EBV Flashcards
EBV structure & classification
Family: Herpesviridae
subfamily: Gamaherpesvirinae
genus: Lymphocryptovirus
species: Human herpesvirus 4
dsDNA linear with icosahedral nucleocapsid, tegument, envelope
Baltimore: I
Tropism: B lymphocytes, T lymphocytes, epithelial cells and myocytes
2 strains: EBV 1 & 2
EBV receptor & replication site
B cell surface molecule CD21 (Rituximab is anti-CD20)
Infection is initiated by the interaction of the major EBV outer envelope glycoprotein gp350/220 with CD21
Gp85 is a relatively minor virus component that is functionally involved in the fusion between virus and cell membranes
Replicates in oropharynx, Monocytes,
EBV replication
Binding to CD21 and the initial phase of penetration are mediated through the major viral coat glycoprotein gp350/220
Dissolution of the viral nucleocapsid and transport of the genome to the B cell nucleus are less well understood.
Once inside the nucleus, the linear EBV genome circularizes.
EBV encodes numerous microRNAs (miRNAs). The function of these miRNAs is poorly understood
The EBV genome is replicated by cellular DNA polymerases during the cell cycle S phase. It persists as multiple, extrachromosomal double-stranded EBV episomes, which are organized into nucleosomes similar to chromosomal DNA.
The hallmark of B lymphocyte infection with EBV is the establishment of latency.
Latency is characterized by three distinct processes:
●Viral persistence
●Restricted virus expression which alters cell growth and proliferation
●Retained potential for reactivation to lytic replication
EBV exploits normal pathways of B cell differentiation to allow it to persist in a transcriptionally quiescent state in memory B cells and thus minimize immune recognition.
Two genes (LMP-1 and LMP-2) encoded by the virus allow an EBV-infected B blast to become a resting memory cell, where EBV persists in a transcriptionally quiescent state.
EBNA-LP and EBNA-2 are the first EBV proteins expressed during latent infection of B cells, reaching their steady state levels within 24 to 32 hours.
EBV transformation proteins & mRNAs
PROTEINS
EBNA-1 — EBNA-1 is required for episome replication and maintenance of the viral genome once the cell has been immortalised. Binds to a specific palindromic DNA sequence on chromosome 11 resulting in breaks and genome instability.
EBNA-2 — EBNA-2 is essential to the process of B lymphocyte immortalization and for the expression of EBNA-1 and EBNA-3. Variations in the EBNA-2 protein impart the most significant biologic difference between the two major EBV types, EBV-1 and EBV-2.
EBNA-3: Unclear function. Mutations renders the virus transformation incompetent.
EBNA-LP — EBNA-LP, or leader protein, is a set of highly polymorphic protein. Unclear -? RNA processing.
miRNAs (microRNAs):
LMP-1 — The second most abundant EBV mRNA species (the EBERs are first) in latently infected B cells encodes an integral membrane protein LMP-1. LMP-1 is essential for EBV-induced transformation of B cells into immortalized lymphoblastoid cells.
LMP-2 — LMP-2 is a substrate for the B lymphocyte family tyrosine kinases.
EBER-1 and EBER-2 — The most abundant EBV RNAs in latently infected B cells. EBER is required for the in vitro growth transformation of B cells.
BART - high levels in tumours - tumourogenesis.
EBV integration
Although most EBV DNA persists in latently infected cells in an episomal form, the EBV genome also integrates into chromosomal DNA.
This integration is neither site specific nor a regular feature of EBV-mediated growth transformation. Furthermore, since LMP-2 is the only EBV latent gene disrupted by linearization of the genome, the integrated form of EBV still retains the potential to transform B cells into permanently growing lymphoblastoid cells.
However, the integrated form of EBV DNA is limited in its ability to infect new cells, since episomal DNA is probably necessary for lytic cycle EBV replication, which has not been reported in cells containing only the integrated form of EBV.
