TCID50 for low titre HIV - (Sep/10/2012 )

I am trying to quantify the TCID50 of a batch of HIV BaL that I have. I infected TZMbl cells with 10 fold serial dilutions of my virus starting with neat virus for 3 hours. After three days of culture I stained the cells using X-Gal and looked for blue cells. My neat wells containing undiluted BaL viral supernatants from T cells were all dead, presumably from the culture medium and not virus, as the next dilution had ~40% blue TZMbl cells. Any suggestions on how I can calculate the TCID50 when I don't have any wells with 100% infected TZMbl cells? I also ran the same experiment in parallel using IIIB viral supernatant collected from transfected 293 cells, which did not show any cell death with neat virus, and also did not have any wells with 100% infection.

Put simply, you can't.