Between surrogate mothers renting womb space and custody battles for frozen embryos, the warp-speed rocket of biomedical ethics is headed for lunar soil.

Six-month-old Marissa Eve Ayala is along for the latest rocky ride.

Is it right to conceive a child for the expressed purpose of using it as a medical donor?

Right or not, it’s already happened.

Marissa was no accident. In fact, her family had plans for her before she was a gleam in her father’s eye.

Abe and Mary Ayala, Marissa’s parents, had exhausted nearly every option to save their 18-year-old daughter, Anissa, who has lived with leukemia for two years.

The Ayalas tried to find a compatible donor among family members who live in Los Angeles. Next, they spent two years hoping to find a donor through the National Bone Marrow Donor Registry. All along, the search was fruitless.

Then they decided to have a baby—Marissa.

The family took a gamble, but fetal tests showed that the baby’s marrow was compatible with Anissa’s—a 1 in 4 chance.

The Ayalas seem like an extremely caring family in a terrible situation. But no matter how well-intentioned they are, the fact remains that Marissa was conceived not for the simple purpose of having a baby, but for her tissue.

If it weren’t for Anissa’s condition, Abe and Mary have said they wouldn’t have wanted another baby. In fact, Abe had to reverse a vasectomy he had 16 years earlier and Mary had greater risks for pregnancy because she is in her mid-40s.

Marissa is now six months old and will undergo the transplant in another six months—sooner than she can babble her first words, much less give her consent.

Her parents are entrusted as legal guardians to weigh the medical needs of one child against the rights and welfare of another.

Just this week, the Ayalas announced they would wait another six months before transplanting Marissa’s bone marrow to her older sister.

The transplant, which has about a 75 percent success rate, was originally planned to take place when Marissa was just six months old. But because Anissa’s condition is relatively stable now, the transplant was postponed to allow Marissa to mature.

The procedure, which involves inserting needles into Marissa’s hip bone to draw out a portion of marrow, is supposed to be painless. Or at least less painful than dying of leukemia.

Marissa is fortunate because her family staunchly defends they’d love the “miracle baby,” as her father once called her, even if she wasn’t a suitable donor.

Even though the Ayala’s situation might have a happy ending, conceiving children for parts presents a tough ethical dilemma between an infant’s welfare and the urgent desire to save another child.

As any first-year philosophy student who’s studied the respect for persons theory can tell you, human beings should be treated as ends in themselves and not as a means for something else.

Marissa—and the genetically compatible marrow within her bones Y is a means to cure her sister’s cancer.