Proviral burden 12 weeks post-challenge with cell-associated FIV in cats previously exposed to heterologous cells/media. Proviral burden was approximately 1 log lower in the Heterologous group. # Less than 100 copies detected. In the LPL, one sample in each group was damaged during processing and therefore unavailable. Within the heterologous group, both the IEL and LPL had two different animals with the same copy number; for IEL 0 copies were seen in two animals, for LPL 5 copies.