In STR PCR, what result suggests failed incorporation of engraftment?

In the context of Short Tandem Repeat (STR) Polymerase Chain Reaction (PCR) testing, the presence of only recipient alleles indicates that there has been a failure of donor cell engraftment. When a donor's cells successfully engraft within a recipient's body, you would expect to see a mixture of both donor and recipient alleles in the STR analysis.

The inability for donor cells to incorporate into the recipient’s system means that there will be no contribution from the donor's DNA, leading to the detection of solely the recipient's alleles. This scenario is critical for monitoring transplant success or the effectiveness of therapies aimed at engraftment. Therefore, the absence of donor alleles, with only recipient alleles detected, provides strong evidence that donor cell engraftment has not occurred.

In contrast, identifying both donor and recipient alleles would indicate successful engraftment, while having both alleles present suggests a mixture or potential engraftment, and the absence of both would imply a complete lack of detectable DNA from either source, which does not specifically indicate a failure of engraftment but rather indicates a different issue entirely.