EBV clinical syndromes
- Primary infection: Mononucleosis
- Primary EBV infections in young infants and children are common and frequently asymptomatic. When symptoms do occur, a variety of manifestations have been observed, including otitis media, diarrhea, abdominal complaints, upper respiratory infection, and IM
- Congenital and perinatal infections — Intrauterine infection with EBV is rare because fewer than 5 percent of pregnant women are susceptible to the virus. In addition, prospective studies of susceptible (ie, seronegative) women have not found evidence of congenital abnormalities among infants of women who did develop primary EBV infection during pregnancy [11]. While isolated cases of infants with some evidence for EBV infection and congenital anomalies (biliary atresia, congenital heart disease, hypotonia, micrognathia, cataracts, thrombocytopenia)
- Chronic active Epstein-Barr virus (CAEBV) infection is a rare, life-threatening lymphoproliferative disorder that may involve B lymphocytes, T lymphocytes, or NK cells. The syndrome is characterized by a persistent infectious mononucleosis (IM)-like syndrome and EBV viremia.
The only treatment regimen that has been curative is hematopoietic stem cell transplantation [25,29]. Other treatment options that have been used include high-dose corticosteroids or antiviral therapy (eg, ganciclovir) used individually or in combination with proteasome inhibitors (eg, bortezomib) or histone deacetylase inhibitors
- oral hairy leukoplakia (OHL), which is an unusual disease of the lingual squamous epithelium
- PTLD
- Malignancies - Burkitt Lymphoma, NHL, HL, NPCa, T cell lymphoma,
EBV diagnostics
heterophile (Monospot) positive in 90% IMN - not used in < 4 years
EBV antibody profile consists of 3 components:
- immunoglobulin M (IgM) - Detection of IgM VCA antibodies in a compatible clinical presentation suggests that acute EBV infection is likely. IgG VCA antibodies are also usually detectable at the onset of clinical illness because of the long incubation period.
- immunoglobulin G (IgG) viral capsid antigen (VCA)
- IgG Epstein-Barr virus nuclear antigen (EBNA) - approximately 5 to 10 percent never develop EBNA antibodies.
- EBV IgG avidity
EBV RT-PCR - targets EBNA1, LMP1 - useful in primary & reactivation in IMMUNOSUPPRESSED patients only
EBERISH: in-situ hybridisation. Probe labels all latent EBV infected cells by hybridising to abundantly expressed EBER transcripts which are concentrated in the nucleus of infected cells.
EBV therapeutics
- Avoid physical exertion for 3-6 weeks
- Acyclovir is a nucleoside analogue that inhibits permissive EBV infection through inhibition of EBV DNA polymerase.
HSCT:
- Rituximab - antiCD20 - preemptive therapy in case of high EBV VL
- Tabelecleucel - T cell specific immunotherapy
PTLD
PTLD comprises a spectrum of lymphoproliferative disorders that includes morphologically benign polyclonal lymphoproliferation; florid follicular hyperplasia; polyclonal or monoclonal polymorphic B cell proliferations; and monoclonal disorders that meet criteria for B cell lymphomas, T cell lymphomas, or Hodgkin lymphoma.
The EBV-infected B cells that give rise to PTLD can originate in the host (transplant recipient) or the donor. Following solid organ transplantation, host-derived PTLD is most common
PTLD in HCT recipients is most commonly donor-derived. In this setting, PTLD is thought to be due to the proliferation of EBV-infected B cells in the absence of normal T cell immune surveillance.
Centers differ with regards to their definition of high-risk patients and the cutoff used to determine EBV positivity. Due to the use of different methods, EBV viral load measurements cannot be compared between institutions. The optimal primer set, the relative importance of intracellular versus free plasma EBV, and the baseline profile in an organ transplant population remain to be established
Since the vast majority of EBV-positive PTLD occurs in the first year after transplantation, it is reasonable to monitor high-risk patients more frequently during the initial posttransplant period and to increase the time span between samples as the time from transplantation increases.
Peak at 1 year & 10 years post transplant.
Ibrutinib- TK inhibitor which stirred a lot of interest for PTLD treatment in combination but TIDal trial only showed small benefit and further investigation wasn’t deemed useful. Consultant mentioned it
EBV interpretation comments
SEE ALBUM
tabelecleucel trial
ALLELE: Tabelecleucel for allogeneic haematopoietic stem-cell or solid organ transplant recipients with EBV-positive PTLD after failure of rituximab or rituximab and chemotherapy (ALLELE): a phase 3, multicentre, open-label trial
Clinical benefit found in interim analysis at the 5 year mark.
