Biotech investors wait on pins and needles for companies to report how their experimental drugs are faring in clinical studies. When the updates aren't great, biotech stocks can tank. But when the results are good, the stocks can take off in a big way.

Three biotech stocks that soared last week on positive pipeline updates were Adverum Biotechnologies (NASDAQ:ADVM)Iovance Biotherapeutics (NASDAQ:IOVA), and MeiraGTx Holdings (NASDAQ:MGTX). Here are the details on why these stocks performed so well and whether they're smart picks to buy now.

Man in a suit appearing to soar with wings drawn with chalk, next to a blue line pointing upward

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1. Adverum Biotechnologies

The removal of a negative can also be a big positive. That's the story for Adverum Biotechnologies. Its stock skyrocketed 38% after the biotech announced on Thursday that the FDA lifted a clinical hold on one of the patient cohorts in a phase 1 clinical study evaluating ADVM-022 in treating wet age-related macular degeneration.

Adversum now expects to begin dosing of its second cohort in the study in June. Results from patients in the first cohort were so robust that it now intends to use a dose three times lower.

The phase 1 study of ADVM-022 isn't totally in the clear, though. The FDA still has a partial clinical hold in effect for dosing patients in the third cohort of the study. Adverum intends to work with the FDA to resolve all remaining issues in the way of moving forward with this third cohort.

2. Iovance Therapeutics

Iovance Therapeutics was the second biggest biotech winner last week, jumping nearly 36%. On Wednesday, Iovance reported promising interim data from clinical studies evaluating two of its experimental immunotherapies, both of which are based on the company's tumor-infiltrating lymphocyte (TIL) technology.

Let's start with the good news for LN-145. Patients with advanced cervical cancer taking the experimental TIL drug in a phase 2 clinical study achieved an objective response rate (ORR) of 44%. ORR refers to the proportion of patients with tumors that shrank by a predetermined amount. How good was this performance? It was a lot better than Merck's blockbuster cancer drug, Keytruda, which achieved an ORR of only 14% in previously treated advanced cervical cancer patients.

Then there's LN-144, also known as lifileucel. Patients with advanced melanoma in one of the cohorts of Iovance's phase 3 study who received lifileucel after checkpoint inhibitors failed achieved an ORR of 38%. And after a 7.4-month median follow-up, melanoma had progressed in only four out of 21 responders.

3. MeiraGTx Holdings

MeiraGTx also turned in a great performance last week. Shares of the clinical-stage biotech vaulted 28% higher for the week. The biotech announced positive data from its phase 1/2 study evaluating gene therapy AAV-RPE65 in treating RPE65-deficiency, a genetic cause of blindness. AAV-RPE65 met the study's primary endpoints of safety and tolerability.

There was more good news for MeiraGTx as well. The company reported that it had completed dosing patients in a phase 1/2 clinical trial of another gene therapy, AAV-CNGB3, in treating achromatopsia, more commonly known as color blindness.

MeiraGTx's gene therapy programs had already shown enough potential that they attracted the interest of Johnson & Johnson. The healthcare giant entered into a collaboration with MeiraGTx in the first quarter to develop and commercialize gene therapies for the treatment of inherited retinal diseases. 

Are they buys?

Iovance looks especially intriguing after the great results for LN-145. If I were to pick only one of these high-flying biotech stocks, Iovance would be it.

But all three of these biotechs still face significant risks. Most investors would be better off waiting to see how well the pipeline candidates perform in late-stage studies. My view is that the smartest strategy right now is to watch Iovance, MeiraGTx, and Adverum from the sidelines. There are other stocks that provide more compelling risk-reward propositions. 

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.