For those who care about such matters, the Vatican recently announced that it is “morally acceptable” to receive a vaccine that was developed with the help of cell lines that originated from aborted fetuses. Testing of both mRNA vaccines in the United States (Pfizer/BioNTech and Moderna) involved such cells, while the adenovirus vaccine from Oxford/AstraZeneca requires such cells for production of the vaccine itself.

Recall that normal cell replication is highly regulated. When this regulatory system breaks down, we essentially have cancer. That makes using normal human cells in the lab pretty challenging because they will eventually die off and you have to keep going back for more. Under the right conditions, however, cancerous cell lines (“immortal”) can be propagated without end in the lab. HeLa cells are probably the most famous of such cell lines, and this line originated from a cervical tumor biopsy that was taken without permission from an African American woman named Henrietta Lacks in 1951 (fortunately, the rules of consent have improved considerably since then).

COVID-19 vaccines have been tested with or are produced using HEK-293 or PER.C6 cells, which were originally derived from normal cells. HEK-293 cells were developed in 1973 by Alex van der Eb when he introduced sheared adenovirus DNA into otherwise normal embryonic kidney cells that were collected from an aborted fetus. Van der Eb’s team managed to immortalize some of these cells while incorporating DNA needed to make a key protein for adenovirus replication. That means we can delete this protein from an adenovirus, and it will still replicate in HEK-293 cells.

Recall that viruses can’t replicate without a cell to do the work, but when we administer a vaccine to a person, we don’t want the virus itself to replicate. We only want it to deliver a DNA package needed to trigger the desired immune response. You can get around this quandary by using cell lines that are capable of replicating a virus that otherwise can’t replicate in normal cells — hence the power of the HEK-293 cells.

PER.C6 cells originated from an aborted fetus in 1985 (“retinoblasts”). These cells were immortalized and were then engineered to express a key protein needed for adenovirus replication. Doing so made PER.C6 cells equivalent to HEK-293 cells with the ability to produce large quantities of the adenovirus vaccine that is otherwise unable to replicate in normal cells.

I haven’t been able to determine why the mRNA vaccines were tested in these cell lines, but it is likely that this was more by chance than necessity. The key distinction is that the mRNA vaccines are artificially synthesized whereas adenovirus vaccines must be replicated in cells like HEK-293 and PER.C6.

Until alternative cell lines are developed, for some people the necessity of using cell lines that were derived from aborted fetuses may be a significant moral barrier to accepting adenovirus-based vaccines. In the U.S., only two mRNA vaccines are approved and neither require cell lines for production. That does not mean that such vaccines are completely independent of fetal-derived cell lines. This is because science builds on a scaffold of knowledge and it is simply impossible to disentangle development of ideas and methodologies from original sources of materials. Thus, if a person is a puritan about such matters, no vaccine much less modern medicine in general, is likely to be acceptable. For people with reservations primarily tied to how these vaccines are produced, however, they can confidently accept mRNA vaccines as an alternative that has less moral uncertainty.

Mass vaccination is the only humane way out of this pandemic, but vaccine supplies will remain tight for the foreseeable future and for some people, vaccine acceptance will hinge on the question of whether or not fetal-derived cell lines were used during vaccine production. Consequently, if equally effective adenovirus-based vaccines become available in the U.S., these should be directed to people who do not have objections to the production process thereby leaving a larger supply of mRNA vaccines for those who will struggle with these issues. Allowing such choices will help us achieve sufficient vaccination coverage sooner than later.

Doug Call is a microbiologist and father of three.He first discovered the Palouse 37 years ago.

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