When it comes to immortality (or longevity), the “immortal cell” cannot be the solution. If it were, further reproduction of cells would have to cease; you see, there’s already a known situation where the cells forget to die and reproduce themselves forever, and it’s called a “tumor” or “cancer“.
But even if there was a way around it, that is to say, to make cells immortal, by unblocking the biological mechanisms that order a cell to die, regardless of it’s current condition and then to prevent the existing cells from further reproducing themselves, to avoid tumors, even then, “immortal” would not guarantee “in perfect condition”; the reason is that, in that case, exhausted, damaged or sick cells would never be replaced! “Normal wear” would take its toll… and inevitably… death would come, perhaps even sooner than before!!
Apparently, the cycle of life and death within our bodies also serves the purpose of getting rid of worn-out, replacing them with new ones…