Long-term follow-up failed to detect in vitro transmission of full-length porcine endogenous retroviruses from specific pathogen-free pig islets to human cells

Aims/hypothesis. Islets from specific pathogen-free (SPF) pigs could preven t the transmission of conventional zoonosis. but not endogenous retroviruse s (PERV), from pigs to diabetic patients. We previously reported that the p ancreas showed the lowest expression of PERV mRNA among pig tissues intende d for grafting. This study aimed to determine whether PERV from pig islets infect human cells during co-incubation. Methods. Human cells (including highly PERV-sensitive 293 cells) were incub ated with SPF pig islet cells under conditions designed to increase contact (a high islet to human cell ratio, extended period of coculture. and repea ted contacts). PK15 and G2 retrovirus-producing pig cells were used in plac e of islet cells as "positive infection controls". Infection of human cells was monitored on cellular extracts and supernatants by PCR or long PCR, an d RT-PCR or long RT-PCR. to detect PERV DNA and mRNA. respectively. Reverse - transcriptase activity was monitored by PERT. Results. Despite the presence of all PERV sequences in pig islet cells, inc luding full-length inserts. no DNA or RNA for gag, pol, and the 3 env sub-t ypes were detected in any human cell line or blood mono- nuclear cells incu bated with pig islet cells, during an 18-week follow-up period. No PERV seq uences or RT activity were detected in supernatants. PERV signals were nega tive even when the pig islet to human cell ratio was increased to 100:1, th e time of co-culture was extended to 5 days and two sequential co-incubatio ns were done. By contrast, all PERV DNA and mRNA were detected in all human cells co-incubated with PK15 or G2 cells. Depending on human cell types, p roductive or non-productive infections were obtained: full-length PERV RNA and RT activity in supernatants were detected or not; and PERV sequences to previously unexposed human cells by PERV-infected human bells were transmi tted or not. Some human cells were not productively infected by PK15 cells but became productively infected after co-incubation with PERV-infected 293 cells. Conclusion/interpretation. SPF pig islet cells, even with PERV inserts and transcripts. have very little probability of transmitting PERV to human cel ls during co-incubation. The sensitivity of human cells to stable and produ ctive infection by PERV depends on the cell type. Human adaptation of PERV was observed.