Felis catus gammaherpesvirus-1 (FcaGHV-1), a candidate lymphomagenic virus discovered in 2013, infects an estimated 200 million cats worldwide. In humans, the gammaherpesviruses (GHV) Epstein-Barr virus (EBV) and Kaposi's sarcoma-associated herpesvirus (KSHV) are causal in up to 95% of HIV-associated lymphomas. In cats, feline immunodeficiency virus (FIV) infection is associated with the development of high-grade B-cell lymphomas. Whether FcaGHV1 plays a role in FIV-associated lymphomas is under investigation.

The gold standard for determining causality in EBV-associated lymphomas is the detection of viral transcripts expressed during latency that promote uncontrolled growth. The aim of this study was to investigate FcaGHV1 gene expression in FIV-associated lymphoma. We targeted 3 FcaGHV1 open reading frames (ORFs). Two were identified by comparative sequence analyses; ORF73, a homologue of EBNA1 which is expressed in all EBV-associated malignancies and F7, a homologue of KSHV vFLIP, which encodes an anti-apoptotic protein. The third, ORF50, was identified during our RNA-seq analyses of feline lymphoma transcriptome. Its homologue is a KSHV lytic cycle activator.

Frozen biopsies from cases of high-grade B cell lymphoma arising in cats seropositive for FIV and seronegative for FeLV were identified in our tissue bank. Cases were included if tumour DNA was positive for FcaGHV1 on PCR. Nine samples met the inclusion criteria.

Total RNA was purified from frozen tissue and treated with DNase. One-step RT-PCR assays amplifying FcaGHV1 ORF73, F7, and ORF50 (mRNA splice product) were designed and optimized. The identity of RT-PCR products migrating at the expected size was confirmed by sequencing. In 5 cases, expression of 1, 2 or 3 FcaGHV1 genes was detected. Four cats tested negative for all three transcripts.

This study demonstrates, for the first time, expression of FcaGHV1 in feline lymphoma tissues. Investigations to localize FcaGHV1 gene expression to cell type and to determine tissue specificity are warranted.

Disclosures

Disclosures to report
This study was funded by the Morris Animal Foundation grant number D15FE-001.