Merck and Moderna announced a successful late-stage trial for a melanoma vaccine. NPR's Leila Fadel talks to Dr. Robert Vonderheide of Penn Medicine and the American Association for Cancer Research.

LEILA FADEL, HOST:

The pharmaceutical company Merck and biotech company Moderna announced a successful late-stage trial of a vaccine for deadly skin cancer. They say this new mRNA vaccine, using the same technology that powered many COVID shots, significantly lessened the recurrence and spread of melanoma. The news raised the stock prices of both companies, which have yet to share the full study.

To learn more about this, we've called Dr. Robert Vonderheide. He is a cancer immunologist who directs the Abramson Cancer Center at Penn Medicine, which was a site for this trial, though he was not involved. He is also president-elect of the American Association for Cancer Research. Dr. Vonderheide, good morning, and thank you for being here.

ROBERT VONDERHEIDE: Good morning, Leila. Nice to be here.

FADEL: So from what you've read, what is your understanding of how this vaccine works and whether it's a potential breakthrough?

VONDERHEIDE: Well, this vaccine works by activating the immune system, adding one more way to do that for our patients with cancer. As you said, it's based on the technology that was developed for the COVID vaccinations, but in this case, it's designed to generate T cells that would attack cancer, and it does so by targeting specific mutations in the patient's tumor. So these vaccines are designed and created for one patient at a time. And in the study, the vaccine was probably enhanced because it was used with another already FDA-approved immune-enhancing drug called pembrolizumab.

FADEL: So it would be a vaccine that you would get only if you've had melanoma?

VONDERHEIDE: Right now, this is for patients who've had melanoma. It is a vaccine to prevent recurrence, which the companies reported yesterday that it did so. We await the data, of course.

FADEL: How significant could a vaccine like this be for people with melanoma?

VONDERHEIDE: Well, I think it's highly significant because it allows people to live without - with a less chance of recurrence, which is what we want, of course. But it's also significant because the technology has the ability and already being adapted for patients with other types of cancer.

FADEL: You said, of course, we await the data. What questions do you have about the data that we haven't seen yet?

VONDERHEIDE: Well, we'd like to see the magnitude of the response. An earlier study from these companies reported earlier this year indicated significant clinically meaningful results. We will see that data when it's reported. We also want to understand did the vaccine work as designed - did it generate a T-cell response in patients? And, of course, were there any new safety signals? So far, the companies indicate not.

FADEL: What steps remain before a drug like this could be available for patients - a vaccine like this could be available for patients?

VONDERHEIDE: So this study is ongoing, and it will complete - it's not enrolling new patients, I'm - I understand, but it's being followed to see what the ultimate impact will be on overall survival for these patients. At some point, the data will be presented to regulatory groups to approve it for use.

The big step is that this type of vaccine, this type of therapeutic really has - for cancer, hasn't yet about (ph). This is quite involved. You have to harvest the patient's tumor, sequence it, identify the mutations, make the vaccine per the patient. So these are large manufacturing challenges.

FADEL: So each vaccine would have to be tailored to each patient?

VONDERHEIDE: Yes, that's right. So this is not just sitting on the shelf where you can get - well, here's a bottle of pills. So that's a challenge, but it's - you know, this was a big study of over a thousand patients, and it seems feasible to ramp it up for worldwide application. That will take some work, of course.

FADEL: And really quickly, I mean, how much of a breakthrough is this, potentially? Could it mean that cancer becomes a preventable disease at some point?

VONDERHEIDE: Well, we certainly hope that. And we think the real power of the immune system one day will be to prevent cancer in the first place. This is preventing relapse.

FADEL: Dr. Robert Vonderheide directs Penn Medicine's cancer center. Thank you for your time and your expertise.

VONDERHEIDE: Thank you.