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In vitro vs in vivo: why cell results often fail in people
In vitro studies test cells in a dish, in vivo studies test a whole living body. Many results that look strong in a dish fade or reverse in animals and people.
In vitro means an experiment done outside a living body, usually on cells, tissue or molecules in a dish or tube. In vivo means the experiment is done inside a whole living organism, whether that is a mouse, a rat or a human volunteer. The difference matters because a result that looks impressive in a dish often disappears, or turns harmful, once a real body is involved.
The terms come from Latin. In vitro means "in glass" and in vivo means "in the living". There is also a middle category, ex vivo, where tissue or a whole organ is taken out of a body and studied while it is still working. We cover that in a separate guide, "What does ex vivo mean?". This page is about the bigger gap: why results from cells so often fail to carry over to whole organisms, with real examples of it happening.
What is the difference between in vitro and in vivo?
In an in vitro experiment the researcher controls almost everything: which cells are used, what they are exposed to, at what concentration and for how long. In an in vivo experiment much of that control is lost, because the body decides what happens to a compound once it is swallowed or injected. Research usually moves through these stages in order.
- In vitro: cells grown in culture, isolated enzymes, or bacteria and viruses in a dish. Fast, cheap and tightly controlled, and no animal or person is exposed to any risk.
- In vivo, in animals: a compound is given to mice, rats or other animals so researchers can see how a whole body absorbs it, breaks it down and reacts to it.
- In vivo, in people: clinical trials, from small first-in-human safety studies to large randomised trials that compare a treatment against usual care or a placebo.
Each step adds things a dish cannot reproduce: digestion, the liver, the kidneys, the immune system, blood flow, and the simple fact that a compound has to reach the right tissue at a high enough level for long enough. Three common reasons for failure are the wrong cells, the wrong concentration, and a body that reacts in ways no dish could show. Each has a well-documented example.
Why did chloroquine work in the lab but not in patients?
Early in 2020, a letter in Cell Research by Wang and colleagues reported that chloroquine, an old antimalarial drug, effectively inhibited the new coronavirus in vitro. Those experiments used Vero cells, a cell line that comes from African green monkey kidney.
Later that year, Hoffmann and colleagues reported in Nature that the result depended on the cells. When Vero cells were engineered to make TMPRSS2, a protein the virus uses to get into lung cells, chloroquine no longer protected them. It also failed to block infection in Calu-3, a human lung cell line. The authors concluded that chloroquine targets an entry route that is not active in lung cells and is unlikely to stop the virus spreading in patients.
The human answer came from RECOVERY, a large UK randomised trial published in the New England Journal of Medicine. The paper notes that hydroxychloroquine and chloroquine had been proposed as treatments on the basis of in vitro activity and small or uncontrolled studies. In the trial, 1,561 hospitalised patients received hydroxychloroquine and 3,155 received usual care. Within 28 days, 27.0% of the hydroxychloroquine group had died, compared with 25.0% of the usual-care group. There was no benefit.
Why does the dose in a dish not match the dose in the body?
Resveratrol, a compound found in red grapes, has shown activity against heart disease and cancer in laboratory models. The question is whether a person's body can deliver it to those tissues. In a 2004 study in Drug Metabolism and Disposition, Walle and colleagues gave six volunteers a single oral dose at a level found in the diet, labelled so it could be traced.
At least 70% of it was absorbed, but only trace amounts of unchanged resveratrol, under 5 ng per ml, could be detected in blood plasma. The gut and liver converted almost all of it into other compounds very quickly. The authors noted it might still act along the lining of the gut, or through its breakdown products. The broader lesson stands: cells bathed in a compound for hours do not tell you whether a body can get that compound to them.
Can animal studies miss the danger too?
Yes. In vivo does not automatically mean human, and animal results can also fail to predict people. In 2006, six healthy young men received TGN1412, an experimental antibody designed to switch on T cells, in its first human trial. The case report in the New England Journal of Medicine by Suntharalingam and colleagues describes how all six developed a severe inflammatory reaction within 90 minutes. Within 12 to 16 hours they were critically ill, with lung injury and kidney failure. All six survived after intensive care.
A 2010 review by Attarwala in the Journal of Young Pharmacists points out that the volunteers received a dose 500 times smaller than the dose that had been found safe in animal studies. The animals and the humans simply did not respond the same way. The review describes how the incident changed the way first-in-human trials are approved and run.
