Delayed seroconversion to STLV-1 infection is associated with mutations in the pol and rex genes

BACKGROUND: Simian T-cell lymphoma/leukemia virus-1 (STLV-1) infection of non-human primates can serve as a model for human T-cell lymphoma/leukemia virus infection. METHODS: Two tantalus and 2 patas monkeys were transfused with intraspecies whole blood infected with STLV-1. Infection was determined by ELISA, western blot and DNA PCR analyses. The entire genome of the STLV-1 Tan 90 strain and some of the STVL-1 Pat74 strain were amplified using over-lapping primer-pairs and subsequently sequenced. RESULTS: Followup studies conducted over 2 years indicated that all 4 monkeys remained healthy despite being infected with STLV-1, as determined by PCR, cloning and sequencing analyses. ELISA and Western blot analyses indicated that both patas monkeys seroconverted within 2 months of transfusion, while one tantalus monkey required one year to seroconvert and the other never fully seroconverted. The tantalus monkey which never fully seroconverted, failed to react to HTLV-1 p24 Gag antigen. Sequence analyses indicated that, while unique, the deduced p24 Gag amino acid sequence of the STLV-1 Tan 90 strain used for infection was still highly homologous to the HTLV-1 p24 Gag amino acids present in the ELISA and WB assays. However, a mutation in the pol sequence of STLV-1 Tan 90 encoded a putative stop codon, while a common deletion in the pol/rex regulatory gene causes significant changes in the Pol, and p27 Rex proteins. These same mutations were also observed in the viral DNA of both recipient infected tantalus monkeys and were not present in the STLV-1 Pat 74 strain. CONCLUSION: Our data suggest that seroconversion to STLV-1 infection may be prolonged due to the above mutations, and that compensatory molecular events must have occurred to allow for virus transmission.