HEK293T cells. Original reference describing their creation?

[Peter O'Brien]

Thanks for the reply, I really appreciate it.  However, HEK 293 cells
(transformed with e1a) were later modified to express SV40 T antigen (to
boost copy number of SV40 ori-containing plasmids?) some time later and
these are referred to as 293T cells.  That's the ref I'm looking for.