS) capable of detecting IGH rearrangements, leading to PD-L1 overexpression. DLBCL with PD-L1 overexpression is often resistant to R-CHOP (rituximab, cyclophosphamide, doxorubicin hydrochloride, vincristine and prednisolone). Our patients responded to a combination of R-CHOP and a PD-1 inhibitor.

DLBCL, IGH, PDL1
The cluster of differentiation 274 (CD274), also known as PD-L1 is a transmembrane protein that interacts with the PD-1 receptor on T cells to activate cellular PD-1 signaling and block T-cell activation. Tumor cells often express PD-L1, which shields tumor cells from immune attacks through the PD-L1/PD-1 signaling axis [1]. PD-L1/PD-1 inhibitors re-sensitize tumor cells to the cytotoxic activity of T-cells and their clinical utilization is a major milestone of our effort to conquer cancer. Food and Drug Administration (FDA) has approved serval monoclonal antibodies (mAb) targeting PD-L1/PD1 signaling for cancer therapy, including three PD-L1 mAb (atezolizumab or Tecentriq, durvalumab or Imfinzi, and avelumab or Bavencio) and three PD-1 mAb (pembrolizumab or Keytruda, nivolumab or Opdivo, and cemiplimab or Libtayo). These PD-L1/PD1 inhibitors are used in late-Xuemei Wu and Si Chen contributed equally to this work.
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.  [2].
PD-L1 is expressed in normal lungs and expressed in many cancers based on the Cancer Genome Atlas database, with the highest expressed cancers being DLBCL, thymoma, and head and neck squamous cell carcinoma (data not shown). Several mechanisms to induce PD-L1 expression include loss of the inhibitory sequence at the 3′ end of the PD-L1, copy number gains and amplification, or promoter swap. In addition, regulation at the transcriptional and translational levels is also important in PD-L1 expression [3]. Dr. Georgiou et al.
We report here two more cases of DLBCL, including a rare splenic   Figure 2E.
Because a previous study showed that the DLBCL patients tolerated well a combination of PD-1 inhibitor pembrolizumab and R-CHOP [5], our patients were treated with a similar regimen with an anti-PD-1 mAb Sintilimab and R-CHOP. Case #1 achieved complete remission after 3 cycles of the combination therapy based on PET-CT. Case #2 was first treated with a combination of R-CHOP and Ibrutinib for one cycle due to adrenal glands tumors and their related high risk of central nervous system (CNS) involvement, and is now being treated with a combination of Sintilimab, R-CHOP, and Ibrutinib. A recent PET-CT evaluation revealed a partial response; however, the treatment regimen has not been completed yet.
The truncation of the 3′-untranslated region (3′-UTR) of the PD-L1, caused by translocations, inversions, small deletions, or small tandem duplications, is the most common genomic change leading to the PD-L1 overexpression [6]. PD-L1 3′-UTR has a negative regulatory role in mRNA stability, therefore, the loss of 3′-UTR results in the increased shell life of PD-L1 transcript [7]. Copy number gain or amplification of PD-L1 is also an important mechanism for PD-L1 overexpression. In relapsed or refractory Hodgkin's lymphoma, PD-L1 and/or PD-L2 were often amplified in Reed-Sternberg cells and these patients showed substantial therapeutic response to PD-L1 inhibitor Nivolumab [8].
Similar PD-L1 amplification was observed in DLBCL [9]. Promoter swap, involving the MHC class II transactivator (CIITA) and PD-L1, was reported in primary mediastinal B-cell lymphoma and Hodgkin lymphoma, leading to increased PD-L1 expression [10]. Overall, PD-L1 overexpression was seen in 26.3% to 61.1% in DLBCL [11][12][13] Two powerful enhancers of the IGH include the intragenic Eμ ing IGH rearrangement and capturing the known and unknown fusion partners, we believe that more cases of the IGH::PD-L1 lymphomas will be discovered. Our two patients with IGH::PD-L1 were detected in 52 DLBCL samples. If this ratio holds true (albeit a small sample size), a significant number of DLBCL will carry the IGH::PD-L1. This is supported by the initial discovery of PD-L1 rearrangement in two out of 20 DLBCL cases [4]. Identifying these patients is important because they are associated with poor response to R-CHOP [14] and may benefit from immunotherapy.

CONFLICT OF INTEREST STATEMENT
The authors report no conflict of interest for the submitted manuscript.

FUNDING INFORMATION
The conduct of this research did not need external financial support.

DATA AVAILABILITY STATEMENT
The data that support the findings of this study are available on request from the corresponding author.

ETHICS STATEMENT
The authors comply to practice guidelines on research integrity and publishing ethics. No patient identifiable images or data have been included in the manuscript. Written consent for publication was obtained from the patient.