cDNA stability?

[Jose McNach]

I normally synthesise my cDNA from RNA using Invitrogen's SuperscriptII
reverse transcriptase, and when done I store it at -20oC. I just make
dilutions from that stock for semiquantitative PCR and it generally
works well, and I can go back to the stocks months later and it's still
okay.

Last November (2 months ago) I prepared a batch of cDNAs, calibrated
them (the dilutions), did a bunch of PCRs, and this time I stored it at
-80, together with the RNA. No particular reason.
A month later I went back to use some of it, and failed. Then Xmas came
and I didn't try again till today... yep, it definitely does not work
anymore.

I think the fact I stored them at -80 and failed is a coincidence...
but I *never* have had this sort of problem before so I'm trying to be
open minded...

Has anybody experienced any problems with cDNA storage at -80?

I wonder if freeze-thawing is more harmful at -80 than -20... yet I
haven't experienced any problems at all with several rounds of
freeze-thawing at -20 in the past...

hmmm...

Any comments? Thanks!

Jose