How often do lab findings hold up in people?
Two well-known analyses give a sense of scale. In 2012, Begley and Ellis wrote in Nature that scientists at the biotech firm Amgen had tried to confirm 53 "landmark" preclinical cancer papers before building on them. The findings were confirmed in only 6 cases, about 11%. The authors argued that many landmark findings are not reproducible, in part because of inadequate cell lines and animal models.
Even compounds that make it into human trials mostly fail. A 2019 analysis in Biostatistics by Wong, Siah and Lo used more than 406,000 clinical trial records covering over 21,000 compounds from 2000 to 2015. For cancer drugs, they estimated a success rate of just 3.4% in their sample.
How should you read an in vitro study?
- Check what was tested. A headline saying a compound "kills cancer cells" or "stops a virus" often describes a dish, not a person. Look for the words in vitro, cell line or cultured cells in the abstract.
- Check the cells. Were they human or animal, and were they the type of cell the disease actually affects? The chloroquine story shows how much the choice of cell line can change the answer.
- Check the concentration. Ask whether a body could reach that level in the right tissue. Resveratrol shows how far apart the two can be.
- Check for follow-up in living organisms. Has anyone tested it in animals, and then in randomised trials in people? If not, the result is an early clue, not evidence of benefit.
None of this makes in vitro research useless. It is how researchers work out mechanisms, screen large numbers of compounds, and spot obvious toxicity cheaply before any animal or person is exposed. The problem is the leap from a dish straight to a claim about people. Think of in vitro work as the bottom rung of a ladder, with ex vivo tissue work, animal studies and human trials as the rungs above it.
This article is for general education about how research is done. It is not medical advice, and nothing here suggests that any compound mentioned is safe or effective for any use.
Frequently asked
- What is the difference between in vitro and in vivo?
- In vitro means the experiment is done outside a living body, usually on cells or molecules in a dish or tube. In vivo means it is done inside a whole living organism, such as a mouse or a human volunteer. In vitro work offers more control, while in vivo work shows what actually happens once digestion, the liver and the immune system are involved.
- Are in vitro studies reliable?
- They are reliable for what they test, which is how cells or molecules behave in a controlled dish. They are not reliable as evidence that something works in people. When scientists at Amgen tried to confirm 53 landmark preclinical cancer papers, they confirmed only 6, about 11%. Treat in vitro results as early clues that still need animal and human testing.
- Is an animal study in vivo?
- Yes. In vivo covers any experiment in a whole living organism, including mice and rats as well as people. Animal results do not always carry over to humans either. In the 2006 TGN1412 trial, six volunteers became critically ill after a dose 500 times smaller than one found safe in animal studies.
- Why did chloroquine work in vitro but not in patients?
- The early lab work used Vero cells, a monkey kidney cell line. A 2020 Nature study showed chloroquine did not block the virus in a human lung cell line, because lung cells use a different entry route. The RECOVERY trial then found hydroxychloroquine did not reduce deaths at 28 days in hospitalised patients.
The studies and sources behind this page
- Wang M, Cao R, Zhang L et al. Remdesivir and chloroquine effectively inhibit the recently emerged novel coronavirus (2019-nCoV) in vitro. Cell Res 2020;30:269-271.
- Hoffmann M, Mosbauer K, Hofmann-Winkler H et al. Chloroquine does not inhibit infection of human lung cells with SARS-CoV-2. Nature 2020;585:588-590.
- RECOVERY Collaborative Group. Effect of hydroxychloroquine in hospitalized patients with Covid-19. N Engl J Med 2020;383:2030-2040.
- Walle T, Hsieh F, DeLegge MH et al. High absorption but very low bioavailability of oral resveratrol in humans. Drug Metab Dispos 2004;32:1377-1382.
- Suntharalingam G, Perry MR, Ward S et al. Cytokine storm in a phase 1 trial of the anti-CD28 monoclonal antibody TGN1412. N Engl J Med 2006;355:1018-1028.
- Attarwala H. TGN1412: from discovery to disaster. J Young Pharm 2010;2:332-336.
- Begley CG, Ellis LM. Drug development: raise standards for preclinical cancer research. Nature 2012;483:531-533.
- Wong CH, Siah KW, Lo AW. Estimation of clinical trial success rates and related parameters. Biostatistics 2019;20:273-286.
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Educational content only. Not medical advice, diagnosis or treatment. Always consult a qualified healthcare professional before changing your health regimen.